)V1ESI.} RETURNING MATERIAL§: PIace in book drop to LJBRARJES remove this checkout from ,___ your record. FINES will be charged if book is returned after the date stamped below. CULTIVAR AND ENVIRONMENTAL IMPACT ON ONTOGENETIC CHANGES IN THE FRUIT CALCIUM STATUS OF PICKLING CUCUMBERS By Cheryl Ann Engelkes A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1987 arm/v 2'12; ABSTRACT CULTIVAR AND ENVIRONMENTAL IMPACT ON ONTOGENETIC CHANGES IN THE FRUIT CALCIUM STATUS OF PICKLING CUCUNBERS by Cheryl Ann Engelkes A field experiment was conducted to determine the ontogenetic changes in calcium concentration and content in pickling cucumber fruit (Cucumis sativus L.) as related to seasonal changes in the environment. Factors studied, whiCh may influence calcium accumulation, were planting date, genotypic variability (cvs. Castlepik 2012, PSX20580, Regal, Tamor), harvest date (0.5-5.5 cm fruit diameter) and tissue type, pericarp and endocarp. Changes in fruit growth were measured by fresh and dry weight, volume, and lengthzdiameter ratio. Mean fruit calcium concentration in a pickling cucumber fruit declined during ontogeny, while total fruit calcium content increased. Calcium concentrations in pericarp (1.1-0.72 dry wt.) and endocarp (0.8—0.2Z dry wt.) tissues declined as fruits enlarged. Genotypic differences in fruit calcium concentration are attributable to differences in rates of fruit calcium accumulation and growth. Environmental factors, primarily soil moisture, had a significant and similar impact on rates of fruit calcium accumulation and growth. To my parents, Marge and Stan Engelkes, who taught me to walk. Your endless love, support, and understanding have given me the courage to take each new step. This is 23; thesis. ii ACKNOWLEDGEMENTS The author expresses her gratitude to Drs. Irvin Widders, Hugh Price and Andrew Hanson, members of the author's Guidance Committee, for their support, advice and constructive criticism during the course of this investigation. She is indebted to Hugh Price for his assistance in designing the field experiment, for Genstat computer program tutoring, and for the many words of encouragement. Many .thanks to the Horticulture Department graduate students, faculty and staff for their contributions. A special thank you to the Horticulture Research Center crew, especially Bill Priest, for helping maintain a "beetle-free" and "weed-free" field plot. Thank you to Dr. David W. Davis, the author's undergraduate advisor, for his professional example and for nurturing her interest in a plant research career. He gave her the confidence and courage to pursue her goals. A sincere thank you to the lmembers of Capitol City Toastmasters for their patient training in public speaking. A heartfelt thank you to the Olivet Baptist Church congregation for their fellowship and prayers through both periods of frustration and success. To Liz Rengel and Gary Miessler a most deserved thank you for the many hours of thesis puzzle-fitting and helping the author maintain her sanity. It was quite a Halloween celebration! Thank you to Jan Engelkes and Jeff Saul, the author's sister and brother-in—law, for printing the final thesis copy. Above all the author is deeply grateful to family and friends who have always been there with a listening ear, 3 heart full of love, and the words "You can do it". iii TABLE OF CONTENTS Page LIST OF TABLES COOOOOOOOOOOOOOOOOOOOOOOOOOOOOIOOOOOOOO Vi LIST OF FIGURES 0.0...OOOOOCOOOOOOOOOOOOOOOIOOOOOOOOOO ix INTRODUCTION 0.0...OOOOOOOCOOOOOOOOCOOOOOO0.0.0.000... 1 LITERATURE REVIEW 0 O O O O O O C O O O O O O O O O O O I O O O O O O O O O O O O I O O O 4 caICium FuDCtj-ons O O O O O O O O C O O O O O I O O I O O O O O O O O O O O O O O 4 Cal-Cium Uptake O O O O O O O O O O O O O O O O O O C O O O O O O O O O I O O C O O O 6 Galoium Transport 0 I O O O O O O I O O I I O O O O O O O C O O O I O O I O O O O 8 caICium Distribution 0.0.0.0...OOOOOOOOOOOOOOOOOOO 12 caICium*relat6d Disorders oooooooeooooooeooooooeoo 14 Factors Affecting the Plant Calcium Status ....... 17 Plant Factors ................................ 18 Environmental Parameters ..................... 20 Cultural Practices ........................... 26 MATERIALS AND METHODS OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO. 3]- Field Experimentation ............................ 31 Fruit and Leaf Harvest ........................... 33 Growth Analysis .................................. 3S Nutrient Analysis ................................ 36 Soil Moisture Content ............................ 37 Statistical Interpretation of Data ............... 37 RESULTS AND DISCUSSION OOOOOOIOOOOOOOOOOI0.0.0.0000... 39 SECTION 1: Calcium Status of Pickling Cucumber Fruits ......................................... 39 Definition of Terms .......................... 39 Fruit Calcium Concentration .................. 42 Fruit Calcium Content ........................ 60 Fruit Calcium Accumulation Rate .............. 69 SECTION 2: Pickling Cucumber Fruit Growth ....... 78 Fruit Fresh Weight and Volume ................ 78 Fruit Growth Rate ............................ 92 Fruit Dry Weight ............................. 103 Fruit Length and Diameter .................... 108 iv SECTION 3 Tissues TABLE OF CONTENTS (Continued) : Calcium and Growth Analyses of Leaf Leaf C81C1um concentration 0....00000000000.00 Leaf caICium Content 00.000000.00.00.000000000 Leaf Dry Weight 000000000000000.000.00.0000000 SECTION 4 : Environmental Impact on Rates of Fruit Calcium Accumulation and Growth .......... Calcium Accumulation Rate Relative to Fruit GIOWth Rate IOIIIIIIIIIIIIIIIIOIIIIIIIIIIIII Environmental Conditions During the Growth Periods IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Effect Of Rainfall IIIIIIIIIIIIIIIIIIIIIIIIIII Relationship of Pan Evaporation .............. Effect of Soil Moisture ...................... Effect Of Temperature IIIIIIIIIIIIIIIIIIIIIIII SUMMARY ..... Mean Calcium Concentration and Content in Pickling Cucumber Fruits During Ontogeny ....... Ontogenetic Changes in Calcium Accumulation Rates Relative to the Growth Rates of Pickling Cucumber Fruits ................................ Effect of Various Environmental Parameters on Pickling Cucumber Fruit Calcium Accumulation and Growth IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII BIBLIOGRAPHY 118 118 122 123 126 126 128 139 146 150 153 160 160 163 166 169 LIST OF TABLES Soil fertility values in experimental blocks ... Pickling cucumber split plot experimental d8318n, 1984 .....OOOOOOOOOOCOO......OOOOOOOOOO. Pickling cucumber fruit and leaf harvest times for eaCh main p10t, 1984 ooooooooooooooooooooooo The effect of planting date and cultivar on the calcium concentration of pickling cucumber fruits, harvested 1 to 11 days after anthesis, 1984 The mean calcium concentrations of pericarp and endocarp tissues of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984 The effect of planting date and cultivar on the calcium concentration of pericarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984 ...................... The effect of planting date and cultivar on the calcium concentration of endocarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984 ...................... The interaction of planting date and cultivar on the calcium concentration of endocarp tissue of pickling cucumber fruits, harvested 11 days after anth3818, 1984 .....OOOOOOOOOOOOOOOOO..... The effect of planting date and cultivar on the mean fresh weight of pickling cucumber fruits, harvested 1 to 11 days after anthesis, 1984 vi Page 31 32 34 44 48 SO 52 54 82 Table 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. LIST OF TABLES (Continued) The effect of planting date and cultivar on the mean fresh weight of pericarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthe818' 1984 ......OOOOOOOIOOOOOOOO The effect of planting date and cultivar on the mean fresh weight of endocarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesis. 1984 ...................... The effect of planting date of the number of days from planting to anthesis for pickling cucumber fruits, 1984 .......................... The effect of planting date and cultivar on the number of days after anthesis for pickling cucumber fruits fo reach specific fresh weights, 1984 ......000...........IOOOOOOOOOOOO. The interaction of planting date and cultivar on the growth rate of 150 g pickling cucumber fruits, 1984 ......OIOOOOOOO.........OOOOOOOOOO. The effect of planting date and cultivar on the dry weight percentages of pickling cucumber fruits, harvested 1 to 11 days after antheSiB, 1984 ...O0............OOOOOOOOOOOOOOOO The effect of planting date and cultivar on the mean length of pickling cucumber fruits, harvested 3 to 11 days after anthesis, 1984 .... The effect of planting date and cultivar on the mean diameter of pickling cucumber fruits, harvested 3 to 11 days after anthesis, 1984 .... The effect of planting date and cultivar on the calcium concentration and content of pickling cucumber leaf tissues, 1984 ........... The effect of planting date and cultivar on the dry weights of pickling cucumber leaf tissues, 1984 O....00............OOOOOOOOOOOOOOO Cumulative rainfall and pan evaporation during pickling cucumber vegetative and fruit development periods, 1984 ...................... vii Page 84 85 93 95 102 107 110 111 120 124 131 LIST OF TABLES (Continued) Table Page 21. Gravimetric soil water percentage within the pickling cucumber main plots, 1984 ............. 133 22. The effect of blocking on the percent soil moisture and on the rate of fruit calcium accumulation and growth of pickling cucumbers, 1984 00.0.0000.........OOOOOO......OOOOIOOOOOOOO 152 viii LIST OF FIGURES Figure Page 1. The effect of planting date and cultivar on the (A)calcium concentration and (B)content of pickling cucumber fruits, harvested 1 to 11 days after anthesis, 1984. Each point is the overall treatment average of 4 repli- cations x 4 planting dates x 4 cultivars ...... 41 2. The effect of planting date on the calcium concentrations of pericarp and endocarp tissues of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 replications x 4 cultivars for 25 to 125 g fruits and an average of 3 replications x 4 cultivars for 150 g fruits ... 57 3. The effect of cultivar on the calcium concentrations of the pericarp and endocarp tissues of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 replications x 4 planting dates for 25 to 75 g fruits, an average of 4 replications x 3 planting dates for 100 to 125 g fruits, and an average of 3 replications x 3 planting dates for 150 g fruits ........... 59 4. The effect of (A)planting date and (B)cultivar on the calcium content of pickling cucumber fruits. harvested 1 to 13 days after anthesis, 1984. (A)Each point is an average of 4 repli- cations x 4 cultivars. (B)Each point is an average of 4 replications x 4 planting dates .. 63 5. The effect of (A)planting date and (B)cultivar on the calcium content of pickling cucumber fruits of specific fresh weights, 1984. (A)Each point is an average of 4 reps x 4 planting dates (PD) for 5 to 75 g fruits, an average of 4 reps x 3 PD for 100 to 125 g fruits, and an average of 3 reps x 3 PD for 150 g fruits. (B)Each point is an average of ix LIST OF FIGURES (Continued) Figure Page 13. The effect of cultivar on the growth rate of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 replications x 4 planting dates for 5 to 75 g fruits, an average of 4 replications x 3 planting dates for 100 to 125 g fruits and an average of 3 replications x 3 planting dates for 150 g fruits ........................ 101 14. The effect of planting date on the relative growth rate of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 replications x 4 cultivars for 5 to 125 g fruits and an average of 3 replications x 4 cultivars for 150 g fruits ... 105 15. The effect of cultivar on the length to diameter ratios of pickling cucumber fruits, harvested 3 to 11 days after anthesis, 1984. Each point is an average of 4 replications x 4 planting dates oooo0000000000000000000000000. 114 16. The effect of planting date on the length to diameter ratios of pickling cucumber fruits, harvested 3 to 13 days after anthesis, 1984. Each point is an average of 4 replications x 4 cultivars ................................... 116 17. The effect of planting date on the fruit growth rate versus calcium accumulation rate for (A)75 g and (B)150 g pickling cucumber fruits, 1984. The rates for each planting date were estimated from regression curves of the fruit calcium concentration and fresh weight of 4 cultivars, each replicated 4 times. The July 5 planting had 3 repli- cations 00.00.0000.........OOOOOOOOOOOOOOOO0.0. 130 18. Maximum and minimum daily air temperatures during the pickling cucumber growth period of the 4 planting dates, 1984. (Data measured by the Michigan State University Weather Service at the Horticulture Research Center) .. 136 19. Maximum and minimum daily soil temperatures during the pickling cucumber growth period of the 4 planting dates, 1984. (Data measured by the Michigan State University Weather Service at the Horticulture Research Center) .. 138 xi Figure 20. 21. 22. 23. LIST OF FIGURES (Continued) Daily rainfall during the growth period of pickling cucumbers from 4 planting dates, 1984. (Data measured by the Michigan State University Weather Service at the Horticulture ResearCh center) 00.0.0.0...IOOOOOOOOOOOOOOOOOO The relationship between daily pan evapor- ation and the (A)ca1cium accumulation rates and (B) fruit growth rates of 150 g pickling cucumbers from 3 planting dates, 1984. The rates for each planting date were estimated from regression curves of the (A)fruit calcium concentration and (B) fruit fresh weight of 4 cultivars, each replicated 4 times. The July 5 planting had 3 replica- tions. (Evaporation measured by the Michigan State University Weather Service at the Horticulture Research Center) ................. The effect of maximum daily soil temperatures on the calcium accumulation rates of (A)25 g, (B)75 g, and (C)150 g pickling cucumber fruits from the different planting dates, 1984. The rates for each planting date were estimated from regression curves of the fruit calcium concentration of 4 cultivars, each replicated 4 times. The July 5 planting had 3 replications. (Temperatures measured by the Michigan State University Weather Service at the Horticulture Research Center) ............. The effect of minimum daily soil temperatures on the calcium accumulation rates of (A)25 g, (B)75 g, and (C)150 g pickling cucumber fruits from the different planting dates, 1984. The rates for each planting date were estimated from regression curves of the fruit calcium concentration of 4 cultivars, each replicated 4 times. The July 5 planting had 3 replications. (Temperatures measured by the Michigan State University Weather Service at the Horticulture Research Center) ............. xii Page 141 149 156 158 INTRODUCTION Although an extensive body of knowledge exists concerning calcium nutrition of plants, Wallace and Soufi (1975) were compelled to comment that "in general the question of the calcium needs of plants is extremely confused, and calcium may be the least understood "1 essential element. Our lack of understanding of the function, uptake and transport of calcium in plants has slowed our progress in controlling the thirty-five known calcium-related disorders of fruits and vegetables and perhaps in recognizing other calcium disorders (109). Fruit calcium concentration is highly correlated with fruit growth and quality in many crops. Calcium is involved in cell division and elongation, cell wall formation, maintenance of membrane integrity and function, and in enzyme activation. Certainly these physiological processes are vital to the normal growth and development of fruits. 1A. Wallace and S. M. Soufi, "Low and Variable Critical Concentrations of Calcium in Plant Tissues," Commun. Soil Sci. Plant Anal., 6 (1975), p. 332. 