The effect of stem growth habit on single seed weight and seed uniformity in soybean (Glycine max (L.) Merrill)

Height to first pod: A review of genetic and breeding approaches to improve combine harvesting in legume crops

Height from soil at the base of plant to the first pod (HFP) is an important trait for mechanical harvesting of legume crops. To minimise the loss of pods, the HFP must be higher than that of the blades of most combine harvesters. Here, we review the genetic control, morphology, and variability of HFP in legumes and attempt to unravel the diverse terminology for this trait in the literature. HFP is directly related to node number and internode length but through different mechanisms. The phenotypic diversity and heritability of HFP and their correlations with plant height are very high among studied legumes. Only a few publications describe a QTL analysis where candidate genes for HFP with confirmed gene expression have been mapped. They include major QTLs with eight candidate genes for HFP, which are involved in auxin transport and signal transduction in soybean [Glycine max (L.) Merr.] as well as MADS box gene SOC1 in Medicago trancatula, and BEBT or WD40 genes located nearby in the mapped QTL in common bean (Phaseolus vulgaris L.). There is no information available about simple and efficient markers associated with HFP, which can be used for marker-assisted selection for this trait in practical breeding, which is still required in the nearest future. To our best knowledge, this is the first review to focus on this significant challenge in legume-based cropping systems.

Characterization of the Common Genetic Basis Underlying Seed Hilum Size, Yield, and Quality Traits in Soybean

Developing high yielding cultivars with outstanding quality traits are perpetual objectives throughout crop breeding operations. Confoundingly, both of these breeding objectives typically involve working with complex quantitative traits that can be affected by genetic and environmental factors. Establishing correlations of these complex traits with more easily identifiable and highly heritable traits can simplify breeding processes. In this study, two parental soybean genotypes contrasting in seed hilum size, yield, and seed quality, as well as 175 F₉ recombinant inbred lines (RILs) derived from these parents, were grown in 3 years. The h² _b of four hilum size, two quality and two yield traits, ranged from 0.72 to 0.87. The four observed hilum size traits exhibited significant correlation (P < 0.05) with most of seed yield and quality traits, as indicated by correlation coefficients varying from -0.35 to 0.42, which suggests that hilum size could be considered as a proxy trait for soybean yield and quality. Interestingly, among 53 significant quantitative trait loci (QTLs) with logarithm of odds (LOD) values ranging from 2.51 to 6.69 and accounting for 6.40-16.10% of genetic variation, three loci encoding hilum size, qSH6.2, qSH8, and qSH10, colocated with QTLs for seed yield and quality traits, demonstrating that genes impacting seed hilum size colocalize in part with genes acting on soybean yield and quality. As a result of the breeding efforts and field observations described in this work, it is reasonable to conclude that optimizing hilum size through selection focused on a few QTLs may be useful for breeding new high yielding soybean varieties with favorable quality characteristics.

Effect of change from a determinate to a semi-determinate growth habit on the yield and lodging resistance of soybeans in the northeast region of Japan

Although an indeterminate growth habit is attractive to develop high-yield soybean varieties with higher number of pods (Glycine max (L). Merr.), lodging in indeterminate varieties remains a problem in Japan. As the semi-determinate varieties have shorter main stem length than the indeterminate varieties, this trait can be useful to improve varieties with high yield and low lodging risk. We introduced the genes Dt1 and Dt2, which regulate stem growth habit, into three determinate varieties by backcrossing and evaluated the resulting effects on yield and lodging tendency under four different growing environments. The yield and lodging degree of the semi-determinate and indeterminate lines were higher and more severe than those of the determinate lines. Despite the lower overall lodging score, the semi-determinate lines had marginally lower overall yield than that of the indeterminate lines. However, the effect of introduction of semi-determinate traits on yield and lodging degree was different in the three backgrounds, with the yield of semi-determinate lines being the highest and the difference in lodging degree between the semi-determinate and determinate lines being under 1.0 in one background. Therefore, semi-determinate growth habit has potential to develop high yielding varieties with low lodging risk.