Seed-filling Period Research Articles

Soybean Plant Introductions Selected for Seed for Seed Filling Period or Yield: Performance as Parents

Soybean [Glyclae max (L.) Merr.] plant introductions (PI) been investigated as sources of unique favorable alleles for yield improvement, even though most PIs are inferior to the best adapted coltivars for yield. A physiological character that is a component of yield might be useful for identifying Pls that might contribute unique favorable alleles for yield. The objective of this study was to compare, in terms of progeny yield, the value as a parent of a PI selected for yield (P1423897) with a PI selected for length of the seed‐filling period (stage RS‐RT) (PI 398401). Each PI parent contributed of the germplasm to separate BCI populations produced with the breeding lines or cultivar A80‐345005, LN80‐9359, and Ripley. Furty random BC1F3‐derived lines from each of the six populations were compared at Lexington, KY, in 1986 and 1987. The progeny groups from the two PIs did not differ for yield or seed‐filling period. The to,yielding 20% of each population were compared at the two Kentucky locations in 1988. The PI 423897 progeny were 8% higher yielding than the PI 398401 progeny, with no significant difference in the length of the seed‐filling period. Seven of the top 10 progeny lines for yield bad PI 423897 as the PI parent. Selection of a PI based on a seed‐filling period longer than the adapted cultivars was not su0erior to selection of a PI based on yield, even though the adapted coltivars were higher yielding than the PI selected for yield.

The development of seed quality in spring barley in four environments. I. Germination and longevity

AbstractSeed development and changes in germination ability and longevity were monitored in control and shaded spring barley (Hordeum vulgareL.)crops grown in two contrasting years. Shading reduced seed dry matter accumulation rates by 24–28% and delayed maturation drying slightly, but had little effect (0–2 d) on the timing of physiological maturity (end of the seed-filling period); final seed dry weights were 76–85% of controls. Moisture contents (wb) at physiological maturity were 48–55%; final mean seed dry weights in the controls were 40.9 mg(S.E. 0.6) in 1988 and 35.2 mg (S.E. 0.5) in 1989. Shading had little orno effect on germination ability or longevity in either year. Seeds fromthe first harvest were viable when dried below 15% moisture content despite being only 34% (1988) to 63% (1989) filled; desiccation promoted germination. Maximum germination achieved after forced desiccation occurredin seeds harvested 7–10 d (1989) to 11–13 d (1988) after physiological maturity, with little subsequent change during the following 14 (1988) or 27 d (1989). Longevity continued to increase during development until a maximum was reached 18–20 d (1988) to 27 d (1989) after physiological maturity (at moisture contents on the mother plant of 18–19% and 14–15%, respectively). In both years, the longevity of these seeds was greater (P<0.005) than that of seeds harvested either subsequently or earlier at physiological maturity. The results contradict the hypothesis that maximum seed quality coincides with physiological maturity and thereafter declines. Rather, maximum seed quality was attained close to when barley seed crops can be combine harvested The subsequent decline in potential longevity on the maternal plant in the field was quantitatively similar to that expected during post-harvest storage.

The development of seed quality in spring barley in four environments. II. Field emergence and seedling size

AbstractThe field emergence ability of a total of 88 seed lots of spring barley (Hordeum vulgare L.) harvested serially during development in 2 years was compared, as was the size of the resultant seedlings. For seedsproduced in each year, field emergence and the mean dry weight of emerged seedlings were significantly greater for seed lots harvested some timeafter physiological maturity (end of the seed-filling period) than for those harvested at or before this developmental stage. This is compatiblewith results for the potential longevity of these lots. It is concluded that barley seed quality continues to increase after physiological maturity, and that the developing seeds attain maximum quality (however this is assessed) close to when the seed crop can be combine harvested. Positive correlations were detected between seedling emergence and seed dry weight (P<0.05) and between the mean dry weight of emerged seedlings and seed dry weight (P<0.005) among seed lots harvested close to when maximum quality was attained in four seed production environments.