1 2 The general calcium uptake characteristics or the calcium status of an entire plant are not indicative frequently of the calcium status of specific organs on the plant. Calcium deficiency symptoms may appear in plants grown on soils where the available calcium content is adequate as well as where the content is low. Deficiency symptoms are seldom expressed in the foliage of field- grown plants. Rather, they appear in fruits, storage roots, tubers and heart leaves of leafy vegetables. Although a calcium—related disorder has never been identified positively in pickling cucumber fruits, Cucumis sativus L., the plant is a good model for investigating fruit calcium nutrition. The plant material is relatively accessible, as fruits may be harvested in less than fifty days after planting. Cucumber fruits may increase in fresh weight up to forty percent within a twenty—four hour period (89), accentuating calcium dilution through ontogeny. This was confirmed in a study of the mineral nutrition of pickling cucumbers by Widders and Price (1984), in which the mean fruit calcium concentration declined as fruits enlarged (137). Other research results suggest that calcium may be a limiting factor in pickling cucumber fruit quality, as well as in fruit development. Adhikari (1980) reported a correlation between an increased incidence of misshapen cucumber fruits and a reduced fruit calcium content when chlorflurenol, an auxin tranport inhibitor, was applied 3 to induce parthenocarpic fruit set (2). Staub (1985) produced the "pillowing disorder", a putative symptom of calcium deficiency in cucumber fruits, by growing cucumbers in a calcium-deficient nutrient solution (119). Most of the limited research on the calcium nutrition of pickling cucumbers has been conducted in controlled environments. In order to understand the importance of calcium in pickling cucumber fruit development and quality, further research is necessary in the field. The objectives of this research were: 1)to quantify the mean calcium concentration and total content in pickling cucumber fruits during fruit ontogeny; 2)to evaluate the ontogenetic changes in calcium accumulation rates relative to the growth rates of pickling cucumber fruits; and 3)to correlate various environmental parameters with fruit calcium accumulation and growth in several pickling cucumber cultivars. LITERATURE REVIEW Calcium has been recognized as an essential mineral nutrient in higher plants for over a hundred years (61,78,84,128). Although classified in the group of ten macronutrient elements, plant calcium requirements are often in the micronutrient range (18,59,60). A rediscovery of the importance of calcium nutrition on plant growth, development, and physiology has taken place in the last decade. Calcium Functions Calcium, an essential element for plant growth, is involved in cell division and specifically in increasing cell elongation (17,18). Root growth ceases within a few hours when calcium is absent in the nutrient medium (61). High calcium ion concentrations inhibit cell elongation (25,27,61). Cleland and Rayle (1977) propose that cytosolic calcium inhibits the biochemical processes of cell wall-loosening, either by competing for hydrogen ion binding sites or by altering wall proteins and/or polysaccharides, which are involved in hydrogen ion-enhanced enzyme reactions (25). 5 The highest calcium concentrations in plant cells are always found in the cell walls (27). By cross—linking pectic polymers, mainly in the middle lamella, calcium brings both structural and physiological stability to cell walls (18,20,23,24,27,34,128). During cell growth calcium is lost from the cell wall, changing the calcium-bridge structure (17,24,25,34,59). Calcium plays a crucial role in maintaining plant membrane integrity. Membrane deterioration, identified by light and electron microscopy, is the first detectable sign of a plant calcium deficiency (4,59,61,62,77,98). Plant tissue senescence can be retarded by the addition of calcium. Corn leaf senescence was delayed by floating leaf disks in a calcium chloride (CaClz) solution (98). CaCl2 sprays and dips are used commercially to reduce the incidence of bitter pit, a calcium disorder of apples associated with senescence (14,15,36,68,79,118). Membrane permeability and selective ion absorption are influenced by tissue calcium levels (17,18,20,31,59,61,65,77,84,98, 116,117,128,134). Calcium-deficient plant tissues are more subject to a heavy metal imbalance than tissues with high calcium concentrations (134). Calcium plays a key role in plant cell metabolism through its involvement in enzyme systems: ATPase (4,28), alpha-amylase (59,131), NADH dehydrogenase (87), quinate- NAD+ oxidoreductase (28), NAD and membrane-bound protein kinases (4,28,87), etc. Many of these enzymes are 6 calmodulin-dependent (28). Changes in cytoplasmic calcium concentrations activate calmodulin, a calcium-binding protein (28,98,120). Calcium is thought to alter enzyme activity, specifically membrane-bound enzymes, by main- taining membrane structure and thus enzyme configurations (4,27,59,61). The calcium-mediated activity of poly— galacturonase (62) and phospholipase A2 (67) is linked with the onset of cell senescence and the loss of membrane integrity (34). Recent reviews have cited increasing evidence that free calcium ions function as a secondary plant messenger (28,87,98,131). When plant cells perceive stimuli, like light or gravity, calcium ions are released into the cytosol (131). It is proposed that these changes in the cytoplasmic calcium concentration result in an activation of calmodulin. Calmodulin in turn activates certain enzyme systems, leading to various plant responses such as phototropism and gravitropism (28,98,131). Calcium Uptake Calcium is the major exchangeable cation in all but the very sandy and strongly acidic soils (43,58). Calcium moves to plant roots by mass flow in the soil solution (60, 83,104). The plant root surface area is highly correlated with calcium uptake (115,122). During exponential plant growth phases, calcium uptake is highly affected by the root growth pattern (70,104,140). Calcium uptake by apple 7 trees continues from flowering to harvest, but the rate tends to decline in the last two months of fruit development, when root growth decreases (56). If plant calcium uptake is neither selective nor active, continuous root growth and a high calcium concentration at the root surface are important for facilitating continuous calcium uptake by the plant. The root calcium "absorbing zone" is believed to be restricted to tissues near the root tip (4,46,47,60,61). The movement of calcium ions into roots is virtually eliminated by suberization of the endodermis or by secondary root thickenings, suggesting that calcium follows the apoplast pathway (4,9,10,23,33,46,47,60,74). Calcium ions are adsorbed onto fixed, negatively charged cell wall surfaces (4,29,60,61,74,78,88). Proponents of passive calcium transport believe that calcium ions simply follow the influx of water into plant roots, moving by exchange reactions through the root cortex and into the xylem without ever being actively absorbed. Calcium uptake is both concentration dependent, limited by the rate of diffusion at higher concentrations, and metabolically controlled, especially at low calcium concentrations (63,72). The metabolism-linked phase of uptake is probably the transport of calcium ions through the endodermis into the stele via the symplast pathway (9,10,46,60). Decreased calcium transmembrane transport, when root tissues are exposed to low temperatures 8 and metabolic inhibitors, provides evidence for an active calcium transport system (9,29,63,72,140). The symplast is not a major pathway for calcium transport, however, as the root cortical cytoplasm contains only micromolar concentrations of calcium and ion mobility is very limited (23,47,74). Calcium Transport The possible pathways of long distance calcium transport in higher plants are the xylem and/or phloem. Calcium is transported almost exclusively in the acropetal direction via the xylem (8,12,23,46,56,61,110,111,138,139). The ions move by exchange reactions along the fixed, negative binding sites of the xylem walls. Other divalent cations compete with calcium for these exchange sites, promoting calcium mobility (8). The xylem pathway has several advantages for distributing root-absorbed calcium ions (12,23,46,66,100,130). The volume and velocity of flow in the transpirational stream enhances the rate of calcium movement from the root to the shoot. The xylem can transport calcium throughout the plant in adequate quantities to support cell growth, since the extracellular xylem sap has virtually no calcium concentration restrictions, unlike the symplastic pathway. Plant organs with a limited xylem water influx generally have low calcium contents (1,5,78,138). The importance of transpiration-driven calcium transport is 9 demonstrated by young, developing lettuce and cabbage leaves (7,94,125). Rapidly transpiring outer leaves accumulate significant quantities of 45Ca in short-period (2-4 hour) uptake studies (94,125). The low transpiring enclosed leaves at the growing point accumulate little 450a in the center one-half of the leaves and none at the leaf margins. Although calcium translocation is often highly correlated with water transport (47,61,66,78,94,139), the relationship is not necessarily directly proportional (9,12,29,80,94,111). Since calcium undergoes continuous loss, exchange or gain with plant tissues as the ions ascend the xylem column, the rate of calcium transport relative to the volume flow rate of water may vary (12). Palzkill and Tibbitts (1977) report a decreasing ratio of 45Ca transported to total plant water use with increasing transpiration rates (94). A reduction in transpiration, due to shoot excision, may not reduce calcium uptake on a short term basis (9). Likewise, a reduction in calcium translocation due to a metabolic inhibitor may not alter water transport. Developing leaves, flowers and very young fruits are major and competing sinks for calcium and water via the xylem (23,37,139). The movement of calcium to these sinks may also be affected by endogenous plant hormones. Basipetal auxin transport seems to influence calcium transport, especially to shoot spices and into developing 10 fruits (3,37,61,118). Auxin synthesis and export from these tissues increases during flowering and fruiting (11). The auxin transport inhibitor, TIBA (2,3,5-triiodobenzoic acid), reduces the calcium concentration of apple fruits (118). It is proposed that during growth, endogenous auxins enhance calcium transport through formation of new cation exchange sites (61). Plant ontogeny alters calcium translocation patterns within an intact plant (46,54,101,127). The distribution of 450a in apple fruits at selected stages of development was monitored by thin section autoradiography, following root—feeding of small apple trees (37,85). Calcium accumulation rates in apple fruitlets are very high in the first 4 to 5 weeks after fruit set. As the fruitlets enlarge, the rate of accumulation gradually declines. After the apples reach the midway stage of fruit development at 11 to 14 weeks after full bloom, the isotope accumulates in the bark and leaves of fruit spurs but not in the flesh of apple fruits. Wiersum (1966) postulates that the decline in the rate of calcium import into rapidly expanding storage organs is due to a change in the mode of water supply (139). Using Light Green dye as a visual tracer for water transport through the xylem, the patterns of distribution of root-absorbed 45Ca and Light Green are highly correlated. During periods of high growth rates, no or only 45 minimal amounts of Light Green or Ca were translocated 11 into tomato and apple fruits, potato tubers, and seeds of broad beans via the xylem. Jones et al. (1983), calculating the probable limits to the influx of water into apple fruits via the xylem and phloem, also report two phases of calcium uptake into apple fruits (56). Although the two pathways may transport similar quantities of water early in the season, the phloem is the predominant mode of water supply into fruits later in the summer. Young fruits have high transpiration rates and are photosynthetically active (37,42,46,57,61,101,127,139,140). The high water demand and the low requirement for additional assimilates can be supplied via the xylem, in which calcium moves freely. Although the import of water into fruits in the phloem is not restricted during the first few weeks of apple fruit development, it is probably rather unimportant compared with xylem transport (127). The rate of fruit transpiration decreases, due to a decline in the surface area to volume ratio, and the assimilate demand increases as fruits mature. Assimilates, nutrients, and water are transported from the leaves to the developing fruits via the phloem. The low calcium contents of mature apple and tomato fruits are similar to the known phloem sap calcium levels (46). The phloem tissues cannot facilitate calcium transport like the xylem (23,33,73,100,102,127,138). Calcium is relatively immobile in the phloem symplasm 12 (4,33,46,47,56,57,60,78,127). The sieve tubes selectively exclude calcium (46,61), and the high pH and phosphate concentration of phloem sap would precipitate calcium as calcium phosphate (78). The obligatorily low calcium concentration of phloem sap is insufficient to support cell growth effectively (23,127). It is essential, therefore, that adequate supplies of calcium reach developing fruits via the xylem during the earliest stages of growth (37,46,78,85,101). Calcium Distribution Calcium is considered the most immobile plant nutrient among the essential elements (35,46). Since calcium moves with difficulty from cell to cell by symplasmic trans- location, this element is unevenly distributed within plant organs (4,5,13,33,35,37,51,68,85,86,101,111, 137). Intact maize plants, fed 45 Ca for 24 hours, partition more of the isotope to apical than to mid or basal leaf segments (33). A declining calcium concentration gradient exists from the stem to the calyx end of tomato and apple fruits. An electron microprobe study for calcium in apple fruit tissues reveals a higher concentration in flesh versus peel tissues, vascular bundles versus the surrounding parenchyma tissue, and in lenticular versus non-lenticular peel tissues (86). Thin section autoradiography also identifies changing patterns in calcium distribution as apple fruits mature (37,85). Root—absorbed 45Ca applied at 4 to 5 13 weeks after full bloom enters the vascular bundles throughout the whole fruit. The calcium concentration is highest in the core towards the stem end, intermediate in the peel, and least in the flesh tissue. Less 45Ca accumulates in the outer cortex when applied at later stages of fruit maturity. Once deposited in plant organs, calcium redistributes to other parts of the plant slowly or not at all (1,11,33, 35,46,61,63,69,78,102). Calcium will move out of fruits to shoot meristems via the xylem, particularly during periods of drought (56,127). If the amount of water imported into fruits through the phloem exceeds the cellular and trans- pirational tissue needs, further calcium may be exported out of fruits in the xylem (139). Older leaf tissues may have very high calcium concentrations (1,5,11,46,69,78, 111). This lack of calcium remobilization is primarily due to limited phloem mobility. Mature leaves contain large quantities of lignin, which has a high affinity for calcium (33,102,110). The suberin deposits in the vascular tissues of older leaves restrict calcium translocation out of the leaves. The deposition of insoluble calcium oxalate crystals in plant tissues is also a factor limiting calcium remobilization (21,37,39,46,49,53,78,82,100,133). Any existing calcium regulatory mechanism in plants appears to operate in the direction of restricting rather than promoting calcium transport and distribution (4,9,55, 78). The calcium contents of plant organs are based on l4 metabolic removal from the vascular system (4,63), rather than on physiological demand (8). Loneragan and Snowball (1969) report deficient and luxury concentrations of calcium occurring simultaneously in different tissues of an individual plant (69). The calcium concentrations of leaf tissues are often several fold higher than those of fruit tissues (1,5,11,36,78,111,137). More calcium is distributed to fruits in the lower part of an apple tree than to fruits from the upper branches (16,57). Calcium-related Disorders Many researchers report a close correlation between the calcium concentration and quality of fruits, storage roots, tubers, and heart leaves of leafy vegetables. Calcium, due to its functions in plants, may affect quality by: reducing respiration (4,34), increasing fruit firmness (4,14,105), delaying fruit ripening and leaf senescence (4,34,76,105), increasing vitamin C content (4), reducing storage rot (4), reducing fruit splitting (l9), and enhancing yield (84,135). Although limestone and marl have been used in agriculture for hundreds of years, calcium has never received the attention growers give to their nitrogen, phosphorus, and potassium fertilizer regimes (58,84). Reports of plant calcium deficiencies are numerous, despite normal soil calcium levels being high enough to meet plant requirements (4,43,58,60,84). Applications of lime have 15 consistently failed to alleviate calcium-related disorders because the deficiencies are localized in the plant (4,58, 60,84,91,111,121). A calcium supply sufficient for leaves may not be sufficient to prevent calcium deficiency symptoms in fruits (111). Shear (1975) lists thirty-five calcium-related disorders in different plant species (109). The characteristic feature of these disorders is a localized calcium deficiency (7,14,16,37,42,60,70). Although root and vegetative tissues may display calcium deficiency symptoms in the field, the most serious economic losses occur from deficiencies in reproductive tissues (84). Localized calcium deficiencies occur in rapidly growing organs (1,4,16,40,44,56,57,91,95,109,111,125,126,133,139). A rapid growth rate results in a steady dilution of the plant organ calcium concentrations, especially if the rates of calcium import and accumulation are low. Normal fruit calcium concentrations, ranging between 200 and 3000 ppm dry weight, are only slightly higher than the fruits' functional requirements (69,134). Rapid growth causes an increase in the