EFFECTS OF <i>Rhizobium</i> INOCULUM CONCENTRATION STRAIN AND COMBINED NITROGEN ON GROWTH AND NODULATION OF A SUPERNODULATING COMMON BEAN AND ITS PARENT LINE

Abstract

Numbers of nodules formed on both the supernodulating common bean (Phaseolus vulgaris L.) line R32-BS (BS) and its parent cultivar (OAC Rico) increased with Rhizobium inoculum concentration up to about 10 5 cells mL −1 . As numbers of nodules increased, their average size decreased. Red nodules as a fraction of total nodules decreased with increasing numbers of nodules: a large proportion of nodules at the higher concentrations appeared to be non-functional. Acetylene reduction (AR) rates per plant did not differ between supernodulator and parent line. AR per gram total nodule fresh weight was greater in the parent line than in the supernodulator, but AR per gram red nodule weight was the same in the two lines. Combined nitrogen had its main effect in increasing plant weight, but had little effect on nodule characteristics. However, nodule weights/numbers per unit plant weight were decreased by combined nitrogen. OAC Rico and BS responded similarly to N. Rhizobium strain TAL182 produced fewer but more efficient nodules than Kim5s.Key words: Rhizobium leguminosarum bv. phaseoli, Phaseolus vulgaris, supernodulation, nodule number, nodule senescence, inoculum concentration