._.. .. I. g. .. g r. 233775193 II II II III IIIIIII II IIII IIII II II Urn; , n. 11 9691 udtflflY i I Ififiirhiggn J51 A3” I. University I This is to certify that the thesis entitled EFFECTS OF BENZYItADENINE AND HAND THINNING ON SIZE OF STARKRIMSON 'DELICIOUS' APPLES, AND PREDICTION OF HARVEST SIZE. presented by Joseph G. Masabni has been accepted towards fulfillment of the requirements for M-S- degree in 1152QO ure Major professor 0.7639 MS U is an Affirmative Action/Equal Opportunity Institution PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE I msu Is An Affirmative Action/Equal Opportunity Inwtmion EFFECTS OF BENZYLADENINE AND HAND THINNING ON SIZE OF STARKRIMSON 'DELICIOUS' APPLES, AND PREDICTION OF HARVEST SIZE BY Joseph Gebran Masabni A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE DEPARTMENT OF HORTICULTURE 1988 ABSTRACT EFFECTS OF BENZYLADENINE AND HAND THINNING ON SIZE OF STARKRIMSON 'DELICIOUS' APPLES, AND PREDICTION OF HARVEST SIZE BY Joseph G. Masabni Starkrimson 'Delicious' is notorious for bearing small fruits as the trees age. Cytokinin application before anthesis, and hand thinning on various dates and to various densities were tested. Neither time of application nor concentration of BA affected size, length/diameter ratio or weight of fruits measured at harvest. Final set was dramatically reduced at 50 ppm. Hand thinning to 20 fruits/100 flower clusters increased size in one orchard, with thinning effective in another orchard when limbs were thinned on June 6 but not thereafter. Fruit diameters were monitored in 3 Michigan orchards over 3 years. The data were used to prepare a prediction table for comparison with the Washington chart. In general, Michigan fruits grew more slowly than would be predicted from the Washington chart, the difference increasing with fruit size. Use of the new table allows prediction of harvest size of 50% of the fruits within 3 mm at 50 days after full bloom. To Nazek and Gebran ii vi.‘ VH‘ u a ACKNOWLEDGMENTS I wish to thank my major professor and friend Dr. Frank G. Dennis, Jr. for his encouragement, guidance, and especially for his helpful suggestions during the preparation of this thesis. I also wish to thank the members of my advisory committee, Dr. J.A. Flore and Dr. R. Hoopingarner for their help and patience during the entire period of my graduate program. I am greatfully indebted to the Department of Horticulture and the Michigan Apple Research Committee for my research assistanship. Finally, I wish to thank my friends for their encouragement to carry on and both Gloria Blake and LuAnn Gloden for allowing me the use of their word processors. iii TABLE OF CONTENTS List of tables List of figures List of abbreviations Literature review Importance of cell division in determining apple fruit size Influence of fruit thinning and growth regulators on cell division in apple flowers and fruits Effects of fruit thinning on size Predicting harvest size Literature cited SECTION I Evaluation of Cytokinin Application to Apple Flowers for Increasing Fruit Size Abstract Introduction Materials and Methods Results Discussion Literature cited iv Page vi viii xii 12 16 17 18 19 21 27 29 Page SECTION II Effect of Timing and Degree of Hand Thinning Starkrimson 'Delicious' Apple Fruits on Harvest Size 30 Abstract 31 Introduction 32 Materials and Methods 35 Results 39 Discussion 47 Literature cited 49 SECTION III Predicting Fruit Size of Starkrimson 'Delicious' Apple in Michigan 51 Abstract 52 Introduction 53 Materials and Methods I 54 Results 65 Discussion 94 Conclusions 97 Literature cited 98 *4 h) LIST OF TABLES Table Page SECTION I 1. Influence of BA on initial and final set of Starkrimson 'Delicious' apple, Leslie, MI. 1987. 22 2. Influence of BA on fruit diameter (mm) of Starkrimson 'Delicious' apple, Leslie, MI. 1987. 25 3. Influence of BA on fruit harvest weight (g) and length/diameter (L/D) ratio of Stark- rimson 'Delicious' apple, Leslie, MI. 1987. 26 SECTION II 1. Fruit density in September on limbs used for fruit thinning experiments, 1987. 36 2. The effects of hand thinning Starkrimson 'Delicious' apple to various levels 15 to 16 days after full bloom on fruit diameter (mm) at harvest. 1987. 40 3. The effect of time of hand thinning Stark- rimson 'Delicious' apple to 30 fruits per 100 flower clusters on various dates on harvest diameter. 1987. 42 4. Effects of hand thinning on Pn and related parameters in two Starkrimson 'Delicious' orchards in 1987. 45 SECTION III 1. Location and age of Starkrimson 'Delicious' apple trees used in the study of harvest size prediction in 1985-1987, Michigan. 55 2. 'Standard' Washington chart established by Batjer, et al. in 1957, for predicting harvest size of Delicious and 'Golden' Delicious for fruits of various size class at harvest. 61 vi Table 10. The coefficients of correlation (r) of the regression lines of fruit size at various days after full bloom (DAFB) vs. harvest size for various orchards and years. The r values are significant at p < 0.05 for 18 to 66 DAFB, and at p < 0.01 for 67 DAFB and after. Predicted diameters in mm. for Starkrimson 'Delicious' apples at various days after full bloom (DAFB), based upon data from 3 orchards over 3 years. Predicted diameters in in. for Starkrimson 'Delicious' apples at various days after full bloom (DAFB), based upon data from 3 orchards over 3 years. Actual fruit diameter at harvest and diameter predicted by using regression equation, based on average diameter at various times prior to harvest over a 3-year period. Wittenbach orchard, Belding, MI, 1985-1987. Actual fruit diameter at harvest and diameter predicted by regression equation, based on average diameter at various times prior to harvest. Mature trees at the Wardowski orchard, Leslie, MI. 1987. Actual fruit diameter at harvest and diameter predicted by regression equation, based on average diameter at various times prior to harvest. Young trees at the Clarksville Horticulture Experimental Station. 1987. Predicted percentages of fruits in various size classes vs. observed percentages based upon combined data for 3 Michigan orchards over 3 years. Prediction based on fruit diameter at 100-102 DAFB. Photosynthetis measurements on old vs. young Starkrimson 'Delicious' trees in Wardowski orchard, Leslie, MI. September 12, 1987. vii Page 66 84 85 86 87 87 88 93 LIST OF FIGURES Figure Section I Effects of BA concentration and time of application in affecting final fruit set of Starkrimson 'Delicious' apple. September 23, 1987 Section II Regression of fruit diameter on fruit density in the Dowd (A), and the Wittenbach orchard (B), Michigan, 1987. Numbers indicate fruits per 100 flower clusters for each treatment Regression of fruit diameter on fruit density in the Dowd (A), and the Wittenbach orchard (B) following thinning on 3 dates, Michigan, 1987 Section III Regression of Starkrimson 'Delicious' fruit diameters (Data for 4 trees) at harvest on diameters of same fruits on 3 sampling dates in 1985 Growth curves of fruits of 4 different harvest diameters, based upon regression of final diameter on diameter at various dates Growth curves of fruits of 4 different harvest diameters, based upon regression of final diameter on diameter at various dates. Values adjusted to 10 day interval Growth curves, based upon the Washington chart, for fruits of 3 different diameters at harvest Regression of Starkrimson 'Delicious' fruit diameters (5 trees) at harvest on diameters of same fruits on 3 sampling dates in 1985 viii Page 23 41 44 57 59 6O 62 67 Figure 6. 10. 11. 12. 13. 14. 15. 16. 17. Fruit diameter prediction curves for Stark- rimson 'Delicious' fruits in one Michigan orchard in 1986 vs. similar curves for Washington 'Delicious' Fruit diameter prediction curves for Stark- rimson 'Delicious' fruits in one orchard in Michigan over 3 years Fruit diameter prediction curves for Stark- rimson 'Delicious' fruits in two Michigan orchards over 3 years Prediction curves for Starkrimson 'Delicious' fruits in one Michigan orchard over 3 years expressed as fruit volume Fruit diameter prediction curves for medium sized fruits in 3 Michigan orchards in 1986 vs. similar curves for Washington Size prediction curves for a young vs. a mature orchard, 1987 Effect of tree age on growth of Starkrimson 'Delicious' apple fruits, Leslie, MI. 1987 Size prediction curves for young vs. mature trees in the same orchard, Leslie, MI. 1987 Growth curves of fruits of 3 different harvest diameters as predicted in Table 4 Averaged fruit diameter prediction curves for Starkrimson 'Delicious' data for 1985- 1987 vs. similar Washington growth curves Actual diameter vs. averaged prediction curves for Michigan for 64, 70 mm harvest size in 1987 Actual diameter in one orchard vs. averaged Michigan prediction curves for 64, 70 mm harvest size ix Page 68 70 71 72 73 75 76 77 78 80 81 82 Figure Page 18. 19. 20. Percentage of fruits whose actual harvest size fell within indicated ranges of predicted size at 50, 100 and 125 DAFB. Steffens orchard, 1985. 