Soybean Crosses Research Articles

Variation in Seed Protein among Nodes of Determinate and Indeterminate Soybean Near‐Isolines

Soybean, Glycinc max (L.) Merr., seed protein differs considerably among seeds from different nodes of indeterminate plants. Determinate soybean plants grown in the northern USA have fewer nodes, shorter flowering periods, but similar reproductive periods compared to indeterminate plants. The objective of this study was to determine nodal variability in seed protein of determinate vs. indeterminate soybean near‐isolines. Ten pairs of near‐isolines from four soybean crosses were included in a 2‐yr study at West Lafayette, IN. Protein content was evaluated for seeds from individual fruiting nodes on three plants from the ten determinate and indeterminate near‐isolines each year. Seed protein increased linearly from 397 at Node 5 to 442 g kg−1 seed weight at Node 11 on determinate plants. On indeterminate plants, seed protein increased from 398 at Node 6 to 441 g kg−1 at Node 14. Protein contents of seeds from Nodes 12 through 16 of indeterminate plants were all high but values did not differ significantly among these upper nodes. The greatest range in protein among all nodes from three plants of an individual line was from 349 to 510 g kg−1 for indeterminate and from 34 to 487 g kg−1 for determinate plants. The data demonstrate that accurate protein determinations for determinate, as well as indeterminate soybean plants, requires adequate sampling to represent the nodal variability occurring in both plant types.

Direct and Indirect Selection for Small Seed of Soybean in Temperate and Tropical Environments

Some food items made from soybean [Glycine max (L.) Merr.] require small seeds. The wild soybean, G. soja Sieb. & Zucc., has been used as a source of genes for small seed size for development of high‐yielding cultivars for specialty markets. The objective of this study was to determine the effectiveness of direct and indirect selection for small seed in three interspecific crosses of soybean (G. max ✕ G. soja) based on seed weight and pod width measurements. Indirect selection was based on pod width. Forty random BC2F2‐derived lines from each of three crosses were evaluated for seed weight and pod width at two environments in Iowa and two environments in Puerto Rico. Broad‐sense heritability estimates among the three crosses based on variance component estimates for seed weight were 35% on a plant, 52% on a plot, and 89% on an entry‐mean basis, and for pod width were 35% on a plant, 51% on a plot, and 87% on an entry‐mean basis. The actual genetic gain averaged across environments and crosses for direct selection of seed weight was 6 mg seed−1 on a plant, 6 mg seed−1 on a plot, and 7 mg seed−1 on an entry‐mean basis. Indirect selection by pod width resulted in an actual genetic gain of 6 mg seed−1 on a plant, 7 mg seed−1 on a plot, and 8 mg seed−1 on an entry‐mean basis. Selection in Puerto Rico was as effective as selection in Iowa. The results indicate that both direct and indirect selection for small seed are effective in the temperate and tropical environments that were studied.

Backcross‐Derived Progeny from Soybean and Glycine tomentella Hayata Intersubgeneric Hybrids

Wild perennial species of the subgenus Glycine Willd, have not been exploited in soybean [Glycine max (L.) Merr.] breeding programs. This paper discusses wide hybridization in the genus Glycine and reports on the origin, identification, and breeding behavior of a synthesized amphiploid soybean ✕ G. tomentella Hayata hybrid and its backcross‐derived progeny. Amphiploid H213‐2a (2n = 118) plants showed almost normal meiotic pairing (0.711 + 57.9811 + 0.33IV), but later meiotic stages were abnormal, showing laggards and bridges, and the plants set only a few pods. The F2, F3, and F4 plants carried the expected 2n = 118 chromosomes, and thus were cytologically stable. A growth‐hormone solution containing 100 mg gibberellic acid (GA3), 25 mg naphthalene acetic acid (NAA) and 5 mg kinetin/L distilled water was sprayed onto the pollinated gynoecia to enhance pod retention (14.19%) in H213‐2a ✕ soybean crosses. Without daily hormone spray, only three pods of the 3417 florets pollinated were harvested 19 to 21 d after pollination. The BC1 plants were obtained in two cross combinations: (i) H213‐2a ✕ ‘Clark 63’ = H562, and (ii) H213‐2a ✕ ‘Essex’ = H564. The H562 plants contained 2n = 76, (BC1; expected 2n = 79), suggesting the loss of three chromosomes. The H564 plants contained 2n = 98 chromosomes and may have originated by the union of a female gamete (n = 59) and an unreduced male (n = 40) spore. All the BC1 plants were totally sterile, and attempts are being made to generate BC2 plants.