Developmental Periods in Soybean: Photoperiod‐Sensitive ✕ Insensitive Crosses Evaluated at Diverse Latitudes

Selection for long duration of seed‐filling period (SFP) in segregating soybean [Glycine max (L.) Merr.J populations may be a way to increase seed yield. Tbe objective of tbe study was to assess the relative effectiveness of selecting for SFP from tropical environments to develop lines for temperate locations in crosses of photoperiod insensitive ✕ sensitive genotypes. A second objective was to determine if selection for longer SFP is possible without delaying date of physiological maturity (R7). Three populations were developed by crossing a photoperiod‐insensitive genotype of Maturity Group (MG) HI to photoperiod‐sensitive genotypes of MG I, II, And III. Random F4‐derived lines were evaluated at Ames, IA, at Isabela, PR (under both natural and lighted environments), and at Hualien, Taiwan, for days from emergence to beginning flowering (Rl), rapid seed‐filling (R5), R7, SFP, and reproductive period (RP). Significant (P < 0.05) differences among lines, environments, and environment ✕ genotype were observed. Phenotypic and rank correlations of Stages Rl, R5, and R7 between environments ranged from 0.22 to 0.83. The range in correlation coefficients for SFP and RP was from 0.06 to 0.62. It is possible to select lines for duration of SFP at PR environments in plantings under natural daylength or under lights. Selections in PR included genotypes ranked in the top 33% at the IA location, and generally included at least one of the five topranked lines. Lines may also be selected with a desired combination of duration of SFP and number of days to reach Stage R7.

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilates to filling seeds of soybean (Glycine max L. Merr.), resulting in higher seed growth rates. The plant growth substance ABA has been implicated in the regulation of assimilate transfer within filling soybean seeds. Thus, we hypothesized that an increased concentration of endogenous ABA in seeds may enhance sucrose accumulation and seed growth rate of soybeans exposed to short-day photoperiods. Plants of cv. Hood 75 were grown in a greenhouse under an 8-h short-day photoperiod (SD) until 11 d after anthesis (DAA) of the first flower, when half of the plants were transferred to a night-interruption (NI) treatment (3 h of low-intensity light inserted into the middle of the dark period). Plants remaining in SD throughout seed development had seed growth rates 43 % higher than that of plants shifted to NI (7-6 mg seed1 d1 vs. 5-3 mg seed1 d1). On a tissue-water basis, the concentration of ABA in SD seeds increased rapidly from 7-6 /tmol I1 at 11 DAA to 65-2 /tmol T1 at 18 DAA, but then declined to 6-6 /jmol I1 by 39 DAA. In contrast, the concentration of ABA increased more slowly in NI seeds, reaching only 47-4 /;mol I1 by 18 DAA, peaking at 57-0 fimo I1 on 25 DAA, and declining to 10-2/tmoll1 by 39 DAA. The concentration of sucrose in SD embryos peaked at 73-5 mmol I1 on 25 DAA and remained relatively constant for the remainder of the seed-filling period. In NI, the concentration of sucrose reached only 38-3 mmol I1 by 25 DAA, and peaked at 61-5 /jmol I1 on 32 DAA. Thus in both SD and NI, sucrose accumulated in embryos only after the peak in ABA concentration, suggesting that ABA may have stimulated sucrose movement to the seeds. The earlier accumulation of ABA and sucrose in SD suggests that ABA may have increased assimilate availability during the critical cell-division period, thus regulating cotyledon cell number and subsequent seed growth rate for the remainder of the seed-filling period.