90 Comparison between growth curves of fruits as measured by Curry (Washington, 1983) and "standard" Washington curve of Batjer, et a1. (1957) 91 Average diameter of Delicious fruits measured by Curry in Washington in 1983 vs. curves for 70 and 76 mm. fruit based upon data of Batjer, et al. (1957) 92 ANOVA BA CHES citowett ctrl DAFB DMRT DNOC GA in. 1 LC L/D LSD MC MI min. mm. pmols/m p1 NAA NAD n.s. PAR PlotIt 2 Sc Sevin Tween-20 VPD WA WUE LIST OF ABBREVIATIONS Analysis of variance Benzyladenine Clarksville Horticulture Experimental Station Alkylarylpolyoxy—glycolether (a surfactant) Control Days after full bloom Duncan's multiple range test Dinitro-ortho-cresol Gibberellic acid Inch(es) Liter Leaf conductance Length/Diameter Least significant difference Mesophyl conductance Michigan Minute Millimeter Micromols per meter squared Microliter Naphthaleneacetic acid Naphthaleneacetamide Not significant Photosynthetically active radiation Interactive Graphics and Statistics Program, Copyright, 1987, Scott.P. Eisensmith. Michigan State University. Net photosynthesis Parts per million Correlation coefficient Determination coefficient Relative humidity Second Stomatal conductance l-naphthyl N-methylcarbamate Polyoxyethylene sorbitan monolaurate Vapor pressure deficit Washington Water use efficiency xi Literature review Fruit size is critical in determining the economic value of an apple crop, for price generally increases with fruit size. Mature trees of Starkrimson 'Delicious' tend to produce small fruit, therefore methods to improve fruit size are needed (8). In this review, I will focus on the importance of cell division in determining size, on the effects of fruit thinning and chemical treatment on cell division and size in apple flowers and fruits, and on predicting harvest size. A. Importance of cell division in determining apple fruit §i_2_e. Apple fruits undergo both cell division and cell enlargement in the course of their development. Most of the cell division occurs within the first 4 weeks after anthesis, whereas cell enlargement continues until harvest. In a study of cell size gradients and changes in cell shape and packing during development of 'Granny Smith' apple, Bain and Robertson (2) confirmed that cell division ceased within 4 weeks of pollination. Final size of fruits was proportional to cell number, whereas cell size was less important. Cell enlargement continued as long as the fruit remained on the tree. Martin and Lewis (20), on the other hand, reported that the difference in fruit size between light and heavy-bearing trees was due to differences in cell size rather than cell number. Denne (11) measured cell size and calculated cell number in large and small unthinned fruits of "Cox's Orange Pippin" apple on M7 rootstocks. Both cell number and size increased as both crop load and fruit weight declined. The diameter of fruits on light cropping trees increased more rapidly than did that of fruits on heavily cropping trees (significant at 12 weeks after full bloom). Denne concluded from her observations that harvest size variation within trees was related to both cell size and number. Goffinet (15) studied the relation between final size of 'Empire' fruits and cell size and number. Fruit diameter was highly correlated with both pith and cortex thickness (r2 of .982 and .998, respectively). Total flesh thickness (cortex and pith) increased linearly with time until the last month before harvest. However, total cell layers in the flesh tripled the first 3 weeks, then increased more slowly, with the cortex having more cell layers than the pith at all times. Cell volume, on the other hand, in the cortex and pith increased rapidly starting about 4 weeks post bloom. Although the cells of cortex and pith expanded in volume at the same rate, they did so in different planes. Cortex cells expanded vertically and tangentially 10% more than did pith cells, but their radial expansion was 16% less. B. Influgnge of fruit thinning and growth regulators on cell 'v's'o ' lowe s a d fruits Starkrimson 'Delicious' is notorious for bearing small fruits as trees age. Previous work in Michigan (8) showed that fruit size was not improved by hand thinning in July. Estimates of costs/returns indicated that growers lost money by thinning even when the cost of hand labor was not included. Westwood, Batjer and Billingsley (22) conducted several experiments to determine the effects of fruit thinning on cell size, number and specific gravity. They found that fruits on light-cropping trees had as many or more cells than those on heavy-cropping trees. NAA application increased cell number in 'Golden Delicious' fruits, probably because of selective thinning by NAA rather than stimulation of cell division. 'Delicious' and 'Jonathan' fruits in Washington had more but smaller cells than Australian fruits of the same cultivars. Their work also showed that: a) early hand thinning usually stimulated cell division and sometimes cell enlargement, particularly in heavy-setting varieties; and b) DNOC blossom sprays increased fruit size mainly by increasing cell number rather than cell size. Westwood, et a1. (22) listed various factors which tend to increase cell size, including few cells/fruit, adequate soil moisture, strong spurs, center-bloom fruits, excess N fertilizer, late season thinning, healthy leaves and excessive chemical thinning. They advised growers, however, that fruits with many cells of medium size are preferable to those with fewer cells of large size. Recently, Iftikhar (17) evaluated the effect of hand thinning of Starkrimson 'Delicious' apple on cell number and size of flowers the following year. Thinning affected neither cell size nor number. Cell number in "king" flowers was similar to that in lateral flowers. Although cell volume in "king" flowers was larger (p < 0.01), inter space was smaller (p < 0.01). Finally, Iftikhar observed that lateral flowers from trees in a mature orchard contained approximately the same number of cells as did those from a young orchard. Cell size, however, was smaller. Goffinet, et al. (16) thinned 'Empire' trees at pink, bloom, and 10-, 20- and 40-days post bloom and compared cell size and numbers of fruits from unthinned and hand thinned trees. Control fruits were significantly smaller than those in any other treatment, with bloom-thinned fruits the largest. The latter contained slightly larger and greater numbers of cells than did control fruits. Regression analysis showed that fruit size was better correlated with cell number than with cell size or interspace. Stembridge and Morrell (21) found that benzyladenine (BA) applied during bloom markedly increased development of the calyx lobes of 'Delicious' apple fruits. This resulted in a larger length/diameter (L/D) ratio. BA and gibberellins 4+7 (GA4+7), applied at either pink or full bloom, also increased L/D ratio. Martin, et al. (19) showed that major elongation of apples occurred when BA was applied at petal fall. According to the authors, differences in L/D ratio between control and treated branches were dramatic, visually noticeable without measurement. Williams and Stahly (24) conducted a similar experiment in Washington. They used several cytokinins (zeatin, BA and phenylglycine) on 'Delicious' blossom clusters 4 days after full bloom. All cytokinin treatments significantly increased the L/D ratio, the greatest elongation being observed when cytokinin and GA4+7 were combined. High concentrations (500 ppm) of cytokinin and gibberellin resulted in overly prominent lobes which gave the fruits a knobby appearance. Ferree, et al. (12), on the other hand, did not observe a significant difference in fruit shape .following Promalin application. C. s ' t ' 'n Early fruit removal reduces competition for carbohydrates and other nutrients thereby increasing fruit size and improving fruit quality and color. Thinning is essential for some cultivars, for it prevents biennial bearing. Fruits can be thinned either chemically or by hand. The most commonly used chemicals include DNOC (dinitro-ortho-cresol), NAA (naphthaleneacetic acid), NAD NH“ .3.“ a: 1'- 4H (naphthalene acetamide); and Sevin (l-naphthyl N- methylcarbamate). Early thinning experiments demonstrated that tar oil distillates were most effective in killing flower buds (1). Later DNOC was shown to prevent pollen germination when applied to stigmata (18), thus initiating extensive research to determine the optimal concentration and time of application. When NAA and NAD were found to reduce harvest drop of apples (14), they were evaluated to determine whether they also increased set if applied during bloom (6). Rather than increasing set, NAA reduced set by up to 77% at 50 ppm (6). This shifted attention from DNOC to growth regulators. Considerable attention was given to timing of NAA sprays. Davidson, et al. (9) obtained effective thinning when the sprays were applied as late as 2-3 weeks after bloom. In 1958, an insecticide (Sevin) was found to possess thinning qualities in 'Delicious' and 'Winesap' apples. Batjer and Westwood (4) later reported that Sevin was a safe and effective thinning agent, rarely over- -or under-thinning. DNOC thinned apples equally well at full bloom and at early petal fall. Many growers, however, prefer to assess the degree of fruit set before applying chemical thinners, thus chemicals which can be applied later were tested. Consistent results were achieved when NAA and NAD were applied 15 to 25 days after full bloom, with Sevin being effective over a wider time period. Consistent thinning results are achieved with cultivars that tend to set heavy crops, such as 'Golden Delicious', 'Jonathan', and 'Rome Beauty'. 