Genotypic differences in symbiotic nitrogen fixation ability and seed yield of climbing bean

Symbiotic nitrogen fixation (SNF) contributes to improve grain yield under nitrogen (N) deficiency. Climbing beans are known to be superior to bush beans in their potential for SNF. The main objectives of this study were to: (i) quantify genotypic differences in SNF ability of climbing beans using N-15 natural abundance method; (ii) identify climbing bean genotypes that combine high SNF ability with high yield potential that could serve as parents in the breeding program; and (iii) test whether delta N-15 in seed can be used instead of delta N-15 in shoot for estimating SNF ability. 98 Climbing bean genotypes were evaluated for SNF ability in terms of nitrogen derived from the atmosphere (%Ndfa). Field trials were conducted at two locations in Colombia. Significant genotypic differences were observed in SNF ability. Good yielding lines with 4.6 t ha(-1) fixed as much as 60% of their N (up to 92 kg of N fixed ha(-1)) without application of N fertilizer to soil. Based on evaluations from both locations, seven climbing bean lines (ENF 235, ENF 234, ENF 28, ENF 21, MAC 27, CGA 10 and PO07AT49) were identified as promising genotypes. Seed samples can be used to determine SNF ability, to select for genotypes with superior SNF ability.