‘IVIESIHJ RETURNING MATERIALS: PIace in book drop to LJBRAfiJES remove this checkout from —c-—. your record. FINES wiII be charged if book is returned after the date stamped beIow. SOYBEAN (GLYCINE MAX (L.) Herr.) S‘ED NUMBER, SIZE AND YIELD RESPONSE TO PARTIAL POD REMOVAL BY Trust Th emba Chigwada A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Crop and Soil Sciences ABSTRACT SOYBEAN (GLYCINE MAX (L.) Merr.) SEED NUMBER, SIZE AND YIELD RESPONSE TO PARTIAL POD REMOVAL By Trust Themba Chigwada Information available on soybean (Glycine mgx (L.) Merrill) response to partial pod removal is inconsistent. This study was undertaken to examine soybean seed number, size and yield to partial pod removal (PPR) treatments applied at mid pod filling stage. Six cultivars and three degrees of pod removal (0, 25 and 50%) at upper and lower half canopy nodes were examined. PPR delayed plant senescence as judged by green color loss. Dry weight, seed yield and seed number were linearly reduced S-Iéfi, 8-2h% and 12-h0% respectively, but not significantly so with no depodding on lower nodes. PPR at lower nodes was negatively correlated with seed number (r=—O.h7) and yield (r=-O.33). Seed size increased h—lbfi. PPR effects expressed as percent of untreated plants were similar for all cultivars. Twenty five percent PPR on upper nodes was established as optimum pod removal degree increasing seed size enough to compensate for pods removed such that yields were maintained. TO THE CHIGI’IADA FAMILY ii AKNOWLEDGEMENTS Special recognition and appreciation is given to my major adviser, Dr. Thomas G. Isleib, for his unselfish interest and dedication in the guidance, encouragement, and constructive criticism throughout this project, and for the opportunity of association and involvement with soybean production in Michigan. Special appreciation is also made to Dr. J.J. Kells and Dr. A.W. Saettler for their invaluable assistance as guidance committee members, and Mr. D.E. Wolfe for his technical assistance in the field work. Gratitude is extende to: The Government of Zimbabwe, for financing this study; Michigan State University, for providing research facilities; and friends within and outside academic circles, who made my stay abroad, a memorable experience. Finally, I want to thank my parents and family, for their endless love, understanding, support, and particularly for looking after my daughter Tendayi, who was born just after I left for this study. It is to them that I dedicate this thesis. TABLE OF C ONT ENTS mmdmmnmmmsu.n.n.n.u.n.u.u.n.u.n.u.u. LIST OF TABLES........................................ LIST OF FIGURES....................................... INTRODUCTION.......................................... REVIEN OF LITERATURE. PHOTOSYNTHESIS................................... NITROGEN FIXATION................................ SEED NUMBER, SIZE AND YIELD...................... CANOPY SITE...................................... PROTEIN AND OIL.................................. SUMMARY,.......................................u. MATERIALS AND NETHODS................................ PROCEDURE FOR 1983 FIELD STUDY................... PROCEDURE FOR 198A FIELD STUDY RESULTS AND DISOUSSION................................ DRY MATTER RESPONSE TO POD RE.IOVAL............... SEED YIELD RESPONSE To POD RENOVAL............... SEED NUMBER RESPONSE TO POD RENOVAL.............. SEED SIZE RESPONSE To POD RENOVAL................ COMPARISON OF SEED YIELD, NUI-IB ER AND SI ZE RESPONSE TO POD REMOVAL... ... .............. .... .. SUBII’IARY AND CONCLUSIONOOOOOOOOOOOOcocoon...cocococoon. LITERATURE CITEDOOOO.0.0.0.000...OOOOOOOOOOOOOOOOOOIO. a: ‘Q Q) (A 14 16 17 19 19 21 30 33 40 46 52 59 62 Table 10 11 12 13 14 15 16 17 LIST OF TABLES Cultivars tested for seed size response to 50% partial pod removal, 1983 ........................................ Partial pod removal and cultivar treatments,1984 ......... Cultivar planting rates adjusted to produce 370,000 plants per hectare ....................................... Half plant height determining upper and lower canopy nodes .................................................... Outline of analysis of variance, 1984 .................... Seed size response to 50% pod removal, 1983 .............. Number of plants harvested from 2 meter row sections of subplots,1984 ......................................... Mean square values and significant levels for the factors in the analysis of variance ...................... Dry weight response to pod removal ....................... Pod removal effect on dry weight expressed as percent of untreated plants ...................................... Seed yield response to pod removal ....................... Pod removal effects on seed yield expressed as percent of untreated plants ...................................... Effects of pod removal on seed number .................... Effects of pod removal on seed number expressed as percent of untreated plants .............................. Seed size response to pod removal (P= 0.01) .............. Seed size response to pod removal (P= 0.05) .............. Pod removal effect on seed size expressed as percent of untreated plants ...................................... Page 20 22 24 26 29 32 34 35 36 37 42 43 47 48 53 54 55 LIST OF FIGURES Figure Page 1 Plot layout with cultivar whole plots and PPR treatments applied to subplots, 1984 ............ 23 2 Dry weight response to pod removal .............. 38 3 Total seed yield response to pod removal ........ 41 4 PPR effects on seed yield expressed as percent of untreated plants ............................. 45 5 Seed number response to pod removal and effects of PPR on seed number when expressed as percent of untreated plants ............................. 49 6 Seed size response to pod removal ............... 57 7 PPR effects on seed size expressed as percent of untreated plants ............................. 58 INTRODUCTION The soybean (Glycine max (L.) Merrill), contais high levels of protein (40%) and Oil (20%) and offer one of the best answers to the world wide shortages of protein and Oil in human diets (LO). Soybeans have a wide range of uses including human consumption, livestock feed, and industrial processes. The Oil is 85% unsaturated and is cholesterol free, making the dietary value Of soybean substantially better than other common vegetables (#0). Soybeans are grown world wide. Increased production has been achieved by increased acreage, genetic improvement and cultural practices. However, yields have tended to plateau over the last years, and to meet increasing demands, yields must be increased faster than in the past. Soybean yield is influenced by various factors that include nutrient and moisture levels (2), diseases and insect pests like Heliothis Zea (Boddie) (44 48), hail injury, and promotion of floral and seed abortion by cool nights. These factors are all linked to the source-sink relationships of the plant. Source—sink relationships determine seed size, number and ultimate yields. Manipulating the various relationships may increase plant yields (30). one such manipulation is partial pod removal (PPR). 1 2 The extent to which soybean plants can compensate for pod loss has not been fully determined (48), and results published are inconsistent. This study was conducted to: -1 Examine the effects of partial pod removal on seed number, size and yield. -2 Examine the effects of pod removal treatments applied on different sections of the soybean canopy. —3 Determine combinations of the degree of pod removal and the canopy site of pod removal that best utilize the phenomenon of compensatory growth. Degree of pod removal, canopy site of pod removal, and cultivars were tested as sources of variation. REVIEW OF LITERATURE PHOTOSYNTHESIS Leaf photosynthesis is the primary source ultimately delimiting crop yields (8), and varietal differences are due to differences in net photosynthesis (20). These differences are attributed to differences in the various biochemical processes (20), and to resistance of the plant tissue to carbon dioxide diffusion to the site of fixation (15). Most of these factors are influnced by manipulating the various sorce-sink relationships of the plant. Causal relationships between reproductive development and senescence in plants have been postulated for many years. Soybeans in particular, show a marked senescence during seed development under field conditions (42,43). Removal of young pods delays or prevents senescence as judged by loss of plant green color (21, 34, 38). Removing all pods causes leaves to remain green and active until killed by frost (55). Senescence or yellowing of leaves has been attributed to various factors: (a) a decline in nutritional and moisture levels during flowering and seed development (47), (b) degradation of leaf protein to provide amino acids to the developing seeds (42), and to various hormonal signals 4 associated with the reproductive sink (34), where there is competition by the growing pods, or a possible production of inhibitors by the developing pods. Leaf senscence lowers photosynthetic activities of the canopy and subsequently reduces seed yields and quality (2, 42, 55). The sole source of carbohydrates for grain filling during pod fill is photosynthesis (4, 56). Fader and Koller (10) report that soybean growth is almost entirely dependent on assimilates exported from the leaves, and that only 4% of the carbon imported by the seed is accounted for by fixation of atmospheric carbon dioxide by the pods. This finding was supported by Hume and Criswell (23), who observed that the carbon-14 assimilated during development is recovered in the seeds at maturity. Net photosynthesis of most varieties begins to increase at the approximate beginning of seed filling (4). Therefore, a delay in leaf senescence following pod removal would be expected to increase seed yields. Contrarily, Mondal gt_ l.