'Delicious' and 'Winesap', on the other hand, do not set heavily on a regular basis, and overthinning often occurs (7). Chemical thinning also reduces the biennial bearing habit of apples so that yield is more consistent from year to year. Although yield is reduced with chemical thinning, total yield over a period of years is generally slightly increased. Various systems have been tested and used by growers in hand thinning, including uniform space thinning, graduated space thinning and removal of small fruits after "June drop". D. c i ha est size Not only does predicting harvest size early in the season help the grower decide whether. any thinning is needed, but also allows estimation of crop size and storage volume needed, whether the crop should be sold for processing or fresh market and, most importantly, what prices to expect. In an 8-year study, Davis and Davis (10) obtained high correlation coefficients between early and final diameters of cling peaches in California. They measured fruits at the beginning of the second growth period and at harvest, and calculated the correlation coefficients for initial vs. final diameter for individual fruits, means of groups of 25 fruits and means of all trees for the season combined. In all 3 cases they obtained significant r values, ranging from 0.462 to 01995. Not only did size at the beginning of the second growth stage correlate well with that at harvest, but little variability in sizing ability was observed. Therefore they recommended that growers and the industry use fruit size measurements to monitor thinning and estimate total yield. Batjer, et al. (3) reported similar work on 'Winesap' and 'Delicious' apples. They found that r values for initial vs. final diameter of individual fruits increased as harvest approached, and that the harvest size of 75-80% of the fruits could be accurately predicted as early as 50 days after full bloom, with greater accuracy for larger fruits. The work of both Davis and Davis and Batjer, et al. encouraged a shift from thinning by spacing fruits uniformly on a branch to thinning by removing only the smaller fruits. Williams, Billingsley and Batjer (23) found that final diameter could be accurately predicted for 83% of pear fruits to within 1/8 in. (3 mm) at 60 days from full bloom. However, the r values calculated were consistently higher for pears than those reported for apples (Batjer, et al. 1957), suggesting that greater confidence could be achieved ' in early season prediction of harvest size with pear. 10 Forshey's work (13) with 'McIntosh' apples in New York's Hudson Valley suggested that, under optimal growing conditions, fruits tended to increase in size at a fairly uniform rate, which makes possible an accurate estimate of final size several weeks before harvest. However, r values calculated for 55 days after full bloom were lower than the values reported by Batjer, et al. (3) for the same time. Forshey concluded that the marked differences were due to the highly variable growing conditions in the Northeast. He confirmed that size of large fruits was more accurately predicted and suggested that smaller fruits are affected more by unfavorable growing conditions such as moisture stress. Hand thinning is not a common practice with 'McIntosh'. Thus early season estimates of harvest size are of little importance in determining when to thin, but can be very useful in planning the order in which orchards are harvested and how fruits are to be marketed. Blanpied (5) measured the weights and volumes of 10 average-sized apple fruits of 7 varieties at weekly intervals over two years. He correlated weekly change-in- volume vs. weekly change-in-weight for each variety and obtained a constant r value of 0.99 for the period of cell enlargement. Cook (8) measured Starkrimson 'Delicious' fruits in mature Michigan orchards and prepared a table to predict harvest size. Values differed considerably from those in the Washington chart, indicating much slower rates of fruit 11 growth in Michigan. However, he based his predictions on a linear, rather than a curvilinear, increase in diameter. Subsequent comparison of actual vs. predicted values indicated considerable error (unpublished data). 12 Literature cited Auchter, E.C., and J.W. Roberts. 1934. Experiments in spraying apples for the prevention of fruit set. Proc. Amer. Soc. Hort. Sci. 30:22-25. Bain, J.M., and R.N. Robertson. 1951. The physiology of growth in apple fruits. I. Cell size, cell number, and fruit development. Austral. J. Sci. Res. 4: 75-91. Batjer, L.P., H.D. Billingsley, M.N. Westwood, and B.L. Rogers. 1957. Predicting harvest size of apples at different times during the growing season. Proc. Amer. Soc. Hort. Sci. 70:46-57. Batjer, L.P., and M.N. Westwood. 1960. 1-naphthyl N- methyl-carbamate, a new chemical for thinning apples. Proc. Amer. Soc. Hort. Soc. 75:1-4. Blanpied, G.D. 1966. Changes in the weight, volume and specific gravity of developing apple fruits. Proc. Amer. Soc. Hort. Sci. 88:33-37. Burkholder, C.L., Iand M. McCown 1941. Effect of scoring and of a-naphthyl acetic acid and amid spray upon fruit set and of the spray upon pre-harvest fruit drop. Proc. Amer. Soc. Hort. Sci. 38:117-120. Chandler, W.H., and A.J. Heinecke. 1927. The effect of fruiting on the growth of Oldenburg apple trees. Proc. Amer. Soc. Hort. Sci. 23:36-46. Cook, R.L. 1985. Does supplemental hand thinning pay? Annu. Rept. Michigan State Hort. Soc. 115:181-185. 10. 11. 12. 13. 14. 15. 13 Davidson, J.H., O.H. Hammer, C.A. Reimer, and W.C. Dutton, W.C. 1945. Thinning apples with the sodium salt of naphthyl acetic acid. Mich. Agric. Exp. Sta. Quart. Bul. 27:352-356. Davis, L.D. and Marie M. Davis. 1948. Size in canning peaches. The relation between the diameter of cling peaches early in the season and at harvest. Proc. Amer. SOC. Hort. Sci. 51:225-230. Denne, M. Patricia. 1961. Observations on cell size and number in relation to fruit size in apples. Annu. Report of E. Malling Res. Sta. for 1960. pp. 120-122. Ferree, D.C., Stang, J.E. and Funt, C.R. 1980. Influence of Promalin on Delicious in Ohio. Res. Cir. Ohio Agric. Res. and Dev. Cent. 259:7-10. Forshey, C.G. 1971. Predicting harvest size of 'McIntosh' apples. New York's Food and Life Sciences Bulletin No. 9. Gardner, F.E., P.C. Marth, and L.P. Batjer. 1939. Spraying with plant growth substances for control of the pre-harvest drop of apples. Proc. Amer. Soc. Hort. Sci. 37:415-428. Goffinet, M.C. 1986. Empire apple studies. 1. Effects of thinning on fruit anatomy. 2. Size potential within the cluster. (unpublished data). 16. 17. 18. 19. 20. 21. 22. 14 Goffinet, M.C., and T.L. Robinson. 1988. Empire apple fruit size and anatomy: A comparison of fruit from unthinned and hand thinned trees. HortScience 23:769 (Abstract). Iftikhar, A. 1987. Effects of tree age and previous treatment on cell size and number in apple flowers. M.S. thesis. Michigan State University. MacDaniels, L.H., and E.M. Hildebrand. 1940. A study of pollen germination upon the stigmas of apple flowers treated with fungicides. Proc. Amer. Soc. Hort. Sci. 37:137-140. Martin, G.C., D.S. Brown, and M.M. Nelson. 1970. Apple shape changing possible with cytokinin and gibberellin sprays. Calif. Agr. 24(4):14. Martin, D., and T.L. Lewis. 1952. Physiology of growth in apple fruits. III. Cell characteristics and respiratory activity of light and -heavy crop trees. Austral. J. Sci. Res. 5:315-327. Stembridge, G.E., and G. Morrell. 1972. Effect of gibberellins and 6-benzyladenine on the shape and fruit set of 'Delicious' apples. J. Amer. Soc. Hort. Sci. 97:464-467. Westwood, M.N, L.P. Batjer, and H.D. Billingsley. 1967. Cell size, cell number, and fruit density of apples as related to fruit size, position in the cluster, and thinning method. Proc. Amer. Soc. Hort. Sci. 91:51-62. 23. 24. 15 Williams, M.W., H.D. Billingsley, and L.P. .Batjer. 1969. Early season harvest size prediction of 'Bartlett' pears. J. Amer. Soc. Hort. Sci. 94:596-598. Williams, M.W., and E.A. Stahley. 1969. Effect of cytokinins and gibberellins on shape of 'Delicious' apple fruits. J. Amer. Soc. Hort. Sci. 94:17-19. §ggtign_1: Evaluation of Cytokinin Application to Apple Flowers for Increasing Fruit Size. 16 Evaluation of Cytokinin Application to Apple Flowers for Increasing Fruit Size. Abstract Starkrimson 'Delicious' is notorious for hearing small fruits as the trees age. One possible method of improving size would be to stimulate cell division early in the season. The cytokinin benzyladenine (BA) was therefore tested to determine its effect on harvest size. Neither timing nor concentration of BA applied as a branch spray before anthesis affected size, length/diameter ratio or weight of fruits measured at harvest. However, final set was dramatically reduced at 25 and 50 ppm. 17 18 Michigan growers often use "Promalin" (benzyladenine + GA4+7 mixture) to increase the length/diameter (L/D) ratio and thereby achieve a more "typey" 'Delicious' fruit, which is more marketable. However, both Promalin and benzyladenine (BA) alone often reduce set of apple (2,3). In many cases, high concentrations (50 to 100 ppm) have been used (5). My purpose was to evaluate the effects of relatively low concentrations of BA (12.5, 25 and 50 ppm) on set and fruit size in Starkrimson 'Delicious', when applied before full bloom. If cytokinins were to increase cell division in the treated flowers, then the fruits might become stronger sinks, hence increasing set and fruit size. 19 Materials and Methods In 1987, five mature (25- to 30-year-old) Starkrimson 'Delicious' trees on seedling rootstocks were chosen in a commercial orchard at Leslie, MI. Trees were of uniform vigor and canopy size. Although the trees were not irrigated, they did not appear to be water stressed during the course of the study. Pruning had been minimal, therefore some of the branches were removed at bud swell to reduce competition. A randomized complete block design was used with whole trees as blocks. Branches of good vigor and bloom were chosen for treatment. BA was applied (a) at pink (April 21) , (b) when king flowers were open (April 30), and (c) on both dates. Full bloom was approximately on May 5. The concentrations 'of BA used were 0, 12.5, 25 and 50 ppm, and all solutions contained a surfactant (Tween-20, polyoxyethylene sorbitan monolaurate, .0.1%). Controls included both non-treated limbs and limbs sprayed with surfactant alone. These treatments were arranged in a 3 (date) x 5 (BA) factorial, and each was applied to one randomly selected limb on each tree. The tagged limbs were sprayed on the designated dates using a 2-gallon knapsack sprayer and a plastic screen to reduce drift. Fruit diameter and number were recorded 29, 63, 73, 91, 105, and 141 days after full bloom (DAFB). Fruits on the tagged limbs were harvested and weighed on September 23 (141 DAFB). Analysis of variance was performed for initial set (May 28), 20 final set (September 23), fruit diameter on each of 6 dates of measurement, and fruit weight at harvest. On some limbs, all fruits abscised before harvest. Due to this loss of replicates, analysis of variance of all variables, except initial and final set, excluded values for Tween-20 and 50 ppm BA. 21 Results Initial set on unsprayed controls was sufficiently heavy to warrant chemical thinning by the grower. However, the experimental trees were not spray thinned. Fruit set on May 28 varied from 16 to 33 fruits per 100 flower clusters among treatments and across dates of application. However, differences among means for treatment and date effects and the interaction of date and time of application were not significant at 5% (Table 1). 