Comparisons of Methods of Estimating the Seed Filling Period in Soybeans*

AbstractAn experiment was conducted at Lexington, K.Y., USA (38° N latitude) utilizing 18 soybean (Glycine max [L.] Merr.) genotypes in three stem termination groups (determinate, indeterminate, and segregating) to compare eight methods of estimating seed filling period in terms of 1) ability to differentiate among genotypes, 2) lack of bias towards any stem termination type, 3) ease of measurement, and 4) consistency across environments. Growth stage estimates R1 to R8, R4 to R7, R5 to R7 and the reproductive period duration (estimate of the time period of the linear increase in harvest index) detected significant differences among the seed tilling periods of the genotypes. Significant stem termination group measurement method interactions were present, but because the indeterminate stem termination group had a shorter seed filling period than the other two groups for most methods, we were unable to evaluate bias towards stem termination type. The growth stage methods required 4x to 10x less time for data collection than the effective tilling period and reproductive period duration methods. Only the R4 to R7 and R5 to R7 growth stage estimates had significant rank correlation coefficients among genotypes across years. From this and previously published evidence we recommend using the R5 to R7 estimate of seed filling period following the separation of genotypes into stem termination classes for the selection of soybean genotypes based on seed filling period duration.

Whole Plant Senescence of Sunflower Following Seedhead Removal

This study was undertaken to further clarify the relationship between seed development and monocarpic senescence of sunflower (Helianthus annuus L.). Field-grown plants with and without seedheads were evaluated for rate and duration of accumulation of dry weight, reduced N, and P by whole shoots, and for partitioning of these constituents within the individual plant parts. Concurrent with seedhead removal, [(15)N]nitrate was applied to the plants in a selected area of the experimental plot. Whole plants (above ground portions) were harvested seven times during the seed-filling period and analyzed for dry weight, reduced N, and P. Although seedhead removal depressed the rates of dry weight, reduced N, and P accumulation by whole shoots, it extended the duration of accumulation of these constituents, relative to headed control plants. As a result, the final whole shoot dry weight and N and P contents at seed maturity were similar for deheaded and headed plants. Seedhead removal also affected the partitioning of dry matter, reduced N, and P but the relative proportions varied as a function of constituent and growth stage. Analysis of (15)N present in whole shoots at physiological maturity showed that similar amounts of nitrate were absorbed during the postflowering period by headed and deheaded plants. These data indicate that the absence of seeds does not affect the total accumulation of dry matter, reduced N, or P, by sunflower plants, but does alter the rates of accumulation and partitioning of these constituents.

Nitrogen accumulation and partitioning by three grain legumes in response to soil water deficits

Few experiments have been conducted to compare the partitioning and accumulation of nitrogen (N) in plant components of grain legumes grown under different soil water regimes. The objective of this study was to determine the effect of soil water deficit on N accumulation and partitioning in soybean ( Glycine max L. Merr.), pigeon pea ( Cajanus cajan L.), and peanut ( Arachis hypogaea L.). In 1984, the three legumes were subjected in a field environment to either well-watered or water-stressed treatments. Nitrogen concentration, total N accumulation, and N partitioning were determined throughout the growing season by measuring N content and concentration in leaves, stems, pod walls, and seeds. Peanut accumulated more total N than either soybean or pigeon pea under both the well-watered and water-stressed treatments. Water stress decreased both N concentration and total N accumulation, especially in soybean and pigeon pea. Less remobilization of N occurred in soybean leaves and stems during the seed-filling period in the stressed treatment because the water stress limited pod addition and subsequent seed demand for N. Loss of N from leaves during seed growth was greater in the crop with the most senescent growth habit (soybean), and lowest in the non-senescent but determinate crop (pigeon pea). Although peanut does not exhibit rapid leaf senescence during seed maturation as does soybean, considerable loss in leaf N was also observed in peanut leaves during the seed-filling period. Soy-bean, peanut, and pigeon pea differed in accumulation and partitioning of N under water-stressed and non-stressed environments. The partitioning and remobilization of N was dependent on the growth habit of the species and was significantly influenced by soil water deficits.