calcium requirement, which the plant often cannot meet (4,40,125). Fruit enlargement, due primarily to cell expansion rather than cell division (113,114), decreases the formation of new calcium binding sites (61). Rapidly enlarging fruits are primarily supplied with water and nutrients, along with the necessary assimilates, in the phloem rather than 16 in the xylem, the major calcium transport pathway (37,57, 61,139). The influx of calcium into developing fruits via the xylem transpiration stream is further restricted as the surface to volume ratios of these fruits decline (4,61). Calcium is preferentially distributed to the more rapidly transpiring leaf tissues (4,56,57,61,78,111). It is for this reason that calcium deficiencies are positively correlated to the rate of vegetative growth (109). Ferguson (1984) separates plant calcium-related deficiencies into two groups: disorders resulting from uneven calcium transport or distribution and senescent disorders (34). Some of the disorders caused by uneven calcium partitioning are blossom-end rot of tomatoes (40,60,61,75,81,90), blackheart of celery (44,60,61), leaf necrosis of seedling carrots (125,126), and tipburn of lettuce (7,60,61), cabbage (94,125), and cauliflower leaves (50). The occurrence of these localized calcium deficiencies indicates that higher plants are not able to adequately regulate their calcium distribution (4,61,78). Bitter pit (34,37,51,60,61,109), senescent breakdown and decay of apples (14) are among the calcium disorders associated with senescence. Calcium retards senescence (4, 14,34,76,105), perhaps by maintaining membrane and cell wall structure (34,123) and by suppressing polygalacturonase activity (34,62,98). Although high calcium concentrations are an advantage in delaying senescence and ripening, normal cell operation 17 requires low cytosolic calcium concentrations (34,74,105). To maintain enzyme activity and membrane functioning, eukaryotes must limit their free, cytoplasmic calcium concentrations to between 0.1 and 10 micromoles (100). The physiologically active calcium concentrations of fruits must decline in order for ripening to occur (14,34,61). Rin, the non-ripening tomato mutant, maintains high levels of calcium throughout ontogeny (98). A calcium deficiency changes the ultrastructure of plant cells. The plasma and vacuolar membranes disintegrate (48,59,62,77), followed by a loss of cohesion in the cell wall (34,48,123). With increased membrane permeability, cell fluids invade the intercellular air spaces of calcium deficient leaf lamina and fruit tissues (40,48,75,81,112, 126). These tissues will appear translucent, which is the initial symptom of most calcium related disorders. This temporary phase is followed by tissue desiccation (1,4,40, 59,75,81,112,125,126). Necrosis is a diagnostic symptom of a plant calcium deficiency. Other observable symptoms which may appear are chlorosis (1,117), leaf cupping and curling (40,59,117), fruit cracking (19,26,112), and decreased root (59), leaf (35), fruit and/or seed (59) development or growth. Factors Affecting:the Plant Calcium Status Loneragan and Snowball (1969) define a plant's functional nutrient requirement as "the minimal 18 concentration of nutrient within the plant organism which can sustain its metabolic functions at rates which do not limit growth."2 Any factor, which affects calcium uptake, transport and distribution, plays a determinant role in meeting the plant's functional calcium requirements (40,109,111). Endogenous plant factors and almost every environmental parameter and cultural practice have been cited by researchers as either aggravating or ameliorating plant calcium deficiencies (46,75,109). Plant Factors The calcium content of a particular plant family, genus and species is to a large extent genetically controlled (61,75). Calcifuge plants attain maximum growth on acid soils (4,18). These plants have low soluble calcium contents and high concentrations of insoluble calcium oxalate (39). Calcicole plants thrive on soils with a high calcium content (4). A cucumber plant, classified as an obligate calcicole, may absorb forty times more calcium than wheat, a calcifuge plant (10,53). Dicotyledons absorb more calcium from a given supply than do monocotyledons (70,75,103). The amount of calcium uptake is highly correlated with root parameters (104). Dicotyledonous roots have a higher cation exchange capacity, 2J. F. Loneragan and K. Snowball, "Calcium Requirements of Plants," Aust. J. Agric. Res. 20 (1969), p. 471. 19 enhancing calcium adsorption (61). The differences in absorption may also be due to a greater total root surface area (70,103), more unsuberized root surfaces (45), and/or calcium specific binding sites (10) in dicotyledons. The most effective control of calcium-related disorders is to develop resistant plant varieties. Genetic differences in calcium uptake and translocation have been discovered in apple seedlings (110). Festuca axing populations have been classified as acidic or calcareous, depending on their ability to absorb calcium from low solution concentrations (116). Plant cultivars have already been identified with varying degrees of resistance to calcium-related disorders: tomato blossom—end rot (30, 43,81,90), cabbage tipburn (91,125), cauliflower leaf tipburn (50), lettuce tipburn (26), and seedling carrot leaf necrosis (126). A number of heritable traits from the diverse plant germplasm pool have been selected for, which enhance resistance to calcium-related disorders. Genetic resistance may be due to more efficient or selective calcium absorption (30,43,50,116). Young developing tissues may differ in their calcium requirements (43,126) or in their calcium utilization (50). Plant cultivars may differ in their transpiration rates (126). Cabbage cultivars with reduced nightly stomatal opening are more resistant to tipburn injury (125). Barker and Maynard (1972) report a 20 difference in calcium accumulation in pea and cucumber shoots based on the form in which nitrogen is translocated from roots to shoots (6). Since plants may grow differently in controlled environments than in the field, selections should be made under both conditions. Although artificial enclosure of young lettuce leaves encourages tipburn in the laboratory, natural leaf enclosure, such as occurs during heading, often does not initiate injury in the field (7). In controlled environments tipburn symptoms develop rapidly even on lettuce cultivars which are highly resistant to tipburn in the field (26). Environmental Parameters Climatic factors affect plant growth rates, which in turn significantly affect the rates of plant calcium uptake and accumulation (46,54,60,140). Water, essential for growth and development, is responsible for conducting minerals from the soil to plant organs. Bangerth (1979) cites water as one of the most "decisive" factors affecting plant calcium distribution (4). Soil moisture and the water potentials of plant organs may also determine the impact which secondary environmental factors, such as light and temperature, have on calcium distribution in the plant. Optimum soil moisture affects the calcium concentration of the soil solution, provides a high soil-water potential, and maximizes plant water and nutrient uptake (125,140). 21 Excess soil moisture inhibits root growth due to reduced aeration (40,42,45,109,125). Since calcium is believed to be absorbed only by young, unsuberized root tissues, any reduction in root growth will retard calcium uptake (4,46,47,60,61). High soil moisture may also cause rapid fruit expansion, diluting the initial fruit calcium concentrations. In contrast, the calcium concentrations of leaf and fruit tissues of mildly drought-stressed plants are generally higher due to lower growth rates (16,90). Low soil moisture may have either a positive or negative effect on calcium availability to the plant. Less calcium leaches out of the rhizosphere during a soil water deficit, but the mass diffusion of calcium ions to root surfaces will be decreased (90,109). A soil water deficit may also reduce calcium uptake by inhibiting root growth and reducing availability of energy rich metabolites to the root system (40,42,45,109,140). Xylem calcium transport is also depressed by a soil water deficit, due to low volume flow rates through the vessels (45,139). Even an intermittent soil moisture deficiency increases blossom-end rot of tomatoes (90). Calcium may be exported from fruits to leaves, due to competition for water and calcium (101,140). Transpiration plays a major role in calcium accum- ulation, as previously mentioned. High relative humidity throughout the day increases the rates of plant growth and decreases calcium transport via the transpiration 22 stream (5,7,26,41,44,48,127,l38). Tomato leaves may become calcium deficient after a prolonged period of cloudy, humid weather (1). Low relative humidity increases plant transpiration rates, but the transpirational stream may bypass low transpiring fruits and storage organs in favor of leaf tissues. This general trend did not occur in a 1983 study by Jones and Samuelson (57). They report that apple fruits with long bourse (swollen stem at base of inflorescence) shoots had higher fruit calcium concentrations than fruits associated with shoots of a lower leaf area. They propose that ‘adequate evaporation from primary leaves plays an important role in achieving, rather than inhibiting, high fruit calcium concentrations. Diurnal fluctuations in a plant's water potential facilitates calcium distribution to low transpiring plant organs (l,4,5,l3,41,94,125,126). Root pressure develops when a plant stops transpiring or when the rate of water uptake exceeds the transpiration rate. A positive pressure develops in the xylem as the root pressure increases, moving calcium to the low transpiring plant organs. This is especially significant during the night when the growth rate of many storage organs is most rapid (4,13,26). Changes in relative humidity and stomatal opening and closing create the diurnal fluctuations in plant-water potentials. High relative humidities only at night, adequate water, and low soil salinity favor root pressure development (l,4,5,l3). Calcium—related injuries in the 23 field are more prevalent when periods of cool, moist weather are interrupted by warm, dry days (90,125). Bradfield and Guttridge (1984) report that night-time humidities have a more significant effect on blossom-end rot incidence than the solute concentration in the soil solution during early tomato fruit development (13). Adams and Ho (1985) attribute a greater importance to high salinity in reducing tomato fruit calcium content than to low relative humidities (1). Transpiration rates and the soil solution concentration often interact, however, affecting calcium uptake. Plant uptake is selective for calcium over magnesium at low transpiration rates and soil solution concentrations (66). In addition, calcium uptake is also affected by the soil pH and the presence of other anions and cations (72). The total amount of available calcium in the soil does not affect uptake as much as the concentration ratio of calcium to the other ions in solution (18,58,60,108). The uptake of monovalent ions by plant roots is largely dependent on the soil solution concentration of the specific ion, while the uptake of divalent cations is proportional to the total salt concentration (66). A low calcium to total salt concentration ratio increases the incidence of calcium- related disorders (40,41,90,109). High salinity may influence calcium uptake by limiting plant water uptake (41,66,125). It also has an unfavorable effect on root pressure development, reducing calcium 24 distribution to low transpiring plant organs (13,41). High salinity also may alter a tomato plant's anatomical structure, increasing the internal resistance to xylem influx from the pedicel into the fruit (1). Low soil pH depresses calcium uptake by many plants (22,64,72). Acid soils contain less available calcium (42). Hydrogen ions compete with calcium ions for uptake in acid soils between pH 3 and 5 (72). High levels of aluminum and manganese in the soil solution, which can be toxic to plants, interfere with calcium metabolism and uptake in acid soils (42,60,64,99). The effect of other ions on calcium uptake may differ whether under field or controlled environment conditions. Soils provide a strong buffering capacity which hydroponic cultures cannot provide. Loneragan and Snowball (1969) also demonstrate convincingly that critical plant tissue calcium concentrations, below which a deficiency develops, are highly affected by the calcium concentrations under which a plant is grown (69). This diminishes the reliability of a critical tissue calcium concentration value apart from the particular experimental conditions under which it was determined. Rapidly absorbed anions, N03 > C1 2 Br > 8042-, enhance calcium absorption (60,72). Both a deficiency and an excess concentration of any of the essential plant cations also affect calcium uptake. The addition of any deficient plant nutrient can stimulate 25 calcium uptake (55,109). If aluminum is present in the soil solution, ammonium ions can stimulate calcium uptake (64). Of the monovalent ions, H+ (72), K+ (40,42,60, 64,72,121), and NH4+ (6,40,43,60,108) compete with calcium for absorption, while Li+ and Na+ have only slight effects (72). Excess nitrogen (40,60,90,91,109, 133), especially the NH4+—N source (38,109), potassium (18,40,42,90,109), magnesium (40,42,51,60,64, 66,109) and possibly phosphorus (109) depress plant calcium uptake and are correlated with calcium deficiencies. Stimulation of excessive vegetative growth with nitrogen can be deleterious to the calcium supply of low transpiring plant organs (42,60,95,108,140). Excess nitrogen, phosphorus, and/or potassium can also stimulate fruit enlargement, diluting fruit calcium concentrations (95). Excess nitrogen fertilizers may increase calcium oxalate production due to enhanced nitrate assimilation (133). Ammonium fertilizers acidify soils, increasing calcium leaching. High NH4+-N levels are also associated with shorter plant roots and even injury to root tips, the active zone for calcium absorption (53,60,108). An excess concentration of any ion. changes the proportion of calcium to total ions in the soil solution and perhaps within the plant. Bitter pit of apples may be due more to a localized magnesium toxicity than to a calcium deficiency (51,109). High levels of fertilizers, such as ammonium fertilizers, may reduce plant water uptake 26 (60,108). Excess phosphorus may precipitate calcium from the root medium in an inactive form (43,55,109). Other ions have a marked influence on calcium transport and distribution within plants (43,46). Boron may stimulate calcium movement into the petioles and midribs of apple leaves and increase the calcium concentration in apple fruits (42, 108, 109, 110, 111). N03--N increases calcium transport and accumulation in mature leaves, while NH4+-N stimulates calcium partitioning into new leaves (110,111). Apple fruits, sprayed with a zinc salt solution, have a higher concentration of soluble calcium and less oxalate bound calcium (108). The oxalate may preferentially bind with zinc rather than with the calcium ions. Warm soils encourage mineral and water uptake and may encourage root pressure flow (26,53,125,l40). Lower soil temperatures, however, may favor calcium uptake over that of potassium if calcium uptake is passive (140). Potassium uptake is more sensitive to fluctuations in metabolic activity than calcium uptake. Warm soils also stimulate plant growth which may be detrimental to the calcium status of plant organs. Cultural Practices Both early planting and late harvesting lower the calcium concentrations and increase the incidence of tipburn of cabbages (91). Seeds sown into cold soils develop roots more slowly, limiting calcium uptake via the transpiration 27 stream. The cold soils also are not conducive to root pressure development. Late harvesting encourages further growth, diluting the calcium concentrations of plant organs. In apple, close spacing may be favorable for the calcium status of plant organs if it decreases plant vigor, achieving slightly smaller and slower growing fruits (140). Close spacing is not beneficial to calcium accumulation if excess pruning is required (42). Excess pruning and thinning can excessively invigorate vegetative growth, resulting in large fruits with lower calcium concentrations (42,57,95). Moderate defoliation may reduce calcium- related disorders by slightly increasing the calcium concentration of fruits, without altering fruit size (95,109). During mild droughts, reducing older and extra foliage can be beneficial to the fruit calcium concentration (1). Low fruit calcium concentrations may occur as a result of biennial bloom patterns. Inadequate thinning encourages heavy fruiting one year followed by a year with sparse, over-sized fruits. Over-sized fruits may also occur due to excessive tree vigor, poor fruit bud formation, an insufficient number of bees and desirable pollen, and frost damage (42). All of these factors will result in a growth-induced dilution of the fruit calcium concentration. Judicious irrigation scheduling may be very beneficial for plant calcium uptake and accumulation in plants (95). Plant calcium nutrition is favored by steady growth rates. 