50 ppm appeared to reduce set, but differences were not significant at 5%. A heavy "June drop" occurred, approximately 40% of the fruits on the controls falling at this time (Table 1). Set (on limbs sprayed with 12.5 ppm was not affected: that on limbs sprayed with 25 ppm was significantly reduced relative ‘to unsprayed controls, but not in comparison with the Tween <:ontrol. However, 50 ppm dramatically reduced set, an eaverage of only 8 fruits per 100 flower .clusters reaching Inaturity, with all the fruits abscising from approximately 25% of the branches by mid-season (data not shown). An eaverage of 3 fruits per 100 clusters reached maturity following treatment with 50 ppm BA on April 30 (Table 1) . Ztn.neither case was the interaction between BA concentration iand, date of application significant at the 5% level (Fig. 11). However, set was consistently lower for the April 30 i:reatment than for the April 21 or double application except for the treatment with Tween-20 alone. In this one case, S3e£.was lowest following the double application. 22 Table 1. Influence of BA on initial and final set of Starkrimson 'Delicious' apple, Leslie, MI. 1987. Control 31 28 34 31 Tween-20 33 28 16 25 BA, 12.5 ppm 33 28 19 27 25 ppm 32 30 25 29 50 ppm 21 17 21 19 ns Timing mean 30 26 23 ns Final fruits/100 clusters, September 23 Control 20 _ 16 19 18 az Tween-20 22 15 8 15 a BA, 12.5 ppm 14 12 13 13 ab 25 ppm 15 8 14 12 b 50 ppm 12 3 9 8 b Timing mean 17 l 11 m 13 lm' z-Mean separation within sets (abc, lmn), by DMRT, 5% level. Treatment X time of application interaction was non- significant in all cases. 223 FIG. 1. EFFECTS OF BA CONCENTRATION AND TIME OF APPLICATION IN AFFECTING FINAL FRUIT SET OF STARKRIMSON 'DELICIOUS' APPLE. SEPTEMBER 23, 1987 FRUITS / IOO FLOWER CLUSTERS 25 20 15 10 l I 23 v—v CONTROL A—A TWEEN-ZO ctrl B—a BA 12.5 ppm o—e 25 ppm H 50 ppm 1 i 4 APRIL 21 APRIL :50 APRIL 214-30 TIME OF BA APPLICATION l 24 Harvest diameter was small (about 67 mm or 2.50 in.), despite the light crop. BA did not affect fruit diameter significantly regardless of concentration or timing (Table 2). Data for only 3 representative dates (29, 91 and 141 DAFB) are presented in Table 2 for simplicity; results for Ithe other 3 dates were similar. Although both Tween-20 alone and 50 ppm BA were not included in the statistical analysis because of loss of replicates, visual comparison of results across date and time show no consistent differences in fruit size. Fruit weight at harvest was likewise not significantly affected by BA treatments (Table 3). 50 ppm appeared to increase fruit weight compared to other concentrations, but loss of replicates prevented statistical analysis. Available data for fruit weight and diameter at harvest for 50 ppm and Tween-20 treatments were paired with appropriate control data and analysis of variance performed. Neither date of BA application nor concentration had any effect on weight of fruits at harvest (data not shown). Time of BA application did not affect either fruit weight or L/D ratio (Table 3). No BA treatment increased L/D ratio. The largest values were 1.048 (control, 4/21) and 1.060 (Tween-20, 4/30). 25 Table 2. Influence of BA on fruit diameter (mm) of Starkrimson 'Delicious' apple, Leslie, MI. 1987. Control 25 25 25 25 Tween-20 - (26)z (25) (25) (25) BA, 12.5 ppm 25 25 25 25 25 ppm 25 24 25 25 50 ppm (25) (24) (25) (25) ns Timing mean 25 25 25 ns Fruit diameter (mm), August 4 Control 58 58 58 58 Tween-20 (57) (55) (57) (56) BA, 12.5 ppm 58 56 56 57 25 ppm 56 59 58 58 50 ppm (55) (55) (58) (56) ns Timing mean 57 57 57 ns Fruit diameter (mm), Sept. 23 Control 68 67 67 . 67 Tween-20 (65) (64) (67) (65) BA, 12.5 ppm 68 66 66 67 25 ppm 65 68 68 67 50 ppm (63) (66) (67) (65) ns Timing mean 67 67 67 ns z- Data in parentheses were not included in statistical analysis and are excluded from the means for main effects because of loss of replicates. No effects were significant at the 5% level by DMRT. Treatment X time of application interaction was non- significant in all cases. Ta 26 Table 3. Influence of BA on fruit harvest weight (g) and length/diameter (L/D) ratio of Starkrimson 'Delicious' apple, Leslie, MI. 1987. Control 127 123 116 122 Tween-20 (131)2 (134) (141) (135) BA, 12.5 ppm 121 131 107 120 25 ppm 120 118 144 127 50 ppm (135) (140) (147) (141) ns Timing mean 123 124 122 ns Fruit L/D ratio, Sept. 23 Control 1.048 1.013 0.955 ’ 1.005 Tween-20 (0.980) (1.060) (0.990) (1.013) BA, 12.5 ppm 0.972 0.970 0.959 0.971 25 ppm 0.987 0.980 0.993 0.987 50 ppm (0.980) (1.020) (1.000) (1.000) ns Timing mean 1.002 0.988 0.972 ns z- Data in parentheses were not included in statistical analysis and are excluded from the means for main effects because of loss of replicates. No effects were significant at the 5% level by ANOVA. Treatment X time of application interaction was non- significant in all cases. was in ha: aft 9f: TM in the m0] 27 Discussion My goal was to increase harvest size by enhancing cell division during the early stages of fruit development. BA was applied before full bloom in order to avoid a reduction in set. However, 25 ppm BA reduced final set. On the other hand, even the highest concentration of BA (50 ppm) did not affect fruit shape, size or harvest weight. The significant difference between means for April 21 and April 30 vs. no difference between April 21 and the double application is probably an artifact. Although initial set was not reduced significantly, final set was drastically reduced by high concentrations of BA. The heavier "June drop" on sprayed limbs may have resulted from stress. BA-treated fruits may have been more susceptible to adverse conditions and thus abscised more readily. The Tween-20 treatment applied at both pink and king bloom also reduced final set slightly (not significant at 5%). Noga and Bukovac (4) found that the surfactant Citowett an alkylarylpolyoxy-glycolether (0.1%) increased the abscission of young apple fruits: Tween-20 was also effective, but only at 10 times this concentration. Thus, Tween-20 may have had a detrimental effect on response to BA in my work. All BA solutions contained Tween-20 and therefore all double applications should have reduced set more than single applications. 28 My results confirm those obtained by Ferree, et al. (2), although they used Promalin while I used BA. My data show that BA reduces set in apple, the effect increasing with concentration, with little or no effect on fruit shape or fruit size. Even low concentration (25 ppm) significantly reduced set (Table 1). Finding chemicals which increase fruit size without reducing set could give the fruit grower a valuable tool to increase production and financial returns. This remains a goal in future research. 29 Literature Cited Dennis, F.G., Jr. 1986. Apple. Chapter 1, pp. 1-44. In S.P. Monselise, (ed.). CRC Handbook of Fruit Set and Development. CRC Press, Boca Raton, FL. Ferree, D.C., E.J. Stang, and R.C. Funt. 1980. Influence of Promalin on Delicious in Ohio. Res. Cir. Ohio Agric. Res. and Dev. Cent. 259:7-10. Martin, G.C., D.S. Brown, and M.M. Nelson. 1970. Apple shape changing possible with cytokinin and gibberellin sprays. Calif. Agr. 24(4):14. Noga, G.J. and M.J. Bukovac. 1985. Impact of surfactants on fruit quality of 'Schattenmorelle' sour cherries and 'Golden Delicious' apples. Unpublished paper presented at the 5th International Symposium on Growth Regulators in Fruit Production. Rimini, Italy. Stembridge, G.E., and G. Morrell. 1972. Effect of gibberellins and 6-benzy1adenine on the shape and fruit set of 'Delicious' apples. J. Amer. Soc. Hort. Sci. 97:464-467. Segtion II: Effect of Timing and Degree of Hand Thinning Starkrimson 'Delicious' Apple Fruits on Harvest Size 30 Effect of Timing and Degree of Hand Thinning Starkrimson 'Delicious' Apple Fruits on Harvest Size Abstract Hand thinning generally increases apple fruit size, the effect decreasing as thinning is delayed. In order to determine the effects of both time and degree of thinning in mature Starkrimson 'Delicious', experiments were conducted in two Michigan orchards. Moreover, photosynthesis was measured to evaluate the influence of thinning on net photosynthetic rates. Hand thinning increased size in one orchard, with a threshold of 20 fruits/100 flower clusters needed for significant effects. Thinning was effective in the second orchard when limbs were thinned on June 6, but not thereafter. Regression lines for other treatments/orchards were non-significant. Effects of thinning on net photosynthesis were inconsistent. 