Canopy Photosynthesis and its Association with Seed Yield in Advanced Generations of a Soybean Cross

Canopy‐apparent photosynthesis (CAP) of soybean, Glycine max (L.) Merr., plants during reproductive development differs among genotypes, is a heritable trait, and is positively associated with seed yield. These responses collectively imply a potential for yield improvement through selection for enhanced CAP. This research was undertaken to: (i) determine if the CAP response patterns of F4 lines remain relatively stable in F6 lines, (ii) determine the association CAP to yield and growth characteristics in F6 lines, and (iii) identify F6 lines with similar maturity and divergent CAP. The experiments were conducted over a 2‐yr period at Athens, GA under field conditions. A l‐min measurement of CAP was made near mid‐day in all plots for three times during reproductive development by use of a closed system and ambient conditions. Other measurements included plant height, stages of plant development, seed wt., length of seed‐fill period, and seed yield. The upper 50% of the F4 lines averaged 11% higher in CAP than the lower 50%. The F6 lines derived from the high CAP F4 lines were 6% (0.9 μmol CO2 m−2 s−1) higher in CAP than F6 lines from the low F4 lines. There was an association between CAP of F4 lines and the mean of the F6 lines derived from them (r = 0.64; P < 0.I). A positive association was found between CAP and seed yield (r = 0.28 to 0.66). Pairs of F6 lines with divergent CAP rates but similar maturity were identified. Results support previous findings that CAP during reproductive development is positively associated with seed yield in determinate soybean genotypes.

Heterosis of interspecific soybean hybrids for traits related to N2 fixation

Three greenhouse experiments were conducted to compare the performance of soybean (Glycine max (L.) Merr.), wild soybean (G. soja Sieb. et Zucc.), and soybean x wild soybean hybrids for traits relating to N2 fixation including nodulation, acetylene reduction, nodule leghemoglobin concentration, and nitrogen (N) accumulation and dry matter (DM) accumulation. In all three experiments G. max generally exceeded G. soja in nodulation, acetylene reduction, and N and DM accumulation while the soybean possessed higher nodule leghemoglobin concentration. In Experiment I, the mean of the hybrids did not differ significantly from the G. max parent in nodule mass, acetylene reduction activity, nodule leghemoglobin concentration, or DM accumulation. The hybrids did exceed the soybean parent in N accumulation, thus demonstrating high parent heterosis. In Experiments IIA and IIB with a more carefully chosen set of G. soja parents, high parent heterosis of individual crosses was common. Across the three experiments average high parent heterosis was 34, 28, and 28%, respectively, for nodule mass, N accumulation, and DM accumulation. If one accepts the assumption that hybrid vigor results from the accumulation of dominant alleles, then these alleles could theoretically be accumulated via selection in a homozygous genotype. If this is true than the results of the experiments reported here suggest that interspecific soybean x wild soybean crosses could serve as sources of homozygous lines which would exceed currently available soybean cultivars in nodule mass, and N and DM accumulation.

