Exploring the genetic resources of Lens and Rhizobium to improve the biological nitrogen fixation (BNF) ability in the lentil crop

Abstract

Lentil plants (Lens culinaris) have the ability to obtain most of the N they need from N fixation by establishing an efficient symbiotic relationship with Rhizobium. Plant-based diets are gaining the recognition they deserve for sustainability and producing legumes without the use of synthetic N fertilizers is the most sustainable approach. The N fixing ability of representative lentil cultivars, as well as accessions from 6 wild Lens species, was evaluated to determine the potential for wild germplasm to contribute positively to breeding for improved BNF. The contributions of diverse Rhizobium strains from 5 species to lentil productivity under local field conditions was also investigated. Subsequently, the level of specificity of the interactions between Lens accessions and Rhizobium strains with desirable N fixing abilities was explored. How traits related to N fixation are inherited was determined in three interspecific RIL populations from parents displaying contrasting phenotypes. Differential N fixing ability was found among cultivars and wild accessions; no particular species stood out. Wild accessions exhibited indeterminate nodulation, root modifications that responded to different N sources, higher seed percentage protein content, and yields comparable to plants fertilized with synthetic N. CDC Greenstar was the only cultivar with similar yield when inoculated or fertilized. CDC Maxim inoculated with the strain NZLR-24 (Rhizobium leguminosarum bv. viciae) had 9% higher yield under field conditions compared to when inoculated the commercial strain BASF 1435 (Rlv) and 15% more compared to a non-inoculated treatment. Some wild accessions demonstrated a promiscuous ability to efficiently fix N with a broad set of strains, but no cultivar did. The higher effective capacity of the strain NZLR-24 (Rlv) was also evident when used to inoculate Lens from 6 species, making it a suitable option for improved inoculants in the Northern Great Plains, as well as showing its value for selection in future breeding efforts. The strain Oyali B (Rlv) was also noteworthy for its superior interaction with wild Lens, and it is an attractive wild-type resource. Sixteen QTL were identified for nodulation traits among the three interspecific populations; eight were meta-QTL found across two or more populations. Chromosomes 1 and 6 had Meta-QTL for number of nodules, nodule weight and specific nodule weight. Chromosome 7 had one for specific nodule weight. This study establishes the necessary groundwork for understanding the role that exotic germplasm can play for the breeding of better N fixation ability in the lentil crop.