31 32 Thinning has been used for centuries to increase fruit size. As early as 1927, Chandler and Heinicke (3) proved through chemical analyses that fruiting is an exhaustive process. Flower and fruit production deplete the tree of carbohydrates, nitrogenous compounds and minerals. Heavy fruiting may prevent a weak tree from surviving the following winter, and increases its susceptibility to insect or disease injury. Other benefits of thinning include reduction of limb breakage due to over-loading and the removal of diseased and insect-injured.fruits. Probably the two most important benefits from thinning are the regulation of biennial bearing and the increase in size of the remaining fruits. Traditionally, apple fruits are thinned to a determined space, usually 6-8". However, Batjer et al. (2) showed that size thinning - -the removal of undersized fruits at any date- - gave better results. This method rests on the principle that "once a small fruit, always a small fruit". Hence early removal of smaller fruits will allow the remaining fruits to grow to a marketable size. Today, size prediction charts are available for Washington growers to help predict harvest size and determine whether or not thinning is necessary. If 'Delicious' apples set a heavy crop one year, flower initiation may be reduced. Reducing the crop load early in the season allows fruiting spurs to flower the next year. About 30-40% of the spurs should flower in a given year in order to assure annual cropping (1,9). Three methods of 33 thinning are practiced, namely hand, mechanical and chemical thinning. Chemical thinning using dinitro-ortho-cresol (DNOC), naphthalene-acetic-acid (NAA), naphthalene-acetamide (NAD) or 1-naphthyl N-methylcarbamate (Sevin) has proven to be the most convenient method. However, rates and times of application vary from one area to another. Mechanical thinning by shaking or "club-thinning" removes fruits effectively in peach, but cannot be used for apples because of mechanical injury. Finally, hand thinning is still practiced by many growers despite the high labor cost: it is normally performed as a supplement to chemical thinning. Cook (4) reported that Starkrimson 'Delicious' fruit did not increase in size when thinned after June drop. Because reduction of yield was not balanced by increases in fruit size, thinning reduced income. Hansen (6,7) has presented evidence that apple fruits acting as "sinks" accelerate the translocation out of near- by leaves of 14C-labeled assimilates. The photosynthetic intensity of such leaves exceeds that of leaves on non- bearing spurs. Gucci (5) demonstrated that net photosynthesis (Pn) in sour cherry leaves dropped after fruit removal at the end of stage III. The purpose of my study was to determine the effect on final fruit size of thinning Starkrimson 'Delicious' to various levels and at different dates early in the season. My goal was to determine when thinning was effective and what level of thinning was necessary. Moreover, in order to 34 better understand what effect thinning has on "sink strength" and on C02 assimilation, photosynthetic rates were measured on thinned and nonthinned limbs. 35 Materials and Methods Mature Starkrimson 'Delicious' trees were used in evaluating both degree and timing of thinning. Two orchards, one at Hartford (Dowd orchard, South-west Michigan), and another at Belding (Wittenbach orchard, West-central Michigan) were used. The trees were 25-30 years old in 1987 and bore a good bloom (60% and 90% of‘the terminal buds flowering on shoots and spurs in the Dowd and Wittenbach orchards, respectively). Two separate experiments were conducted at each of the two locations in the spring of 1987. The density of thinning experiment, performed about 2 weeks after full bloom, consisted of adjusting fruit load to 3 levels (30, 20, or 10 fruits per 100 flower clusters) for comparison with non-thinned limbs. Actual fruit numbers after "June drop" are given in Table 1. The trees were thinned on May 21 (16 days after full bloom (DAFB)) in the Dowd orchard and on May 25 (15 DAFB) in the Wittenbach orchard. The same experimental design was adopted at both locations, the only difference being the use of 5 replicate trees in the Dowd orchard, 4 in the Wittenbach orchard. Uniform trees were chosen in one row and the treatments were randomly assigned to individual scaffold limbs. The limbs were large and extended back to the main trunk, hence were considered to be independent from one another. A randomized complete block design was used with whole trees as blocks, each tree containing the four treatments. 36 Table 1. Fruit density in September on limbs used for fruit thinning experiments. 1987. Orchard Experiment Fruit density (fruits / 100 flower clusters) Intended Actual Dowd Timing - 37 30 23,32,29z Density - 59 10,20,30 11,20,31 Wittenbach Timing - 73 30 38,31,33z Density - 88 10,20,30 15,24,34 - Values for lst, 2nd, and 3rd dates of thinning, respectively. Underlined value denotes the treatment' not used in Pn measurements. 37 The same statistical design was used for the time of thinning experiment, with thinning on various dates as treatments. Fruits were thinned approximately 2, 4, and 8 weeks after full bloom in the Dowd orchard, and 2, 4, and 6 weeks after full bloom in the Wittenbach orchard. "June drop" occurred about 4 to 5 weeks after full bloom, therefore limbs were thinned before, during and after "June drop“ in both locations. Final fruit set on non-thinned limbs was 37 and 73 fruits per 100 clusters in the Dowd and Wittenbach orchards, respectively. Fruit load after hand thinning averaged 28 fruits per 100 flower clusters in the former and 34 fruits per 100 flower clusters in the latter. Fruit diameters were measured using a hand caliper (Cranston Machinery Co., Oak Grove, OR) on various dates throughout the season. Statistical analysis (ANOVA and regression) was performed separately for each experiment and orchard. In order to evaluate the effects of timing and severity of thinning on photosynthesis, readings were taken on two occasions (August 6 and September 3) in the Dowd orchard, and on one occasion (September 4) in the Wittenbach orchard. Because some treatments were located on the north side of the tree where light levels were not saturating (PAR < 1000 pmols/mZ/s), Pn readings were not available for all treatments on all dates. Leaf area, ambient C02, relative humidity (RH) in the chamber, ambient RH, leaf temperature, 38 differential C02 and photosynthetically active radiation (PAR) were recorded for each leaf, using a portable open gas exchange system equipped with a Parkinson broad leaf chamber (model ADC LCA-2, Analytical Development Co., Hoddesdon, England) operated at the following conditions: saturating light intensity, PAR > 1000 pmols/mZ/s, ambient C02 of 330 to 340 pl/l, inlet relative humidity (RH) 6-11%, as by Gucci (5). A BASIC program (8) was used to convert the raw data to C02 assimilation, VPD, leaf conductance, stomatal conductance, transpiration and internal C02. Table 1 lists the intended and actual fruit densities in all treatments. 39 Results Effegt of fruit density on fruit size: In the Dowd orchard, initial fruit set was only moderate (59 fruits/100 clusters) and thinning to 30 fruits/100 clusters had no effect on fruit diameter as measured on various dates throughout the season (Table 2). However, thinning to 20 and 11 fruits/100 clusters increased size significantly relative to the control treatment on all dates from 69 to 140 DAFB. Differences among thinning treatments were generally non-significant. Regression analysis performed for orchard 1 showed no significant correlation (r2=0.22) at the 5% level between severity of thinning and fruit diameter at harvest (Fig. 1A). Data for only 3 of the 4 replicates were available for regression analysis in the Wittenbach orchard. Hand thinning did not affect fruit size relative to controls at any date of measurement (Table 2). Regression analysis, in fact, showed an increasing trend in harvest size as fruit density increased (r2=0.12, n.s. at 5%) (Fig. 1B). WW9: In the Dowd orchard, a heavy "June drop" reduced fruit density on control limbs to a level similar to that on thinned limbs (Table 1). Thinning to an average of 28 fruits/ 100 clusters did not affect fruit size regardless of timing (Table 3). Although average diameters recorded for fruits thinned on June 6 and July 2 (32 and 29 'fruits/loo 40 Table 2. The effects of hand thinning Starkrimson 'Delicious' apple to various levels 15 to 16 days after full bloom on fruit diameter (mm) at harvest. 1987. Orchard Fruits/100 Date of measurement flower clusters (DAFB) 57 69 92 119 1402 Dowd 59 (control) 44 ns 51 ay 59 a 65 a 66 a 31 45 52 ab 60 a 66 ab 68 ab 20 47 54 b 63 b 69 b 71 b 11 47 54 b 63 b 68 b 70 b 19 49 105 1402 Wittenbach 88 (control) 11 ns 35 ns 58 ns 65 ns 34 11 34 58 62 24 ll 35 58 62 15 11 35 60 65 z-Harvest date. y_ Mean separation within orchards and dates of measurement by LSD (5%). FIG. la,b. 40a REGRESSION OF FRUIT DIAMETER ON FRUIT DENSITY IN THE DOWD (A), AND THE WITTENBACH ORCHARD (B) MICHIGAN 1987. NUMBERS INDICATE FRUITS PER 100 FLOWER CLUSTERS FOR EACH TREATMENT FRUIT DIAMETER (mm) FRUIT DIAMETER (mm) 80 78 76 74 72 70 68 66 64 62 70- 68 66 64 62 60 58 56 41 _ (A) 00w0, Y=—0.071X+58.61, r2=0.22 I I I I 1- l O I I CONTROL 30 20 10 XXOQ 1 X r L1 10 ; CONTROL 30 20 l . l ; JD 30 I 50 70 90 I 110 FRUITS/100 FLOWER CLUSTERS X¥O< I I v CONTROL 7 F o THINNED ON 5/22 v I x 6/6 ,_ 1 X 1 . 6/120 . 4 . 1 . 1 . 1 20 30 4O 50 60 7O 80 FRUITS/100 FLOWER CLUSTERS Effects of hand miming m Pu and related parateters in M Starkrimsm 'Delicious' orchards in 1%7. Table 4. HE rub] (112/1101 H20 mnmmmflw 1 grits per Assimilation VPD mmml owes (ME [MMMHW|%M% Wand Date Tine 13 8/6 same 0 o e HNNN .0 IUD '6 1.04090) 8688 45 can: 833 adv-IN fine era 89% 10.010 mum: NOON 0:0)“, §§2 488 NNN fine "2‘8“! 39:3 Hittetbach '8 “fin 8E8“ NNNN 19°25! 83317318 floss can-HO Lnd'l-Dln IO «3.0.0 tom—1o $I3935? A .I A 3 70 mm AF 69" A A/A’ .4 fiAA A 1 A11 A R 64 mm A A 63" ’Q A --1 2A AAAA A A AA 57 mm 57 _ A A 0 X 0 SH - 1x r=.98AT1280AFB o r=.81 AT TOODAFB 45 A r=.58 AT 60 DAFB 30 35 4O 45 50 55 60 65 7O 75 80 FRUIT DIAMETER (mm) 58 harvest) at 2.50 in. (64 mm) provided an estimate of the diameters of these fruits at each sampling date (i.e., points of intersection with regression lines). These values were then plotted to give the growth curve (Fig. 2). Interpolation was used to provide an estimate of fruit size at 10 day intervals for the final graphs (Fig. 3). Regression analysis was performed for each orchard/year separately. In addition, the data were combined for different orchards for a given year. The Washington fruit growth chart presents average diameters of 'Winesap' and 'Delicious' apples in various box-size groups at 5-day intervals beginning 35 DAFB (Table 2). To compare my data with those of the Washington chart, diameters at 10-day intervals of 'Delicious' fruits whose diameters were 2.50 in. (64 mm), 2.75 in. (70 mm) and 3.00 in. (76 mm) at 140 DAFB were selected from the Washington chart. The values were then converted to mm and stored in "PlotIt" format for further use (Fig. 4). Using these data as a base, graphs were generated to check for uniformity, divergence or goodness of fit. The three main comparisons were comparisons among orchards within years, comparisons within orchards among years, and comparison across orchards among years. Two additional comparisons were performed to test for differences between old and young trees. Data for old trees in one orchard at Belding were compared with those for young trees (planted 1980) at the Clarksville Horticultural Experiment Station 588 Fig. 2. Growth curves of fruits of 4 different harvest diameters, based upon regression of final diameter on diameter at various dates FRUIT DIAMETER (mm) 80 7O 60 50 40 30 20 r T I— L111 1 30 4O 50 59 L L l 60 7 80 ST) 100 110 120 13 DAYS AFTER FULL BLOOM L L l L 76 mm 70 mm 64 mm‘ 57 mm 0 140 Fig. 3. 