(38) observed that although contually depodded plants had dark green leaves, their photosynthetic rates declined significantly, starting at the same time and rate as in the control plants. Phillips £3.11- (42) report that certain genetic lines of soybean produce mature seed, but show a delayed leaf senescence (DLS) phenotype in which leaves remain green until killed by frost. Inhibition of photosynthesis by pod removal is reported 5 elsewhere (28, 38). Koller and Thorne (28) reported that inhibition of photosynthesis resulting from removal of rapidly growing pods was due to partial closure of stomata and changes in leaf orientaion that led to a marked reduction in gas exchange. Mondal g_ gl.(38) observed a decline in photosynthesis in desinked plants irrespective of the presence of dark green leaves. These workers found that the presence of pods stimulates photosynthesis. Three mechanisms may explain this effect: 1- sink alleviation of the end product inhibition by soluble carbohydrates, 2- sink promoted reduction of starch accumulation in the chloroplasts, an example being an increased phosphorylase starch degradation proposed by Koller and Thorne (28), 3- sink mediated hormonal signals (34). Measurements of gas exchange in soybeans indicated that pod removal increased stomatal diffusion resistance (4, 28), and changed leaflet orientation (28). Dornholf and Shibles (4) reported that varietal differences in net photosynthesis were mainly a result of differences in diffusive resistance to carbon dioxide diffusion. Huck gt gl.(22) observed that significant reductions net carbon fixation rate generally accompanied a decrease in stomatal closure on upper leaf surfaces than the lower surfaces, and that the degree of stomatal closure was proportional to the number of nodes depodded. The stomatal response occurred in a leaf even when pods at that particular node remained on the 6 plant, or when pods were removed from the stem above or below the test leaf. The combined effects of stomatal closure and vertical leaflet orientation reduce gas exchange, and may serve to reduce photosynthate production to levels commensurate with the reduced assimilate demand of depodded plants. Loveys and Kriedemann (35) reported that there was an increase in leaf abscisic acid (ABA) that was associated with the increased stomatal resistance. ABA influences several physiological processes in the plant including stomatal closure, abscission, senscence, dormancy, cell division, cellular elongation, nucleic acid and protein synthesis, water relations, photosynthesis and flowering(53). The mode of action of ABA on these traits is not presently well understood. It has been hypothesized that ABA acts by enhancing ribonuclease ( RNase) activity, an effect that leads to lower levels of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), and a consequent decline in the rate of protein synthesis, cell division and growth. A decline in these rates may serve to explain why ABA inhibits traits like germination and flowering, while on the other hand it accelrates certain other traits like senescence, stomatal closure and abscission (53). Contrarily, Ciha gt 21. (3) found that ABA levels in the leaves were not affected by the presence or abscence of developing pods. NITROGEN FIXATION. Nelson gt gl.(41) cited Thibodeau and Jaworski's model explaining the role of nitrogen and its relationship to soybean seed development. The model consisted of several parts. Soybeans use nitrate exclusively during vegetative development. At or near flowering, plants fail to use nitrate, resulting in the initiation of dinitrogen fixation activity, which peaks at the beginning of seed development, but declines rapidly as pods develop because the nearness of the pods to the source makes them a better sink. Nitrogen fixation gradually declines and the plant; derives the remainder of the season's nitrogen from redistribution. Lawn and Brun (31) reported that the symbiotic nitrogen fixation, as measured by both nodule fresh weight per plant and specific nodule activity (SNA) (micro moles of ethylene released per plant per hour) (5) increased during the pre-flowering and flowering stages. However, SNA and total nodule activity (TNA) decline markedly in the early pod filling stage due to limitations on the supply of photosynthates from the shoot to the nodules (31, 32, 33). Such decline in activity may have serious impact on the ability of the soybean plant to meet the requirements for nitrogen in developing seeds. It would be more deleterious under low soil nitrogen levels, when the plant strongly relies on symbiotically fixed nitrogen, and may present a barrier to the attainment of high yields. 8 Lawn and Brun (31) reported that pod removal increased nodular activity. Such a response may increase yields. This is supported by Phillips _t _l.(42), who reported that leaf yellowing, an obvious visual characteristic of senescence, was associated with decreases in foliar nitrogen concentrations, symbiotic nitrogen fixation, and soil nitrate utilization. They proposed that senescence limits assimilation of carbon and nitrogen at a time when they are required for seed development. The combined reports of Lawn and Brun (31, 32, 33), and Phillips gt gl.(42, 43) imply that there could be an association between an increase in biological nitrogen fixation following pod removal, and manifestation of delayed leaf senscence (DLS) phenotype that would result in a increase in photosynthesis, thereby increasing seed size and yields by better supporting the carbon and nitrogen requirements for developing seeds. Distinct genotypic differences in the ability of soybean cultivars to support symbiotic fixation exist. Acetylene reduction assays indicated that symbiotic fixation for "Chippewa 64" was substantially lower than for "Clay" at similar stages of development (32, 33). However, in both cultivars, partial pod removal raised nitrogen fixing nodular activity well above controls. SEED. Under normal conditions, particular cultivars produce characteristic seed yields and fairly definite seed size, 9 normally ranging from 12 to 18 grams per 100 seeds, although seed size ranges from 4 to 55 grams per 100 seeds exist within Glycine max (8). Various hypotheses have been proposed to explain the observed variation in seed size. They include: genetic control(5,7), differential seed growth rates and dry matter accumulation in the seed (ranging from 3.38 to 8.32 mg/seed/day) (7), and differences in the duration of the filling period. Egli (5) observed no significant differences between rates of dry matter accumulation and grain yield, seed weight or final number. Hanway and Weber (17) observed that the rate of dry matter accumulation in seeds of cultivars tested was similar (99 kg/Ha/day) from 30 days after stage 5 (9 to 10 trifoliate leaves unrolled and plants in full bloom) to stage 10 (30 to 50% leaves yellow with many falling and the lower pods yellowing). However, if growing 'conditions were unusually favorable or adverse during the life cylce, or during a critical stage of development, both the number and the size of the seeds produced would be far from normal. Results published on the effects of PPR on seed size. number and yield are inconsistent. Lawn and Brun (31) found that the total plant yield at maturity (seed + pod + stem) was relatively unaffected by depodding at the end of flowering, but that pod number/plant, seed/pod and seed size increased. McAllister and Krober (36) found that increases in seed weight and size compensated for 17 and 22% fewer 10 pods in "Haweye" and "Lincoln" cultivars repectively so that total seed yield per plant was not reduced. Severe depodding (80%) reduced seed yield but increased seed size. Moderate depodding (40%), resulted in a 17% actual decrease in pod number. Seed size increased sufficiently to offset pod loss. In both cultivars, seed weight did not increase proportionately with the more severe PPR treatments. Treatments were applied when the plant had an occasional flower in the terminal inflorescences of the main axes or branches. Pods from the first open flowers at the sixth and eight nodes contained one third more fully formed seeds while pods at the upper nodes were still elongating and showed very little development of seeds. Smith and Bass (48) also observed nonsignificant yield reductions until 40% or more of the pods were removed. PPR treatments were applied at different stages of plant maturity beginning when pods were at maximum fullness and hardiness. The above findings suggest that the extent to which 1 soybeans can compensate for poor pod set by increasing seed size depends both on cultivar and degree of pod removal. Different cultivar responses are reported elsewhere (11, 36). Fehr _t _l.(11) found that determinate cultivars "Hill" and "Lee" had significantly greater yield reductions from altering source- sink ratios than indeterminate cultivars "Hark" and "Beeson". Egli gt l.