28 Adequate soil moisture maintains uninterrupted, passive calcium uptake and upward translocation in the transpiration stream (140). Overhead misting of mildly water—stressed plants may also minimize the development of necrotic tissues, which is associated with a localized calcium deficiency (44). Selective shading may encourage higher fruit calcium concentrations (95,106,109,127,139). More calcium accumulates in vegetative tissues which are growing under high light intensities. These tissues are major calcium sinks, due to their high growth rates and increased transpiration rates (109,127). Competition for available calcium between leaf and fruit tissues is accentuated. Higher light intensities also enhance photosynthesis, providing the necessary assimilates for increased fruit enlargement. This will further dilute the calcium that is able to move into the fruits (109). It is desirable to reduce high vegetative transpiration rates which favor calcium distribution primarily to leaf rather than fruit tissues. In addition to shading, other means of reducing high transpiration rates are shelterbelts to reduce wind speeds, antitranspirant oil sprays, and overhead sprinkling (140). Dilute or concentrated calcium sprays and dips are used to increase the calcium concentration of fruit flesh tissues (15,79,95,118). The calcium will move into the fruit tissues only if the spray is applied directly onto the 29 fruit surface (36,109). Although only very limited quantities of calcium can be supplied in this way, sprays reduce leaf necrosis in seedling carrots (125,126), sweet cherry splitting (19), and are commercially used to reduce bitter pit (36,68,118) and senescent breakdown (15) in apples. Lewis and Martin (1973) find calcium sprays to be much more effective in increasing the calcium concentrations of apple fruits than soil applications (68). Despite the benefit to fruits, calcium chloride sprays may cause leaf injury, especially following a wet, cool spring (15,42). Proper timing of the spray applications is crucial to maximize the benefit. Rapidly growing leaf tissue may require daily sprays to prevent tipburn (125). Sprays applied closer to harvest are more effective in increasing apple fruit calcium concentration than sprays applied earlier in the season (15,19,42,118). Although applications of TIBA, an auxin transport inhibitor, reduce the calcium concentration of apple fruits (4,118), exogenous auxin applications do not substantially increase the calcium content of pollinated fruits (3). If the seeds synthesize sufficient quantities of auxin, it is understandable that sprays would be ineffective. Foliar boron sprays reduce the calcium-related corking disorder of apples (42,109). Boron increases calcium accumulation, especially in plant tissues containing marginal calcium concentrations (108, 111). Shear and 30 Faust (1971) postulate that the boron effect may be due to an increased metabolic activity, especially if the tissue had been boron deficient (111). MATERIALS AND METHODS Field Experimentation A field experiment was conducted at the Horticulture Research Center in East Lansing, Michigan in 1984. The field was a sandy loam soil with a sloping terrain running north to south. Due to soil fertility and moisture gradients, the four replications were arranged in an east to west direction (Table 1). Table 1. Soil fertility values in eXperimental blocks. Soil Lime P K Ca Mg Calc. Block pH index (lb./A) CEC 1 6.3 72 200 280 1347 240 5 2 5.7 70 233 320 1095 209 4 3 5.4 67 182 280 1263 228 8 4 5.6 64 292 296 1347 240 12 The experimental design was a split plot, with four planting dates and four pickling cucumber (Cucumis sativus L.) cultivars (Table 2). The main plots (planting date) were randomized within each block and the sub-plots (cultivar) were randomized within each main plot. Two 31 week intervals 19, provided diverse Potential four cultivars: environmental genetic variability 32 between successive plantings, June 7 to July growing conditions. was assessed by planting Castlepik 2012, PSX20580, Regal and Tamor. Table 2. Pickling cucumber split plot experimental design, 1984. Main plot Sub-plot 4 planting dates 4 cultivars Planting, Date Cultivar Seed company 1 June 7, 1984 Castlepik 2012 Castle 2 June 20, 1984 PSX20580 Peto 3 July 5, 1984 Regal Harris 4 July 19, 1984 Tamor Asgrow The main plots were disked prior to planting. Seeds were directly sown 5 cm apart within rows, using a Heath vacuum precision planter, m wide and 9 m long. plots and at the ends of four replications were emergence plants were resulting in a cm between rows. Approximately 2.5 irrigation after sowing No further irrigation separated by thinned cm of water was applied was used on 3-row flat beds which were 2.13 Guard rows were planted between main each experimental block. The 5.2 m alleys. At to about 90 plants per row, spacing of approximately 10 cm within and 71 by sprinkle the seeds in the June 20 planting. in the experiment. The 33 July 5 planting (main plot) in replication 3 was lost due to a heavy rain after planting. The soil became crusted, thus preventing seedling emergence. Many seeds decayed in the water-logged soil. Ethalfluralin (Sonalan), a pre-emergence herbicide, was applied after each planting. The main plots were cultivated twice. Weeds within rows were removed by hand. The striped cucumber beetle (Acalymma vittatum), which vectors bacterial wilt (Erwinia tracheiphila), was controlled with the insecticides, endosulfan (Thiodan) and malathion (Carbofos). Plants infected with bacterial wilt were removed from the field. Fruit and Leaf Harvest When the majority of plants in a main plot were flowering, post—anthesis flowers and the fruits were removed to insure that physiologically similar fruits were evaluated. The following day, beginning at anthesis, fruit samples were randomly harvested from the center row of each sub-plot. Fruits from the lowest fruiting node were selected approximately every other day for a total of six harvests per planting date (Table 3). In the third planting fruits were harvested 7 times. The sample size per sub—plot was 15 fruits in the first harvest and 8 fruits in the other harvests. Twenty leaf samples were collected near anthesis from each sub-plot (Table 3). The most recent fully expanded 34 leaf, which was generally the fourth leaf from the apex,was selected. The leaves were rinsed in distilled water, separated into leaf lamina and petiole tissues, then placed into the drying ovens at 600 C. Table 3. Pickling cucumber fruit and leaf harvest times for each main plot, 1984. Fruit Harvest dates harvest Planting l Planting 2 Plantingi3 Planting 4 number Date DAAz Date DAAz Date DAAz Date DAAz 1 7-18 1 7-29 1 8-12 1 8-23 1 2 7-20 3 7-31 3 8-14 3 8-25 3 3 7-23 6 8- 2 5 8-16 5 8-27 5 ix \1 I N U1 0:) 8- 4 7 8—18 7 8—29 7 7—27 10 8— 6 9 8—20 9 8-31 9 6 7-30 13 8- 8 11 8-22 11 9— 2 11 7 8-27 16 Leaf harvest 7—18 1 7-31 3 8-13 2 8-23 1 2Days after anthesis. 35 Growth Analysis Fruit fresh weight. The peduncle and flower were excised from each fruit with a razor blade. Fruit samples from harvests 1 and 2 were massed, while fruits from the later harvests were individually weighed (g). Volume. The volume of the massed fruit samples was determined using a graduated cylinder, 100 ml to 2000 ml size. The fruits were submerged in distilled water within a partially filled graduated cylinder. The new volume (ml) minus the initial volume (ml) of the distilled water in the graduated cylinder was recorded. Length and Diameter. The length and diameter (cm) of each fruit from harvests 2 through 7 were measured. Tissue Fresh Weight. Fruits from harvests 3 to 7 were cut longitudinally with a knife and sectioned into pericarp (fruit wall) and endocarp (seed cavity) tissues with a cork borer. The fresh weight (g) of each tissue was determined. Fruit tissue subsamples of approximately 20 g were selected for nutrient analysis, placed into pre-weighed pie tins, and then re-weighed. Dry Weight. Whole fruit tissues from harvests 1 and 2 and pericarp and endocarp tissue subsamples from the later harvests were dried in an oven at 600 C for 72 hours. Dry weights (g) of both fruit and leaf tissues were measured and percentage dry matter in the tissues was calculated. 36 Nutrient Analysis Leaf and fruit samples were re-dried in an oven at 600 C overnight. Leaf tissues were ground in a Wiley mill to pass through a 20—mesh screen. Fruit tissues were ground with a mortar and pestle. Tissue samples of 0.1 g were weighed and placed into 50 ml volumetric flasks for wet—ashing. The tissue was digested overnight at room temperature (22° C) with 10 ml of analytical grade nitric acid. The mouth of each flask was covered with a washed marble. The nitric acid was evaporated off using an electric hot plate under a hood. When the acid digest was approaching dryness, several drops of hydrogen peroxide were added to each flask to complete the oxidation. The volumetric flasks were removed from the hot plate when the contents were almost colorless and allowed to cool. The flasks were made to volume with deionized water (10 mega v min. resistance). A 20 ml aliquot from each flask was transferred to a plastic vial for storage. Calcium concentrations in leaf and fruit tissues were determined using an IL Video 12, atomic absorption/ emission spectrophotometer. Standard solutions were prepared, containing 1000 ppm lanthanum (La) from stock LaCl3 solutions and varying concentrations of calcium (0.0, 0.5, 1.0, 2.0, 3.0 ppm). These standard solutions were used to produce a standard curve and tested until the instrument gave reproducible results. The unknown tissue samples were diluted with a LaCl3 solution to 37 achieve a final La concentration of 1000 ppm and calcium concentrations in the range of 1 to 3 ppm. The calcium concentrations in the unknown samples were determined by atomic absorption spectrophotometry. The tissue calcium concentrations, expressed on a dry weight basis, were calculated by correcting for dilution. Soil Moisture Content Soil moisture content was determined gravimetrically. Soil samples, four per main plot, were gathered weekly from August 2 to September 2 from the main plot being harvested. Approximately 5 cm of top soil were removed with a shovel before inserting a Veihmeyer soil corer. The soil samples were from a 7 to 20 cm depth. Glass containers were weighed, the soil sample placed in the jar and then re-weighed. The dry soil weight was determined after oven-drying at 1050 C for 72 hours. Statistical Interpretation of Data Data gathered from the later harvest times are dependent on the earlier development of the fruit, preventing statistical analysis as a split-split plot, with harvest time as the sub-subplot factor. Analysis of variance using a split plot design was conducted on each harvest time and estimated mean fruit fresh weight. Significant differences between means were tested by the Least Significant Difference (LSD). 38 A Tektronix cubic spline computer program was used to estimate mean fruit fresh weight, pericarp and endocarp calcium concentrations, fruit calcium content, fruit growth rate and calcium accumulation rate at specific times after anthesis. A regression curve was generated by inputting the number of days after anthesis when fruits were harvested as the X variable and the mean fruit fresh weight data as the Y variable for each subplot. From this curve the number of days after anthesis to reach specific fruit fresh weights of 5, 25, 50, 75, 100, 125, 150 g could be estimated. Fruit growth rates for these estimated harvest times were determined by taking the first derivative of the regression curve function. Regression curves were also generated for the time course changes in calcium concentration and content in developing pickling cucumber fruits. The X variable was again fruit harvest time (days after anthesis). The calcium concentrations of pericarp and endocarp fruit tissues and fruit calcium content were the Y variables. By inputting the previously estimated times when fruits reached 5, 25, 50, 75, 100, 125, 150 g fresh weight size, the fruit calcium status of these fruits was estimated from the curve. Calcium accumulation rates were estimated by calculating the first derivative of the regression curve function. RESULTS AND DISCUSSION - SECTION 1 Calcium Status of Pickling Cucumber Fruits Definition of Terms Results of plant mineral analyses are expressed in terms of concentration and/or content. "Concentration is defined as the (net) amount of a particular element or substance which is present in a unit amount of a solution or compound (solid material); whereas content is defined as the amount of a particular element or substance present in a specific amount of a solution or compound, (such as a whole fruit)."3 The two terms cannot be used interchangeably. The calcium concentration and the content of developing pickling cucumber fruits are quite different (Figure 1). The calcium concentration, expressed on either a fresh or dry weight basis, declines as fruits mature. The calcium content of pickling cucumber fruits continues to increase as the fruits develop to marketable size. 3M. B. Farhoomand and L. A. Peterson, "Concentration and Content," Agronomy Journal, 60 (1968), p. 708. 39 40 Figure 1 (A-B). The effect of planting date and cultivar on (A) the calcium concentra- tion and (B) content of pickling cucumber fruits, harvested 1 to 11 days after anthesis, 1984. Each point is the overall treatment average of 4 replications x 4 planting dates x 4 cultivars. MEAN FRUIT CALCIUM CONCENTRATION (% dry wt.) FRUIT CALCIUM CONTENT (mg Ca / fruit) 41 2.0 A ‘ Concentration = amount of Ca (mg) unit wt. of fruit (9) 1.5- 1.0- 0.5 r I I r I T 1 3 5 7 9 11 DAYS AFTER ANTHESIS 50‘ B Content = amount of Ca (mg) _ fruit 40— 30- 20‘ 10- OJ I I I I U— 5 7 9 DAYS AFTER ANTH ES IS 11 42 Although concentration is independent of the sample size, it is defined and influenced by both the amount of calcium present and the amount of plant biomass, which is determined by the growth rate of the fruit (32). An average pickling cucumber fruit at 3 days after anthesis has a calcium concentration of 1.13 percent on a dry weight basis (Figure 1A). By 11 days after anthesis the fruit calcium concentration averaged 0.62 percent dry weight. This decline could have been achieved either by a reduced rate of calcium import into the developing fruits or by a rapid fruit growth rate, which would have a dilutionary effect on the pickling cucumber fruit calcium concen- tration. Content is dependent on the sample size (32). As the pickling cucumber fruits enlarged, the calcium content increased due to a continuous calcium uptake from 1 to 11 days after anthesis (Figure 1B). Although the fruit calcium concentration was approximately the same at 9 and 11 days after anthesis, the calcium content increased from an overall average of 26.19 mg per 85.65 g fruit to 47.74 mg per 148.23 3 fruit during this period. Fruit Calcium Concentration The mean fruit calcium concentration declined from approximately 1.75 percent to less than 0.70 percent (dry weight basis) during fruit ontogeny (Table 4). This decrease in the calcium concentration was consistent with 43 the 1983 pickling cucumber calcium concentration data of Widders and Price (137). Since similar sized fruits were evaluated, rather than bulking all fruits on the vine, the differences in concentration between harvests were even more accentuated in this study. The most rapid decline in the mean calcium concentration occurred during the first 5 days after anthesis (Table 4). During these early ontogenetic stages, the pickling cucumber fruit calcium concentrations were significantly affected by an interaction between planting date and cultivar. Fruits from the June 7 planting tended to have the lowest concentrations, while fruits from the July 19 planting had the highest calcium concentrations at l and 3 days after anthesis. Within the planting dates, there were no consistent differences between the declining fruit calcium concentrations of the four cultivars evaluated. It may be postulated that the very high relative growth rates of these developing fruits, combined with low rates of calcium import, resulted in the dramatic decline in the calcium concentrations. By 7 days after anthesis the fruit calcium concen- trations began to plateau (Table 4), coinciding with a leveling off of the relative growth rates of the pickling cucumber fruits (see Results and Discussion - Section 2). Both planting date and cultivar had an impact on the calcium concentrations of fruits from the later harvests. The calcium concentration of fruits from the July plantings were Table 4. The the calcium harvested 1 to 11 days after anthesis, effect of 44 planting concentration of date and 1984. cultivar on pickling cucumber fruits, Fruit calcium concentration (Z dry wt.) Days after anthesis Parameter 1 3 5 7 9 11 Planting date (PD)z June 7, 1984 1.37 1.05 0.90 0.69 0.50 0.52 June 20, 1984 1.71 1.05 0.85 0.93 0.78 0.79 July 5, 1984 1.62 1.16 1.04 0.87 0.62 0.60 July 19, 1984 1.94 