Cultivars Of Maturity Groups Research Articles

Predictions of soybean harvest index evolution and evapotranspiration using STICS crop model

AbstractIn the last century, soybean [Glycine max (L.) Merr.] genetic improvements have resulted in increased yield partly due to an increase in harvest index (HI). To account for these genetic improvements, an update of the soybean calibration of the STICS soil‐crop model was carried out. The model was calibrated and evaluated for two sets of soybean plant parameters using datasets from the Ottawa region (ON, Canada); a low HI cultivar calibrated using datasets (1993–2008) of cultivars of maturity groups (MGs) 00 and 0 and a high HI cultivar calibrated with more recent datasets (2016–2017) of cultivars of MGs 0 and I. The model succeeded in reproducing the HI increase. Leaf area index (LAI), shoot biomass, and yield were also well predicted for the high HI cultivars with a normalized root mean square error (NRMSE) of 34, 10, and 14%, respectively, which was a great improvement compared to the default parametrization proposed in STICS for soybean. Under rainfed conditions, accurate simulation of evapotranspiration is a critical point to achieve good model performance. A comparison of the two crop evapotranspiration approaches available in STICS was also carried out. It showed that the resistive approach (NRMSE of 36%) was more efficient than the crop coefficient approach (NRMSE of 67%). This good performance of the model in predicting evapotranspiration allowed the model to perform equally well under water stress and non‐water stressed conditions. The model could therefore be used in future studies to simulate the impact of water stress on soybean growth in eastern Canada.

Water Use Efficiencies of Different Maturity Group Soybean Cultivars in the Humid Mississippi Delta

Introducing alternative cultivars with enhanced water use efficiencies can help alleviate pressure on groundwater for crop irrigations in Mississippi (MS) Delta. A two-year field study was conducted in 2019–2020 to compare the water use efficiencies (WUE) of recently released and pre-released soybean {Glycine max (L.) Merr.} cultivars in maturity group (MG) III (‘P37A78’, ‘LG03-4561-14’), IV (‘Dyna-gro 4516x’, ‘DS25-1, DT97-4290’), and V (‘S12-1362’, ‘S14-16306’) in the MS Delta. The experimental design was a split-plot with cultivar as the first factor and the second factor was water variant irrigation (IR) and no irrigation (RF, rainfed), replicated three times. The MG IV cultivar Dyna-gro 4516x recorded the highest grain yield and WUE: grain yields were 4.58 Mg ha−1 and 3.89 Mg ha−1 under IR and RF, respectively in 2019, and 4.74 Mg ha−1 and 4.35 Mg ha−1 in 2020. The WUE were 7.2 and 6.9 kg ha−1 mm−1, respectively, in 2019 under IR and RF, and 13.4 and 16.9 kg ha−1 mm−1 in 2020. The data reveals that ‘Dyna-gro 4516x’ (MG IV), ‘LG03-4561-14’ (MG III), and ‘P37A78’ (MG III) are best adapted to the early soybean production system (ESPS) in MS Delta region for sustainable production for conserving water resources.

Genetic Improvement of US Soybean in Maturity Groups V, VI, and VII

Soybean [Glycine max (L.) Merr.] is an important source of protein and vegetable oil. Genetic improvement of soybean seed yield and composition are ultimate breeding goals. During the past 80 yr, breeders have selected for high yield and other desired traits to make genetic improvements. To quantify the genetic changes to seed yield, yield stability, and other important agronomic and end‐use quality traits, we evaluated 93 soybean cultivars in Maturity Groups (MG) V, VI, and VII that were released from 1928 to 2008. Replicated yield trials specific for each MG set of cultivars were conducted during 2010 to 2011 in a total of 27 southeastern US year‐location environments. A mixed linear model was used to calculate best linear unbiased predictors (BLUPs) for each cultivar for each measured trait within each MG. Regressed cultivar effect BLUPs of each trait by year of cultivar release revealed positive linear trends for annualized genetic yield gains of 17.6, 13.5, and 10.3 kg ha−1 yr−1 for MG V, VI, and VII, respectively. Averaged across MGs, the annualized rate of genetic gain was estimated to be 13.7 kg ha−1 yr−1. Yield stability analyses revealed significant differences in regression coefficients (b), which were >1.0 for newer cultivars but <1.0 for older cultivars. Overall, the average annualized rate of genetic gains for seed yield reported herein are equivalent to those previously reported, indicating that a yield plateau has not been reached for MG V, VI or VII soybean cultivars.