(6, 8) reported a trend towards reduced seed yield and increased seed size following pod removal 11 treatments applied at the end of the flowering period before there was substantial seed development. They observed that pod removal resulted in a decline at maturity in yield, pods/plant, and seeds/plant, while seed size, pod wall weight and stem weight increased. At 21 and 28 days after pod removal, seeds from depodded plants were significantly heavier than controls. Kincade gt gl.(26), in an experiment simulating bollworm (Heliothis zea (Boddie) ) injury on soybean pods, observed nonsignificant difference in the sizes of depodded and control plants. However, 100 seed weights were progressively higher, but not significantly so in plots with higher injury levels. The combined effects of defoliation and depodding vary in reducing seed yields depending on their severity and on the stage of plant growth at which the treatments are applied (52). Pod removal treatments have the most important effect in reducing seed yields (52). Floral bud removal results in morphologiacl and chemical changes resembling the effect of depodding, but removal of floral buds early in their development had no effect on seed size or total seed yield per plant (21), Soybeans flower abundantly, but a large proportion of the flowers and young pods abscise rather than develop into mature pods (19). Thirty to 85% of the buds/flowers produced abort, with 20% of the abortion occurring during the early bud stage, and 75% during full bloom (21). The cause of this abortion is unknown. It has been suggested 12 that pod set is regulated by the supply of assimilates to developing flowers and pods. Because light penetration into the soybean canopy decreases from the top to the bottom, photosynthetic rates are lower for leaves deeper in the canopy. Heindl and Brun (19) propose that if assimilate supply regulates pod set, then pods/node, seeds/node, and seed weight/node would be expected to decrease at progressively lower levels. Removal of flowers or young pods reduces seed abortion (21, 36, 48). The explanation proposed by McAllister and Krober (36) is that the naturally high floral abortion does not occur in depodded plants because excess flowers are removed mechanically by pod removal. Total pod number per plant was not affected by removal of up to sixty floral buds per plant randomly over all nodes. Explanations for the different seed character responses observed following pod removal are inconsistent too. The vegetative tissue of the soybean plant serves as a reservoir for mineral nutrients during the vegetative growth of the plant and the minerals are translocated to the seed during pod filling. Losses from leaves, stems and pods account for the majority of the nitrogen, phosphorous and potassium in the mature seed (16, 29). Ninety-six percent of the carbon in the seed is imported from the leaves, and only 4% is fixed by the pod (10). Pod removal changes the pattern of photosynthate production and translocation resulting in seed weight increases to compensate for 19 to 13 22% pod loss such that yields are not significantly changed (36). Comparing C-14 accumulation in depodded and control plants, Egli and Leggett (7) observerd higher levels in labelled leaves and in the stem both above and below the node of the labelled leaf, following pod removal. Kollman _t_ £429) suggested that there was 1 positive relationship between sink size and photosynthetic rate, because the dry matter of the shoots increased with increasing sink size. Reductions in sink size by pod removal resulted in large increases in dry weights of stem and leaves. Major increases in individual seed size would therefore be expected as the number of fruits per plant was reduced. Yoshida (56) concluded that although the contribution of stored carbohydrates to grain yield may be as high as 50% for some species, the main source of carbohydrates for grain filling is photosynthesis. McAllister and Krober (36) indicated that there can be a limited amount of carbohydrate accumulation in soybean stems but the availability of this material for grain filling was questioned. They proposed that the most reasonable explanation for the apparent recovery of pods and seed yield in depodded plants is a result of reduced pod abortion. The normally high pod abortion in control plants is not observed in depodded plants. Abortion of pods in control plants is possibly a result of over- production of pods and the limited capacity of the plant to supply food for continued pod development. 14 The size of the seed has been recognized for many years as a factor influencing seedling vigor, subsequent plant growth and seed yield. Positive relationships between planted seed size and seed yield have been reported (49). Contrarily, Hartwig and Edwards (18) reported that lines selected for larger seed in programs of backcrossing produce yields similar to those of the recurrent parent, suggesting no close relationship between planted seed size and yield. However, many workers (4, 13, 49, 50) have reported greater plant growth and seed yield from progeny grown from large than from small seeds. In this context, because pod removal increases soybean seed size (6, 8, 11, 36, 52), it can be used as a technique to increase future soybean yields. CANOPY SITE AND POD REMOVAL. Different sections of the plant contribute differently to total seed yield (19). Heindl and Brun (19) reported that seed weight/node and seed weight/section were significantly greater in the middle section than the top or bottom section of cultivar "Evans", and that the middle section account for at least 75% of the main stem yield. There is only slight variation among sections in flowers produced, and therefore the primary cause of differences in pod number/node and ultimate seed yield for the various canopy sections is differential flower and pod abscission. Other possible causes are differences in amount of 15 light intercepted (45, 46), and in leaf area (27). Koller (27) observed that the lower main stem produces the most leaf area, but due to abscission of lower leaves, the middle section has the most leaf area by the time of rapid seed development. This may explain why the middle section contributes the most to total yield. The seed's relative growth rate does not vary with position on the plant, an indication that supply of assimilates limits seed growth to no greater extent at lower nodes than at upper nodes. Koller (27) concluded that there was a downward translocation of assimilates to offset the potentially decreasing photosynthesis towards the bottom of the canopy. Seed growth rate therefore appears to be contolled primarily by regulatory mechanisms within the seed, rather than by external availability of assimilates. Response to pod removal differs with canopy site of depodding (11, 12, 21). Hicks and Pendleton (21) reported that the section of the plant without pods following pod or floral bud removal remained green and vegetative until killed by frost, while the untreated sections senesced normally. They observed that pod number and yield per plant were unaffected by bud removal from any 1/3 section of the plant, but decreased when buds were removed from either the lower or upper 2/3 of the plant. Seed weights increased, but yields decreased. Because pod number was not reduced by PPR from any 1/3 section of the plant, Hicks gt g1. (21) proposed that the natural shedding of buds or 16 flowers was reduced in other sections of the plant. There is translocation of assimilates from leaves subtending the section of the plant whose buds are removed, and this explains the increase in seed size. An interaction exists between canopy levels and plant density during pod filling, and is due to an alteration in the pattern of translocation, and an inability of the lowest leaves to respond to increased light intensities following pod removal (24, 54, 56). The thinning treatments induced by PPR have greatest effct at the top of the canopy, with progessively diminishing effects towards the bottom (55). Varietal differences also exist, with significantly greater yield reductions in determinate than indeterminate cultivars at any canOpy site depodded (11, 12). PROTEIN AND OIL A number of investigations have examined the influence of pod removal on seed chemical composition, and results obtained are inconsistent. Lawn and Brun (31) observed nonsignificant, relatively small variation in seed protein content. McAllister and Krober (36) reported that pod removal increased protein content, lowered oil content and iodine number of the oil. Protein content increased proportionally with increase in pod removal extent. Hicks and Pendleton (21) observed that seed protein and oil content were not affected by floral bud removal. Neber (54), simulated hail injury to soybeans, to examine the effects of defoliation and topping and reported a 1% 17 reduction in oil content. SUMMARY. Total soybean seed yield is a function of the number and size of the seeds. Manipulating source- sink relationships of the soybean plant influences plant growth and subsequent seed yields. Effects of altering these relationships by partial pod removal have not been consistent. Reported reductions in yields have been attributed to the actual reduction in pod number ( which tends to have been severe), inhibition of photosynthesis, changes in translocation patterns, stomatal closure, and changes in leaflet orientation. Increases in seed size great enough to compensate entirely for reduced seed number and maintain total yields have been reported This has been explained by delays in senescence, higher nitrogen supplies to developing seed, better light penetration into the canopy, and a subsequent better plant performance. Increasing the size of the seed to be planted increases yields to be harvested. PPR increases seed size, and attains a more or less uniform seed size. This has potential to increase soybean yields, especially in view of the relative ease of grading soybean seeds. Also a more precise spacing in the row, and better plant uniformity obtained by planting uniform seed size, may be basic in achieving higher total yields. 