1.26 1.04 0.83 0.52 0.59 LSD szY 0.19 0.14 0.12 0.09 0.05 0.04 1% 0.28 NS NS 0.14 0.08 0.06 Cultivar (CV)x Castlepik 2012 1.67 1.15 0.96 0.89 0.59 0.65 PSX20580 1.76 1.14 0.95 0.80 0.68 0.65 Regal 1.61 1.10 0.97 0.91 0.61 0.66 Tamar 1.60 1.13 0.93 0.71 0.54 0.54 LSD szy 0.11 NS NS 0.06 0.04 0.04 1% NS NS NS 0.09 0.06 0.06 Interaction PD x CV ** * NS NS NS NS 2Each entry is an average of 4 replications x 4 CV. yLSD is significant at the 5% (*) or 1% (**) level or nonsignificant(NS). anch entry is an average of 4 replications x 4 PD. 45 similar and higher than the concentrations of fruits from the June plantings, harvested 5 days after anthesis. As the fruits matured, fruits from the June 20 planting tended to have higher calcium concentrations than fruits from the other plantings, while the lowest calcium concentrations were found in fruits from the June 7 planting. The higher calcium concentrations of fruits from the June 20 planting indicate that the fruit calcium accumulation rates relative to the rates of fruit growth were higher than those of fruits from the other plantings. Cultivar differences in the pickling cucumber friut calcium concentration occurred from 7 to 11 days after anthesis (Table 4). Regal and Castlepik 2012 fruits had similar calcium concentrations. Tamor fruits were consistently low in calcium concentration throughout the experimental harvest period. By 11 days after anthesis, the mean calcium concentration of Tamor fruits was 0.54 percent dry weight, which was significantly lower than the calcium concentrations of Castlepik 2012, PSX20580 and Regal fruits. Tamar plants may be less efficient in calcium uptake, partition less calcium to the fruits and/or have a lower requirement for calcium within the fruit for normal development than the other cultivars. It is interesting that the impact of environment and genotype on the calcium concentrations of pickling cucumber fruits varied throughout fruit ontogeny (Table 4). The main treatment effects on fruit calcium concentration were 46 consistent over a wide range of conditions for the more mature fruits. The differential effect of cultivar on the fruit calcium concentration under different environmental conditions indicates that pickling cucumber fruits are most sensitive to changes early in development. The plant has just completed the transition from a vegetative to a reproductive mode of growth, with major physiological changes in hormone and enzyme activity and in assimilate demand and partitioning. Any alteration in these physiological changes is likely to affect the rates of fruit calcium accumulation and growth, which determine the mean fruit calcium concentration. Mean fruit calcium concentration does not indicate differences in specific fruit tissue calcium concen- trations. Tracer studies with apple fruits, using radioactive calcium (45Ca), have shown an uneven distribution of calcium throughout the fruits (68,85,86, 101). Calcium concentrations were highest in the core towards the stem end, intermediate in the peel, and lowest in the flesh tissue. Differences in the calcium partitioning between pericarp and endocarp fruit tissues occurred with pickling cucumbers (Table 5). The pericarp calcium concentrations were always higher than those of the endocarp tissues. While the pericarp concentrations declined gradually with increasing fruit size, the endocarp calcium concentrations declined dramatically to a low of 0.20 47 percent dry weight or less at 11 days after anthesis. Such low calcium concentrations are considered a deficient level for growth in many plants (17,40,81,111,117,134). The observed calcium concentration differences between the two pickling cucumber fruit tissues may be due to a higher growth rate and/or lower calcium accumulation rate of endocarp versus pericarp tissues (Table 5). The expansive cell growth rates of endocarp fruit tissues exceed the pericarp growth rates (see Results and Discussion — Section 2). A higher endocarp tissue growth rate relative to the calcium accumulation rate would cause a lower calcium concentration due to a greater dilutionary effect. The endocarp may also contain fewer vascular tissues than the pericarp. The necessary water for growth may diffuse into the endocarp tissues via the symplastic pathway, through which the calcium ions move with difficulty. This would decrease the rate of calcium import relative to the endocarp tissue growth rate. The pericarp calcium concentrations of the pickling cucumber fruits were affected by both the time of planting and by cultivar (Table 6). At 5 days after anthesis the calcium concentration was higher in the pericarp of fruits from the July plantings in comparison with fruits from the June 20 planting. As the maturation period increased, fruits harvested from the June 20 planting maintained a higher calcium level in the pericarp tissues, whereas pericarp calcium concentrations of fruits from the June 7 48 Table 5. The mean calcium concentrations of pericarp and endocarp tissues of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984. Calcium concentration (2 dry wt.)2 Days after anthesis Pericarp tissue Endocarp tissue 5 1.04 0.79 7 0.92 0.60 9 0.73 0.29 11 0.80 0.23 2Each entry is an average of 4 replications x 4 planting dates x 4 cultivars. 49 and July 19 plantings declined. Tamar fruit tended to be the lowest in pericarp calcium concentrations (Table 6). The calcium concen- trations of the pericarp tissues of Castlepik 2012 and Regal fruits were similar throughout the four harvests. These cultivars consistently maintained higher pericarp calcium concentrations than Tamar, except at 9 days after anthesis, when the concentrations were not significantly different. The calcium concentrations of PSX20580 pericarp tissues fluctuated at an intermediate level. Only at 9 days after anthesis did the mean concentration of PSX20580 pericarp tissue exceed the concentrations of the other three cultivars. It should be noted that the trends in the pickling cucumber fruit pericarp concentrations changed at 11 days after anthesis (Table 6). The pericarp calcium concen- trations, which declined from 5 to 9 days after anthesis, increased at day 11. Although this concentration increase was unexpected, it consistently occurred in all four planting dates and for all of the cultivars except PSX20580. It may be postulated that the observed calcium concentration increase was due to a decrease in the pericarp growth rate relative to the rate of calcium import into the tissue. Schapendonk and Brouwer (1984) report that pickling cucumber fruits in the lower nodes begin to lose their dominance by approximately 12 days after anthesis (106). If less water is transported into these fruits, the calcium 50 Table 6. The effect of planting date and cultivar on the calcium concentration of pericarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984. Pericarp tissue Ca concn (% dry wt.) Days after anthesis Parameter 5 7 9 11 Planting date (PD)z June 7, 1984 1.00 0.75 0.61 0.68 June 20, 1984 0.92 1.03 0.92 0.99 July 5, 1984 1.14 0.98 0.77 0.79 July 19, 1984 1.09 0.90 0.61 0.75 LSD szY 0.14 0.11 0.08 0.06 1% NS 0.16 0.11 0.08 Cultivar (CV)x Castlepik 2012 1.08 1.02 0.70 0.83 PSX20580 1.03 0.86 0.83 0.83 Regal 1.06 1.02 0.71 0.84 Tamor 0.98 0.77 0.67 0.70 LSD 5%y 0.07 0.08 0.06 0.06 1% NS 0.11 0.08 0.08 Interaction PD x CV NS NS NS NS 2Each entry is an average of 4 replications x 4 CV. yLSD is significant at the 5% or 1% level or nonsignificant (NS). anch entry is an average of 4 replications x 4 PD. 51 concentration would be higher, due to a lower dilutionary effect. Planting date and cultivar also had an impact on the calcium concentrations of the endocarp tissues (Table 7). Fruits from the July 19 planting had the highest endocarp calcium concentrations at 5 and 7 days after anthesis. It is interesting that the concentrations of calcium in the pericarp (Table 6) and endocarp tissues were similar for fruits from this planting at 5 days after anthesis. By 9 days after anthesis, fruits from the June 20 planting had the highest mean endocarp calcium concentration. Among the four cultivars examined, Tamor fruits had the highest mean endocarp calcium concentration at 5 days after anthesis and the lowest concentrations at 9 and 11 days after anthesis (Table 7). The calcium concentrations of the endocarp tissues were similar for Castlepik 2012 and Regal, as had been observed with the pericarp calcium concentrations (Table 6). PSX20580 fruits had intermed- iate concentrations of calcium in the endocarp tissues. At 11 days after anthesis there was a significant interaction between the effects of planting date and cultivar on the endocarp calcium concentrations (Table 8). As with the main treatment effects, the June 20 planting consistently had the highest mean endocarp calcium concentration within the cultivars, although not always significant. Tamor fruits generally had the lowest endocarp calcium concentrations within the planting dates. Only in 52 Table 7. The effect of planting date and cultivar on the calcium concentration of endocarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984. Endocarp tissue Ca concn (% dry wt.) Days after anthesis Parameter 5 7 9 11 Planting date (PD)z June 7, 1984 0.68 0.54 0.23 0.16 June 20, 1984 0.67 0.62 0.39 0.31 July 5, 1984 0.80 0.58 0.28 0.20 July 19L 1984 1.02 0.66 0.28 0.23 LSD szY 0.10 0.05 0.04 0.04 1% 0.15 0.07 0.05 0.06 Cultivar (CV)x Castlepik 2012 0.68 0.56 0.34 0.26 PSX20580 0.80 0.64 0.28 0.20 Regal 0.77 0.60 0.36 0.26 Tamor 0.91 0.60 0.20 0.18 LSD 52’ 0.08 0.04 0.03 0.03 1% 0.10 0.06 0.04 0.04 Interaction PD x CV NS NS NS * 2Each entry is an average of 4 replications x 4 CV. yLSD is significant at the 5% (*) or 1% level or non- significant (NS). anch entry is an average of 4 replications x 4 PD. 53 the June 20 planting did PSX20580 have the lowest calcium concentration. This interaction at 11 days after anthesis was as surprising as the rise in the pericarp calcium concen- trations (Table 6,8). A treatment interaction had not affected either the total fruit or pericarp calcium concentrations of the more mature pickling cucumber fruits (Tables 4,6). It may be hypothesized that hormonal changes may have occurred as these fruits lost their dominance. Perhaps the auxin synthesized by the seeds increased the sensitivity of the fruits to environmental changes and of the genotypic response of the four cultivars, affecting the rate of calcium accumulation. The concentration results may be confounded when comparing the calcium concentrations of pickling cucumber fruits from the four plantings according to harvest time. Differences may occur in fruit size and, consequently, in the physiological stage of development of these sampled fruits. Since the calcium concentration of any tissue is affected by the growth rate of the tissue, the calcium concentration data were estimated and standardized for similar fruit fresh weights (Figures 2,3). (A pickling cucumber fruit fresh weight of 100 g corresponds to a fruit diameter of approximately 2.5 cm.) Planting date and cultivar treatments interacted, significantly affecting the pericarp calcium concentrations of 25 g pickling cucumber fruits and the endocarp calcium 54 Table 8. The interaction of planting date and cultivar on the calcium concentration of endocarp tissue of pickling cucumber fruits, harvested 11 days after anthesis, 1984. Endocarp tissue Ca concn (% dry wt)2 Cultivar (CV) Planting date (PD) Castlepik 2012 PSX20580 Regal Tamar June 7, 1984 0.17 0.16 0.22 0.10 June 20, 1984 0.34 0.24 0.36 0.30 July 5, 1984 0.24 0.21 0.21 0.16 July 19, 1984 0.28 0.22 0.26 0.16 Significant effects LSD 5% within PD 0.06 within CV 0.06 2Each entry is an average of 4 replications. 55 concentrations of 25 to 100 g fruits (Figures 2,3). It was surprising that this interaction occurred in the smaller fruits, since it had not been observed when analyzing the tissue calcium concentrations by harvest times. Vari- ability in the fruit fresh weights apparently masked this interaction. It is also interesting that the endocarp tissue calcium concentrations were more sensitive to environmental changes and different genotypes than the pericarp calcium concentrations. Planting date significantly affected the pericarp calcium concentrations of pickling cucumber fruits weighing 50 to 150 g (Figure 2). By eliminating the variability due to fruit size, the calcium concentrations of fruit pericarp tissues from the June 7 planting were not the lowest (Table 6). Fruits from the July 19 planting had the lowest pericarp calcium concentrations, while the pericarp tissues from the June 20 planting had the highest mean concentrations, though not always significant. The pericarp calcium concentrations increased only in mature fruits from the June 20 planting. The pericarp calcium concentrations of fruits from the June 7 and July 5 plantings were similar and intermediate, compared with the concentrations of fruits from the other plantings. Planting date also had an impact on the endocarp calcium concentrations as pickling cucumber fruits enlarged to 125 to 150 3 (Figure 2). The calcium concentrations of the endocarp tissues were similar in fruits harvested 56 Figure 2. The effect of planting date on the calcium concentrations of pericarp and endocarp tissues of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 replications x 4 cultivars for 25 to 125 g fruits and an average of 3 replications x 4 cultivars for 150 g fruits. .N ouswwm A3 59m; 18$ :2: 26.2 57 ('TM MP %) NouvaiNaaNoa WfllO'IVO anssu 1Im:I_-I N‘v’I-IW on? R: on: on on mm o b b b . P. _ nXUAU $.st o1. emImIs xIw ...mIomIo mIm ...mITo «I. Toad 9:25.. 13.0 L m nu w v Iood 01 / a /. . g d IOQ.O H: m Au .. I V . - - . m u .- roo.F 58 Figure 3. The effect of cultivar on the calcium concentrations of the pericarp and endocarp tissues of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 replications x 4 planting dates for 25 to 75 g fruits, an average of 4 replications x 3 planting for 100 to 125 g fruits, and an average of 3 replications x 3 planting dates for 150 g fruits. 59 A3 Eon; IBE 5E 26: .m shaman om: mm? cop mm on mm o — _ _ _ — — AXUAU NSN ximfimfiv «La . ommomxmn. ml”. mt ..., some I load . n mozfi. Ola . ,u Toto . 3 _ N 0 m K -85 d GI o Aw\Av/®/a drillllllldrllllllllw 4c .IanAU m 0 w d .100; ('IM Mp %) NouvsiNaaNoo wnIa‘Iva 30380 1108:! NVBW 60 from the June plantings as compared with the similar and lower concentrations from the July plantings. It should be noted that while the endocarp tissue calcium concentrations declined as fruits from the June 20 planting matured, the calcium concentrations of the pericarp tissues remained relatively constant. This would suggest that the environment affects calcium import into and accumulation in pickling cucumber fruit tissues differently and perhaps also the growth rates of the pericarp and endocarp tissues. The drought during the early stages of development of fruits from the July 19 plantings and throughout development in the July 5 planting appeared to depress the calcium concentrations of endocarp tissues more than the pericarp concentrations. Cultivar affected the pericarp calcium concentrations of 50 to 150 g fruits and the endocarp calcium concentrations of 125 to 150 g fruits (Figure 3). Regard- less if the fruit tissue calcium concentrations were analyzed by harvest time (Tables 6,7) or by fruit fresh weight, Tamor consistently had the lowest calcium concen- trations in both pericarp and endocarp tissues. Within the fruit fresh weight range of 25 to 150 g, Regal maintained the highest endocarp calcium concentrations. Fruit Calcium Content The mean calcium content of pickling cucumber fruits increased through ontogeny. The period of most rapid 61 calcium accumulation was generally between 9 and 11 days after anthesis, as the fruits approached harvestable size (Figure 4). This accumulation pattern is somewhat different from that of fruits of other species, which have a rapid increase in calcium content during the very early stages of fruit ontogeny but then level off as these fruits approach maturity and harvest (1,56,81,101,123,127). It must be recognized that pickling cucumber fruits are harvested at a relatively immature stage when the fruits are still rapidly growing, even though they may be relatively large at horticultural maturity. At all harvest times, except 3 and 11 days after anthesis, planting date and cultivar interacted, having a significant effect on the calcium contents of pickling cucumber fruits (Figure 4). The calcium contents of the fruits harvested 3 days after anthesis differed significantly with respect to the time of planting only, while at 11 days after anthesis both planting date and cultivar had an impact on the fruit calcium contents. It is unknown why the treatment interactions were not significant at 3 and 11 days after anthesis. Since content is dependent on sample size, the differential effect of the four pickling cucumber cultivars on fruit calcium contents under different environmental conditions may have been largely due to the size of these fruits. The calcium contents were similar and higher for fruits from the two June plantings, compared with the similar but 62 Figure 4 (A-B). The effect of (A) planting date and (B)cultivar on the calcium content of pickling cucumber fruits, harvested 1 to 13 days after anthesis, 1984. (A) Each point is an average of 4 replications x 4 cultivars. (B) Each point is an average of 4 replications x 4 planting dates. 