598 Growth curves of fruits of 4 different harvest diameters, based upon regression of final diameter on diameter at various dates. Values adjusted to 10 day interval FRUIT DIAMETER (mm) 80- 70 I 60 I 50 T 401- 30 T OLL 1— 1 2. 30 40 50 6O L L L l J l 60 70 8 90 150 110 12 DAYS AFTER FULL BLOOM 761nn1 70rnn1 64tnn1 O 130 140 61 Table 2. 'Standard' Washington chart established by Batjer, et al. in 1957, for predicting harvest size of 'Delicious' and 'Golden Delicious' for fruits of various size class at harvest. DAFB Projected box size 163 150 138 125 113 100 88 80 72 present size, inches in diameter 35 .90 .93 .95 .98 1.00 1.03 1.05 1.08 1.10 40 1.06 1.09 1.12 1.14 1.16 1.19 1.22 1.25 1.29 45 1.19 1.22 1.24 1.26 1.29 1.34 1.36 1.40 1.42 50 1.30 1.33 1.35 1.39 1.43 1.47 1.50 1.54 1.57 55 1.40 1.43 1.45 1.49 1.54 1.59 1.63 1.67 1.70 60 1.51 1.54 1.56 1.60 1.65 1.69 1.74 1.79 1.83 65 1.62 1.64 1.67 1.70 1.75 1.80 1.85 1.90 1.95 70 1.71 1.75 1.78 1.81 1.86 1.92 1.97 2.03 2.09 75 1.80 1.84 1.88 1.92 1.95 2.02 2.08 2.14 2.20 80 1.88 1.92 1.95 1.99 2.04 2.10 2.18 2.26 2.32 85 1.95 1.99 2.03 2.08 2.13 2.19 2.27 2.34 2.42 90 2.02 2.07 2.10 2.16 2.22 2.28 2.36 2.43 2.51 95 2.08 2.13 2.17 2.23 2.29 2.36 2.43 2.52 2.59 100 2.13 2.19 2.23 2.29 2.36 2.43 2.51 2.60 2.68 105 2.18 2.24 2.29 2.36 2.42 2.51 2.58 2.68 2.77 110 2.23 2.29 2.35 2.41 2.49 2.58 2.66 2.75 2.84 115 2.28 2.34 2.39 2.46 2.54 2.63 2.72 2.82 2.92 120 2.32 2.38 2.44 2.51 2.58 2.68 2.78 2.88 2.98 125 2.36 2.42 2.48 2.54 2.62 2.72 2.83 2.93 3.04 130 2.38 2.45 2.52 2.58 2.66 2.77 2.87 2.98 3.09 135 2.42 2.48 2.54 2.62 2.69 2.80 2.91 3.02 3.13 140 2.44 2.51 2.57 2.64 2.73 2.84 2.94 3.06 3.17 145 2.47 2.53 2.59 2.67 2.77 2.88 2.98 3.08 3.20 150 2.48 2.56 2.62 2.69 2.79 2.91 3.01 3.11 3.22 618 Fig. 4. Growth curves, based upon the Washington chart, for fruits of 3 different diameters at harvest FRUIT DIAMETER (mm) 80 70 60 50 40 30 20 62 1 76 mm 70 mm 64 mm r LL 1 L 1 L 1 L __L L 1 30 40 50 60 70 80 90‘ 100 110 120 130 14 DAYS AFTER FULL BLOOM 0] WE In 63 (CHES), with the data for old and young trees in the same orchard at Leslie constituting the second comparison. The Washington curves were included as a reference in some graphs. To determine how the accuracy of prediction compared with Washington values, three ranges of accuracy were adopted, namely f 1/8" (~ 3 mm), 1 1/16" (~ 1.6 mm) and 1 1/32" (- 0.8 mm). As an example, the percentage of fruits falling within each range was determined by calculating the difference between the actual harvest diameters measured and the harvest diameters predicted from measurements taken on 50, 100, and 125 DAFB. In addition, harvest diameter was predicted based on the regression coefficients of the Michigan chart and on actual diameter measurements at various dates after full bloom, in 3 orchards. Fruit diameter in 4 Washington orchards in 1983 were supplied by Dr. Eric Curry of USDA, Wenatchee, WA. These were graphed for comparison with the data of Batjer, et al. (1) to determine if any differences were evident. To determine whether tree age affected photosynthetic activity, the trees used for fruit size measurement in the Wardowski orchard were also used to measure C02 assimilation. Two trees of each age (old & young) were used and photosynthesis was measured in eight spur leaves per tree on September 1987, about 2 weeks before harvest. Non-fruiting spurs were chosen in order to avoid any influence Of adjacent fruits . The fully expanded leaves 64 were well exposed to light and showed no visual symptoms of insect or physical damage. Leaf area, ambient C02, relative humidity (RH) in the chamber, ambient RH, leaf temperature, differential C02 and photosynthetically active radiation (PAR) were recorded for each leaf, using a portable open gas exchange system equipped with a Parkinson broad leaf chamber (model ADC LCA-2, Analytical Development Co., Hoddesdon, England) Operated at the following conditions: saturating light intensity (photosyntheticallly active radiation 1000 pmols/mZ/s), ambient C02 of 330-340 pl/l, flow rate of 0.4 l/min, inlet relative humidity (RH) of 6-11%, as described by Gucci (6). A BASIC program (7) was used to convert the raw data to C02 assimilation, VPD, leaf conductance, stomatal conductance, transpiration and internal C02. Data were analyzed by ANOVA and LSD. 65 Results As expected, r values for fruit diameters at date of measurement vs. diameter at harvest improved in accuracy as harvest approached (Table 3). In 1985, r values increased from an average of 0.63 at 48 DAFB to 0.95 at 126 DAFB. Similar trends were observed in other years (Table 3). All the tabulated correlation coefficients were significant at 1% beginning 66 DAFB. Regression curves (see example in Fig. 1) were significant at 5% for 50 DAFB, and at 1% -for the remaining two dates of measurement. As expected, deviation from the regression line declined with time. The analysis was repeated with data from another orchard in 1985 and comparable results were Obtained (Fig. 5). When the prediction curves of an individual orchard were plotted against similar curves for Washington fruits, two differences were noteworthy (Fig. 6). Firstly, diameters of Michigan fruits for a given date were greater than those of Washington fruits of similar harvest size. Secondly, for early season measurements particularly, the difference in diameter increased with increasing harvest size. These data indicate that Washington fruits grow at a faster rate than do Michigan fruits in the early part of the season. A Michigan grower using the Washington chart early in the season would therefore be likely to overestimate in predicting harvest size. The necessity of a Michigan chart to serve local growers is clearly evident. OH x OH x OH x VIVID 66 Amend ma ma ma ><><><>< loonuxueoue x moonav MGOwuc>uomno MO .02 use .mm A one onwm um0>ucc .m> Ammsov aooan Adam nouns whom macauc> awash mo nosed :ofimmouoon on» no any :Ofiunaouuoo mo mcucnouo um dawn msofiuo> med med nva NVH Ned and and Lemmas dump umm>uo= now wNH ImNH .pomflomnm scan: mufisum mad ImHH mum. mam. MHH NOH IOOH 1 «Hm. I won. men. 1 sea as loos Ion «no. own. I can. I «no. and sea moo. omm. mus. New. mam. one. one. one. on up too Imp Amman. hm Hmm. awe. ucoamusmmoa «0 even .uouuo can mm msflmmfla mu mmmqlawv ncoeeoum Camax comma comma Booncouusz mcoueoum mama comma BooacouuH3 mcoemoum atoms phonouo \Hcou .n OHQMB FIG. 5. 668 REGRESSION OF STARKRIMSON 'DELICIOUS' FRUIT DIAMETERS (DATA FOR 4 TREES) AT HARVEST ON DIAMETERS OF SAME FRUITS ON 3 SAMPLING DATES IN 1985 HARVEST DIAMETER (mm) (142 DAFB) HARVEST DIAMETER (mm) (142 DAFB) 67 82 I j r T I I I I T I STEFFENS ORCHARD .I 1985 75‘I A o 1 A o 70_1 A AAA A 0 0° )5 x .. AA , <10 5% A @AA/AA 08/0 000 I 54‘ £6 0:00 <><> x q A A A o O A] 2 A 00 0 ° 1 A's/11$ g/OV o 58-1 /AAAA 0,00 °x§ .. A ’ 0 ‘V A A o 0 0% A o x/ 524 / . A 0 x/ A o x 46-1 - x r = .98 AT 125 DAFB I o =.82AT900AF8 40 A r=.62AT50 DAFB 25 30 . .35 40 45 50 55 60 65 70 75 FRUIT DIAMETER (mm) 80 67a FIG. 6. FRUIT DIAMETER PREDICTION CURVES FOR STARKRIMSON 'DELICIOUS' FRUITS IN ONE MICHIGAN ORCHARD IN 1986 VS. SIMILAR CURVES FOR WASHINGTON 'DELICIOUS' FRUIT DIAMETER (mm) 80 70 60 50 40 .30 68 1986 75 V 70 I. L I. 1' -I I . v—v‘WfiflflEMCH A J g 4 L . L_ J LHJWASEflNGTQN 40 60 80 100 120 140 DAYS AFTER FULL BLOOM 69 To be of value, however, the data must be reliable. Therefore two comparisons were made: - a comparison of growth curves among years within orchards. - a comparison of growth curves among orchards within years. Growth curves for small (64 mm) and large (76 mm) fruits from one Michigan orchard, compared over the three years of study, clearly show some variability from year to year (Fig. 7). Similar variability was noted for other orchards (Fig 8a, b). The available data show that the MI growth curves differed in slope from the WA curves throughout the season. Major differences were evident early in the season, whereas differences late in the season were small. Data for a single year therefore cannot be used to predict harvest size in other years. The data in Figure 7 were used to calculate fruit volume, assuming fruit shape to be spherical. Small differences in fruit diameter become much larger when converted to volume (Fig. 9).. Comparison of growth curves of medium sized (70 mm harvest diameter) fruits in Michigan orchards in 1986 indicated that fruits in the Wittenbach orchard grew more slowly than fruits of similar harvest size in the other two orchards (Fig. 10). Variability among orchards in 1986 resembles that among years within a single orchard (compare Fig. 7, 8 and 10). Thus variability within orchards and years appears to rule out the use of any growth curve based upon a single orchard or year as a reference for Michigan growers. 698 FIG. 7. FRUIT DIAMETER PREDICTION CURVES FOR STARKRIMSON 'DELICIOUS' FRUITS IN ONE ORCHARD IN MICHIGAN OVER 3 YEARS FRUIT DIAMETER (mm) 80 7O 60 50 40 .30 70 I I '— STEFFENS, Ml ,. .I L / H 1987 , e—e 1986 L l L 1 L _l L l L H I 1985. l 40 60 80 100 120 140 DAYS AFTER FULL BLOOM 708 FIG. 8a,b. FRUIT DIAMETER PREDICTION CURVES FOR STARKRIMSON 'DELICIOUS' FRUITS IN TWO MICHIGAN ORCHARDS OVER 3 YEARS. DIAMETER (mm) FRUIT 70 60 50 40 30 71 ” (b) RASCH, MI 5 .1 t 64 _. I. . r I L / . / J F 41—16 1987 1 e—e 1986 __L J L I .__A_1 g l fi‘1q85 . .1 40 60 80 100 120 140‘ DAYS AFTER FULL BLOOM FIG. 9. 