Characteristics of initial growth of hypernodulation soybean mutants, NOD1-3, NOD2-4 and NOD3-7, affected by inoculation of bradyrhizobia and nitrate supply

Abstract

The characteristics of plant growth of hypernodulation soybean mutant lines NOD1-3, NOD2-4 and NOD3-7 were compared with their parent cv. Williams. The plants were grown using hydroponics in an illuminated growth chamber with or without seed inoculation of bradyrhizobia, and in the absence or presence of nitrate in the culture solution. When the plants were grown without inoculation, the total dry weight of all mutant lines was not different statistically from Williams, both in the absence and presence of nitrate. When they were grown with inoculation of bradyrhizobia, however, the total dry weight of each mutant line was significantly lower than that of Williams, both in the absence and presence of nitrate. These results indicate that the reduced accumulation of total dry matter of hypernodulation mutant lines compared with the wild type may be a secondary effect passively resulting from the large number of nodules, while the hypernodulation trait is a primary effect of the mutated gene. When the plants were grown with inoculation, the nodule number was decreased by the presence of nitrate in Williams, NOD1-3 and NOD2-4, but not in NOD3-7. NOD3-7 may be the most tolerant to nitrate inhibition of nodulation among the NOD mutant lines. In contrast, leaf growth of NOD3-7 and NOD1-3 was different from the wild type; the expanded leaf was smaller, but the leaf emergence rate was faster compared with Williams under all conditions. This indicates that NOD3-7 and NOD1-3 might decrease the ability for leaf expansion or may have a faster leaf emergence rate. © 2007 Japanese Society of Soil Science and Plant Nutrition.