Soya bean (Glycine max L. Merr.) genotype response to early-season flooding:: I.: Root and nodule development

Soya bean is often grown in regions subject to periodic flooding, with the rooting zone most affected by flooding due to its proximity to the source of stress. Our objectives were to examine the effects of flooding soya bean on its primary roots, adventitious roots and root nodules, and to determine relationships between root morphological changes and early-season flood tolerance. The experiment was conducted in Belle Glade, FL with 11 soya bean genotypes subjected to (i) no flood, (ii) 2-week flood 21-35 days after sowing (DAS) or (iii) 4-week flood 21-49 DAS. All plants were harvested 49 DAS. Flooding reduced soya bean primary root weight, length and volume across genotypes. Adventitious root length and volume were greater in the 4-week than the 2-week flood. Soya bean nodule dry weight was threefold higher in the non-flooded treatments. Genotypic differences in root development and tolerance to flooding were noted, with early-season flood tolerance correlated with primary root dry weight, length and surface area, and adventitious root dry weight. However, there was no correlation between this study's early-season root development and late-season flood tolerance based on seed yield from previous studies. Our results indicate that full season trials may be necessary to identify flood-tolerant soya bean germplasm.