63 13 DAYS AFTER ANTHESIS Figure 4. ...IJ Q0 Fae—w m Mu AH 17m u“ , A m we? 1...... 2 amam m mm “0 HHHH _. wmmm :2 A B wwwwwwmfi wwwwmw as: \oo 85 22080 95 .sz.rzoo 23.0.20 :31... 25: 0.25200 23.0.7.0 tam... 2(a) 64 lower fruit contents from the July plantings (Figure 4A). By the last harvest, the calcium content averaged 60 mg per fruit in the June plantings and was half that level in fruits from the July plantings. Fruits from the July plantings were smaller than those from the June plantings when compared at similar harvest times (see Results and Discussion — Section 2). The average fresh weight of fruits from the July 19 planting did not reach 100 g by 11 days after anthesis. The greatest differences in calcium contents between the cultivars were encountered at the later stages of fruit maturity (Figure 4B). Tamor had the lowest content and Regal fruits generally accumulated the highest calcium levels of the four cultivars evaluated. Variability in the fruit sizes of the different cultivars at a specific harvest time, however, reduced the possibility of measuring significant cultivar differences, especially at the later harvests. The fruit calcium content data were reevaluated and statistically analyzed again after standardization for fruit fresh weight (Figure 5). The calcium contents were similar for all fruits weighing 5 g. As the fruits enlarged to 25 and 50 g, the contents of the fruits differed due to an interaction between planting date and cultivar. By eliminating the variability in fruit size, this interaction became nonsignificant in affecting the calcium contents of fruits larger than 50 g. The contents of fruits within the 65 fresh weight range of 75 to 150 g were significantly affected by planting time and cultivar. Surprisingly, the calcium contents of 100 g fruits were affected only by cultivar. Both 25 and 50 g Tamar fruits generally had the lowest calcium contents within the planting dates (Figure 5). Within the cultivars, 25 and 50 g fruits from the July 19 planting had the lowest calcium contents. The pickling cucumber fruit calcium concentrations were also the lowest in Tamar fruits and fruits from the July 19 planting, so the low fruit calcium contents were not surprising. It was also observed that a significant interaction affected the calcium concentrations of the pericarp and endocarp tissues of the smaller pickling cucumber fruits (Figures 2,3). This suggests that these fruits had low rates of calcium accumulation relative to the fruit growth rates. The increase in calcium content relative to fruit weight was almost linear within the fruit fresh weight range of 5 to 150 g for planting date (Figure 5A). Once again, the June 20 planting tended to have fruits with higher calcium contents, while fruits from the July 19 planting tended to accumulate less calcium than fruits from the other plantings. Unlike the ontogenetic trends in calcium content evaluated by harvest time (Figure 4A), fruits from the June 7 and July 5 plantings had similar contents when the calcium content data were normalized for fruit fresh weight (Figure 5A). At 125 and 150 g, fruits from these 66 Figure 5 (A-B). The effect of (A) planting date and (B)cultivar on the calcium content of pickling cucumber fruits of specific fresh weights, 1984. (A) Each point is an average of 4 reps x 4 planting dates (PD) for 5 to 75 g fruits, an average of 4 reps x 3 PD for 100 to 125 g fruits, and an average of 3 reps x 3 PD for 150 g fruits. (B) Each point is an average of 4 reps x 4 cultivars (CV) for 5 to 125 g fruits and an average of 3 reps x 4 CV for 150 g fruits. 67 O O 0| 0 L MEAN FRUIT CALCIUM CONTENT (mg) 01 O 20. ' H 6—7-84 H 6-20-84 1 o- H 7-5-34 H 7-19-84 0 r T I I I I . 0 25 50 75 1 00 1 25 1 50 1 15 MEAN FRUIT FRESH WEIGHT (9) ’3 3 50- B ~ I— z . _ 11.4 . z 40* o 0 z . 2 so 3 ‘ // < -. 0 2°“ o—o TAMOR I: . /= H REGAL 03: H PSX20580 L1. 10' ' ’ H CASTLEPIK 2012 E , 2 O I T I T T I 0 25 50 75 100 125 150 175 MEAN FRUIT FRESH WEIGHT (9) Figure 5. 68 plantings remained similar in calcium contents and lower than those of fruits from the June 20 planting. It was not unexpected that the trend differences between the fruit calcium contents analyzed by harvest time (Figure 4A) and by fruit fresh weight (Figure 5A) would be most notable in the larger pickling cucumber fruit sizes. The variability in fruit sizes between the planting dates was highest during the later harvests. The similarities between the lower calcium contents of fruits from the June 7 and July 5 plantings indicate that less calcium was being imported into these fruits than into fruits from the June 20 planting, when comparing fruits of equal fresh weight. It was very dry during the later stages of development for fruits from the June 7 and July 5 plantings, suggesting that water was a rate limiting factor in pickling cucumber fruit calcium accumulation and growth (see Results and Discussion - Section 4). Even after normalizing fruit fresh weight, Tamar fruits usually had the lowest calcium contents (Figure SB). This is consistent with the relatively low fruit tissue calcium concentrations previously discussed (Figure 3). The comparatively low calcium contents of Tamor fruits were established early in fruit development and maintained throughout ontogeny. The fruit calcium contents of the other cultivars fluctuated relative to one another as the fruits developed. The calcium contents of the pericarp and endocarp fruit 69 tissues were analyzed by harvest periods (Figure 6). The calcium contents of pickling cucumber fruits are much higher in the pericarp tissues than in the endocarp tissues, consistent with the concentration data for these tissues (Tables 6,7). The pericarp calcium contents dramatically increased from 5 to 11 days after anthesis, while the endocarp tissues maintained low and nearly constant calcium contents. Variability in the size of the fruits and of the fresh weights of the two tissues being compared confound the content results, since content is dependent on sample size. The data do suggest, however, that there is a higher and continuous accumulation of calcium in the pericarp tissue than in the endocarp as a pickling cucumber fruit matures. It may be postulated that this is a result of more vascular tissues in the pericarp, facilitating calcium import into this tissue. Fruit Calcium Accumulation Rate The calcium accumulation rate of pickling cucumber fruits is the estimated amount of calcium (mg) which is imported into a fruit per unit time (day). The impact of planting date and cultivar on the fruit calcium accumulation rates is confusing (Figures 7,8). Genetic variability affected the calcium accumulation rates in small, immature pickling cucumber fruits, weighing 5 g (fresh weight). Planting date and cultivar interacted, affecting the import rates of calcium into 25, 50 and 150 g fruits. Only the 70 Figure 6. The effect of planting date and cultivar on the calcium content of pickling cucumber fruit tissues, harvested 5 to 11 days after anthesis, 1984. Each point is the overall average of 4 replications x 4 planting dates x 4 cultivars. 71 A—A PERICARP Ia—EI ENDOCARP r-CD L-I\ “-03 I T I T T ‘ F T O O O 0 d” I") (\I ‘— (enSSH/DO 5w) 1N31NOO wnmva 30330 was NVEIW DAYS AFTER ANTH ESIS Figure 6. 72 planting date main treatment had a significant effect on the calcium accumulation rates of 75 to 125 g fruits. Environmental conditions (see Results and Discussion - Section 4) appeared to have a significant effect on the ontogenetic trends in calcium accumulation rates (Figure 7). Similar rate trends were observed for fruits from the June 7 and July 5 plantings. Fruits from the June 7 planting reached their maximum import rate at 50 g and then plateaued at approximately 9 mg of calcium per day. The calcium accumulation rates for fruits from the July 5 planting were consistently low throughout ontogeny, suggesting that some factor was limiting calcium import into the pickling cucumber fruits. Upon reaching 75 g, fruits from the July 5 planting peaked in their calcium accumulation rates, which then declined to lower rates for 150 g fruits than for 5 g fruits. Fruits from the June 20 and July 19 plantings never reached their maximum calcium import rates, increasing continually in an almost linear manner. The fruits from the June 20 planting had a twenty- fold higher calcium import rate than that of 150 g fruits from the July 5 planting. Although fruits from the July 19 planting had an initially low calcium accumulation rate, 75 g fruits had similar rates as fruits from the June plantings. It is interesting to note that the calcium import rates of Castlepik 2012, PSX20580 and Tamor fruits increased through ontogeny (Figure 8). Regal fruits had a rapid 73 Figure 7. The effect of planting date on the calcium accumulation rate of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 repli- cations x 4 cultivars for 5 to 125 g fruits and an average of 3 replications x 4 cultivars for 150 g fruits. 74 .n muswflm 30 Eon; 18¢... tax... 252 om P mm P 00F an on mm o _ _ _ _ _ _ o Iv «I a. 3 I@ IN_. .vmlm F In Ola a *mlmlh I ¢mlomlm film 10 P .lehlo «la Quiz/3a TON (App/03 6w) 31w NOIlV'IflWflOOV WfllO‘IVO 75 increase in import rates early in development but then began to level off in 75 g fruits. Tamar fruits, with low calcium concentrations and contents, had the lowest calcium accumulation rates during the earliest stages of development. These results suggest that if calcium is proven to be critical for pickling cucumber fruit growth and/or quality, genetic variability could be exploited in a breeding program. Tamor fruits may have lower tissue calcium requirements, due to more efficient ion utilization. English and Barker (1983) report that tomato strains vary in calcium efficiency (30). Calcium-efficient strains grow well in a medium with a low calcium supply and accumulate less calcium compared with the calcium-inefficient strains. Pickling cucumber cultivars may have different fruit calcium accumulation rates because of varying efficiency in calcium uptake. Some cultivars may have more selective calcium absorption and/0r differing efficiency of loading calcium ions into the xylem vessels. Pickling cucumber fruit growth is highly competitive with root growth (96,106). Perhaps this competitive sink strength differs among cultivars. Variable fruit growth rates may also affect the calcium accumulation rates of pickling cucumber fruits, due to dilutionary effects and altered fruit to shoot ratios. 76 Figure 8. The effect of cultivar on the calcium accumulation rate of pickling cucumber fruits of specific fresh weights, 1984. Each point is an average of 4 repli- cations x 4 planting dates for 5 to 75 g fruits, an average of 4 replications x 3 planting dates for 100 to 125 g fruits and an average of 3 replications x 3 planting dates for 150 g fruits. 77 mhw .w muswfim 3 Eon; Imam... SE 252 omw mmw Om: m% on mN O r — b L O «Pom x_au.:m<0 «In ommomxmn. EA. .205. I mos/x... Ola (Asp/03 5w) 31378 NOIlV'IflWflOOV WDIO'IVO RESULTS AND DISCUSSION - SECTION 2 Pickling Cucumber Fruit Growth Fruit Fresh Weight and Volume The growth of pickling cucumber fruits was measured by fresh weight, volume, dry weight, length and diameter. The mean fruit fresh weight (g) and volume (ml) of pickling cucumber fruits were highly correlated (Figure 9). For every 1 ml increase in volume there was a 0.96 g increase in the fruit fresh weight. The largest increase in fruit fresh weight and volume coincided, occurring between 9 and 11 days after anthesis (between 8 and 10 days after anthesis for fruits from the June 7 planting). Planting date and cultivar had a similar effect on pickling cucumber fruit fresh weight and volume (Figure 9). The fruit density was not altered by the treatments. Both parameters were significantly affected by the planting date (Table 9). Cultivar also had an impact on the fruit fresh weights and volumes at all harvest dates except at 3 days after anthesis. Planting date and cultivar interacted at 7 days after anthesis, affecting pickling cucumber fruit size. The largest fruits were from the June 7 planting, ranging in weight from 0.701 g to 216.83 g at l and 11 days 78 79 Figure 9. The effect of planting date and cultivar on the correlation between mean volume and fresh weight of pickling cucumber fruits, harvested 1 to 11 days after anthesis, 1984. 80 .o Opswfim 9.5 339 :3”: 262 I V 0mm com of co, om o . . ._ L _ _ r b . E It Au , M 10m N - 3 H 0 Too, .Ii. . 3 H 3 Ion, S H .. M 3 Ioom mm H II.— a» /.\ scam 81 after anthesis, respectively (Table 9). These higher fruit fresh weights were due to a one day delay in harvesting (Table 3) and to high fruit growth rates. Compared with the other plantings, fruits from the June 20 planting were intermediate in size. At 5 days after anthesis, fruits from the two June plantings had similar fresh weights, although the fruits from the first planting were more mature. Fruits from the two July plantings had low and similar fresh weights and volumes throughout the harvest period, averaging only a little more than 100 g (approximately a 2.5 cm diameter fruit) by 11 days after anthesis. Low soil moisture was a limiting factor to growth in both plantings (see Results and Discussion - Section 4). Genetic variability generally resulted in higher individual fresh weights at the specific harvest times for Castlepik 2012 and Regal fruits than for PSX20580 and Tamar fruits (Table 9). Although the weights of Castlepik 2012 and Regal fruits were not significantly different, Regal produced the heaviest fruits throughout the harvest period. Both PSX20580 and Tamor fruits had lower growth rates, resulting in smaller fruits. It was observed that PSX20580 plants often wilted more quickly than the other pickling cucumber cultivars during periods of drought. It is interesting that at 7 days after anthesis pickling cucumber fruit fresh weight and volume were affected by a significant treatment interaction (Table 9). Table 9. mean fresh weight of pickling cucumber fruits, 1 to 11 days after anthesis, The effect of planting 82 1984. date and cultivar on the harvested Mean fruit fresh weight (g) Days after anthesis Parameter 1 3 5 7 9 11 Planting date (PD)z June 7, 1984 0.701 2.913 14.168 75.46 157.80 216.83 June 20, 1984 0.411 1.905 12.747 41.63 83.05 169.81 July 5, 1984 0.386 1.672 6.426 30.246 58.31 101.18 July 19, 1984 0.425 1.281 4.358 17.091 43.44 105.10 LSD 5%y 0.104 0.291 3.357 15.15 17.10 28.01 1% 0.151 0.423 4.884 22.04 24.87 40.76 Cultivar (CV)x Castlepik 2012 0.503 2.033 10.355 44.88 90.55 152.31 PSX20580 0.383 1.951 9.875 37.294 76.51 135.30 Regal 0.558 2.061 10.440 49.10 98.03 161.16 Tamar 0.477 1.726 7.028 33.154 77.51 144.16 LSD 52y 0.042 NS 1.552 4.21 9.89 15.95 1% 0.057 NS 2.089 5.67 13.32 NS Interaction PD x CV NS NS NS ** NS NS 2Each entry an average of 4 replications x 4 CV. yLSD is significant at the 5% 1% (**) level or nonsignificant (NS). anch entry an average of 4 replications x 4 PD. 83 Schapendonk and Brouwer (1984) report that maximum cucumber fruit abortion occurs at 8 days after anthesis, coinciding with a steadily decreasing amount of available assimilates (106). An assimilate shortage also inhibits the rate of pickling cucumber fruit growth. It may be hypothesized that the fruits are very sensitive to environmental and genetic variability during this critical fruit development period. At the last four harvests, the fresh weights of the pericarp and endocarp fruit tissues were also analyzed. The pericarp tissues always weighed more than the endocarp tissues (Tables 10,11). Planting date and cultivar interacted, affecting the weights of the pericarp tissues at 5 and 7 days after anthesis and of the endocarp tissues at 7 days after anthesis. The main treatment effects of planting date and cultivar on the weights of both fruit tissues were highly significant at the later stages of fruit development. Consistent with the total fruit fresh weight data (Table 9), fruits from the June 7 planting had the highest fresh weights for both the pericarp and endocarp fruit tissues (Tables 10,11). The tissue weights were usually intermediate for fruits from the June 20 planting and the lowest for the similar weight fruits from the July plantings. It is also not surprising that cultivar affected the specific tissue fresh weights and the total fruit fresh weights similarly over time. Castlepik 2012 and Regal fruits again tended to have similar and higher pericarp and Table 10. 84 The effect of planting date and cultivar on the mean fresh weight of pericarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesisL71984. Mean pericarp fresh weight (g) Days after anthesis Parameter 5 7 9 11 Planting date (PD)z June 7, 1984 11.051 54.35 113.43 149.90 June 20, 1984 9.782 32.151 61.46 119.77 July 5, 1984 4.823 22.416 41.51 69.38 July 19, 1984 3.373 12.925 31.78 74.04 LSD 5%? 