Variation among Soybean Breeding Lines in Relation to Yield and Seed‐Fill Duration

AbstractThere are exceptions to the positive relationship between seedfilling period (SFP) and seed yield in soybean [Glycine max (L.) Merr.]. Studying genotypes that do not show a positive relationship between SFP and yield may aid in identifying factors that influence seed yield or SFP, or both. The objective of this research was to analyze groups of soybean genotypes that differed in their SFP‐yield relationship, and determine which factors affected seed yield. Eight experimental lines were selected from a ‘Williams’ ✕ ‘Kanrich’ cross to represent the four SFP‐yield combinations of long or short SFP and high or low yield. Replicated field plots were grown in 1984 and 1985 at Urbana, IL, on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll). Data taken in each year included: SFP, seed yield, harvest indices for dry matter and N, total flowers, total pods at three stages (5 mm long, pod containing a seed 3 mm long, and mature pod), and total N and dry matter at the beginning and end of SFP. Early flowering was related to SFP, but not to yield. Rate as well as duration of seed fill can influence seed yield. Total N in the plant at the end of SFP was related to yield, but not to SFP. Total N and dry matter assimilated during SFP, harvest indices for N and dry matter, and final seed yield were all related.

Response to Selection for Time of Flowering in Soybean

Previous research demonstrated that the duration of the seedfilling period (SFP) in soybean [Glycine max (L.) Merr.) could be genetically modified. Long SFP was associated with early flowering. The objectives of this research were to evaluate the effectiveness of divergent selection for time of flowering while maintaining similar dates of maturity and to determine the influence of such selection on other agronomic characteristics. Genetic male sterility was used to intermate populations selected for time of flowering from a single cross. Pedigree selection was practiced to identify lines with similar maturity and extremes in flowering date. Data from 22 lines were collected on the center two rows of four‐row plots and included dates of R1, R5, R7, and R8, lodging, plant height, and seed yield. In each of 2 yr, the experiment was replicated twice at each of two locations. Selected lines flowered significantly earlier or later than the commercial cultivars in the experiment. Lines with similar time to maturity differed by as much as 24 d in time to flowering. The time from R1 to R5 was a nearly constant proportion of the time from Rl to R7. Because of this relationship changes in duration of SFP were much smaller than changes in time to flowering. The mean SFP (RS–R7) for the six earliest‐flowering lines was 5 d greater than the mean SFP for the six latest‐flowering lines. One line significantly exceeded the SFP and seed yield of ‘Williams’, the higher yielding parent.

Post-flowering photoperiodic effect on reproductive efficiency and seed growth in soybean

Photoperiod not only controls soybean ( Glycine max (L.) Merr.) flower induction, but also affects later stages of reproductive growth. Its effect on different yield-determining processes, however, is not well understood. The objective of this work was to determine the post-flowering photoperiodic effect on yield components, reproductive efficiency, and assimilate partitioning to developing seeds in the soybean cultivar Hood 75. Plants were induced to flower in short days. After flowering, three photoperiodic treatments were applied: (1) short days ( SD); (2) short days with interrupted night ( NI); and (3) a sequential combination of both ( NI-SD). Flower differentation, pod lenthening, and seed-filling periods were shortest in SD, intermediate in NI-SD, and longest in NI. The number of differentiated flowers, pods, and seeds were doubled by NI as compared to SD, but the percentages of setting and retained pods were not changed. The percentage of seeds that completed development was, however, increased by SD. More assimilates were partitioned into the seeds in SD, while NI increased the proportion partitioned into shoots. The nitrogen content of seeds was similar in NI and SD, while NI-SD seeds showed a slight increment in their N content. The N content of carpels, however, was high in NI, medium in NI-SD, and low in SD. Compared to NI, duration of the seed-filling period was decreased but the seed-growth rate and final seed size were increased by SD. Final yield was similar for plants in NI or SD, because seed number and seed growth rate compensated each other. Plants in NI-SD has a significantly higher yield, however, as a result of sequential increase in seed number caused by NI, followed by an increase in the rate of seed-filling caused by SD. The results support the existence of two sequential photoperiodic effects on soybean reproductive development: (1), the number of growing seeds is enhanced by NI and decreased by SD; and (2), the assimilate partitioning to seeds is enhanced by SD and decreased by NI. A non-destructive method for seed growth-rate calculation is also described.

