RECIPROCAL GRAFTING AND BACTERIAL STRAIN EFFECTS ON NODULATION OF SOYBEAN GENOTYPES

It is known that the soybean (Glycine max [L.] Merr.) genotype PI 4175 66 has restricted nodule development when inoculated with Bradyrhizobi um japonicum strain USDA 110 and grown at low temperature. The current experiments were conducted to determine if the restricted nodulation of PI 417566 roots could be overcome by grafting them to a hypernodula ted shoot, since it is known that grafted shoots of hypernodulated mut ants induce hypernodulation on roots of normally nodulated soybean. Re ciprocally- and self-grafted NOD1-3 (a hypernodulation mutant) and PI 417566 (a plant restricted nodulation genotype) plants were evaluated for nodulation in a growth chamber at constant 20 degrees C. Seedling roots of self-grafted PI 417566 were normally nodulated when inoculate d with USDA 123, while USDA 110 resulted in restricted nodulation. Gra fting of NOD1-3 shoots to PI 417566 roots did not enhance nodulation w hen inoculated with USDA 110, but did enhance nodulation when inoculat ed with USDA 123. It appears that the shoot of NOD1-3 has the ability to alter autoregulatory control of nodulation of the PI 417566 genotyp e only when challenged with a compatible rhizobial strain. The shoot o f PI 417566 significantly inhibited nodule formation on NOD1-3 roots w hen inoculated with either USDA 110 or 123. The restriction of nodulat ion on the PI 417566 roots inoculated with USDA 110 appears to be prim arily controlled by root factors. It was concluded that restricted nod ulation and autoregulatory control of nodulation appear to be separate phenomena.