2.396 10.326 12.82 19.86 1% 3.487 15.024 18.66 28.89 Cultivar (CV)x Castlepik 2012 7.784 32.316 64.18 104.84 PSX20580 7.643 28.190 56.49 95.53 Regal 8.204 36.614 71.51 112.88 Tamor 5.398 24.718 56.00 99.83 LSD 52’ 1.152 2.996 6.87 11.33 1% 1.551 4.035 9.25 NS Interaction PD x CV * ** NS NS 2Each entry is an average of 4 replications x 4 CV. yLSD is significant at the 5% (*) or 1% (**) level or nonsignificant (NS). xEach entry is an average of 4 replications x 4 PD. 85 Table 11. The effect of planting date and cultivar on the mean fresh weight of endocarp tissue of pickling cucumber fruits, harvested 5 to 11 days after anthesis, 1984. Mean endocarp fresh weight (g) Days after anthesis Parameter 5 7 9 11 Planting date (PD)z June 7, 1984 2.511 20.269 42.70 65.68 June 20, 1984 2.698 8.914 20.872 48.21 July 5, 1984 1.464 7.380 15.998 30.678 July 19, 1984 0.857 3.835 10.850 29.915 LSD 52’ 0.897 4.865 4.312 8.658 1% 1.305 7.078 6.274 12.596 Cultivar (CV)x Castlepik 2012 2.285 11.997 25.359 46.08 PSX20580 1.928 8.591 19.107 38.477 Regal 1.950 11.903 25.496 46.94 Tamor 1.368 7.927 20.458 42.99 LSD 52’ 0.378 1.259 3.045 4.914 1% 0.509 1.695 4.101 6.617 Interaction PD x CV NS ** NS NS 2Each entry is an average of 4 replications x 4 CV. yLSD is significant at the 5% or 1% (**) level or non- significant (NS). anch entry is an average Of 4 replications x 4 PD. 86 endocarp tissue weights than PSX20580 and Tamar fruit tissues. The ratios between the pericarp to endocarp fresh weights declined as the pickling cucumber fruits matured (Figures 11,12). The endocarp tissue weights increased more than the pericarp weights. Sinnott (1939) reports that cell division ceases first in the endocarp region and successively later in the outer tissues of Cucurbita pepo fruits (113). If this is also true in cucumber fruits, it would mean that greater cell expansion must occur in endocarp tissues than in pericarp tissues, in order to achieve the more rapid growth rates. This may also account for the dramatic calcium concentration decline which was observed in the endocarp fruit tissues (Table 5). There was generally an inverse correlation between the fruit tissue fresh weight and the tissue calcium concentration. Planting date significantly affected the pericarp to endocarp fresh weight ratios of pickling cucumber fruits at 7 to 11 days after anthesis (Figure 10). The cultivar effect was highly significant throughout the sampling period (Figure 11). The treatments interacted only at 9 days after anthesis. The highest fresh weight tissue ratio, although not significant, occurred at 5 days after anthesis for pickling cucumber fruits from the June 7 planting (Figure 10). It is very surprising that the ratio of these fruits then dramatically declined to the lowest value at 7 days after 87 Figure 10. The effect of planting date on the pericarp to endocarp fresh weight ratios of pickling cucumber fruits, har- vested 5 to 11 days after anthesis, 1984. Each point is an average of 4 replications x 4 cultivars. 88 N— .oH ouswwm m_mu1._.z< «Eu? m>.—LL..—.:>b>_ O ozEpE % 82:50? E m LOO r-s— O (\I (0.) S3801V838W31 81V MIva WflWINIV‘I an wamwi mN I on 100 . \\\\\\\\\\\\\\\\\\ ...... :\\\\\\\ flflfififirttttttxtttgmfi . ”aflg . c. QMHZSL \\\\\\\\\\\\\\\\\\ .......... ~\\\ Emsgttttttttt13%.:...m. 3. _ a. 4. Ru . \\\\\\\\\\ \.:....:::: EEEEEEA“ 3.3mm... Us? WHEN 137 Figure 19. Maximum and minimum daily soil temperatures during the pickling cucumber growth period of the 4 planting dates, 1984. (Data measured by the Michigan State University Weather Service at the Horticul- ture Research Center.) 138 .83 upswfis Hmmm 03¢. >335 mza. 3.. vm 5 9 n hN ON 2 0 mm NN m— m P L»_LL:_C_:_:L-EEL...__._._.:___._:L:_..._:::_...—:73;er.:_LE..—::L O \\\\\\\\\\\\\\\\\\\\V ~~~~~~~~ --\\ Egttttttttst£3. .. .r E . \\\\\\\\ . ENE: \ELLNNRNQAEE. .353 \ttitxddttmmm.“domlwfimt m I. uWV .3 855A 3 M .m. 32. \ W W or ...m 0 ~~~~~~~~~ -fi~w W W V 19 m. N mm 0 mu .8 S M V W. l O ImN I W O 0 Ion 0 W m m \08 ozEaE E ran/Om 82250“; g O V 139 temperatures. The air temperatures generally increased from 1 to 8 days after anthesis for the July 19 planting and then declined. Effect of Rainfall The growth rates of water-stressed plants are much lower than those of non—stressed cucumber plants (92). Fruiting plants tend to have an even greater total water consumption than nonfruiting plants (71). Adequate moisture is especially critical during flowering and early fruit set (93), when the rate of water use increases (71). Larger fruits are less affected than smaller cucumbers by drought (92). Large fruits continue to enlarge at the expense of the small fruits, which cease enlarging and then shrivel. These larger fruits in the lowest axils lose their dominance after approximately 12 days, coinciding with a period of decreasing fruit growth rates (106). Since moisture is very important, especially during the critical growth stages of early cucumber fruit set (93), it is important to look at the timing of the rainfall (Figure 20) and how it affected rates of calcium accumulation (Figure 7) and fruit growth (Figure 12). It may be hypothesized that pickling cucumber fruits that receive adequate moisture should have the highest rates of calcium accumulation and growth. More calcium should be available in the soil solution. Optimum soil moisture 140 Figure 20. Daily rainfall during the growth period of pickling cucumbers from 4 plant— ing dates, 1984. (Data measured by the Michigan State University Weather Service at the Horticulture Research Center.) 141 .om mtamfis .Emm 03< >333 m23 ENDS ...Rowfl m 339 m ozEam... E 36:8”; E \\\\\\\\\\\\\\\\\N\\\ ~~~~~~~~~~ -NV gttttxttttttmew.. ”3.1.35; \\\\\\\\W\V\\\N\NV11~¢--W~NV~ ow 05:. \ quTjVj \\\\\\\\\\\\\.:cmp MW. .33. 3 F Ifivnv .2. 6. 3r. c'». «'2 N N .— .. 0 (w?) ‘I‘IV3NIV8 A'IIVCI I C? NT 142 levels during the vegetative growth period supports cucumber root growth, providing new sites for calcium uptake. During expansive fruit growth, net water movement into fruits via the xylem occurs in response to a water potential gradient. Calcium import into the developing pickling cucumber fruits via the xylem should be enhanced to some extent by the greater volume of water, also. It is interesting to note that fruits from both the June 7 and July 5 plantings exhibited maximum rates of calcium accumulation (Figure 7) and growth (Figure 12) at or before the average fruit fresh weight reached 100 g. While the June 7 planting received approximately 8 cm of rain during the vegetative growth period, the July 5 planting received the largest amount of rain, 11 cm (Figure 20). Substantial amounts of the rain during the vegetative growth periods fell 10 days prior to anthesis for the June 7 and July 5 plantings, 3.73 and 5.97 cm, respectively. The June 7 planting also received 0.71 cm of rain during the fruiting period. Fruits from the June 7 planting peaked in their calcium accumulation rates at 7 days and growth rates at approximately 9 days after anthesis (Figures 7,12). Among the four plantings, fruits from this first planting had the highest rates of calcium accumulation and growth until the average fruit fresh weights exceeded 75 g and 100 g, respectively. There was a sharp rise in the rates after the 0.15 cm rain at 4 days after anthesis (Figure 20). No 143 increase in calcium accumulation rates and only a small increase in fruit growth rates occurred following the 0.46 cm rain at 7 days after anthesis. The fruit calcium accumulation rates remained almost constant as fruits enlarged from 75 to 150 g. The fruit growth rates declined, especially as fruits enlarged from 125 to 150 g. Since the July 5 planting received the largest amount of rain 10 days prior to anthesis, water should not have been a limiting factor to early pickling cucumber fruit growth (Table 20). Small fruits, weighing 50 g or less, from this planting did have similar calcium accumulation and growth rates as those of fruits from the other plantings (Figures 7,12). When the fruits from the third planting reached 75 g and larger, the rates declined to the lowest levels among the plantings. This was the only planting that received no rain during the fruiting period (Table 20). Several hypotheses may be proposed to explain the calcium accumulation rate and growth rate trends for the June 7 and July 5 plantings (Figures 7,12). As the initial pickling cucumber fruit enlarges and new fruits begin to develop on the vine, the assimilate demand increases. Due to the low amounts of rainfall during fruiting, there may have been a shortage of both water and assimilates in the later stages of pickling cucumber fruit development. As previously mentioned, maximum cucumber fruit abortion occurs at 8 days after anthesis, coinciding with a steadily 144 decreasing amount of available assimilates (106). The maximum calcium accumulation and growth rates peaked around 8 days after anthesis in the June 7 planting. The brief rain shower at 7 days after anthesis probably was not sufficient to maintain the high rates of fruit calcium accumulation and growth. At 6 and 7 days after anthesis, the minimum night air temperatures of 210 and 190 C, respectively, were the highest in the fruiting period (Figure 18). These high temperatures further accentuated the water stress. The large fluctuations in moisture between the vegetative and the fruit growth periods may be deleterious (Figure 20). The plants cannot grow at a steady rate. Plant metabolism may be traumatized by water stress. Plants from the July 5 planting often wilted in the afternoons. During the night the plants would regain turgidity. This would slow fruit growth as more energy was expended for maintaining the water-stressed cells, decreasing the energy available for further growth. Fruit hormonal changes also may have affected the calcium accumulation and growth rates. The larger, dominant pickling cucumber fruits may have grown by drawing moisture and assimilates from any smaller fruits on the vine. The July 5 fruits reached their maximum rates (Figures 7,12) at approximately the time that the fruits in the lower nodes would begin to lose their dominance (106). The fruits from the June 20 and July 19 plantings had 145 an almost linear increase in the rates of calcium accumulation and growth (Figures 7,12). Since these fruits never reached their maximum rates, this would suggest that there was not an assimilate or water shortage. Both plantings received about 7 cm of rainfall during their vegetative growth periods, of which 0.71 cm and none fell 10 days before anthesis for the June 20 and July 19 plantings, respectively (Figure 20). It rained 5.10 cm during fruiting in the June 20 planting, the highest amount amongst the four plantings. The July 19 planting received 0.91 cm of rain during the fruiting period. It took a greater number of days after anthesis to reach a specific fruit fresh weight for the July 19 planting (Table 13). Fruits from the last planting averaged only 75 g at 10 days after anthesis. The pickling cucumber plants started fruiting earlier in plant development than in the other plantings. This would suggest that there was less photosynthetic leaf area, decreasing the production of assimilates. The percent soil moisture was low at the beginning of the fruiting period, which also affected fruit development and calcium accumulation rates (Figures 7,12). The 25 g fruits from this planting had significantly lower calcium accumulation rates than fruits from the other plantings. It is possible that these fruits were drawing water from the smaller fruits on the vine, thus decreasing calcium import more than growth. The pickling cucumber plants from both the June 20 and 146 July 19 plantings received rain between 6 and 8 days after anthesis (Figure 20). This is the critical period of time during which assimilates often become limiting for pickling cucumber fruit growth (106). Both calcium accumulation and fruit growth rates increased for 25 and 50 g fruits from the July 19 and June 20 plantings, respectively, following these rains (Figures 7,12). In contrast to the declining rates for the June 7 and July 5 plantings, fruits from the June 20 planting continued to increase in calcium accumulation and growth rates as they enlarged to greater than 100 g (Figures 7, 12). It had been cloudy during the last two harvests, which may have increased water and calcium movement to the fruits by enhanced root pressure flow. Since the final pickling cucumber harvest was at 11 days after anthesis, it is unknown if fruits from the July 19 planting would have continued to increase in their rates of calcium accumulation and growth like fruits from the June 20 planting or would have reached maximum rates like the fruits from the June 7 and July 5 plantings. Relationship of Pan Evaporation Diurnal fluctuations in plant transpiration rates, created by dry days, humid nights and good soil moisture levels, increase the import of calcium into weakly transpiring tomato fruits (1). Root pressure flow only develops at night when the transpiration rate is low. This 147 would suggest that the development of a positive root pressure at night may be extremely important for facilitating calcium transport into developing pickling cucumber fruits. Scatter plots were prepared of the total daily pan eva- poration amounts versus the rates of calcium accumulation and growth on the day pickling cucumber fruits weighed 25, 75 and 150 g (fresh weight). The location of points in the different quadrants are nearly identical for both the calcium accumulation rate and the growth rate plots (Figure 21). The location of these points from the different planting dates differed for the three fruit weights. Since there was greater separation of points from the different plantings for 150 g fruits, only these plots are presented. The points for each planting date (Figure 21) are almost stacked in ascending order of the amounts of rainfall received during fruiting (Table 20). The July 5 planting had the lowest rainfall and rates of fruit calcium accumulation and growth, the June 7 planting had intermediate values, and the June 20 planting had the highest rainfall and rates. The points for the June 7 planting overlapped more with the July 5 points for fruit growth rates than for calcium accumulation rates. This may be due to greater growth rate differences among cultivars for 150 g fruits. Pan evaporation did not have a major effect on either calcium accumulation rates or fruit growth rates in this 148 Figure 21 (A-B). The relationship between daily pan evaporation on the (A) calcium accumulatin rates and (B)fruit growth rates of 150 g pickling cucumbers from 3 planting dates, 1984. The rates for each planting date were estimated for regression curves of the (A) fruit calcium concentration and (B)fruit fresh weight of 4 cultivars, each replicated 4 times. The July 5 planting had 3 replications. (Evaporation measured by the Michigan State University Weather Service at the Horticulture Research Center.) 149 n % 25... 150 g MEAN FRUIT FRESH WEIGHT \ .5». 20’ E 3:233 ”W - .9 E15; 1!. ..Zfi'i‘.‘ I: g a" 8‘3. ‘5 E V 5 17. a O O i . r I r -b— 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Daily Pan Evaporation (cm) 70 f\\ 150 g MEAN FRUIT FRESH WEIGHT 60-- I? 241-1831 0 IE O-ZO-Gfl Plant“ a ...; ———— g5 50- ILL-2:533 , (A 3% D ”1:18 4.: 6‘5 404 ‘ i I L . 0.: § r at a! 30‘ - .1 av A Ll. fl A A A . 204 ' I . ‘ B \ I A 10 I I I M. ‘ T 0.0 0.1 0.2 0.3 O. . 0.6' 0.7 0.8 Daily Pan Evaporation (cm) Figure 21. 150 experiment (Figure 21). At any one pan evaporation amount the rates of pickling cucumber fruit calcium accumulation and growth were very different. The lack of response may be due to the fact that the pan evaporation data were daily totals, which do not reflect diurnal fluctuations. A positive root pressure, which develops during the night, may be very important in affecting water and calcium movement into the pickling cucumber fruits. Also, the other environmental parameters could not be controlled in the field as the amount of daily pan evaporation changed. Pan evaporation is not the same as transpiration from a plant. Water is evaporating from an open pan rather than from a leaf with stomatal opening and closing or from the small lenticels of fruits. Cucumis is one of the most sen- sitive crop species to ultraviolet beta (UV—beta) radiation, which decreases the leaf diffusive resistance to water vapor (124). In mild water-stressed Cucumis species, UV-beta rad- iation reduces stomatal closure. Transpiration rates also increase in fruiting versus nonfruiting cucumber plants. Effect of Soil Moisture No clear trends occur between percent soil moisture and the rates of pickling cucumber fruit calcium accumulation and growth (Table 22). Due to the differences in fruit maturity and environmental conditions, comparisons can only be made between replications at each sampling time but not between samplings. At 1 and 4 days after anthesis the 151 percent soil moisture was around 20 percent in replication 4 of the July 5 and 19 plantings. The calcium accumulation rates and fruit growth rates were reduced at these high soil moisture levels. Replication 4 was flooded from the heavy rain on August 4 and 8 (Figure 20). This most likely created anaerobic conditions in the rhizosphere, which are not conducive to water and nutrient uptake by the pickling cucumber roots. At 8 days after anthesis soil moisture was positively correlated with the rates of fruit calcium accumulation and growth, since percent soil moisture was not in excess (Table 22). As noted previously, water plays a crucial role in pickling cucumber fruit growth and calcium accumulation. More frequent soil sampling would have provided a broader base from which to draw conclusions about the effect of soil moisture on these rates. Although the highest calcium accumulation rates are usually associated with the highest fruit growth rate at any given soil moisture percentage, there were some exceptions at 1,5 and 8 days after anthesis (Table 22). Further work is needed to assess why these differences occur. It would also be interesting to compare the rates of numerous fruits of similar sizes to determine if soil moisture affects calcium accumulation rates and fruit growth rates differently at various ontogenetic stages of fruit development. 