English

The world economic importance of soybean (Glycine max (L).) crop is consolidated, and tests to verify the best sowing season for yield gain of cultivars are demanded. The aim of this study is to analyze the effect of sowing season on soybean cultivars of different maturity groups, since the determination of the optimum time for planting soybeans and the cultivar most suited to the region under study can increase yield components and consequently productivity. The experiment was conducted in Currais, State of Piaui, Brazil, and involved evaluation of 12 treatments resulting from the interaction between: 1) sowing seasons: 11/22/2014; 11/29/2014; 12/6/2014; 12/13/2014; 12/20/2014 and 12/27/2014 and 2) two cultivars of maturity groups 8.2 and 8.6. The experiment was a randomized complete block design with four replications, in subdivided plots, and the nested effect in the plot was sowing dates. Data were analyzed using ANOVA and Tukey’s test (p £ 0.05). Interaction was significant for number of pods, pod length, dry mass of stem, dry mass of pods and number of grains per plant, but not for productivity and one thousand seed mass. In the agricultural year 2015/2016, the climatic factors worked directly on the components of soybean production, and it is possible to adopt any period of November and December for its planting. Key words: Glycine max, climatic elements, yield components, photoperiod.

N and S concentration and stoichiometry in soybean during vegetative growth: Dynamics of indices for diagnosing the S status

Information regarding the pattern of sulphur (S) accumulation in shoots is scarce for field crops and few comprehensive analysis were performed on N:S stoichiometry. Particularly, the need to study the patterns of uptake, allocation and stoichiometry of S and N in soybean is two-fold. First, the main areas for soybean production in the world have been recently reported as S-deficient. Second, S concentration (%S) and N:S ratios are relevant for diagnosing S deficiency.The aim of this work was to analyze, in a gradient of S availability, the dynamics of nitrogen concentration (%N), %S and N:S ratio in soybean lamina, stem and shoots during vegetative growth. Experiments were performed at Balcarce, Argentina during two growing seasons. Two soybean cultivars were evaluated: DM2200 (maturity group II) and DM4970 (maturity group IV), sown in optimum dates for the region (mid-November). DM2200 was also sown late (early January). We sampled crops between biomass≈1Mgha−1 and R5. Shoots were separated in lamina, stem and petiole, and pod.The adjusted S dilution curve for S-sufficient treatments was attenuated in soybean (S=2.8W−0.11), with no differences among cultivars of maturity groups II and IV, and sowing dates from November to January. For the same treatments, the N:S ratio was stable in shoots during vegetative growth (N:S=12.2), supporting the use of a unique threshold for diagnosing the S status during this period. Sulphur concentration in stems was more responsive to the availability of S than%S in lamina. In addition, the concentration of N in stem tended to be constant with variation in %S while %N and %S correlated in lamina. This produced a greater response of N:S in stem than in lamina. Thus, the determination of%S and N:S in stem are good candidates as indicators of S status of soybean.

Soybean shows an attenuated nitrogen dilution curve irrespective of maturity group and sowing date