18 Partial pod removal has been shown to increase seed size (6, 8, 11, 36, 52). Response has varied with cultivars, sites of depodding, and the extent of depodding. Research is required to determine the best combination of these factors that will fully utilize the potential for increased seed size. METHODS AND NATERIALS EXperiments to investiPate the effects Of partial pod removal (PPR) on soybeans “ere conducted at the Crop Science Research Farm on the campus of Michigan State University at East Lansing, Michigan., during the growing seasons of 1983 and 1984. Both experiments were conducted on Capac loam 2.5b (fine loamy, mixed, mesic Aerie Ochraqualfs) soils previously planted to small grain. In 1983, seventeen cultivars of soybean (Table l) were planted in an unreplicated nursery. Each plot comprised of four rows, 5m long and spaced 50cm apart. Ten plants were selected at random in each plot. Five were treated and five used as controls. Treatments consisted of 50% depodding of all nodes. When pods at any node reached mid pod filling stage, determined visually when seeds in the pods at that particular node half.filled the available seed space, 50% pod removal treatments were applied mechanically by hand removal of one in every two pods. Treatment was applied at all nodes. At maturity, the height of control plants was measured. All plants were harvested by hand, dried and threshed individually. Seed yield (g/plant) and number of seeds per plant were determined. Seeds from similarly labelled plants from each plot were mixed thoroughly, and two samples, each comprised of 100 randomly drawn seeds, 19 20 TABLE 1. Cultivars tested for seed size response to 50% partial pod removal, 1983. Cultivar Average 100 seed weight (grams) Agate 25.30 Altona 18.69 Beeson 19.69 Corsoy 79 21.40 Harcor 17.92 Hodgson 78 16.68 Lakota 18.01 Manchuria 20.94 Mandarin 20.82 Maple Arrow 18.80 McCall 20.53 Morsoy 21.78 Mukden 20.54 Norman 21.30 \ Renville 20.30 Neber 16.20 Mirth 17.65 21 were made. The samples were weighed and the 100 seed weights were used to calculate seed size response for each cultivar, using the formular: % seed size increase = 100 x (A-B) where A = Average weight in grams of 100 seeds from depodded plants in a plot B = Average weight in grams of 100 seeds from untreated plants in the same plot. The seed size response (Table 6) were used to select six cultivars: two exhibiting large response of seed size to pod removal, two exhibiting medium response, and two exhibiting low seed size response to pod removal. The cultivars selected were used in the 1984 study. Sources of variation examined in 198A (Table 2) were six cultivars and three degrees of pod removal (0, 25 and 50%) at two sites of pod removal (upper versus lower half canopy nodes). The factorial set of 54 treatments were arranged in a split-plot design with cultivars occupying whole plots. Each whole plot consisted of 12 rows 50cm apart and 18.3m long, arranged in a randomized block design with two replications. Subplots were 2m sections of single rows, and treatments were applied randomly to sub- plots within whole plots. Figure 1 shows a block of the plot layout. The six cultivars were planted on June 05, at a depth of 3.8-5.0 cm. Planting rates (Table 3) were adjusted for each cultivar to produce a plant population of 370,000 per TABLE 2. 1984 Treatments. Partial Pod Removal Treatments 22 Treatment %pods removed at % pods removed at number upper (top % canopy) lower (lower % canopy) nodes nodes 1 O O 2 O 25 3 0 50 4 25 O. 5 25 25 6 25 50 7 50 0 8 50 25 9 50 50 25% PPR- One in every four pods removed. 50% PPR— One in every two pods removed. Cultivar Treatments Cultivar Name Maturity group 1983 response A Corsoy 79 11 Medium B Hodgson 78 I Medium C Lakota I Low D Maple Arrow 0 High E Neber I High F Nirth I Low 23 Main plots--Cultivars Harvested row section 'Sub plot j/ I'll“ I I I I 1 meter '%'1 2 meters 1%| .1 |‘||l llil I 1 meter lllli 5 meter (20 inches) row spacing Figure 1. Plot plan. Cultivars and Partial Pod Removal (PPR) treatments were applied randomly to whole plotsand sub plots respectively. 24 TABLE 3. Cultivar planting rates adjusted to produce 370,000 plants/Ha 1984. Cultivars Mean 100 seed 500 seed weight Actual seed (g) weight (g) required/plot (g) planted/plot Corsoy 79 16.60c 83.00 83.00 Hodgson 78 18.80 94.00 92.60* Lakota 17.50b 87.50 87.50 Maple Arrow 19.10a 95.50 , 95.50 Weber 12.10c 60.50 60.50 Nirth 17.10bc 85.50 80.00* *- limited seed supply Means followed by the same letter are not significantly different from each other by the LS0 test at P= 0.05 25 hectare assuming complete emergence of germinating seedlings. Two hundred twenty five Kg/ha of 6:2hz2h fertilizer was incorporated in the soil prior to planting. Granular rhizobial inoculant was applied in the planting furrow. Needs were controlled by application of a combination of preplant incorporated (PPI) and postemergence herbicide treatments. The PPI treatment was Zlbs/A a.i. chloramben mixed with llb/A a.i. Trifluralin incorporated into the top 5 cm of the soil one day before planting. A tank-mix combination of bentazon (llb/A a.i.) and fluazifop—butyl (%lb/A a.i.) was applied at 2 and 5 weeks after planting. Plots were hand weeded to control weeds not killed by the herbicides. A wooden stake was driven into the soil at each end of the treatment row, such that the height of the stake above the ground equalled half the plant height for the particular cultivar, as calculated from the previous year plant height measurements (Table A). A string was tightly secured between the two stakes to indicate average half plant height (dividing the canopy into top and lower halves) along the row. When pods began to form, they were examined visually on a daily basis to evaluate the mid pod filling stage. This was determined when seeds in the pods half filled the available seed space and could not be crushed under slight finger pressure. At this stage of pod development, pod removal treatments were applied to the respective canopy 26 TABLE 4. Half plant height calculated from 1983 height measurements. Cultivar Mean height (cm); E Plant height (cm) Corsoy 79 120 60 Hodgson 78 130 65 Lakota 140 70 Maple Arrow 78 39 Weber 120 60 Wirth 100 50 27 sites. Treatments were applied progressively from the base to the top of the canopy, from August 0A to September 02. At maturity, plants in the middle 2 meters of depodded and control rows were counted, harvested by hand, and their fresh weights measured. Plants of each treatment were bagged together, dried at 410C for AS hours, reweighed and threshed. Total seed yield and number were determined. Three 100 seed samples were randomly drawn from each treatment plot and weighed. Average 100 seed weights and percent 100 seed weight changes were calculated and used as a measure to compare seed size response to partial pod removal within and among cultivars. STATISTICAL ANALYSIS. Lack of replication of treatments in the 1983 pre- liminary experiment did not allow statistical analysis of the data. Seed weight changes (Table 6) were used as a guide in selecting the six cultivars used in l98h, and in grouping the cultivars into high, medium and low seed size response (to PPR) cultivars. The 198h data were subjected to Analysis of Variance appropriate to a Split—plot design using MSTAT (39) and GENSTAT computer packages of statistical programs. Cultivar main effects were partitioned into among and within the high, medium and low response (to PPR) groups. The main effects of pod removal at upper and lower nodes were partitioned into linear and quadratic components and 28 their interactions with the different cultivar groups. These components were included in the partitioning of the interactions between cultivar and depodding treatments. The form of the analysis of variance used is shown in Table 5. When a significant "F" was obtained for treatment effects, treatment means were separated by the Least Significant Difference (LSD) test according to Steel and Torrie (51). Unless otherwise stated, the level of significance used was P=0.05. 