Identifying quantitative trait loci for symbiotic nitrogen fixation capacity and related traits in common bean

Symbiotic nitrogen fixation (SNF) through association with root-nodulating rhizobia effectively contributes to improved nitrogen nutrition of leguminous plants and is an ecologically sound and low-cost strategy for improving pulse productivity. One of the main factors determining the efficiency of SNF is the plant genotype, but little is known about the plants' genetic contribution to SNF in the case of common bean. Therefore, quantitative trait loci (QTL) analysis for SNF and related growth traits was performed in a common bean recombinant inbred line (RIL) population under both greenhouse and field conditions. The RIL population was generated from the cross G2333 x G19839. Additionally, the existing genetic map of the population was improved through the mapping of 42 markers out of a set of 108 nodulation gene-based markers. All greenhouse and field experiments showed significant differences between RIL genotypes for most SNF and related growth traits. In the first greenhouse experiment, two QTL for percent nitrogen (N%) fixed were identified on linkage groups b01 and b04, explaining 21 and 20 % of the observed phenotypic variance, respectively. The QTL on linkage group b01 overlapped with a QTL detected for total N content at harvest in the field experiment (R (2) = 14 %). In the second greenhouse experiment, two QTL for total plant N fixed were identified on linkage groups b04 and b10 (R (2) = 18 and 17 %, respectively). The field experiment also yielded one QTL for the N% fixed at harvest on linkage group b04 and another for the total N fixed in the shoot at late pod-filling stage on linkage group b01. The latter two QTL identified in the field explained 19 and 21 %, respectively, of the observed phenotypic variance. DNA sequence comparison of markers closely linked to QTL identified some potential candidate genes underlying the QTL. One of these genes encodes for an auxin-responsive transcription factor which could explain differences in growth and possibly yield and N accumulation between climbing beans and bush beans. Another putative gene was identified for an AP2/ERF-domain-containing transcription factor underlying the QTL for the total amount of symbiotic nitrogen fixed in the field.