It is generally accepted that the nitrogen (N) dilution curves relating shoot nitrogen concentration (%N) and shoot biomass (W) are similar among genotypes from the same species. However, differences in the pattern of biomass ratio between lamina and stem (Wlam:Wste) with increasing biomass would change the curve. Shoot biomass at flowering also affect biomass and N allocation in legumes and would affects the N dilution. In soybean, maturity groups (MG) or sowing dates can lead to differences in Wlam:Wste and in time from sown to flowering and hence the parameters of N dilution curves could be affected. The aims of this study were: (i) to determine the growth and allocation patterns of soybean as affected by maturity group (MG IV vs II) and sowing date and (ii) to establish allometric relations between growth and nitrogen, including N dilution curves. Our working hypothesis is that the reference N dilution curve in soybean is similar to the critical N dilution curve of non-legume C3 crops.Four experiments were performed at Balcarce, Argentina during three growing seasons with the aim to generate a wide range of growing conditions. Two soybean cultivars were evaluated: DM2200 (MG II) and DM4970 (MG IV), sown in optimum dates for the region (mid-November). DM2200 was also sown late (early January). We sampled crops between W≈1Mgha−1 and R5. Shoots were separated in three compartments: lamina (Wlam), stem and petiole (Wste) and pod (Wpod).Despite the marked decrease in Wlam:Wste with increasing biomass, the N dilution curve was attenuated in soybean, with no differences among cultivars of maturity groups II and IV, and sowing dates from November to January. We propose that early pod onset and the constant%N in lamina and stem between R1 and R5 attenuated the N dilution curve in all MG and sowing date. Timely-sown MGIV showed a greater Wlam:Wste ratio at W=1Mgha−1 and a more pronounced depletion of the ratio with increasing biomass. However, the N dilution curves were similar between maturity groups II and IV, and sowing dates from November to January. This could be attributed to the lower%N in lamina at V6 in comparison to R1 in timely-sown MGIV.

Meloidogyne incognita Resistance in Soybean under Midwest Conditions

Soybean cultivars of maturity groups II to IV were tested in the greenhouse for resistance to Meloidogyne incognita (Kofoid and White) Chitwood. Selected cultivars were tested in a field of sandy loam soil naturally infested with M. incognita and Heterodera glycines Ichinohe (2004) or in a silt loam soil artificially infested with M. incognita (2005). In 2004, H444NRR was resistant to M. incognita, but not to H. glycines; LS94‐3207 and LNX97164‐35‐5 were resistant to both nematodes; Gateway 427, H444NRR, LNX97164‐35‐5, and SB4399CT were moderately resistant to M. incognita in greenhouse tests; HF9665‐2‐15 was resistant to M. incognita but highly susceptible to H. glycines In 2005, LS94‐3207, H444NRR, LNX97164‐35‐5, and Manokin were resistant to M. incognita In microplots with two sandy loam soils, HF9665‐2‐15 exhibited tolerance to increasing inoculum levels of M. incognita High‐yielding soybean cultivars in maturity groups II to IV with resistance and tolerance to M. incognita were identified. Under field conditions, resistance to the more widespread nematode H. glycines, combined with resistance to M. incognita, is highly desirable to reduce the risk of yield reduction and to improve cropping sequences that include soybean.

Soybean Sowing Date: The Vegetative, Reproductive, and Agronomic Impacts

The sensitivity of soybean [Glycine max (L.) Merr.] main stem node accrual to ambient temperature has been documented in greenhouse‐grown plants but not with field‐grown plants in the north‐central United States. Biweekly V‐node and R‐stage, stem node number, internode length, and other traits were quantified in an irrigated split‐plot, four‐replicate, randomized complete block experiment conducted in Lincoln, NE, in 2003–2004. Main plots were early‐, mid‐, late‐May, and mid‐June sowing dates. Subplots were 14 cultivars of maturity groups 3.0 to 3.9. Node appearance was surprisingly linear from V1 to R5, despite the large increase in daily temperature from early May (10–15°C) to July (20–25°C). The 2003 and 2004 May planting date regressions exhibited near‐identical slopes of 0.27 node d−1 (i.e., one node every 3.7 d). Cold‐induced delays in germination and emergence did delay the V1 date (relative to planting date), so the primary effect of temperature was the V1 start date of linearity in node appearance. With one exception, earlier sowings led to more nodes (earlier V1 start dates) but also resulted in shorter internodes at nodes 3 to 9 (cooler coincident temperatures), thereby generating a curved response of plant height to delayed plantings. Delaying planting after 1 May led to significant linear seed yield declines of 17 kg ha−1 d−1 in 2003 and 43 kg ha−1 d−1 in 2004, denoting the importance of early planting for capturing the yield potential available in soybean production, when moisture supply is not limiting.