Heritability of Tolerance to Soybean Cyst Nematode in Soybean

Tolerance to Heterodera glycines Ichinohe, soybean cyst nematode (SCN), has recently been identified as an additional control strategy to limit yield losses in soybean, Glycine max (L.) Merr. Heritability estimates are necessary for determining breeding strategies to increase tolerance to SCN. The objectives of this study were to determine the heritability of tolerance in three soybean crosses and determine the degree of association between tolerance and seed yield in untreated and nematicide‐treated plots. A tolerance index (TI) was calculated using the formula: (seed yield of untreated subplot ÷ seed yield of nematicide‐treated subplot) ✕ 100. Fifty‐four F2‐derived lines in the F4 and F5 generations and parents were evaluated for TI in SCN‐infested soil for 2 yr at two locations. The Athens, GA location was infested with SCN Race 3 and Waynesboro, GA with SCN Race 4. Heritability for TI averaged 19% based on variance component estimates (three replications and two locations) and 26% for realized estimates (selection of top 11% of lines based on two‐location means). There was a positive association between TI and seed yield in untreated subplots (r = 0.78 to 0.90), but there was an inconsistent association between TI and seed yield in nematicide‐treated subplots. The variance component estimates of heritability for seed yield in untreated subplots averaged 31% (three replications and two locations). These results indicated that susceptible genotypes can be evaluated for seed yield without nematicides in SCN‐infested soil in the early phases of a breeding program to increase tolerance.

Inheritance of seed protein and seed oil content in early maturing soybean

The inheritance of seed protein, seed oil, and the sum of protein and oil was investigated in two early maturing soybean crosses, 'Maple Presto' × 'Sioux' and 'Maple Presto' × X446-2-1, in 2 years (1981 and 1982) at one location (Winnipeg). Analyses of variance of the parental performance over years indicated that the parents differed significantly for all three traits studied and that genotype by year interactions were effectively zero. Generation means analysis indicated that gene action for seed protein was primarily additive, with partial dominance for low protein. Seed oil was also conditioned primarily by additive gene action. Partial dominance was not consistently detected over years and therefore was of minor importance. Additive × additive epistatic effects for seed oil were also detected but were not consistent over years. The sum of seed protein and oil was conditioned solely by additive gene action. Variance analyses indicated a predominance of additive genetic variance for all three traits. Dominance variance was also detected for both seed protein and the sum of protein and oil. Broad sense heritability for the F2 generation ranged from 76 to 83% for seed protein and from 68 to 86% for the sum of protein and oil, while narrow sense heritability ranged from 34 to 72% for seed protein and from 39 to 65% for the sum of protein and oil. Narrow sense heritability values equalled broad sense values for seed oil and ranged from 58 to 68%. Heritability was also estimated from standard unit parent – progeny regression analyses and values for all three traits were found to approach the variance analyses estimated broad sense heritabilities. Comparisons with the results of late maturing soybean crosses are made and implications of the results obtained in this study on early maturing soybean breeding programs are discussed.Key words: Glycine max, heritability, 00 and 000 maturity groups, breeding strategies.

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.

Variability Within and Among F1 Families from Diverse Three‐Parent Soybean Crosses1

In three‐parent crosses, gametes produced by the F1 of the two‐parent cross differ genetically. Therefore, variability will exist among families derived from different F1s of the three‐parent crosses. The objective of this study was to determine the relative variability for agronomic characteristics among and within different F1 families from crosses involving plant introductions and cultivars. Four lines within each of 20 F1 families from each of two three‐parent soybean [Glycine max( L) Merr.] crosses ([cultivars ✕ plant introductions] ✕ cultivars) were evaluated for 2 years at West Lafayette, IN. Differences among F1 family means were significant for seed yield, date of maturity, lodging, and plant height. Variability among lines within families was at least 1.4 times as great as variability among families for all characteristics except maturity in one cross. In both crosses the highest yielding 10% of the lines were from different F1 families than the lowest yielding 10% of the lines. In one cross, lines witht he earliest maturity, shortest plant height, and lowest lodging scores all came from different F1 families than lines with late maturity, tall plants, and high lodgings cores. In the second cross one family contained lines in both the highest and lowest 10% of the population for maturity and lodging scores. Two families contained lines in both the highest and lowest 10% of the population for plant height. The data suggest there maybe merit in maintaining the identity of lines from individual F1s in diverse three‐parent crosses. Selection for individual lines could then be concentrated in those families with high mean performance for specific characteristics.