152 Table 22. The effect of blocking on moisture and on the rates of fruit calcium and growth of pickling cucumbers, the 1984. percent accumulation Sampling % Soil Ca accum. Growth rate Planting time moisture rate (mg (g fr. wt./ date DAAz Rep (g/g)y Ca/day)x day)x June 20 5 1 7.88 4.52 9.72 2 8.86 5.84 11.49 3 9.40 3.82 7.90 4 10.34 4.64 9.36 July 5 1 1 12.31 0.32 0.32 2 13.44 0.10 0.38 4 20.87 0.14 0.26 8 1 6.99 3.18 10.12 2 8.71 1.00 14.69 4 15.95 5.25 18.51 July 19 4 1 7.49 0.87 0.92 2 9.42 1.56 2.32 3 9.10 0.98 1.34 4 18.82 0.61 0.78 11 1 5.32 11.98 41.16 2 7.33 7.32 22.88 3 6.94 7.16 22.27 4 18.12 11.70 41.90 2Days after anthesis. yAverage of 4 soil samples at a 7-20 cm depth. xAverage of 4 cultivars. soil 153 Effect of Temperature Warm soils encourage mineral and water uptake and positive root pressure development, which should stimulate fruit growth and/or calcium transport rates. The rate of pickling cucumuber fruit production was reported to have increased as the night temperatures rose (132). Schapendonk et al. (1984) attributed earliness of fruit production to increased irradiance rather than to higher temperatures (107). Scatter plots were prepared of the maximum (Figure 22) and minimum (Figure 23) daily soil temperatures for the days when pickling cucumber fruits weighed 25, 75 and 150 g versus the rates of calcium accumulation of fruits at these specific fresh weights. Similar scatter plots were also generated for maximum and minimum daily soil temperatures versus fruit growth rates and maximum and minimum daily air temperatures versus the rates of fruit calcium accumulation and growth, which will not be presented. The points for both the calcium accumulation and growth rates were in similar locations for all of the temperature plots. The plots were also similar for the air and soil temperatures. The soil temperatures showed a corresponding increase as the maximum daily air temperatures increased, but the daily soil minimum and maximum temperatures fluctuated less than the air temperatures. Ingestad (1973) noted an increase in ion uptake in cucumbers (cv. Bestseller OE 0219) with an increase in root 154 temperatures. In the present experiment, similar soil temperatures were associated with very different calcium accumulation rates at the different fruit weights examined (Figures 22,23). The calcium accumulation rates did increase with increasing minimum soil temperatures for 150 g fruits (Figure 23C). For 150 g fruits from the different plantings, the points were in separate quadrants of the plots, arranged in the order of the amount of moisture received during fruiting (Table 20). If a positive root pressure affects both ion and water uptake in pickling cucumbers, the primary effect of water may have altered the secondary effect of temperature on calcium uptake (4). Since only the main effects of soil moisture and temperature on the rate of fruit calcium accumulation were studied, this possible interaction was not identified. The points for the different planting dates overlapped in the plots of 25 and 75 g fruits (Figures 22A-B,23A-B). The 25 g fruits from the June 7 planting had higher calcium accumulation rates at the higher maximum daily soil temperatures. Points for the June 20 and July 5 plantings overlapped for both minimum and maximum soil temperatures. There was adequate moisture for fruit growth in both main plots at this fruit size. The lowest calcium accumulation rates generally occurred in 25 g fruits from the July 19 planting and in 75 g fruits from July 5 planting (Figure 7). At these low calcium accumulation rates, it was extremely dry. The high minimum and maximum daily soil 155 Figure 22 (A-C). The effect of maximum daily soil temperatures on the calcium accumula- tion rates of (A)25 g, (B)75 g, and (C)150 g pickling cucumber fruits from the different planting dates, 1984. The rates for each planting date were estimated from regression curves of the fruit calcium concentration of 4 cultivars, each repli- cated 4 times. The July 5 planting had 3 replications. (Temperatures measured by the Michigan State University Weather Ser- vice at the Horticulture Research Center.) 156 \ I I / B 33 I I 3'1 T 25 I 21 2 Maximum Daily Soil Temperature (°C) (£99 90 6W) E 35 mass» fl 0 a n a a . a a a I -- - 37 35 I Maximum Daily Sail Temperature (°C) r-a‘r‘-:E.-3'I"’Lis :mliflig C 31 ‘ 25 20 15 10 5- £0 a 5a: “108 NWT/mam 2J-II'II‘JIIKD I 2. 2‘7 Maximum Daily Sail Temperature (°C) 1 I I 0 o n o 15 2 KO 0 61a 0103 uggaf/wgoev {ungolao 0-1 Figure 22. 157 Figure 23 (A-C). The effect of minimum daily soil temperatures on the calcium accumula- tion rates of (A)25 g, (B)75 g, and (C)150 g pickling cucumber fruits from the different planting dates, 1984. The rates for each planting date were estimated from regression curves of the fruit calcium concentration of 4 cultivars, each repli- cated 4 times. The July 5 planting had 3 replications. (Temperatures measured by the Michigan State University Weather Ser- vice at the Horticulture Research Center.) 158 .mN ouswwk GOV ecsaeceaEeh :00 2.3 E2553 3 an «a . a an 2 Se - - III!-' I I- r. . . 0 ‘ ‘. « I'I'lllF~ I“ m 9 4 m. . c .2 Wm D a 5m- ,» mflH-HU .2 mm c E /m a g mm. a 3...... -e« (m a 8 E :89 .89.... 5E 26: a 8. -8 m 8% 23209:: ..om 3.3 5.5—...: . A000 e ..3e tea—5.... ..am Qua 625:5 on mu «m ..u eta a.- .. ...... a «a as 2 al. - “I ’l/ N MW _ . . - C . fl. )nWH .. .11 _ m. w w a,” « O O; 10 6 3 C r O O . Mum _ _ .2 Wm. m n 2 .... m - $1...- .. . .H . ... (m. a... «WI-WI h. 3 ..c— U menu-I E «i L w E In”! -2 a a 38... Son; :05 e3... 25: e an a. 35... a. no 6w) (My 0103 uonoI wnaav magmas 159 temperatures would have further depleted the limited available moisture by evaporation and transpiration. The plants would not have been able to regain turgidity as rapidly during the night, due to the high temperatures and lack of moisture. SUMMARY Mean Calcium Concentration and Content in Pickling Cucumber Fruits During Ontogeny The mean pickling cucumber fruit calcium concentration declined from approximately 1.75 percent to less than 0.70 percent (dry wt.) during fruit ontogeny. The most rapid decline in calcium concentration occurred during the first 5 days after anthesis. The differential effect of cultivar on the fruit calcium concentration under different environmental conditions indicates that pickling cucumber fruits are most sensitive to changes early in development. Planting date and cultivar had an impact on the calicum concentration of fruits from the later harvests. Fruits from the June 20 planting had the highest calcium concentrations (0.78-0.93% dry wt.) from 7 to 11 days after anthesis. Tamor had the lowest fruit calcium concentrations (0.54-1.60% dry wt.) throughout ontogeny. Differences in calcium partitioning between pericarp and endocarp tissues occurred in pickling cucumber fruits. While the pericarp calcium concentration (1.1-0.72 dry wt.) declined gradually with increasing fruit size, the endocarp calcium concentration (0.8-0.2% dry wt.) declined 160 161 dramatically to a low of 0.20 percent, a deficient concentration for many crops. Expansive cell growth rates of the endocarp fruit tissues exceeded pericarp growth rates in the more mature pickling cucumber fruits, having a dilutionary effect on the tissue calcium concentration. The endocarp may also contain fewer vascular tissues than pericarp tissues, decreasing the rate of calcium import into the tissue. Endocarp tissue calcium concentrations are more sensitive to environmental changes and different genotypes than the pericarp calcium concentrations. A higher concentration of calcium accumulated in leaf tissues (3.1% dry wt.) than in pickling cucumber fruits (1.94% dry wt.). The calcium concentrations of leaf lamina tissue (l.8—3.1Z dry wt.) were always higher than petiole tissue (1.4—1.8% dry wt.) calcium concentrations of pickling cucumbers. The petiole tissue calcium concentration is not as sensitive to changes in the environment as the leaf lamina tissue. It may, therefore, be more accurate to sample leaf lamina rather than petiole tissue for non—mobile nutrients like calcium. Leaf tissue is not a good indicator of mature fruit tissue calcium concentrations, suggesting that factors other than calcium uptake by a plant are contributing to variations in calcium levels within the plant. As pickling cucumber fruits enlarged, the calcium content (0.54-67.74 mg Ca/fruit) increased due to a continuous calcium uptake during ontogeny. The period of 162 most rapid calcium accumulation was generally 9 to 11 days after anthesis, as the fruits approached harvestable size. The increase in calcium content relative to fruit fresh weight was almost linear within the fruit fresh weight range of 5 to 150 g for planting date. The June 20 planting tended to produce fruits with the highest calcium contents (3.71-55.03 mg Ca/fruit), while fruits from the July 19 planting generally had the lowest calcium contents (3.92-20.89 mg Ca/fruit). The greatest differences in fruit calcium contents between cultivars occurred in the more mature fruits. The comparatively low calcium contents of Tamor fruits (3.62-41.54 mg Ca/fruit) were established early in fruit development and maintained throughout ontogeny. If calcium is proven to be critical for pickling cucumber fruit development and quality, it would be advantageous to increase the fruit calcium concentration. Calcium sprays or dips, which are used to increase the concentration in apple fruit flesh, could not increase the low calcium concentrations of endocarp tissues. The applied calcium only moves superficially into fruit tissues. Calcium fertilizers may increase fruit calcium concentration if applied during the early stages of fruit development. Genetic variability could be exploited in a pickling cucumber breeding program. A pickling cucumber cultivar, such as Tamor, may have a lower tissue calcium requirement due to more efficient ion utilization, more selective calcium absorption and/or differing efficiency of loading 163 calcium ions into xylem vessels. The calcium contents of plant organs are based on metabolic removal from the vascular system rather than on physiological demand. The effect of calcium competition between fruits on a vine needs to be studied. More calcium may be distributed to fruits lower on the vine than from the upper nodes. It is also unknown if ontogenetic changes in pollinated pickling cucumber fruit calcium concentration and content are the same as in a parthenocarpic fruit. It has been proposed that endogenous auxin formed by seeds may enhance calcium transport. In this study the mean fruit calcium concentration was quantified. A calcium fractionation study would elucidate if the calcium is in a soluble and/or insoluble form and if the solubility changes through ontogeny. Further research is also needed to determine the physiological consequences of the changing calcium status of pickling cucumber fruits. Ontogenetic Changes in Calcium Accumulation Rates Relative to the Growth Rates of Pickling Cucumber Fruits The calcium accumulation rate of a pickling cucumber fruit is the amount of calcium (mg) imported into the fruit per unit time (day). The fruit growth rate is the fresh weight (g) gained per unit time (day). Environmental factors had a significant and similar impact on the rates of pickling cucumber fruit calcium import and growth. Trends in calcium accumulation rates and growth rates 164 were similar for fruits from the June 7 and July 5 plantings and from the June 20 and July 19 plantings. The average maximum calcium accumulation rate peaked in 50 g fruits from the June 7 planting (9 mg Ca/day) and in 75 g fruits from the July 5 planting (5 mg Ca/day). Growth rates declined after fruits averaged 100 g in the June 7 and July 5 plantings at 40.5 and 21.6 g/day, respectively. Fruits from the June 20 and July 19 plantings exhibited a continual rise in rates of calcium accumulation and growth throughout the harvest period. The highest average calcium accumulation rate (21 mg Ca/day) and growth rate (50.3 g/day) were estimated for 150 g fruits from the June 20 planting. Pickling cucumber fruits from the July 19 planting grew more slowly than fruits from the June plantings, averaging less than 100 g by 11 days after anthesis. It is important to look at the calcium accumulation rate relative to the growth rate, as a high growth rate and/or low calcium import rate will cause a decline in the pickling cucumber fruit calcium concentration. Even though the environment during fruit development was different for these plantings and affected both growth and calcium import, the rates of growth relative to rates of calcium accumulation were similar. The largest increase in pickling cucumber fruit fresh weight and volume occurred between 9 and 11 days after anthesis, which was also the period of most rapid calcium accumulation. These trend similarities suggest that a correlation exists between the rates of 165 pickling cucumber fruit calcium accumulation and growth. Approximately 7 days after anthesis appears to be a critical period in pickling cucumber fruit development. Planting date and cultivar interacted, affecting fruit fresh weight, volume, and length to diameter ratios. Fruits from the June 7 planting reached their maximum rates of calcium accumulation and growth during this time period. Schapendonk and Brouwer (1984) report that maximum cucumber fruit abortion occurs at 8 days after anthesis (106). Available assimilates often become limiting during this period of high fruit growth rates. In this study, pickling cucumber fruit growth rates were inversely proportional to the fruit dry weight percentages. Steady fruit growth rates are preferable to high fruit growth rates in maintaining adequate calcium levels in pickling cucumber fruits. Closer plant spacing may favor the calcium status of pickling cucumber fruits if plant vigor is reduced slightly, resulting in smaller, slower growing fruits. Further research is needed to identify the physiological plant processes which control calcium accumulation. If these processes are the same as those controlling growth, it would suggest further methods of increasing the fruit calcium status. 166 Effect of Various Environmental Parameters on Pickling Cucumber Fruit Calcium Accumulation and Growth Under certain environmental conditions a significantly higher rate of calcium accumulation was achieved for a given fruit growth rate, suggesting that differences exist in calcium transport or accumulation efficiency in pickling cucumber fruits. Soil moisture significantly increased the rates of pickling cucumber fruit calcium accumulation and growth, if the soil moisture did not exceed 20 percent. Optimum soil moisture affects the calcium concentration of the soil solution, provides a high soil-water potential, and maximizes plant water and nutrient uptake. Pickling cucumber plants from the June 7 and July 5 plantings received the majority of rain during their vegetative growth phases. Fruits from both plantings reached their maximum fruit growth rates and calcium accumulation rates before the fruits averaged 100 g. The lowest rates of fruit calcium import and growth occurred in the July 5 planting, the only planting which received no rain during fruiting. Fruits from the June 20 and July 19 plantings, which never attained maximum rates of calcium accumulation and growth, received 5.10 cm and less than 1 cm of rain during fruiting, respectively. This rain fell between 6 and 8 days after anthesis, the critical time period during which assimilates often become limiting to pickling cucumber fruit growth. Both the rates of fruit 167 calcium accumulation and growth increased following these rains. Pickling cucumber fruits, especially in the early stages of development, are very sensitive to water stress. It would be interesting to compare rates of fruit calcium accumulation and growth of pickling cucumbers of similar size to determine if soil moisture affects these rates differently at various ontogenetic stages. Judicious irrigation scheduling, especially around 8 days after anthesis, would appear to be very beneficial for pickling cucumber fruit calcium accumulation and growth. Neither pan evaporation nor temperature had a direct effect on pickling cucumber fruit calcium accumulation or growth. 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