Genetic Diversity of Canadian Soybean Cultivars and Exotic Germplasm Revealed by Simple Sequence Repeat Markers

Genetic diversity assessment of improved crop germplasm can facilitate the expansion of the genetic base in a plant breeding program, but little effort has been made to assess the Canadian soybean [Glycine max (L.) Merr.] gene pool established over the past century. Simple sequence repeat (SSR) markers were applied to assess the genetic diversity of 45 Canadian soybean cultivars released from 1934 to 2001 and 37 exotic germplasm accessions. Thirty‐seven SSR primer pairs were applied and 234 polymorphic bands were scored for each accession. The frequencies of the scored bands ranged from 0.01 to 0.90 and averaged 0.17. The proportion of total SSR variation occurring between exotic and Canadian germplasm was 9%; among the Canadian cultivars of three breeding periods 10%; and between the cultivars of maturity groups 0 and 00 4%. More diversity was found for exotic germplasm than the Canadian. More diversity was observed in the cultivars of the recent breeding period than the early. The Canadian cultivars were clustered into seven major groups, partially congruent to the known pedigrees, and they were more related to germplasm from Russia, Sweden, and Ukraine and less to the Asian germplasm. The six genetically most distinct cultivars were PS86 RR, Gaillard, Manitoba Brown, Beechwood, Maple Isle, and 92B91. These findings are useful for the selection of genetically distinct or less related soybean materials to improve the genetic background of the soybean gene pool.

Genetic Variability for Phytic Acid Phosphorus and Inorgaic Phosphorus in Seeds of Soybeans in Maturity Groups V, VI, and VII

Phytic acid (PA; myo‐inositol 1,2,3,4,5,6 hexakisphosphate) in soybean [Glycine max (L.) merr.] meal is a major source of P in animal excreta, a serious environmental pollutant. Genetic mutants in which seed PA is reduced by 60% have been developed. The objectives were to assess (i) natural variation in seed PA‐P and inorganic phosphorus (Pi) concentrations in soybean breeding lines and cultivars of Maturity Groups (MGs) V, VI, and VII; (ii) genotype × environment (G × E) interactions for Pi and PA‐P, and (iii) relations among PA‐P, Pi, and seed protein concentrations. Three sets of cultivars and breeding lines were tested separately in two or three environments. Variation among lines was highly significant, ranging from 3.77 to 5.07 g kg−1 PA‐P and from 0.19 to 0.37 g kg−1 Pi The G × E interactions were highly significant for Pi concentration, but significant variation for PA‐P concentration was observed only among cultivars, not across environments nor as G × E interactions. Rank correlation coefficients for Pi concentrations between environments were large (0.65–0.88), suggesting that the G × E interactions were due to differences in average Pi concentration in various environments. Variation in seed protein was highly significant in all three sets, but protein was not correlated with PA‐P and was correlated with Pi (r = 0.56) only in the MG V breeding lines test. Therefore, genetic relationships between protein and either PA‐P or Pi could not be established. Significant natural genetic variation indicates that PA level of potential adapted parents may be useful in breeding low‐PA soybeans.

Effect of Sclerotinia Stem Rot on Yield of Soybean Inoculated at Different Growth Stages.

The effects of Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, on yield of soybean were evaluated in the field with two cultivars in maturity group 0. Plants were inoculated at two growth stages, R3 and R5, using two inoculation methods. Seed weight, seed and pod numbers, seed protein, and oil content were measured. The effects of disease on yield were variable. Disease resulted in significant seed weight loss, with reductions per diseased plant ranging from 18.8 to 38.6%. The estimated yield loss per 10% disease incidence ranged from 83.2 to 229.0 kg/ha, with an average loss of 136.6 kg/ha for four field experiments. A reduction in the number of seeds and pods per plant and seed oil content occurred in some, but not all, experiments. Seed protein was not affected. When disease reduced seed weight, seed and pod numbers, or oil content, there was no growth stage × treatment interaction in the experiments, indicating that inoculation at R5 compared with R3 had a similar effect on yield.