Sink Removal and Leaf Senescence in Soybean

Three cultivars of soybean (Glycine max [L.] Merr. cvs Harper, McCall, and Maple Amber) were grown in the field and kept continuously deflowered throughout the normal seedfill period. For all cultivars, deflowering led to delayed leaf abscission and a slower rate of chlorophyll loss. Compared to control plants, photosynthesis and ribulose 1,5-bis-phosphate carboxylase/oxygenase (Rubisco) level declined slightly faster for deflowered Harper, but for both McCall and Maple Amber, leaves of deflowered plants maintained approximately 20% of maximum photosynthesis and Rubisco level 1 month after control plants had senesced. Deflowering led to decreased leaf N remobilization and increased starch accumulation for all cultivars, but cultivars differed in that for McCall and Maple Amber, N and starch concentrations slowly but steadily declined over time whereas for Harper, N and starch concentrations remained essentially constant over time. SDS-PAGE of leaf proteins indicated that for all cultivars, deflowering led to accumulation of four polypeptides (80, 54, 29, and 27 kilodaltons). Western analysis using antisera prepared against the 29 and 27 kilodalton polypeptides verified that these polypeptides were the glycoproteins previously reported to accumulate in vacuoles of paraveinal mesophyll cells of depodded soybean plants. The results indicated that depending on the cultivar, sink removal can lead to either slightly faster or markedly slower loss of photosynthesis and Rubisco. This difference, however, was not associated with the ability to synthesize leaf storage proteins. For any particular cultivar, declines in chlorophyll, photosynthesis, and Rubisco were initiated at approximately the same time for control and deflowered plants. Thus, even though cultivars differed in rate of decay of photosynthetic rate and Rubisco level in response to sink removal, the initiation of leaf senescence was not influenced by presence or absence of developing fruits.

The relationship between seed-filling period and seed yield in selected soybean germplasm accessions

The objective of this research was to determine if selection among unadapted germplasm accessions for duration of seed fill would identify differences in seed yield. Fourteen accessions in each of maturity groups II and III were tested with seven selected for short and seven for long duration of seed fill. The experiment was conducted over two years with three replications per year. Time of flowering and maturity, an estimate of seed-filling period (SFP), and seed yield were noted for each plot. Seed yield was significantly different between SFP categories for both maturity groups with the long SFP category having higher seed yields. Early flowering was associated with long SFP's but also with long delays between flowering and the beginning of seed fill.

Relationship between Seed‐Filling Period and Yield among Soybean Breeding Lines1

It has been suggested that seed‐filling period (SFP) and seed yield are positively related in soybeans [Glycine max (L.) Merr.]. The purpose of this study was to evaluate the relationship between seed yield and SFP among F5 lines. Estimates of SFP were also made in the F4 and F5 generations, and a reproductive period estimate was also made in the F2. All genotypes came from the cross ‘Williams’ ✕ ‘Kanrich’ and were selected for differences in SFP. Replicated yield and SFP data were taken in 1982 and 1983; soil types for those years were a Drummer silty clay loam (Typic Haplaquall) and a Catlin silt loam (Typic Argiudoll), respectively. Data taken in the F2 and F4 were on single plants and those taken in the F5 were on unreplicated rows. The relationship between reproductive period in the F2 and combined 1982 and 1983 yield data was nonexistent (r = 0.00), while that between SFP in the F4 and F5 and the combined 1982 and 1983 yield data was significantly positive. Within 1982 and 1983, in three maturity groups, a positive relationship between yield and four estimates of SFP was found in most cases, the exception being Maturity Group II lines in 1983. In addition, the three highest yielding lines, over years and maturity groups, all came from F4 plants selected as having a long SFP in the F4 generation. These data suggest a positive relationship between SFP and yield and that progress for yield may be made by selecting for SFP.

