Procedure for Obtaining Efficient Root Nodulation of a Pea Cultivar by a Desired Rhizobium Strain and Preempting Nodulation by Other Strains

Abstract

The specificity between the sym-2 gene bred into certain cultivars of pea ( Pisum sativum L.) and the nodX gene, present only rarely in isolates of Rhizobium leguminosarum , can be exploited to preempt competition or nodulation blocking by a Rhizobium strain indigenous to a soil environment. The principle is to isolate an R. leguminosarum strain prevalent in a locale, convert it into a strain that will nodulate a desirable pea cultivar carrying sym-2 by establishing nodX in it, and then use the resulting Rhizobium strain with the pea cultivar carrying sym-2 . To accomplish this, we first constructed a transposon Tn 5 derivative called Tn 5nodX and an efficient delivery vehicle that is suicidal in R. leguminosarum . We tested the potential utility of the system in greenhouse experiments. The results are encouraging enough to warrant extensive experiments under field conditions.