Soybean Cyst Nematode Population Development and Associated Soybean Yields of Resistant and Susceptible Cultivars in Minnesota.

The soybean cyst nematode (SCN), Heterodera glycines, is a major soybean yield-limiting factor, and the use of resistant cultivars is one of the most effective means to manage the nematode. During the past decade, a number of resistant cultivars in maturity groups I and II have been developed and made available to growers. A total of 47 resistant cultivars and nine susceptible cultivars were evaluated at 15 SCN-infested field sites and two noninfested sites during 1996 to 1998 in Minnesota. As expected, more nematodes developed on susceptible cultivars than on resistant cultivars. Egg density on susceptible cultivars increased by 1.9- to 10.6-fold during the growing season at 12 sites and did not change at the other three sites. Average egg density decreased over time for resistant cultivars at all sites, except where the initial egg density was low (≤455 eggs per 100 cm3 soil). Nematode reproduction factors (Rf = egg density at harvest/egg density at planting) for individual resistant and susceptible cultivars were highly consistent across the eight sites where initial SCN density was more than 1,000 eggs per 100 cm3 soil. Resistance, however, varied among the cultivars, with the average Rf of individual resistant cultivars across the sites ranging from 0.3 to 1.7. Resistant cultivars produced an average yield of 3,082 kg/ha compared with 2,497 kg/ha by susceptible cultivars at eight of 10 sites where egg density at planting was greater than 700 eggs per 100 cm3 soil. In contrast, no difference in yield was observed between resistant and susceptible cultivars at sites where egg density at planting was lower than 500 eggs per 100 cm3 soil. Yield differences between resistant and susceptible cultivars increased with increasing initial SCN egg density. In six fields infested with initial densities of more than 5,000 eggs per 100 cm3 soil, resistant cultivars produced 28.4% (676 kg/ha) more yield on average than susceptible cultivars. Soybean yield increased when cultivars with increasing resistance to the SCN (lower Rf or females formed on roots) were grown in fields infested with SCN. Average relative yield (yield of a cultivar/average yield of all resistant cultivars at a site) of individual resistant cultivars across all SCN-infested sites ranged from 0.76 to 1.10. Yield consistency of soybean cultivars was low among the different sites, indicating that many other factors affected yield. Our results suggest growing resistant cultivars is an effective method to manage SCN in Minnesota while minimizing yield loss due to SCN.

Yield and Quality of Forage Soybean

Tall forage soybean [Glycine max (L.) Merr.] cultivars in maturity groups V, VI, and VII have been developed to supply forage. Our objective was to determine the effect of harvest date and row spacing on the forage yield and quality of these new soybean cultivars. We grew forage and standard grain soybean in Minnesota with harvests in early and late September. Average maturity of tall forage soybean was R3 (early harvest) to R4 or R5 (late harvest) and average maturity of grain soybean was R6 (early harvest) to R7 (late harvest). Herbage of forage soybean was mostly leaves and stems at both harvests, whereas herbage of grain soybean contained an average of 400 and 595 g kg−1 pods at the early and late harvests, respectively. There was no harvest date × soybean entry interaction for forage yield or forage quality. Forage and grain soybean had similar forage yields (∼8.8 Mg ha−1). Because adapted grain soybean was more mature and had a greater pod proportion than forage soybean, grain soybean had greater crude protein (CP) and lower fiber concentration than forage soybean. Average forage CP for forage and grain types was 146 and 218 g kg−1, respectively, while neutral‐detergent fiber (NDF) concentration was 523 and 400 g kg−1, respectively. Decreasing row width from 76 to 25 cm increased forage yield 0.8 Mg ha−1 but had no effect on total herbage quality.