718 PREDICTION CURVES FOR LARGE (76 mm. DIAMETER AT HARVEST) VS. SMALL (64 mm. AT HARVEST) STARKRIMSON 'DELICIOUS' FRUITS IN ONE MICHIGAN ORCHARD OVER 3 YEARS EXPRESSED AS FRUIT VOLUME FRUIT VOLUME (ch) 240 220 200 180 160 140 120 100 80 60 4O 20 72 r I I I r r STEFFENS, MI 41-8. 1987 76 F 81—61 1986 .. L _1 AL L J A L HJ 1985; I 40 60 80 100 120 140 DAYS AFTER FULL BLOOM 728 FIG. 10. FRUIT DIAMETER PREDICTION CURVES FOR MEDIUM SIZED FRUITS IN 3 MICHIGAN ORCHARDS IN 1986 VS. SIMILAR CURVE FOR WASHINGTON FRUIT DIAMETER (mm) 80 7O 60 50 4O 30 73 I I P I 1986 v—v WASHINGTON B—EI STEFFENS, Ml e—e RASCH, Ml H. WITTENBACLH. M11 L . k . 1 1 40 60 80 100 120 140 DAYS AFTER FULL BLOOM 74 Two comparisons were made in 1987 to determine if the growth curves of fruits varied with tree age. Data from the Wittenbach orchard at Belding (mature) were first compared with those from trees planted at the Clarksville Horticultural Experiment Station (CHES) in 1980. The fruits from the young trees were larger at harvest than those in the Wittenbach orchard. Nevertheless, growth curves constructed from regression data (Fig. 11) indicated that fruits of similar harvest size grew at approximately the same rate regardless of tree age from 100 DAFB to harvest. Note also that the predicted growth curves for 76 mm fruits were similar in both orchards, despite the fact that the mature trees bore few (7%) fruits of this size whereas the young trees bore many (33%). The second comparison involved trees of differing age within one orchard (Wardowski). Average diameter was consistently larger on young than. on old trees (significant at 5% on each date) (Fig. 12). However, except for some differences early in the season, the two size prediction curves were very similar (Fig. 13). Differences early in the season reflect low r values presented in Table 3. The data from the Rasch, Steffens and Wittenbach orchards for the 3 years of study were combined to obtain composite curves for comparison with similar data from the Washington chart (Fig. 14). The Michigan growth curves were compared with growth curves for fruits of similar harvest 743 FIG. 11. SIZE PREDICTION CURVES FOR A YOUNG VS. A MATURE ORCHARD, 1987 FRUIT DIAMETER (mm) 80 7O 60 50 40 30 75 )- l H WITTENBAOH, MI. (OLD TREES) fir H CHES. MI. (YOUNG TREES) l_‘ L 76 64 100 go I ED DAYS AFTER FULL BLOOM 120 _140 75a FIG. 12. EFFECT OF TREE AGE ON GROWTH OF STARKRIMSON 'DELICIOUS' APPLE FRUITS, WARDOWSKI ORCHARD, LESLIE, MI. 1987 FRUIT DIAMETER (mm) 76 80 H OLD TREES _ H YOUNG TREES O) O 1 01 O r 4:. O T 30r- J I l 40 60 80 160 DAYS AFTER FULL BLOOM 120 140 76a FIG. 13. SIZE PREDICTION CURVES FOR YOUNG VS. MATURE TREES IN THE SAME ORCHARD, LESLIE, MI. 1987 FRUIT DIAMETER (mm) 80 7O 60 50 4O 30 77 H OLD TREES L H YOUNG TREES l l 76 64 60 80 160 DAYS AFTER FULL BLOOM 120 140 77a Fig. 14. Growth curves of fruits of 3 different harvest diameters as predicted in Table 4 FRUIT DIAMETER (mm) 78 30 L l .L J L 50 80 IOO I 120 DAYS AFTER FULL BLOOM 35—! MICLIIGAN . 140 79 diameter taken from the Washington chart (Fig. 15). Here again the differences between Washington and Michigan curves early in the season increase with increasing harvest size. However, the Michigan values on certain DAFB closely resemble those of Washington fruits for the first time. The largest fruits grew at comparable rates only after 100 DAFB, those of 70 mm fruits after 90 DAFB. In both cases final fruit size would have been overestimated by using the Washington data prior to these dates. In contrast, data from the Washington curve for small fruits (64 mm) between 70 and 130 DAFB slightly underestimated Michigan fruit size, whereas earlier data were very similar for the two states. Fig. 16 compares the growth curves of small and medium sized fruits ( 64 and 70 mm, respectively) for the Steffens orchard in 1987 with similar curves from the Michigan prediction chart. Using the Michigan chart for medium sized fruits allows for accurate prediction of harvest size as early as 70 DAFB, but it overestimates harvest size for small fruits. The same comparison was repeated for 1985 and comparable results were obtained (see example in Fig. 17). Although a slight difference exists between actual and predicted growth curves of 70 mm fruits, the difference is negligible when compared to that of 64 mm fruits in either year. 793 FIG. 15. AVERAGED FRUIT DIAMETER PREDICTION CURVES FOR STARKRIMSON 'DELICIOUS' DATA FOR 1985-1987 VS. SIMILAR WASHINGTON GROWTH CURVES . FRUIT DIAMETER (mm) 80 7O 60 50 4O 3O 80 . , . H MICHIGAN _ e—o WASHINGTON I I l L l I.__._._. __l k so 80 I 100 DAYS AFTER FULL BLOOM 120 140 803 FIG. 16. ACTUAL DIAMETER IN ONE ORCHARD VS. AVERAGED MICHIGAN PREDICTION CURVES FOR 64, 70 mm HARVEST SIZE. 1987 FRUIT DIAMETER (mm) 80 7O 60 50 4O 30 81 f j STEFFENS, 1987 70 ,/‘ .l/ / A—A predicted L l . l l k 1 fl] Obseived J 40 60 80 1 00 1 20 1 40 DAYS AFTER FULL BLOOM 81a FIG. 17. ACTUAL DIAMETER IN ONE ORCHARD VS. AVERAGED MICHIGAN PREDICTION CURVES FOR 64, 70 mm HARVEST SIZE, 1985 FRUIT. DIAMETER (mm) 80 7O 60 50 4O 3O 82 f ' l STEFFENS, 1985 70 l H predicted QX—XJ obsegved A 80 100 120 140 DAYS AFTER FULL BLOOM 83 The combined data for all three Michigan orchards were used to prepare tables for predicting harvest size, based upon diameters at 5 day intervals from 40 to 140 DAFB (Tables 4 and 5). In order to test the accuracy of the prediction curves for 1985—1987 in Michigan, the averaged regression equations on various dates of measurement were used to predict average harvest size in one orchard; these values were then compared with actual size at harvest (Table 6). Predicting harvest size of fruit on old trees in another orchard gave similar results (Table 7). Use of the averaged prediction equations for Michigan allowed estimates of actual size within 2-3 mm. Similar results were obtained when harvest size was calculated for fruits on young trees (Table 8). Prediction based on measurements taken at 48 DAFB was less accurate than predictions based on measurements for other dates. Another necessary test to determine the validity of using the calculated Michigan chart consisted of comparing the predicted percentages of fruits in various size classes vs. the observed percentages (Table 9). Differences between predicted and observed values were 10% or less in comparisons 2, 4, 8, and 9, and 13% or less in comparisons 1, 5, & 7 (Table 9). Only in comparisons 3 and 6 did differences' reach 20% or greater; in both cases predicted values were larger than observed ones. 84 Table 4. Predicted diameters in mm. for Starkrimson 'Delicious'apples at various days after full bloom (DAFB), based upon data from 3 orchards over 3 years. DAFB Fruit diameter at harvest (mm) 51 57 64 70 76 83 40 23.3 26.2 27.6 32.0 36.3 37.9 45 26.4 29.7 31.1 36.2 41.4 42.9 50 29.6 33.2 34.5 40.5 46.5 48.0 55 31.2 35.1 36.7 42.8 48.8 50.7 60 32.9 37.0 38.9 45.0 51.1 53.4 65 34.4 38.7 41.1 47.1 53.1 55.8 70 35.9 40.4 43.3 49.2 55.0 58.3 75 37.5 42.2 45.4 51.3 57.3 60.9 80 39.0 43.9 47.5 53.5 59.5 63.4 85 40.3 45.4 49.1 55.3 61.5 65.5 90 41.6 46.8 50.7 57.0 63.4 67.6 95 42.9 48.3 52.5 58.9 65.2 69.8 100 44.3 49.8 54.3 60.7 67.0 71.9 105 45.2 50.8 55.5 61.9 68.2 73.4 110 46.1 51.8 56.8 63.1 69.4 74.8 115 46.8 52.6 57.9 64.1 70.3 76.0 120 47.5 53.5 59.0 65.1 71.3 77.2 125 48.3 54.3 60.0 66.1 72.3 78.4 130 49.0 55.1 61.0 67.1 73.3 79.6 135 49.9 56.1 62.2 68.4 74.5 81.1 85 Table 5. Predicted diameters in in. for Starkrimson ‘Delicious' apples at various days after full bloom (DAFB), based upon data from 3 orchards over 3 years DAFB Fruit diameter at harvest (inches) 2.00 2.25 2.50 2.75 3.00 3.25 40 0.92 1.03 1.09 1.26 1.43 1.49 45 1.04 1.17 1.22 1.43 1.63- 1.69 50 1.16 1.31 1.36 1.59 1.83 1.89 55 1.23 1.38 1.45 1.68 1.92 2.00 60 1.29 1.46 1.53 1.77 2.01 2.10 65 1.35 1.52 1.62 1.85 2.09 2.20 70 1.41 1.59 1.70 1.94 2.17 2.30 75 1.47 1.66 1.79 2.02 2.25 2.40 80 1.54 1.73 1.87 2.11 2.34 2.50 85 1.59 1.79 1.93 2.18 2.42 2.58 90 1.64 1.84 1.99 2.25 2.49 2.66 95 1.69 1.90 2.06 2.32 2.57 2.75 100 1.74 1.96 2.14 2.39 2.64 2.83 105 1.78 2.00 2.19 2.44 2.69 2.89 110 1.81 2.04 2.24 2.48 2.73 2.95 115 1.84 2.07 2.28 2.52 2.77 2.99 120 1.87 2.10 2.32 2.56 2.81 3.04 125 1.90 2.14 2.36 2.60 2.85 3.09 130 1.93 2.17 2.39 2.64 2.89 3.13 135 1.96 2.21 2.45 2.69 2.93 3.19 86 Actual fruit diameter at harvest and diameter predicted by using regression equation, based on average diameter at various times prior to harvest over a 3-year period. Wittenbach orchard, Belding MI, 1985-1987. Table 6. Year DAFB Intercept Slope Actual Predicted Actual size harvest harvest (mm) size (mm) size (mm) a b X Y=a+(b*X) 1985 48 35.03 0.815 36.5 64.7 67 22.76 0.973 44.7 66.2 75 16.26 1.016 49.1 66.1 90 15.61 0.898 54.2 64.2 101 8.19 0.998 58.0 66.1 119 -1.06 1.087 63.2 67.6 126 0.54 1.023 63.2 65.2 140 66.3 1986 67 22.76 0.973 41.4 63.1 75 16.26 1.016 45.5 62.5 101 8.19 0.998 54.7 62.7 134 61.1 1987 48 35.03 0.815 34.4 63.0 67 22.76 0.973 44.3 65.8 101 8.19 0.998 55.6 63.7 119 -1.06 1.087 60.4 64.6 140 65.3 87 Table 7. Actual fruit diameter at harvest and diameter predicted by using regression equation, based on average diameter at various times prior to harvest. Mature trees at the Wardowski orchard, Leslie, MI. 1987. DAFB Intercept Slope Actual Predicted Actual size harvest size harvest size (mm) (M) (In!!!) a b x Y=a+(b*X) 48 35.03 0.815 36.4 64.7 67 22.76 0.973 46.5 67.9 75 16.26 1.016 49.9 66.9 90 15.61 0.898 54.8 64.8 140 64.8 Table 8. Actual fruit diameter at harvest and diameter predicted by using regression equation, based on average diameter at variouS‘ times prior to harvest. Young trees at the Clarksville Horticultural Experimental Station. 