Heritability of Tolerance to Phytophthora Rot in Soybean1

Heritability estimates would be useful in determining breeding strategies for tolerance to phytophthora rot caused by Phytophthora megasperma Drechs. f. sp. glycinea Kuan and Erwin in soybean [Glycine max (L.) Merr.]. The objectives of our study were to determine the heritability of tolerance to phytophthora rot in three soybean crosses and to determine what effect majorgene, race‐specific resistance has on tolerance. Parents and F3‐derived lines from three soybean crosses were evaluated for tolerance to phytophthora rot using the greenhouse, mycelium‐inoculum‐layer method. Also, each F3‐derived line was tested for race‐specific resistance. Herltability estimates for tolerance were determined for susceptible lines, resistant lines, and combined lines for each cross using the components of variance method. Heritability estimates ranged from 79 to 87% on an entry‐mean basis and from 49 to 63% on a plot basis. Herltability estimates were not affected by major‐gene resistance. However, lines carrying major‐gene resistance had a higher mean tolerance rating than lines which did not carry genes for race‐specific resistance. This suggested that major‐gene resistance and tolerance were not completely independent. The high heritability estimates indicated that considerable genetic gain should be expected from selection for tolerance in crosses where genetic variability is present.

Inheritance of reaction to two viruses in the soybean cross ‘York’ × ‘Lee 68’

Inheritance of reaction to two viruses in the soybean cross ‘York’ × ‘Lee 68’

Estimates of selection parameters associated with protein and oil content of soybean seeds (Glycine max (L.) Merr.)

Three crosses of soybean involving United States and other germplasm were examined in the F3 and F4 generations at two locations, one near the coast, the other on the Darling Downs. Line and line x location interaction variances within crosses for most traits were almost all significant, except for protein, oil, and protein plus oil yield where line variances were non-significant when data were combined over locations. Line variances were considerably smaller for all traits when estimated across, rather than within, locations. For protein, oil, and protein plus oil percentage, the line x location interaction variance component generally was smaller than the line variance component in two crosses, but larger in a third even though the latter cross had the largest line variance for these traits. The line x location interactions may have been related in some cases to lower protein and oil percentages of late-maturing lines in that location where cold conditions prevailed late in the season. Heritability percentages computed from F4 variance components ranged from 49 to 89% and were largest for the chemical pexentage traits within locations. Standard unit heritability percentages estimated from F3–F4 generations were lower than those computed via the variance component method, and approached zero for oil percentage, protein plus oil percentage, and the chemical yield traits in some crosses if the generations were grown in different locations. Genotypic correlations between protein percentage and seed yield ranged from –0.50 to 0.16 across crosses and were opposite in sign to those between oil percentage and seed yield. Genotypic and phenotypic correlations between protein and oil percentage were highly negative in two crosses (–0.62 to –0.96) but much less negative in the third cross (–0.24 to –0.35). Predicted genetic advance (percentage of population mean) ranged from 5.9 to 26.1% for the chemical yield traits and from 1.5 to 6.3% for protein or oil percentage. Indirect selection for chemical yield through seed yield was 90–109% as efficient as direct selection, and a selection index that combined seed yield and either protein, oil, or protein plus oil percentage generally was no more efficient than direct selection for the corresponding chemical yield trait. Indirect selection for chemical yield through chemical percentage was much less efficient than direct selection for chemical yield.

Effectiveness of Early‐generation Yield Selection of Heterogeneous Lines in Soybeans1

AbstractF2−derived, heterogenous soybean [Glycine max (L.) Merr.] lines (HL) were selected for high seed yield by the early‐generation yield‐testing procedure (EGT), based on F3, F3−F4, and F3−F4−F5 combined generation means in four soybean crosses. Pure lines (PL) were selected for high seed yield from these same four crosses by the pedigree selection (PS) and single‐seed‐descent (SSD) procedures.Selection of superior‐yielding HL in the F3, F4, and F5 generations decreased the coefficient of genetic variability in each generation of selection. The yield performance of the selected HL in the 1970 uniform preliminary test II also suggested that the HL were uniform among lines in yielding ability and the HL from one cross were equal in yield to the reference varieties.The results indicated that in one of the four crosses PL selected by the SSD procedure were significantly higher in yield and earlier in maturity than the HL. In the other crosses, no significant yield differences existed between PL and HL, although the PL were usually earlier in maturity than the HL. These results suggested that pure lines from a cross will be equal to or higher in yield than F2−derived heterogeneous lines.