29 Table 5. Form of analysis of variance Source of variation Total Replication CULTIVARS Among groups high vs. low medium vs. low Within groups within high within medium within low Error (a) UPPER NODES Linear Quadratic Cultivar x upper nodes Among groups x upper linear Among groups x upper quadratic Within groups x upper linear Within groups x upper quadratic high x upper linear high x upper quadratic medium x upper linear medium x upper quadratic low x upper linear low x upper quadratic LOWER NODES Linear Quadratic Cultivar x lower nodes Among groups x lower linear Among groups x lower quadratic Within groups x lower linear Within groups x lower quadratic high x lower linear high x lower qudratic medium x lower linear medium x lower quadratic low x lower linear‘ low x lower linear Upper x lower Linear x linear Linear x quadratic Quadratic x linear Quadratic x quadratic Cultivar x depodding treatments Cultivar x upper nodes Cultivar x lower nodes Cultivar x upper x lower Error (b) H O \J HHHHHwaNNOHHN mHt—IHwHHNmt-I HHHHHHNNNNOHHN RESULTS AND DISCUSSION The choice of applying pod removal treatments at mid pod filling stage (determined visually when seeds in the pod half filled the available seed space) was influenced by attempts to maintain nearly equal time intervals between full pod (Stage RA) and full seed (Stage R6). This period takes as long as A6 days, and is very critical in changing yield production patterns, if a treatment influencing any of the various plant source-sink relationships is applied. It is important to know how yield production is changed during that time. Therefore to properly assess the effects of partial pod removal, it was decided to apply treatments within this critical growth stage, and mid pod filling stage appeared as near the middle as possible. Just before harvesting in both 1983 and 1984, ‘ recognizable differences were observed among cultivars, and between depodded and untreated plants within a cultivar. The early maturing cultivars such as Maple Arrow were fully mature and completely dry two to three weeks before the late cultivars matured. Cultivar differences in both plant size and pod size were apparent. Within a cultivar, control plants senesced fully, showing a general yellowish- brown coloration over the entire plant canopy. Pods were dry and would crack under slight finger pressure. Depodded plants on the other hand had a complement of dark green leaves, thick green stems, and light green pods that would 30 31 not crack under the same finger pressure. There was about lO-lA days' time difference between complete senescence and drying in control and depodded plants. Within the depodded plants, the sections without pods following pod removal were characteristically greener than the untreated sections. Pods from depodded plants were visibly more plump than those from untreated plants. Pod plumpness was more pronounced in sections from which pods had been removed than in undepodded sections. Pod size and plumpness appeared to increase as degree of pod removal increased. Lack of replication of treatments in the 1983 study did not allow statistical analysis of data, and seed weight changes were used as a guide in selecting the six cultivars used in the following year, and in grouping the cultivars into high, medium and low seed size response (to PPR) cultivars (Table 6). Seed size increases ranging from 1 to 2A% were observed, with cultivars Mandarin, Mukden and Wirth giving the lowest response, and Agate and Altona being among the high seed size response cultivars. Seed size increases of 5% and below were considered low response, 5—l5% considered medium response, and above 15% was high response. Table 6 shows that there were cultivars which should have been selected for further testing in 198A, but were not selected. This was-due to limited supply of seed for planting in the 1984 study. Limited seed supplies reduced planting rates for cultivars Hodgson 78 and Nirth. 32 TABLE 6. 1983 Cultivars, mean 100 seed weights and % seed size increase response to 50% pod removal, Mean 100 seed weight (grams) % Seed size Cultivar Control (B) Depodded (A) Increase Agate 25.30 31.35 23.91(*) Altona 18.69 21.50 15.03(*) Beeson 19.82 24.38 23.01(*) Corsoy 79 21.40 24.06 12.43** Harcor 17.92 19.40 8.26 Hodgson 78 16.68 18.90 13.31** Lakota 18.01 18.90 4.94* Manchuria 20.94 21.76 3.92 Maple Arrow 18.80 21.59 14.84*** McCall 20.53 22.71 10.62 Morsoy 21.78 22.81 4.73 Mukden 20.54 20.80 1.26 Norman 21.30 23.39 9.81 Renville 20.30 21.50 5.91 Weber 16.20 19.44 20.00*** Wirth 17.65 17.90 1.42* % seed size increase = 100 g (A-B) *,** and*** - respectively low, medium and large seed size response cultivars selected for 1984 study. (*) - Limited seed supply prevented cultivar selection. 33 Despite the reduced planting rates for some cultivars, there were no significant differences among cultivars in the number of plants harvested from 2m row sections of sub- plots (Table 7), an indication that any differences Observed in other traits was not due to non—uniform experimental plots, but due to the cultivar and pod removal treatments themselves. No significant changes in fresh weight (pods + stem + leaves) were observed among cultivars. Mean square values (Table 8) from the analysis of Variance indicates that there were no differences in total dry weight (pods + stem + leaves) yields among cultivars, but significant linear dry weight reductions following pod removal at both the upper and lower nodes. An interaction between the linear response to pod removal at upper nodes and dry weight yields within the high and low seed size response cultivars was apparent. Pod removal treatments reduced dry weight yields by as much as 16% (Tables 9 and 10, and Figure 2). In cultivars Maple Arrow, Weber and Wirth, the dry matter reductions were not significant. Similar responses were observed in Corsoy 79 and Hodgson 78, except for significant reductions in treatment 6 (25:50 depodding ratio on upper:lower nodes) for both cultivars and treatment 4 (25:0) in Hodgson 78. However, these reductions are unlikely to be related to pod removal, since the more severe pod removal treatments maintained dry weight yields. The overall mean column in Table 10 indicates that 34 .mo.o an mm “mm“ am; we» >3 emgpo comm ace» “cmgmmwwu xpucmuwm_cmwm yo: men meum_ mamm ms» mcwcmgm meme: em.a "Amo.ov ems .mcowumowpamg 03p to mmmem>m w mm~.~m am~.em mmm.eec mpcm_a to acmnE:z .m m4mau~=u mcoe< ..N.oflm ..m.mmom a.N.oHNN m.mm~ aaNH.vH eamwson c.mmomch .mfiwmv a mec_4 ..mo.NoN .«m.¢mNH ..H.m¢~v m.¢om c.mo.m camemflN acn~mmNmH .mvufim N move: Lose; .om.om~ m~.oom N.NNv aoo- u-.v mHNm ouNNN .oHHmm H Lamc__ Luau: x unseen zen mm.mm mw.mmfi mm.va o~.m~¢ mm." vvmfl mmuoe acmHNNmH m Looc__ Luau: x «quota Ln>Lu_:u algal: ..mmN~ ..mNNH «commm .Nm.omnm we¢N.Hm «gamma aamvomNm~ .mmmmm a Lou=_4 ..NN.qu .N.vvm ..m.meN .N.omo acmm.m~ «Home .emNNva ammoom N move: Luau: No.~mH m.NmN m.mmNH N.Hon an.“ NNNN wmmvv nmNNfl m Auv Locum mmm NNN em.NH Nam .amm.No .NNNQN ammcm “mead H maaocm co>«a_=u 30. canal: Nae New o.mHm o.~«~ .Nm.o mom .vNNmoo amowm u museum Lo>vu_=u annue =_cu.z v~.mv 0mm meav mN.mN ..on mmNo~ aemNHNm «OMN H «Quota L.>_u_=u new; alga.: av.mmm mm.mmm _m.mom~ mo.ovN canmomNmH mNmoH .cHQONe mammN m ”La>.a_=u No “quota cwcu.3 .ficmfi oven men nmoa NH o mmmm com NN.o A zap .u> sswvmz mm.mm mmflfi QNNM mac c.m~.om aconmm .vOONNm NNooN ~ “cacao .m> cal: mm.~mo om.Nom~ om.Nom~ om.oNN~ camm.mN. cmNmQON Nomvmm -.-mm~ .N acu>vu_:u . No ”quota ocaoe< “m.va m.omm oN.Nan on.mmo a.mo.~m «mason cHHNman NNQNN .m measly—nu u co.aau._ao¢ .Nofl page» V _ocucou No a pogucou No a —otucou No a Focucou No a o~_m voom vpu_a,vaum Lanes: voom «gm—o: Do Nu .cewuo_go> No oucaom an o~_m ovum u~o.» uwmm no Logan: voum «a u;o*oz Ago .mucouwmpcmwm do Pm>op ecu mo=~m> «Logan cam: .mw m_auoh 36 .mmeo: Naocmo w Luzop um Pe>oEmL eon pmwucma N 1 % .mmeoc aaocmu N Long: as Pm>oemc eon Pawugwa N u e .mo.o "a pm pmmp awn mg» an emcee comm seem pcmcmmm_e appcmuvmwcmwm No: man cmupmg mamm ms» mcwcmgm caspou m cw;u_3 meow: HN.om umcowpeowFamc ecu mcm>wp_:u mmogom memes mo.ov own mo.nm~ ugm>wpp=u m c_cp_z mcmmz mo.ov own mm.mH umpcwEummLp P395L voa N.>.u mN.NH u mcm>wupsu N.>.u nmo.ooo mm.mom mo.mmm mo.~mo uo.~¢o nom.mmm amm.omm om om m nmm.mom mm.mmo mo.Nmm mm.mmm oo.mm¢ amm.mmm amo.mvo mm om w nmo.m¢m mo.mo~ mm.an mo.moo onm.m~m amo.mHo nwm.Hom o Om m nmo.mmo mo.wmo mm.mmm mo.wom nem.wwm nm.¢m¢ ao.mmm om mm o amo.mom mm.mmm mo.¢mm mo.¢mm unmo.on amm.¢mm awo.mmm mm mN m nmNm.nmm mm.mNo mm.Nmm mm.nmm onmm.mHo no.o~m nam.mmm 0 mm c ammo.meo mm.Nom eo.omo mo.m¢o uamm.mmo amm.mmm neo.mum om o m ammN.wa mm.oNo mo.mwm mm.mmm amo.vmm noo.¢~o nwm.mmm mm o N A....----aw...-am..w NEW imam ....Mmm_-------we . o . mcmmz zung Lwnwz ZOLL< wpamz muov—m.‘ mu commUOI mu home—CU m < {an—:3: N e “swayemcp .Fm>oemg eon op mmcoqmmc pcmwmz Ago .m NLm‘ 288.8 [:3 L11 L1J U‘l 278.8 .a aim Cl 1:} H -5.88 >. Q U m-1a. U) 2 H L‘J-‘SI U z m I u-zo .\‘ -2s.ea Figure 41 \ —- PPR at upper nodes 1 \ -- PPR 1?. lower nodes 25 58 DEGREE OF POD REMOVRL (7.) — PPR at upper nodes 1 -- PPR 3?. lower nodes 25 58 DEGREE OF POD REMOVFIL (7.) Effects of pod removal on seed yield (g/2m row section of subplot) and the percent change in seed yield. 42 .mmno: maocmo m Luzofi um Pm>osmc non Pawugma & u % .mmuo: xaocmu w Lana: um Pm>oemg non pmwugma a u e .mo.o "a pm “wow om.— mcu ”E mevo comm EOLL. pcmxmm¥wt %Ppchwkwcmwm p0: mLm Lmuuop mEMm mcu. GCwmem £53.00 0 awe—p.25 mcwmz om.mm umcopmeVPng ucm mgm>qu3u mmoguw meow: Amo.ov om; mm.mw ugm>wp_:o m cwsuwz mammz Amo.ov om; om.m~ nmpcmsummcu Pm>osmg non &.>.u mm.HH umcm>wupzu N.>.u um.mmm m¢.mvm am¢.-m mo.mmm um.mm~ n¢.mmm an.HmN om om m um.mom mm.¢om an.omN mm.omm unm.om~ am.mom aoo.mmm mm om m uamm.wmm m¢.wom nom.oom mm.-m unmo.~m~ 3H.HNN nmN.on o om N unH.HmN mm.Hom nH.N¢N mo.H¢m nm~.mum nm.mom amm.HmN om mm m um.mmm m¢.nom nmm.mHm mo.mmm amm.¢¢m nu.¢m~ ne.mm~ mN mm m amu.¢om m~.mmm mm.wmm mm.~mm nm~.omm av.mmm mo.mmm o mm c unm.mmm m~.mmm amm.mwm mm.omm oamm.H¢N nm.m- am.~¢m om o m uno.mmm av.mmm nu.¢¢m mm.~¢m amm.mmm amm.wmm amo.¢m~ mm o N mm.mmm mo.HNm mm.mmm mo.mmm mm.mwm wm.-m mo.~¢m o o H ----n------------n--u------A:OFpumm so; po_qn:m EN \ mango cw upm_>~-u- cam: gpng Lmamz zoxg< «Pam: muoxmA mu cemmvo: mm xamgou m < Lungs: % e acmEpmmL» ._m>oemc con op mmcoqmmc v_mw» comm .Hfi u4m