Arthropod Populations in Early Soybean Production Systems in the Mid-South

We compared the severity of insect problems in early and conventional soybean, Glycine max (L.) Merrill, production systems in the mid-South. The conventional soybean production system (cultivars in maturity groups V–VII planted in May) experienced significantly higher populations of late-season defoliators than the early soybean production system (cultivars in maturity group IV planted in April). However, the early soybean production system harbored significantly larger populations of southern green stink bug, Nezara viridula (L.) and threecornered alfalfa hopper, Spissistilus festinus (Say). Predators were significantly more abundant in the early soybean production system compared with the conventional soybean production system, early in the growing season. Late in the growing season, predator populations were lower in both productions systems and differences between the two systems were not significant. The results from the current study illustrated the benefits of early-planted early-maturing cultivars (early soybean production system) in avoiding lepidopterous and coleopterous defoliators that occur late in the growing season. However, our data also indicate that arthropod management will be essential in the early soybean production system because widespread use of this system will result in an abundance of suitable hosts for early-season pests.

Soybean Varietal Response and Yield Loss Caused by Sclerotinia sclerotiorum.

Soybean Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, has recently emerged from being a minor problem in areas where soybeans of maturity groups 0 to I are grown to a significant cause of soybean yield losses in the north-central region, which produces 80% of soybean in the United States. Studies were conducted in Iowa to quantify varietal response to S. sclerotiorum for cultivars of maturity groups I to III in fields that had uniform infestation histories. Over the course of the study, disease incidence was generally high at the northern Iowa sites but low in central Iowa, with disease incidence of susceptible standards >60% and <30%, respectively. Regression analysis showed that maturity class significantly affected disease incidence, with greater effects in environments where susceptible standard cultivars had high disease incidences. Consistency of varietal response among the environments was quantified using Pearson correlation analysis. When disease incidence was high, varietal responses measured by disease ratings and yield were consistent among locations, but the responses were inconsistent when disease incidence was low. Pearson correlation coefficients ranged from 0.80 to 0.94 for disease incidence and 0.58 to 0.81 for yield among the experiments having high disease incidence in susceptible standards. The relationship between disease incidence and yield was well described by linear regression models with coefficients of determination (r2) ranging from 0.59 to 0.83. Based on regression slopes (significant at P < 0.0001), yield losses are estimated to range from 170 to 335 kg/ha for each 10 percentage points of disease incidence. Regression analysis also showed that maturity groups had a linear relationship with disease incidence (r2 = 0.18 to 0.39, P < 0.01).

Environmental Adaptation of Long‐Juvenile Soybean Cultivars and Elite Strains

AbstractA long‐juvenile (LJ) trait that delays flowering under short‐day conditions has been incorporated into adapted soybean [Glycine max (L.) Merr.] germplasm. Little is known about the performance of recently developed LJ cultivars and elite strains as influenced by planting systems typical of the southeastern USA. Therefore, a field study was undertaken using two LJ cultivars and four elite LJ Florida strains at Blackville and Pendleton, SC. Planting dates were early (late April), normal (late May), and late (late June), in 1993 and 1994. The LJ genotypes exhibited neither genotype × planting date nor genotype × location interactions for seed yield or seed quality, indicating consistency of genotype performance across environments. Although variation among LJ genotypes for yield was not detected, all four elite strains all ranked higher in yield than the two cultivars. Maturity varied among LJ genotypes but seed yield did not, indicating the possibility of developing LJ genotypes that have relatively short life cycles and high seed yield. Additionally, LJ genotypes were compared with two conventional cultivars: Maturity Groups (MG) IV, V, and VI at early plantings; MG V, VI, and VII at normal plantings; and MG VI, VII, and VIII at late plantings. As planting date was delayed, growth and agronomic responses of LJ genotypes became similar to those of successively later conventional cultivars. The LJ genotypes were similar in yield to conventional cultivars in maturity groups V to VIII across planting dates, but had 56% higher yields than MG IV cultivars at the early planting. Seed quality ratings of LJ genotypes were 54 and 23% better than MG IV and V cultivars, respectively, at the early planting. In general, LJ genotypes showed superior photoperiodic adaptation to different planting date environments.