Selection for Seed‐Filling Period in Soybean1

The duration of seed fill may be a physiological indicator of soybean [Glycine max (L.) Merr.) genotypes possessing high yield capabilities. In order for it to be of use in yield improvement programs, it must be highly heritable and be highly correlated with yield. The objective of this research was to determine if early‐generation classifications for seed‐filling period (SFP) can be maintained in later generations. Divergent selection for reproductive period was conducted on F2 single plants created by crossing ‘Williams’ ✕ ‘Kanrich’. Divergent selection for SFP was carried out in the F4 on single plants and in the F5 on unreplicated plant rows. Selected F4‐derived lines were grown at Urbana, IL in the F6 (1982) and F7 (1983) in replicated field plots to be evaluated for SFP classification. Soil classifications for the 1982 and 1983 experiments were a Drummer silty clay loam (Typic Haplaquall) and a Catlin silt loam (Typic Argiudoll), respectively. There was no relationship between reproductive period in the F2 generation and SFP in subsequent generations, but positive associations between SFP classifications in early generations (F4 and F5) and SFP classifications in later generations (F6 and F7) were found. This suggests the possible use of SFP in yield improvement programs for soybeans.

Defining the Seed‐filling Period in Soybeans to Predict Yield1

The duration of seed fill has been shown to be related to seed yield in soybean [Glycine max (L.) Merr.]. However, several different growth stages have been used to delimit the seed‐filling period (SFP). This study was conducted to determine which growth stages delimit the SFP most highly correlated with yield. Twenty‐eight indeterminate accessions, 14 from each of Maturity Groups II and III, were selected from the USDA Soybean Germplasm Collection. These lines were selected for differences in length of SFP and similarities in other agronomic traits. Field experiments were grown in a Flanagan silt loam (Aquicarguidoll) and a Catlin silt loam (Typic Argiudoll) in 1980 and 1981, respectively. Data collected included the date of all reproductive (R) stages and seed yield. Genotypic and phenotypic correlation coefficients were determined for various reproductive or seedfilling periods and seed yield.Phenotypic correlation coefficients demonstrated a positive relationship between the duration of seed fill and seed yield but could not define the most appropriate seed‐filling period to predict yield. The genotypic correlations between various SFPs and seed yield provide evidence that supports the use of R4 or R5 as estimates of the beginning of seed fill and R7 as the termination. These data suggest that the currently defined R‐stages of soybean reproductive growth can provide reasonable estimates of the duration of seed fill and the seed‐filling periods so defined had a high correlation with seed yield among the lines in this experiment.

Reproductive Duration and Date of Maturity in Populations of Three Wide Soybean Crosses1

Greater seed yield may be related to a longer reproduction period (RP) in soybean [Glycine max (L.) Merr.]. Unique combinations of genes controlling photoperiod sensitivity may allow selection for longer RP without delaying date of physiological maturity (R7). Three single‐cross populations of F2‐derived soybean lines were made from a diallel crossing of two photoperiod‐insensitive determinate plant introductions, PI317.334B and PI317.336, and an indeterminate cv. Harosoy 63 in an attempt to develop populations in which the correlations of date of R7 with length of the seed‐filling period (SFP) and RP are small. Genetic variability and response to selection of these traits were also studied. Time from beginning of flowering (R1) to beginning of rapid seed filling (RS) of determinate lines averaged 12.6 days and 7.3 days shorter than those of indeterminate lines in two crosses, while SFP, days from R5 to R7, averaged 11.2 and 6.7 days longer for determinate lines than for indeterminate lines. These results are likely due to the difference in estimating stage R5 (seeds 3 mm long in one of the top four plant nodes) between determinate and indeterminate lines rather than biological differences in SFP between determinates and indeterminates. Associations of SFP and RP with R7 in crosses of Harosoy 63 with either plant introduction were weaker than those previously reported for US‐adapted germplasm. Estimates of realized heritabilities of RP ranged from 0.63 to 1.17, even when RP was adjusted for differences in R7. Realized heritability estimates of SFP ranged from 0.40 to 1.02, except for indeterminates where considerably less genetic variance was observed. Reproduction period and SFP of selected F4 populations were lengthened by F3 selection up to 6.4 and 6.1 days, respectively, relative to population means, without significantly changing R7. These results suggest that selections from two of the three crosses should be useful for incorporation of longer SFP and RP into adapted germplasm to enhance yield potential without delaying date of R7.