osmg cog _mwugma a u * .mmuo: xaocmu M Long: pm _m>osmc won mepcma a u e .mo.c um um umma om; mgu >3 gmcpo comm soc; ucmgm$wwu xFHCmuww_cmwm yo: mum LmuumF mswm any mcwgmzm :E:_ou m cwgng mcomz mm.oH u mcowumuv—amg can mcm>wu_:o mmogum meow: “mo.ov om; NH.m~ ugm>wppau m cwcpwz mcmmz Amo.ov om; ¢¢.mH umucmsummgu Fm>oamg com a.>.u -.o umgm>wppzu N.>.u umo.¢m mmm.um nwmfi.om www.mm umm.mm nmm.¢m oom.~m om om m uqm.om www.mm ammo.wm wvo.om unmm.mo amm.ow onmmm.mm mm om w unHo.¢H www.mm ammv.¢m www.mm unwoo.mm nm~.mm unmoH.Hm o om m umm.m~ m~m.vm n~m.mm mmm.mm mmv.vm nmn.¢m unwm.mn om mm o uwm.om wov.mw amom.ww mmm.mm ammm.mm nom.mo umv.um mm mm m ammm.m moo.om amov.vm mvm.mm m¢¢.mm aom.mm ammm.mm 0 mm c unmfi.wfi wov.mm ammm.Hw moo.mm amma.~w nvm.oo umH.~m om o m uaofi.ofi mmm.mm nmw.mo mvm.mm ammH.mw nmm~.nm unmwm.mm mm o N moo.o moo.ooH moo.ooH woo.ooH moo.oo~ moo.ooH moo.oo~ o o H mmmmgomu spew; gmnmz zoEL< «Pam: mpoxmq mm commwo: m“ xomcou m < Lmnszc N :mmz % e “cmeummgh .mucmpa Fogpcoo mo pcmocma mm nmmmmgqu n_mwz nmmm co mpummmm _m>osmc noa .mfi m4m— D LaJ LaJ-18.88 .. U) 2 H 8-15.88 +\ ‘ z \ m g ‘5 --------- .\.__>_ 5‘. _ ' ‘-<;:-----A..~ L) 28.88 \+__~.~..‘___________... .\° -- ~~~~~ -2s.88 . -\‘ 8 25 58 PPR at upper nodes 8.88 ‘ x Q -— 8?. PPR at upper node: E .5.88 —- 25>: PPR at. upper nodes >_ --- 58?. PPR at upper nodes 5} *'\ uJ-la.aa \\ U) \ Z \\ H \ w-IS.88 A ~~~~~~ \ . g ...... \x """"" \ Q “~. I “~~§ __... __..: 0'28.88 *-\*‘_‘____..._.——-—-—‘" . .\' .......... -25.88 ' H- 8 25 58 PPR at lower nodes Figure 4. Seed yield (g/Zm subplot section) response to pod removal at upper nodes (top) and lower nodes (bottom) expressed as untreated plants. a percentage of 46 SEED NUMBER RESPONSE TO POD REMOVAL. The analysis of variance for seed number for the harvested 2m row sections of subplots showed significant cultivar differences and significant seed number reductions following pod removal (Tables 8 and 13). Differences in seed number were observed within the high response cultivars Maple Arrow and Weber, and between these two and the rest of the cultivars. Significant differences in seed number were also obtained within the low response cultivars (Lakota and Wirth) and the medium response cultivars (Corsoy 79 and Hodgson 78). When seed number was expressed as percent of control, cultivar differences were not expressed, while pod removal effects remained significant at the 1% level (Tables 8 and 1h), again indicating that the proportional effect of PPR was similar in all cultivars. However, the interactions among the groups of cultivars and the linear effects of pod removal at the lower nodes remained significant(Figure 5). Tables 13 and 1h show that between the extremes of pod removal, seed number was reduced 16 to 39%, but that only Treatment A (25:0) maintained seed number. Highly signi— ficant linear components for seed number reduction at both canopy sites were obtained, and a significant interaction was obtained between cultivar groups and pod removal. Response within individual cultivars was variable. In Corsoy 79, seed number was reduced by all pod removal ' treatments except 2 (0:25), 8 (25:0) and 7(50:0). As much 47 .mmvoc zaocmo m cmzop um Fm>osmg non mepch N u % .mmuo: zaocmo » Lona: pm pm>oEmc non _mwpgma & u e .mo.o um um ammo om; .mn logoc some seem ucogmmwwu >chmowmwcowm “o: mew LoppoF msmm mg» mcwgmgm cszpoo m cwcpwz mcmoz qo.¢ON umcowpmoVFch ncm mcm>wp—:o mmogom memo: Amo.ov om; ma.ma¢ newswopzu a algal; mama: Amo.ov ems os.m~ umpcmEpmmcs pa>oamc sea a.>.o as.HH "mea>_olso a.>.o mmoofi nmmm onomqfl mmmHH onm onN oNHoH om om m oummofi nqmofi onmomH momHH oaovw onwoofi onHNNH mN om w c-aommH nmNmmH onmoqfl mwNNH oommmfifl onmmHH nmcflmfi 0 cm N m-ooHHH nomHH oooHH mMNNH ammHNH omau onNNHH om mN o m-pmmHH nmoHH onmxmfl moon omoHNH oamwofi oamHHH mN mN m ammqvfi ammwmfi nmfimoH mmmNH ammmNH amowNfi mHmNH o mN a o-no¢NH nMNmmH onmfivfi mmmNH amoomfi _unNmm onHmHH om o m onoumfi amvmmfl oanNfi mmmmH mmomH ammumfi oamNmmfi mN o N ammofi mNHNH meoHN mmme meamfi moeoH mHmNH o o H ----------------------AmpoFanm mo cowuoom 2o; EN seem mvomm av-----u cam: cola: Loam: zogc< oFQuz mooxmu mu commvo: mu Newcoo m < conga: % e “cospamcp .po_an:m mo mcowuoom so; Looms N sage empmo>cmg amass: zoom Page“ :0 Pm>oEmg cog mo mpommwm on» .mH mumcwc mvomm mo conga: mgu co _m>osog non —mwpgoa mo muommwm mm “.\L J¢>ozwm Dom LO mmmuwm mm 8 auto: 8830— an mam ll mono: coma: an mam .ll .m ogzmwu a mall Go 14 Sam” :4 nu Mm m mam: 8 14 NH mavl Sam“ 50 3.88 ‘ f —— 8. P E) -S.88 + 7 P R It lower node: 1 92:3 -- 257. PPR It lower node: 3-13.38 . --- $87. PPR at lower node: B-l5.88 r- a L.) 'l\ U) \ ~28. \ Z 88 l \ g H \ hJ-ZS.88 ‘5 ....... \\'\\ i U ...... \ X Z “““““ CE ~38.88 - ------ \ \ \ . I ~~~~~ A \ u ~~~~~~ "‘- ...... \‘+ \-35.88 » ......... . -48 88 1 ‘13 8 25 58 PPR at upper nodes 8.88 fl 1 LJJ -S.88 -— 87. PPR at upper nodes ‘ [I] Z -— 255: PPR at. upper node: 3-1888 - - Z --- 58’: PPR at. upper nodes t\ D ”_1Seaa b \ LaJ \ Ul \ 2-28 88 AL‘ \ H “~\ \ w -25 . 88 - \‘x \ : L9 “~. a \+~ - -38.88 - ‘~. “"*—-—~_ q I “~\ x x \_L L) ‘xg \o-35.88 '- A ........... ' -48.88 ‘ -15 8 25 58 PPR at lower nodes Figure 5 cont. Partial pod removal effects on seed number expressed as percent of untreated plants. 51 as 45% reduction in seed number was observed in treatment 9 (50:50). In Hodgson 78 and Wirth, treatments 2,3,0 and 7 maintained seed number. The more severe depodding levels reduced seed number by as much as 36 to 55%. In Lakota, seed number became significantly reduced past the 50:0 PPR treatment. Weber maintained seed number in treatment 0 (25:0) only, while in Maple Arrow, seed number was not reduced by pod removal. There was essentially the same number of seeds per pod regardless of treatment within each cultivar. 52 SEED SIZE RESPONSE TO POD REMOVAL. Seed weight expressed as grams per one hundred seeds was used as the most sensitive measurement of seed size response to partial pod removal. The analysis of variance obtained was significant for both cultivar differences and pod removal effects at the 1% level (Table8). Differences were significant for for both among and within groups of cultivars. Differences within cultivar groups serve to indicate that the grouping of cultivars which was based on results of the preliminary (1983) experiment was incorrect, or that the response to pod removal by the cultivars was inconsistent. When 100 seed weights were expressed as percent of untreated plants,cultivar differences were nonsignificant, while pod removal effects remained significant, an indication that the effects of pod removal on seed size was proportionately the same in all cultivars, and was independent of cultivar differences. Between the two extremes of pod removal, individual cultivars showed a wide range of seed size response (Tables 15, 16 and 17). In Corsoy 79 and Hodgson 78, 100 seed weight changes resulting from pod removal treatments were not different from controls at P=0.01. At P=0.05 however, all pod removal treatments in Corsoy 79 induced a significant seed size increase ranging from 3 to 11%, while in Hodgson 78 seed size remained the same except for an unexpected decrease in treatment 0 (25:0) which however was .Ho.o um um ummu emu on“ an cmzuo comm soc» “cocomwwn zHucmonwcmvm we: ohm LmupmH osmm oz» mcwgesm asaHou m canny: memo: mm.H uaamcmwe Lm>Fszu HHo.ov emu ON.N umtm>l8_=u cl;o_3 meme: AHo.ov emu om.o u ’.23.: acmEpeoLu Hm>oEoL to; HHo.ov om; mm.¢ nocoeuemgu H525L no; N.>.u mm.¢ umgm>wquu &.>.u nem.wH www.mH mmm.HN eoN.mH on¢¢.NH uoo¢.mH wwcmoz nee.mH www.mH nmm.mH nHm.NN ammm.mH mNm.wH moH.NH om om m uee.wH comN.cN ammo.oH ammo.HN amNm.oH moH.mH emH.NH mN om w u-nmm.~H uunNm.mH nemN.mH ammN.oN nem.mH onNm.mH mmm.oH 0 cm N as comm.NH n-nwe.mH ammo.mH amm.NN amON.mH oumom.NH eNm.mH om mN 0 Pa oumNo.~H u-nem.mH ammo.mH ameo.NN ammu.mH ouee¢.NH emm.mH mN mN m o-mNo.NH ammm.NH anN.mH ammo.NN nmNn.eH oom.mH mmN.mH o mN e onmN.NH o-mNm.NH ammm.mH aem¢.HN neem.eH oumm¢.NH mHN.oH om o m ammm.oH nmNm.NH neNN.¢H neHo.HN amom.mH omm.mH mHo.oH mN o N ewN.mH mmm.mH emH.eH mmo.ON mmm.eH oummm.NH mmv.mH o o H -----mnmom ooH we mango cw ozmwoz mm ummmmgaxm mNHm voomulu----------- «cam: soLH3 Loam: zocc< mHaez mooxmu mm commeo: mm NomLou m < conga: * a ueosomoc» AHo.o "av He>oeoc cog ow omcoamoc mNWm ummm .mH mum

oemg woe Hmwumme & u * .mmuo: eeocmo w cmee: pm Hm>oemc woe Hmwpgme a - e me.e um om ammo emu mew me cmeoo comm some pcmcmmem ercmowmwcewm no: mmm LmupmH mamm me» ecwmmem esseoo m cmeuwz mcmmz He.H uwxmcmms gm>on=e Ame.ev emu mm.H nmgm>HpHao :Peon memmz Ame.ev emu No.0 ummcmme acmEpmmmu Hm>oemg woe Ame.ev emu em.¢ "mucmEHmmLp Hm>oemg woe &.>.e nn.¢ umpm>wquu w.>.u eem.eH mem.mH mmm.HN uem.mH oe¢¢.NH me¢.mH «acmmz mee.mH eoee.eH omm.mH on.NN oummm.mH emNm.wH eeH.NH em em e mem.mH eeN.eN oeme.mH o-mme.HN oeNm.mH meH.eH emH.NH mN em m u-eNm.NH u-eNe.mH o-mmN.mH emmm.eN oem.mH muon.eH emm.mH e em N mmmm.NH oeee.mH o-mmm.mH oeNm.NN oumeN.eH unmee.NH eNm.mH em mN m mome.NH eneme.mH o-mme.mH meme.NN oummm.mH m-eve.NH emm.eH mN mN m oeNe.NH emm.mH oumHN.mH meme.NN emvm.eH mmm.mH emN.mH e mN e m-emN.HN eem.NH o-mem.mH mumme.HN emem.¢H muem¢.NH eHe.mH em e m eme.mH emNm.NH emNN.mH o.mmHHN oemm.eH meme.mH eHe.eH mN e N meN.eH mem.mH mmH.¢H - mme.eN mme.eH . mummm.~H mme.mH e e H -u---------mmmmm eeH we mamas Cw pecwmz mm ummmmmcxm mem ummm----------- *cmmz some; Lmemz zocm< mHemz mpoxmu mm comemo: en acmcoe e < gmesec * e pcmEpmmmp .Hme.e uev Hm>oemg toe op mmcoemmg mem emmm .mH eue