1987. DAFB Intercept Slope Actual Predicted Actual size harvest size harvest size (M) (M) (min) a b X Y=a+(b*X) 48 35.03 0.815 39.3 67.1 75 16.26 1.016 55.7 72.8 101 8.19 0.998 64.8 74.0 119 -1.06 1.087 69.8 70.4 88 Table 9. Predicted percentages of fruits in various size classes vs. observed percentages based upon combined data for 3 Michigan orchards over 3 years. Prediction based on fruit diameter at 100- 102 DAFB. Diameter (mm) Compari- ---------------------------------- son Orchard Year <57 57+ 64+ 70+ 76+ 1 Rasch 1985 Predicted 2 30 48 20 0 Observed 3 24 37 33 3 lef. -1 6 11 -13 -3 2 1986 Predicted 11 64 22 3 0 Observed 9 54 31 6 ' 0 Diff. 2 10 -9 -3 0 3 1987 Predicted 0 30 53 17 0 Observed 10 70 20 0 0 Diff. -10 -40 33 17 0 4 Steffens 1985 Predicted 8 42 39 11 0 Observed 15 39 35 11 0 Diff. -7 3 4 0 0 5 1986 Predicted 0 7 34 38 21 Observed 1 9 23 50 17 Diff. -1 -2 11 -12 3 6 1987 Predicted 0 4 30 54 12 Observed 0 12 50 38 0 Diff. 0 -8 -20 16 12 7 Wittenbach 1985 Predicted 1 31 54 13 1 Observed 3 30 43 19 5 lef. -2 1 11 -6 -4 8 1986 Predicted 7 56 36 1 0 Observed 13 61 26 0 0 Diff. -6 -5 10 1 0 9 1987 Predicted 0 37 36 20 ' 7 Observed 3 40 30 20 7 89 Accuracy in harvest size prediction was similar to that obtained by Batjer, et al. in 1957. By 50 DAFB, predicted harvest size of about 50% of the fruits fell within 3 mm of actual harvest diameter; this increased to 87% by 100 DAFB (Fig. 18). Percentages of fruits falling within 0.8 mm were 14% and 53% at 50 and 125 DAFB, respectively. Data supplied by Curry for 2 of the 4 Washington orchards are compared with those from the Washington chart in Fig. 19. Average fruit diameters for individual orchards agreed well with those in the Washington chart. The other 2 curves for individual orchards varied, but their harvest diameter fell within the 70-76 mm range (data not shown). The average curve for all 4 orchards also fell within the same range (Fig. 20). Although sample size differed between Batjer, et al. and Curry's work - - 8 orchards x 5 years and 4 orchards x 1 year, respectively - - agreement was close. Thus, the Washington chart appears to be valid for Washington growers despite the passage of 26 years. C02 assimilation did not differ significantly between old and young trees when measured on September 12, 1987, nor did leaf or stomatal conductance (Table 10). However, vapor pressure deficit, transpiration rate, and transpiration ratio were significantly higher, and internal C02 and water use efficiency lower, in leaves on young trees. Thus, although the leaves on young trees transpired more, assimilation was similar to that in old trees. 893 FIG. 18. PERCENTAGE OF FRUITS WHOSE ACTUAL HARVEST HARVEST SIZE FELL WITHIN INDICATED RANGES OF PREDICTED SIZE AT 50, 100, AND 125 DAFB. STEFFENS ORCHARD, 1985 90 Steffens, 1985 Z%//////I////////////// §_ F Z////////I////////// g F ) V//A/////// I I 50 :3 i 1/32" ( .8 mm) - *1/16 ( 16 mm Em 1' 1/8" ( 3 mm) D. _ 0 20- . . b L . O 0 O 0 0 7 6 5 4. 3 IOOF 90L 80- E 3:53:30 mozé BB :06 z. ESE Lo 58%: 125 100 DAYS AFTER FULL BLOOM 903 FIG. 19a,b. COMPARISON BETWEEN GROWTH CURVES OF FRUITS AS MEASURED BY CURRY (WASHINGTON, 1983) AND "STANDARD" WASHINGTON CURVE OF BATJER, ET AL. (1957) DIAMETER (mm) FRUIT 80 60 91 (a) CURRY'S DATA 1983 VS. BATJER'S DATA 1957 I (WASHINGTON) - 40 I- - 20 I" - o—o BATJER ; L I I I I H C-URBY I (b) 50 .. 70 q 40 I- H 20 I' - e—e BATJER J L; I Lg I 1_ I g I .__ H CLJRBY I; 20 40 60 80 100 120 140 I 60 DAYS AFTER FULL BLOOM FIG. 20. 91a AVERAGE DIAMETER FOR DELICIOUS FRUITS MEASURED BY CURRY IN WASHINGTON IN 1983 VS. CURVES FOR 70 AND 76 mm. FRUITS BASED UPON DATA OF BATJER, ET AL. (1957) 80 60 40 FRUIT DIAMETER (mm) 20 92 I 1 r ' ' r r r . —r CURRY'S DATA 1983 VS. BATJER'S DATA 1957, WASHINGTON STATE. H Batjer. 3.00" H I L I L J L I L 94-6 CLUE);- avg .I 2.75" 40 so 80 100 120 DAYS AFTER FULL BLOOM 140 160 93 Table 10. Photosynthesis measurements on old Vs. young Starkrimson 'Delicious' trees in Wardowski orchard, Leslie, MI. September 12, 1987. Tree age Observation Old Young Vapor pgessure deficit 2.02 2.96 * (KPa/m /s) CO assimi ation 9.03 9.24 ns (pmols/dm /hr) Leaf conducta ce 220.54 205.14 ns (millimols/m /s) Stomatal condgctance 137.84 128.21 ns (millimols/m /s) Internal C02 252 241 * (pmol/mol) Transpiration 4.49 .6.24 * (millimols/mZ/s) ' Transpiration ratio 514 707 * (mol HZO/mol C02) Water use efficiency 2.07 1.46 * (pmol COz/mol H20) * Significant effect of tree age at 5% level (LSD) 94 Discussion Forshey (5) suggested that major differences in climatic conditions between Washington and New York's Hudson Valley were reflected in differences in fruit growth curves in the two areas. Forshey worked with 'McIntosh' to determine whether harvest size could be predicted. Although no comparison between his and Washington charts was intended, Forshey realized that varietal differences between 'McIntosh' and 'Delicious', and, more importantly, differences in growing conditions between the two areas, prevented the use of the Washington chart for predicting harvest size of 'McIntosh' in New York. The sunny days and cool nights in the apple producing areas of Washington might explain the more rapid growth rates of fruits there. In the Hudson Valley, suboptimal growing conditions such as cloudy and cool days were considered by Forshey to be responsible for the variability in growth rates. Conditions in Michigan resemble those in New York, therefore the observed inconsistencies might be attributed to weather conditions. Weather conditions alone, however, could not account for the variability among orchards in any given year. Cultural and management practices, such as crop load, tree vigor, irrigation and fertilizer regimes, and insect control, obviously affect harvest size. Only the Wittenbach orchard was irrigated. Although no visual evidence of water stress was noticeable in any of the orchards, moderate water stress may have 95 occurred. Neither soil water potential nor leaf water content was measured at any time, therefore no concrete conclusions can be drawn. Another cause of variability may be the method used in calculating the predicted growth curves. Since the measurements were not taken at regular 10-day intervals, interpolation may have been a source of error. However, unless measurement is too infrequent, interpolated data should be just as accurate as actual data. They might even be more accurate because unusual and irregular data are averaged out.. Another potential cause of inconsistencies in the results is the volume of data used in preparing the size prediction tables. Batjer, et al. (1) used more data in preparing their growth curves (8 years x 4-6 orchards in Washington vs. 3 years x 3-5 orchards in Michigan). However, they do not provide information as to orchard-to- orchard and year-to-year variability, for.they present only one table for 8 years x 4-6 orchards. Therefore one cannot determine whether data for any one orchard and year fit the curve. In addition, Batjer et a1. do not specify what strain of 'Delicious' was used, although 'Starking' was probably the most abundant strain at that time. Thus strain differences could be responsible for the observed differences in growth curves. However, the fact that the data supplied by Curry closely parallel those in the table prepared by Batjer, et al. suggests that the differences in growth rates observed are related to climatic, rather than 96 strain differences. Young trees bear larger fruits than do old trees, yet growth rates of fruits of similar harvest size on young and old trees were parallel from mid-summer to harvest. Thus fruit size potential is established very early in the season. C02 assimilation in September did not differ appreciably in leaves on old vs. young trees in one orchard, although earlier measurements might have revealed significant differences. Transpiration rate was higher in young trees, resulting in lower water use efficiency. However, this is unlikely to have affected fruit size. Accuracy in predicting harvest size was comparable to, if not better than, to those obtained by Batjer, et al. Thus, although many variables can affect harvest size of Starkrimson 'Delicious' fruits in Michigan, the use of the Michigan chart allows reasonably accurate prediction of harvest size. 97 Conclusions 1- In accordance with the findings of Batjer, et a1. and of Forshey, final fruit size of Starkrimson 'Delicious' can be predicted reasonably accurately by measuring fruit diameters beginning in mid-summer. 2- Final size is determined early in the season. Therefore fruits of the same harvest size on young vs. old trees grow at similar rates during the final half of the growing season. 3- In general, Starkrimson 'Delicious' fruits in Michigan grow more slowly than would be indicated by the Washington chart. Therefore predicted values based on this chart generally overestimate actual size at harvest. 4- The available data suggest that harvest size can be predicted Treasonably accurately when the data are averaged for several orchards over several years. The earliest time for reliable prediction is 90 to 100 DAFB (mid-August). 5- A size prediction chart has been prepared based upon data for Starkrimson 'Delicious' in Michigan (Table 4, 5). This chart is only partially reliable because of variation within orchards and within years. Environmental and/or cultural effects may be responsible for some of these differences. 98 Literature cited Batjer, L.P., H.D. Billingsley, M.N. Westwood, and B.L. Rogers. 1957. Predicting harvest size of apples at different times during the growing season. Proc. Amer. Soc. Hort. Sci. 70:46-57. Cook, R.L. 1985. Does supplemental hand thinning pay? Annu. Rept. Michigan State Hort. Soc. 115:181-185. Curry, E. 1983- (personal communication) Davis, L.D. and Marie M. Davis. 1948. Size in canning peaches. The relation between the diameter of cling peaches early in the season and at harvest. Proc. Amer. Hort. Sci. 51:225-230. Forshey, C.G. 1971. Predicting harvest size of 'McIntosh' apples. New York's Food and Life Sciences Bulletin No. 9. ‘Gucci, R. 1988. The effect of fruit removal on leaf photosynthesis, water relations, and carbohydrate partitioning in sour cherry and plum. Ph. D. Thesis. Michigan State University. Moon, J.W., Jr., and J.A. Flore. 1986. A BASIC program for calculation of photosynthesis, stomatal conductance, and related parameters in an open gas exchange system. Photosynthesis Research 7:269-279. Williams, M.W., H.D. Billingsley, and L.P. Batjer. 1969. Early season harvest size prediction of 'Bartlett' pears. J. Amer. Soc. Hort. Sci. 94:596-598.