Exotic Germplasm for Yield Improvement in 2‐way and 3‐way Soybean Crosses1

We evaluated homozygous populations froin 2‐way adapted × exotic and 3‐way (adapted × exotic) × adapted soybean (Glycine max (L.) Merrill) crosses for seed yield. The average yield of our 3‐way populations was significantly greater than the 2‐way population mean, but differences were not significant in some 2‐, 3‐way sets. Mean population performance was generally predictable from parental performance, although a masking inhence of genes from the third parent was observed in the 3‐way crosses.Estimates oC genetic variance for 3‐way populations generally were larger than for 2‐way populations for yield. Transgressive segregation was observed in all populations, but in most 2‐, 3‐way sets, the 3‐way cross produced more of the superior lines for yield than the 2‐way cross.

Incorporation of High‐Protein, Exotic Germplasm into Soybean Populations by 2‐ and 3‐way Crosses1

Exotic high‐protein parents were studied as sources of variability for protein, oil, and protein + oil in soybean (Glycine max (L.) Merrill) populations derived from 2‐ and 3‐way crosses. Random lines from homozygous 2‐way adapted × exotic and 3‐way (adapted × exotic) × adapted soybean crosses were evaluated. Significant genetic variability was detected for the three characters in each population. The high protein content of the exotic strains was transmitted readily to their offspring; and selection of high‐yielding, high‐protein strains from crosses involving exotic strains was possible.Both 2‐ and 3‐way population means were determined primarily by additive effects, but instances of epistatic effects were noted. The rank of population means was predictable from parental performance.Genetic variance estimates, heritabilities, and correlations between characters were similar for our 2‐ and 3‐ way populations. The 3‐way populations generally had significantly higher mean protein, oil, and protein + oil than the 2‐way populations and were more useful sources for selection of all characters. Selection for protein + oil was successful in increasing the protein level of the population while maintaining the oil content at the level of the unselected population.

Correlated Truncation Selection for Yield in Soybeans1

Random genetically heterogeneous, F2‐derived maternal lines and genetically homogeneous, F5‐derived daughter lines of two soybean crosses were evaluated for nine characters in three environments in the F0‐F7 generations.Heritability was relatively consistent across environments for all traits except seed yield. For yield, heritability was greatest under favorable growth conditions and least when moisture stress was alleviated by irrigation. Variability over environments in correlations of all traits with yield was related largely to the degree of moisture stress in each environment. Crosses revealed similar magnitudes of correlation with yield for all traits except chemical composition. This was related to the chemical composition of parents used in these crosses. Correlations of early lodging with yield in genetically homogeneous lines were generally greater than for genetically heterogeneous lines. This was related to the relative uniformity of the plant canopy in these populations.Because of the inconsistency in character associations, predictions of yield advance from selection in any environment were inaccurate estimates of actual advance evaluated over environments. Selection of yield invariably resulted in maximum actual yield advance. Chemical composition was generally the best yield predictor for heterogeneous lines, while early lodging was the most effective trait for correlated yield selection in genetically homogeneous lines.