oemg woe Hmwpcme N - * .mmmoc eeocmo M cmee: um Hm>oEmL woe Hmwpgme & u e .me.e um um pmmu emu men an ngoo comm some ocmcmwwwu eHocmovwweewm mo: mam LmupmH mEmm mew e:_cm;m caeHoo m :Hemwz mcmmz me.¢ umcowpmoHHemg new mgm>on=o mmocom mcmmz Hme.ev emu e.eH ummm>pr=o :Hcpwz mcmmz Ame.ev emu Hm.¢ "mucmeommmo Hm>oemL mom N.>.e ee.m umcm>on=e &.>.e mee.mH moem.mN+ mum.mH+ mum.NH+ oemmm.~+ mmm.~+ ewm.eH+ em em e mmm.mH mum.mN+ oeNm.mH+ ammo.w+ UeH.NH+ mem.e+ eee.HH+ mN em m momm.m moeNH.eH+ oeeH.HH+ emem.m+ oe¢.mH+ oeeH.e- emeH.m+ e em N muNw.e oemm.mH+ oeem.eH+ eem.HH+ meme.eH+ emmH.N+ emmH.N+ em mN e meN.m oeNe.~H+ oeem.eH+ eme.eH+ oemNN.N+ oemv¢.e- emeN.m+ mN mN m oemm.e eem.eH+ eme.HH+ eme.e+ mHe.e+ on.e- emNm.m+ e mN e uoeme.m eeH.NH+ oemH.eH+ emmN.n+ emmm.H+ oemmN.e- emee.m+ em 0 m emm.¢ emmm.eH+ emme.¢+ emee.m+ oee.NH+ oNe.e- emem.m+ mN e N A Auvmmmmmomm co H+vmmmmmozw & usewmz emmm nmmmcae mco v mee.ee mem.mH mmH.¢H mmo.eN mmm.¢H oemmm.NH mme.mH e e Homoeoe AmummmmLoCH mNWm epcwz cmemz zomc< mHemz mpoumu mN commno: em mammoe e < Lme52: emmm memgm>< m e pcmEummLp .mpchQ Umpmmcfic: .+o uthLwQ mm vommmLwa mem Ummm co pom.+.+m _.m>OEm¢_ tom .NH mum”: 56 not significant when expressed as a percent of untreated plants. In Lakota, Maple Arrow and Weber, seed size was increased after the 25:50 pod removal treatment. In Wirth, treatment 3 (0:50) to 9 (50:50) showed significant seed size increases, and as much as 25% increase in seed size was observed. There was a significant linear increase in seed size following pod removal (Table 8). Seed size increased as intensity of pod removal increased (Figures 6 and 7). but not proportionally so, ranging from 16.28 to 18.5h grams per 100 seeds (Tables 15 to 17). This represents a h to 13% seed size increase induced by partial pod removal across cultivars and replications. A comparison of seed yield, seed number and seed size (Figures 3 to 7) indicates that soybean seed size was increased enough to compensate for 25 to 50% pod removal on the upper half canopy nodes, such that total seed yield was maintained. 57 28.88 1 f‘ -- PPR at upper nodes 2 -- PPR at lower nodes I‘U L 19.88 )- < m g... I U H 18 L1] 3 C1 LsJ Ld U) 1?. S 5) 8.88 ‘ 8 25 58 DEGREE OF POD REMOVRL (Z) .\' LIJ U) (I U (E U 2 H L1] .N l G x’ D l a 3.88 r -- PPR at upper nodee Ul .— 2.88 P PPR at lower nodee ) 888 ‘ 8 25 58 DEGREE OF POD REMOVRL (Z) Figure 6. Seed size (expresssed as weight in grams of 100 seeds) response to pod removal. 58 P 1488 1 2:3 _4‘4 H 7"/ Ll] ."‘ 1 3 12.88 (",7 0"" / Cl -o" / Ld . a ,.-’ LL?” l8 8 "(A / / '1 ® 888 » """"" // 8 '," / u—o "" / Z ’t' / / H S 88 A / 1 / Lu .1/ U1 4 . 88 l ‘ E -— 831 PPR at lower node: g 2.33 _ -— 257. PPR u. lower node: H --- 587. PPR at lower nodee .\' 8.88 ‘ l 8 25 58 PPR at upper nodes p. I 14 88 'A .............................. 1 U x" H 'x LJJ D ”' 3 12.88 "x. S "”’O a 18.88 - ”'x _.._. ".- ___ ___,.... 8 Al / fl.— ’ E 8.88 - / ' u—e / / / Z - . H 6.88 / / . w V” U) 4.88 - ‘ E —- 83 PPR at upper nodes CK .. L) 2.88 _ 253: PPR at upper nodes E --- 58?. PPR at upper node: N 8.88 ‘. ‘ 8 25 58 PPR at lower nodes Figure 7. Partial pod removal effects on seed size (weight in grams of 100 seeds) expressed as a percentage of untreated plants. 59 The apparent recovery of seed yield in the treatments not depodded on lower half canopy nodes may be explained by changes pod removal induces in the patterns of light interception, seed or pod abortion and assimilate redistri- bution. About 90% of the light interception in soybeans occurs primarily at the periphery of the canopy, and when the space within and between rows is closed, light interception is restricted to the very top of the canopy (58). Thus the lower leaves function in relatively low light intensities. Removing 25 to 50% of the pods on the upper half canopy nodes could have increased light interception and distibution in the canopies, both which have been long recognized to contribute dominant roles to crop productivity (28,86,54). In this study, no measurements of light levels were made, and the hypothesis that pod removal at upper nodes changes canopy light regimes may require further substantiation. Soybeans produce many more flowers than mature pods. As much as 85% of the flowers may abort, with 75% abortion occuring during the full bloom stage (21). Pod removal has been shown to reduce pod and floral abortion (21,36,88). All cultivars used in this study were indeterminate types (types that continue vegetative growth during flowering), and their upper half canopy nodes would be producing flower buds long after the lower nodes would have stopped. Because pod set is genetically controlled, if the lower half 60 canopy fails to contribute its full share of pods, they may be compensated for by an increased pod set in the upper half nodes. The maintainance of seed yield and number in plants receiving no depodding at lower nodes (Traetments 4 (25:0) and 7 (50:0)) would be expected, because the normally high pod abortion in the entire plant canopy is not duplicated in those partially depodded. However, Treatment 7 (50:0) significantly lost seed number and seed yield, and this is possibly because 50% PPR was just too severe to be fully compensated for. The A to 18% increase in seed weights of depodded plants (Tables 15 to 17) has been reported by other investigators (6,8,11,36,52), and is most likely a reflection of a larger leaf area supplying assimilates to a smaller number of seeds. Begum and Eden (2) have reported significant yield reductions following defoliation treat- ments applied when beans were half grown in the pods, an indication that at this stage, soybean seed growth was rapid and highly dependent on assimilate supply from the leaves. Removal of pods at mid pod filling stage would therefore be expected to reduce competition for assimilates in the remaining seeds, resulting in seed size increases that compensate for part or all of the pods removed. The yield reduction observed in all PPR treatments except number 4 (25:0) could be a result of failure of the remaining seeds to fully utilize the increased assimilate supply, or because pod removal past the 25:0 mark becomes severe for plants to withstand. 61 According to Metz EEHEE' (37), plants that produce high seed yields should possess characters believed to influence photosynthetic efficiency, partitioning of dry matter to seed production, and prevent seed yield losses through lodging resistance. Among such characters are vertical leaf orientation, high leaf area duration, thick stout stems, and minimum intraplant compettition. In this study, pod removal achieved most of these characters. Depodded plants had thicker greener stems compared to untreated plants. ‘Removal of pods reduced the sink size thereby reducing intraplant competition in the remaining seeds. Pod removal extended the leaf area duration as is evident from the visually observed delay in the onset of senescence and leaf abscission. Thus depodded plants would be expected to yield comparably to controls, but in this study, all pod removal treatments except number A (25:0) had significant yield reductions, an indication that 25 and 0% pod removal on upper and lower nodes respectively was the maximum pod removal degree increasing seed size enough to compensate for pods removed, such that yields were maintained. SUMMARY AND CONCLUSION Field experiments were conducted at Michigan State University, East Lansing, during the 1983 and 198A growing seasons, to study the effects of partial pod removal (PPR) on soybean (Glycine max (L.) Merrill) seed number, size and yield. Sources of variation examined were cultivars, degree of pod removal (0, 25 and 50%), and site of pod removal (upper versus lower half canopy nodes). The factorial set of treatments was arranged in a split plot design with whole plots in randomized complete blocks. Six cultivars occupied whole plots and pod removal treatments were applied to subplots. Pod removal treatments were applied when beans in the pods were half grown. At maturity, plants were harvested and dried. Dry matter yield (pod + stem + leaves), seed number, size and yield were determined. Seed size was expressed as weight in grams of 100 seeds. Pod removal delayed soybean leaf senescence (visually judged by loss of green color) and leaf abscission (visually determined by the amount of leafage at harvest). Cultivars were significantly different in dry weights, seed numbers, seed sizes, and seed yields. Differences were significant for both within and among cultivar groups, 62 63 grouped on the bases of their response to 50% pod removal in the 1983 study. Differences within cultivar groups serve to indicate that the criteria used to group them was incorrect, or that the cultivar response to pod removal was not consistent over the two years of this study. When PPR effects were expressed as percent of untreated plants, cultivar differences were nonsignificant for all seed characters examined, indicating that pod removal affected all cultivars similarly. Overall means obtained by averaging across replications and cultivars showed general trends for linear dry weight, seed number, and seed yield reduction following pod removal. Between the extremes of pod removal, dry weight decreased 8 to 16%, but decreases up to 10% were not signi- ficant in plants not depodded on one site of the canopy, suggesting that at least 25% PPR was required on both the upper and lower canopy nodes to significantly reduce dry matter production. Up to 25% reduction in seed yield was observed with 50% pod removal on both canopy sites. Seed yield was maintained in plants not depodded on the lower canopy nodes. There was greater seed yield reduction as intensity of pod removal at lower nodes increased (r = 0.47 at P=0.01). Seed number was reduced by pod removal, except in the 25:0 (25 and 0% PPR at upper and lower nodes respectively) treatment. 