Effect of Moisture Stress on Seed Growth in Soybeans1

AbstractThe growth of an individual soybean [Glycine max (L.) Merr.] seed is an important part of the yield production process. An understanding of the effect of environmental factors on the growth of individual seeds is needed to enhance our understanding of the effect of the environment on yield. Soybeans were grown in the field on a Maury silt loam soil (fine, mixed, mesic Typic Paleudalfs) for 3 years (1979 to 1981) and subjected to varying levels of moisture stress to investigate the effect of moisture stress on seed growth. Irrigated controls were compared with moisture stress treatments from planting to beginning seed fill (growth stage RS), during seed filling (growth stage R5 to R7) or from planting to maturity (severe stress). Fruits were tagged at beginning seed fill and sampled at weekly intervals to estimate the seed growth rate and the effective filling period (EFP). Although the stress treatments reduced yield and vegetative growth, the rate of seed growth (mg seed−1 day−1) was not affected. The seed‐filling period (estimated as days from growth stage R5 to R7 or EFP) was shortened by the severe stress treatment in 1979 and 1981 (statistically significant only in 1979), and there was a trend for the period of R5 to R7 to be shortened by late stress in 1980 and 1981. The data suggest that the rate of individual seed growth is less sensitive to moisture stress than other plant processes. The seed filling period was more sensitive to moisture stress than seed growth rate and the effect of moisture stress on the duration of seed fill may be one way that stress reduces soybean yield.

Use of principal factor analysis in the study of three stem termination types of soybean

The study was conducted to identify plant characters associated with seed yield in close soybean plant spacings. Lines selected from two F6 soybean populations in the F10 generation segragating for degree of stem termination were grown in two locations. Traits measured included lengths of developmental stage. plant and canopy height, number of nodes, lodging at different stages, raceme lengths, and number of nodes and branch number of nodes. One problem in analyzing data and drawing conclusions from such a study is related to the complex nature of the interrelationships of a large number of traits. Another, not unrelated problem, involves the calculation of multiple-regression equations with multicolinearities. Because of these problems, factor analysis was used to study the correlation matrix to identify sets of variables related to the same biological concept or function. The variables within sets were determined for each stem termination type, and measurements of these variables were standardized. Means were calculated by using the sum of the standardized variables for each set. Multiple regression was used to study the relationships between sets as the independent variables and yield as the dependent variable. Individual traits were selected from within each set and substituted in the multiple regression equations calculated with the mean value for each set. With use of this technique to determine multiple regression equations, the resulting equations involved measurements of different biological functions instead of repeated measurements of the same function in the plant. It was found that, in the determinate stem type, the measurement of the seed-filling period and branch number of nodes could possibly be used to predict yield while, in the semideterminate stem type, the measurement of the ‘fixed capital’ function and terminal raceme length were possibly useful. Finally, in the indeterminate stem type, the measurement of the ‘fixed capital’ could be used, but it had a very low predictive value.

Effect of soil and foliar application of nitrogen during pod development on the yield of soybean (glycine max (L.) Merr.) plants

Abstract The peak of the nitrogen (N) requirement curve for soybean cv. Clark when grown in sand culture was at the seed-filling period. Mineral N uptake and N2 fixation did not meet the N demand of the developing seeds during the period of pod-fill and N was translocated to the seeds from both leaves and roots. In sandy loam soil cultures, Clark soybean plants were either soil-fertilized with 35, 70 or 105 kg N ha−1 or foliar-sprayed with 0.5 or 1.0% urea at the R6 stage of plants development. Application of N at pod-filling stage either to the soil or to the foliage increased fruit-set, weight of pods, and the yield of oil and protein in seed. The most effective treatment was a foliar application of 1.0% urea.