Identifying the Genes Underlying Low N Tolerance & Nitrogen Use Efficiency (NUE) of Sorghum

Improving Nitrogen use efficiency (NUE) of the cultivars facilitates low input, environment friendly agriculture. NUE is a complex trait, controlled by many genes. To better understand the genetics of NUE in sorghum, mapping of quantitative trait loci (QTL) associated with NUE using recombinant inbred (RIL) mapping population was carried out. The linkage map consisted of 180 simple sequence repeats (SSR’s) and 840 single nucleotide polymorphisms (SNPs) spanned a length of 3450 cM genome size with an average distance of 3.4 cM between adjacent bins. QTL analysis was performed and a total of 17 major QTLs were detected for eleven agronomically important traits under two contrasting N environments. The phenotypic variation explained by individual QTLs varied from 6% to 11.2%. The high accuracy and quality of this map was evidenced by the finding that genes underlying two cloned QTLs, Dw3 for plant height (chromosome 9) and Ma1 for flowering time (chromosome 1), were localized to the correct genomic regions. The close associations between genomic regions on chromosomes 3, 6 and 9 with multiple traits suggested the existence of pleiotropy or tight linkage. Several major QTLs for chlorophyll-2, plant height, biomass moisture content,  grain moisture content, grain to stover ratio and test weight were detected consistently under both N environments, providing useful information for understanding the genetic mechanisms of the agronomically important traits responsible for the change of NUE.