30 to 80% seed number reductions were observed in the more severely depodded plants. 64 Seed size (expressed as weight in grams of one hundred seeds) increased by as much as 13%, from 16.28 in untreated plants, to 18.85 in plants receiving 50% pod removal on both canopy nodes. The following conclusions were drawn from the results of this study: 1 Soybean plants were more sensitive to partial pod removal in terms of dry matter yield, seed yield, and seed number, compared to pod removal at the upper nodes. Pod removal effects (on the seed characters) expressed as percent of untreated plants were similar in all cultivars, an indication that the effect of pod removal was proportionally the same in all cultivars, and was independent of cultivar differences. Dry weight, seed number, size and yield response to pod removal was linear. much of the capacity of the soybean plants to compensate for pod loss was by increasing seed size rather than by increasing or maintaining seed number. 25% PPR at upper nodes and 0% PPR at lower nodes was the highest pod removal combination inducing the least seed number and seed yield reductions (13 and 8.5% respectively), such that a 5% increase in seed size obtained was enough to compensate for pods removed, thereby maintaining total seed yield. 10 11 BIBLIOGRAPHY Begum, A. and w.c. Eden. 1964. Influence of defoliation on yield and quality of soybeans. J. Econ. Ent. 58:591- 592. Caldwel, B.E. 1976. Soybeanszlmprovement, Production and Uses. A.S.A. Madison, Wisconsin. Ciha, A.J., M.L. Brenner, and W.A. Brun. 1978. Effect of pod removal on abscisic acid levels in soybean tissue. Crop Sci. 18:776-779. Dornhoff, G.M. and R.M. Shibles. 1970. Varietal differences in net photosynthesis of soybean leaves. CrOp Sci. 10:42-45. Egli, D.B. 1975. Rate of accumulation of dry weight in seed of soybeans and its relationship to yield. Can. J. Plant Sci. 55:215-219. Egli, D.B., D.R. Gossett, and J.E. Leggett. 1976. Effect of leaf and pod removal on the distribution of C-14 labelled assimilates in soybeans. Crop Sci. 16:791-794. Egli, D.B. and J.E. Leggett. 1973. Dry matter accumulation patterns in determinate and indeterminate soybeans. Crop Sci. 13:220-222. Egli, D.B. and J.E. Leggett. 1976. Rate of dry matter accumulation in soybean seeds with varying source-sink ratios. Agron. J. 68:371-373. Egli, D.B., J.E. Leggett, and J.M. Wood. 1978. Influence of soybean seed size and position on the rate and duration of filling. Agron. J. 70:127—130. Fader, G.M. and H.R. Koller. 1983. Relationships between carbon assimilation and export in leaves of two soybean cultivars. Plant Physiol. 73:297-303. * Fehr, W.R., C.E. Caviness, and J.J. Vorst. 1977. Response of indeterminate and determinate soybean cultivars to defoliation and half-plant cut-off. Crop Sci. 17:913-917. 65 12 13 14 15 16 17 18 19 20 21 22 23 24 66 Fehr, W.R., D.R. Hicks, S.E. Hawkins, J.H. Ford, and W.W Nelson. 1983. Soybean recovery from plant cutoff. breakover and defoliation. Agron. J. 75:512—515. Fontes, L.A.N. and A.J. Ohlrogge. 1972. Influence of seed size and population on yield and other characteristics of soybean (Glycine max (L.) Merrill). Agron. J. 64:833-836. Frazer, J., D.B. Egli, and J.E. Leggett. 1982. Pod and seed development in soybean cultivars with differences in seed size. Agron. J. 74:81-85. Gaastra, P. 1959. Photosynthesis of crop plants as influenced by light, carbon dioxide, temperature, and stomatal resistance. Wageningen 59:1-68. Hanway, J.J. and C.R. Weber. 1971 Accumulation of N, P and K by soybeans. AQFOH- J. 63:406-408. Hanway, J.J. anc C.R. Weber. 1971. Dry matter accumulation in eight soybean (Glycine max (L.) Merrill) varieties. Agron. J. 62:64-65. Hartwig, E.E. and C.J. Edwards, Jr. 1970. Effects of morphological characteristics upon seed yield in soybeans. Agron. J. 62:64—65. Heindl, J.C. and W.A. Brun. 1984. Patterns of reproductive abscission, seed yield, and yield components in soybean. Crop Sci. 24:542-545. Hesketh, J.D. 1963. Limitations to photosynthesis responsible for differences among species. Crop Sci. 3:493-496. Hicks, D.R. and J.W. Pendleton. 1969. Effects of floral bud removal on performance of soybeans. Crop Sci. 9:435-437. Huck, M.G., K. Ishihara, C.M. Peterson, and T. Ushijima. 1983. Soybean adaptation to water sress at selected stages of growth. Plant Physiol. 73:422-427. Hume, D.J. and J.C. Criswell. 1973. Distribution and utilization of C-14 labelled assimilates in soybeans. Crop Sci. 13:519-524. Johnston, T.J. and J.W. Pendleton. 1968. Contribution of leaves at different canopy levels to seed production of upright and lodged soybeans (Glycine max (L.) Merr.). Crop Sci. 8:291-292. 25 26 27 28 29 30 31 32 33 34 35 b) O\ 67 Kaplan, S.L. and H.R. Keller. 1974. Variation among soybean cultivars in seed growth rate during the linear phase of growth. Crop Sci. 14:613-614. Kincade, R.T., M.L. Laster, and E.E. Hartwig. 1971. Simulated pod injury to soybeans. J. Econ. Ent. 64:984- 985. Koller, H.R. 1971. Analysis of growth within distinct strata of the soybean community. Crop Sci. 11:400-402. Koller, H.R. and J.H. Thorne. 1978. Soybean pod removal alters leaf diffusion resistance and leaflet orientation. Crop Sci.:18:305—307. Kollman, G.E , J.G. Streeter, D.L. Jeffers, and R.B. Curry. 1974. Accumulation and distribution of mineral nutrients, carbohydrates, and dry matter in soybean plants as influenced by reproductive sink size. Agron. J. 66:549—554. Lafite, H.R. and R.L. Travis. 1984. Photosynthesis and assimilate partitioning in closely related lines of rice exhibiting different source—sink relationships. Crop Sci. 24:447-452. Lawn, R.J. and W.A. Brun. 1974. Symbiotic nitrogen fixation in soybeans. I Effect of photosynthetic source-sink manipulations. Crop Sci. 14:11-16. Lawn, R.J., K.S. Fischer, and W.A. Brun. 1974. Symbiotic nitrogen fixation in soybeans. I; Inter- relationship between carbon and nitrogen assimilation. Crop Sci. 14:17-21. Lawn, R.J. and W.A. Brun. 1974. Symbiotic nitrogen fixation in soybeans. 111 Effect of supplementary nitrogen and intervarietal grafting. Crop Sci. 14:22-25. Leopold, A.C., E. Niedergang-Kamien, and J. Janick. 1959. Experimental modification of plant senescence. Plant Physiol. 34:570-573. Loveys, B.R. and P.E. Kriedemann. 1974. Internal control of stomatal physiology and photsynthesis. I. Stomatal regulation and associated changes in endogenous levels of abscisic acid and phaseic acids. Aust. J. Plant Physiol. 1:407—414. McAlister, D.R. and O.A. Krober. 1958. Response of soybeans to leaf and pod removal. Agron. J. 50:674—677. 37 38 39 40 41 42 43 44 45 46 47 48 68 Metz,_G.L., D.B. Green, and R.M. Shibles. 1984. Relationship between soybean in narrow rows and leaflet, canopY, and developmental characters. Crop Sci. 24:457- 462. Mondal, M.H., W.A. Brun, and M.L. Brenner. 1978. Effects of sink removal on photosynthesis and senescence in leaves of soybean (Glycine max L.) plants. Plant Physiol. 61:394-397. MSTAT (Version 2.03). 1983. A microcomputer program for the design, management, and analysis of agronomic research experiments. Created by the MSTAT Develoment Team, Michigan State University. Nelson, A.I., M.P. Steiberg, and L.S. Wei. 1978. Development of whole soybean foods for home usezRational, concept and examples. International Agricultural Publications Intsoy Series # 14. Nelson, D.R., R.J. Bellville, and C.A. Porter. 1984. Role of nitrogen assimilation in seed development of soybean. Plant Physiol. 74:128-133. Phillips, D.A., R.0. Pierce, S.A. Edie, K.W. Fosster, and P.F. Knowles. 1984. Delayed leaf senescence in soybean. Crop Sci. 24:518-522. Pierce, R.0., P.F. Knowles, and D.B. Phillips. 1984. Inheritance of delayed leaf senescence in soybean. Crop Sci. 24:515-517. Ratcliffe, R.H., T.L. Bissell, and W.E. Bickley. 1960. Observation on soybean insects in Maryland. J. Econ. Ent. 53:131—133. Sakamoto, C.M. and R.H. Shaw. 1967. Light distribution in field soybean canopies. Agron. J. 5927-9. Shaw, R.H. and C.R. Weber. 1967. Effects of canopy arrangements on light interception and yield of soybeans. Agron. J. 59:155-159. Sinclair, T.R. and C.R. DeWit. 1975. Photosynthate and nitrogen requirements for seed production by various crops. Science 189:565—567. Smith, R.H. and M.H. Bass. 1972. Relationship of artificial pod removal to soybean yields. J. Econ. Ent. 65:606—608. 49 50 51 52 53 54 55 56 69 Smith, T.J. and M.H. Camper, Jr. 1975. Effects of seed size on soybean performance. Agron. J. 67:681-684. Suetsugu, I. and I. Anaguchi. 1954. Relationship between size of seed and the yielding efficiency in soybeans. Proc. Crop Sci. 22:3-4. Steel, R.G.D. and J.H. Torrie. 1980. Principles and Procedures of Statistics. A Biometrical Approach. p. 377-395. Thomas, G.D., C.M. Ignoffo, K.D. Biever, and D.B. Smith. 1974. Influence of defoliation and depodding on yield of soybeans. J. Econ. Ent. 67:683-685. Wareing, P.F. and I.D.J. Phillips. 1981. Growth and Differentiation in Plants. Third Edition. Weber, C.R. 1955. Effects of defoliation and topping simulating hail injury to soybeans. Agron. J. 47:262-266. Wei, R.R. and A.J. Ohlrogge. 1976. Components of soybean seed yield as influenced by canopy level and interplant competition. Agron. J. 68:583-586. Yoshida, S. 1972. Physiological aspects of grain yield. Amm. Rev. Plant Physiol. 23:437-464.