Non‐Nodulating Mutants in Common Bean

Abstract

Estimates of nitrogen fixation by common bean (Phaseolus vulgaris L.) have been made using non‐nodulating soybean or other nonfixing plant species to measure soil nitrogen because non‐nodulating bean lines are not available. Such lines are also needed for studies on the genetic control of nodulation. The objective of this study was to obtain (using induced matagenesis) nodulation mutants of the bean lines ‘RIZ 30’ and ‘RIZ 36’. One hundred and twelve nonnodulated plants were identified in the M2 generation following treatment of imbibed seeds with 0.08 M ethyl methane sulfonate for 4 h. Screening was carried out in perlite with a nitrogen‐free nutrient solution, and seeds were inoculated with a mixture of Rhizobium strains CIAT 632 and CIAT 899 before emergence. Plants were uprooted 3 wk after planting, and those without nodules were transferred to soil for seed production. The absence of nodulation by eight lines was confirmed in the M3 and M4 generations following inoculation with several other strains of Rhizobium, and in the M5 generation two mutant lines were evaluated in soil. Seed set in these lines is poor, though improved by applying nitrogen.