Effect of waterlogging during vegetative stage on growth and yield in supernodulating soybean cultivar Sakukei 4

The supernodulating soybean cultivar Sakukei 4 was previously characterized by its superior capabilities of nitrogen (N) fixation and photosynthesis, and was expected to be high yielding. Since the N absorption by Sakukei 4 is largely dependent on N fixation, it may be strongly affected by waterlogging during the vegetative stage, which occurs frequently in major soybean producing areas. In this study, we investigated the reduced growth and yield resulting from waterlogging during vegetative stage and the subsequent recovery in Sakukei 4, in comparison with those in the normally-nodulating cultivar Enrei and non-nodulating genotype En1282. Under the field conditions, the reduction of growth and yield by waterlogging was greatest in En1282 among the three genotypes, indicating that capability of N fixation is essential for the recovery from waterlogging-induced injury. The waterlogging-induced yield reduction in Sakukei 4 resembled that in Enrei, although growth reduction was greater in Sakukei 4 than in Enrei. Irrespective of cultivar, the yield was associated more closely with the crop growth rate (CGR) during the post-treatment stage than with that during the waterlogging treatment. In the pot experiments, yields positively correlated with both above- and underground plant parts irrespective of cultivar, not significantly, but significantly with root dry weights in Enrei and with nodule dry weights in Sakukei 4. These results indicate that Sakukei 4 exhibits a marked decrease in dry matter production by waterlogging, but yield decrease is compensated to a level similar to that of Enrei because of its enhanced nodule growth during the recovery stage.