Heritability of Pod Dehiscence and Its Association with Some Agronomic Characters in Soybeans1

Individual plant measurements of parental, F1, and F2 populations and F3 progenies of four soybean crosses involving three varieties of the domestic species, (Glycine max (L.) Merr.), and a plant introduction of the wild species, (G. ussuriensis Regel and Maack), were used to determine heritability and associations of pod dehiscence (shattering) and some important agronomic characters in soybeans. Broad sense heritability estimates for pod dehiscence, date of flowering, date of maturity, and days from flowering to maturity generally were high (above 90%) and varied only slightly in the different crosses. Estimates for seed size varied from 40% in the cross between the largest and smallest seed parents to 69% in the cross between parents with the smallest seeds. There also was a tendency for the characters pod dehiscence, date of flowering, date of maturity, days from flowering to maturity, and seed size of individual Fe plants to persist in the F3 generations as indicated by highly significant regression coefficients.Genotypic and phenotypic correlation coefficients indicated that associations between pod dehiscence, and date of flowering, date of maturity, days from flowering to maturity, seed size, and oil and protein content presented no serious limitation to breeding for these characters, especially in crosses where both parents were classified as G. max. There was evidence of an association between pod dehiscence and date of maturity in two populations derived from crosses of the wild and domestic species and between pod dehiscence and seed size in one interspecific cross and in one cross involving only the domestic species.

Inheritance of Pigment Color in the Soybean1

Fourteen soybean crosses, Glycine max (L.) Merr., were used to study the inheritance of pigment color and pattern. Black and brown seed coat and hilum colors were controlled by two gene pairs, Tt and Rr, their expression being modified in certain gene combinations by Oo and W1w1. The distribution or dilution of the pigment color was controlled by the locus (Ktiki). Brown seed coat (TrO) was dominant over reddish brown (Tro) and green seed coat (G) over yellow (g). The I allele for light hilum gave gray hilum with TR and tKW1 genotypes and yellow hilum with Tr, tRw1 and tr genotypes.Difficulty was experienced in classifying plants for saddle pattern, due to the possible interaction of pigment promoting factors. In three crosses the saddle pattern gene ik was dominant over self black seed, whereas in one cross self black seed appeared to be dominant over ik. Saddle patterns were not observed on seed having brown or buff seed coats. These phenomena may be due to pigment‐promoting factors masking the expression of the gene ik.

Inheritance and Association of Plant Height and Its Components in a Soybean Cross 1

Inheritance and association of plant height and its components were studied in a soybean (Giycine max (L.) Merr.) cross, ‘Lee’ ✕ R61-900, at Fayetteville, Arkansas. Effectiveness of selection for plants possessing a large number of nodes on the main stem and short average internode length was evaluated. A single major gene pair appeared to condition node number on the main stem, and this component had a greater effect on plant height at maturity than average internode length. A high degree of phenotypic dominance was evident for node number and plant height. Frequency distributions for average internode length gave no evidence for any type of discrete segregation. Heritability estimates were relatively high for both node number and plant height, but somewhat lower for average internode length. Although there was a close association between node number and plant height, two plants were observed in the F2 generation which possessed a large node number and short average internode length. By intensive selection in progenies from these plants in the F3, and F4 generations, true breeding types were isolated which were less than 90 cm in height and contained more than 20 nodes on the main stem. It appeared that selection had been effective in isolating partially indeterminate types which possessed rather short internodes.

Inheritance of Resistance to Bacterial Blight (Pseudomonas glycinea Coerper) in Soybeans ( Glycine max L. )1

Parents and F3 families of seven soybean crosses were studied for reaction to the bacterial blight organism, Pseudomonas glycinea Coerper. Six of the crosses were tested in both the field and the greenhouse to a single colony isolate of the organism obtained at St. Paul, Minnesota, and four were tested under similar conditions to an isolate from Morris, Minnesota.The two isolates gave distinctly different reactions on the populations studied, indicating the presence of pathogenic races. Also, varietal reactions varied somewhat with the environments used in testing.Resistance to the St. Paul isolate, designated race 1, was attributed to a single dominant gene, possessed by the varieties ‘Norchief,’ ‘Harosoy,’ and P.I. 132,207. The proposed symbol for this gene is Rpg1. The inheritance of resistance to the Morris isolate, race 2, appeared to involve more than one gene. Delineation of detail, however, must await further study.