Genetic Variability for Flooding Tolerance in Soybeans

The flooding tolerance of U.S. soybean [Glycine max (L.) Merr.] cultivars under field conditions has not been reported. In this study, 84 soybean cultivars of maturity groups II, III, and IV were grown at two locations, London and Lakeview, in Ohio. The cultivars differed in their resistance and tolerance to Phytophthora sojae M.J. Kaufmann &amp; J. W. Gerdemann as determined in separate field and laboratory studies. While the production practices and historic yield potential at the two locations were similar, the nearly flat, slowly permeable Milford silty clay soil at Lakeview was saturated during most of July 1992 because of excessive rainfall (17 cm more than normal). The average yield of the 84 soybean cultivars at the flooded location (Lakeview) was 25% lower than at the non‐flooded location (London). Flooding tolerance can be defined as high yield under flooding stress. When the 84 soybean cultivars were ranked in their flooding tolerance according to this definition, many cultivars were found to exhibit both flood tolerance at Lakeview and high yield at London. Flooding tolerance was independent from Phytophthora tolerance, Phytophthora resistance, and plant relative maturity. This study documented that differences in flooding tolerance exist among U.S. soybean cultivars.

Changes in Yield and Seed Growth Traits in Soybean Cultivars Released in the Southern USA from 1945 to 1983

The successive release of new cuitivars over time implies that crop yield, and perhaps the physiological traits which influence it, have been improved or altered. For soybean [Glycine max (L.) Merr] cultivars released in the southern USA, there is little information on the impact of cultivar improvement on physiological traits. The objectives of our studies were to (i) estimate the genetic change in seed yield relative to year of cultivar release for a set of cultivars released over nearly a 40‐yr period, and (ii) assess what concomitant changes occurred in the above‐ground biomass at the beginning of seed growth, dates of reproductive stage R5 (beginning seed‐fill) and R7 (physiological maturity), final harvest index, dry matter allocation during seed growth, and seed filling duration. Eighteen determinate soybean cultivars of Maturity Groups (MG) VI through VIII released in USA from 1945 to 1983 were field tested in eight environments, four in Florida and four in Argentina. Annual rates of genetic gain in seed yield were significant and positive in only two U.S. environments (1.59 and 1.87 g m−2 yr−1). The newest cultivars exhibited superior yields over the oldest cultivars only within MG VII and VIII, when the analysis included all four USA environments. In Argentina, no increase in yield was observed in relation to year of cultivar release, even in an environment where the mean seed yield exceeded 4000kg ha−1, which was 73% higher than the best USA trial. In fact, some of the oldest released cultivars were found to have the highest yields in the Argentina environments. None of the physiological traits measured at the USA locations were found to change appreciably with year of cultivar release. In fact, seed yield within and across environments was not found to be consistently associated with any of the measured seed growth traits. Seemingly, a number of alternatives for combining seed growth traits have been used in the succession of released soybean cultivars.

Evaluation of Northern USA Soybean Cultivars for Maturity in Chile

Selection for maturity of soybean [Glycine max (L.) Merr.] genotypes in winter nurseries may increase the efficiency of soybean breeding programs. The objective was to determine if soybean adapted to Minnesota and Wisconsin would mature similarly in the USA and Chile. Six cultivars of Maturity Groups 00, 0, and I were evaluated for maturity differences at Prescott, WI and Rosemount, MN in the summers of 1984 and 1985 and at Santiago and Buin, Chile during the northern hemisphere winters of 1984–1985 and 1985–1986. Cultivar ✕ location interactions were not significant (P ≥ 0.10) within countries. When maturity differences among cultivars were compared between the two countries, the cultivar ✕ country and cultivar ✕ years/countries interactions were significant (P &lt; 0.01), but the interactions were due to differences in magnitude rather than differences in rank. Selection for maturity can be done effectively in Chile for soybeans of Maturity Groups 00, 0, and I.

Field studies on osmoconditioning soybeans

Abstract Germination and emergence are frequently poor when soils are cold and wet. Osmoconditioning of soybean [Glycine max (L.) Merr.] seed has been suggested as a means to improve emergence under these soil conditions. The objective of this study was to field test three osmoconditioning treatments against an untreated control on cultivars in maturity groups 00 through V to evaluate the potential of this technique. The osmoconditioning treatments included polyethylene glycol (PEG), mannitol and water-soaking. Combined results from 1983 and 1984 indicate that PEG improves (P