Development and exploitation of a set of contiguous segmental substitution lines in pearl millet[Pennisetum glaucum (L.) R. Br.]

Over the past three decades, the application of molecular markers and genetic linkage maps using conventional mapping populations has allowed the identification of specific regions of the genomes controlling polygenic traits, called ‘Quantitative Trait Loci’ (QTLs), in all major crop species including pearl millet. The resolution power of QTL identification is limited in conventional mapping populations due to the overshadowing effect of major QTLs preventing effective estimation of 1) the number of independently segregating minor QTLs and 2) the interactions between pairs of unlinked QTLs. To overcome such limitations and considering the several utilities of introgression lines, the present study aimed to develop a set of pearl millet substitution lines from an advanced backcross population derived from two agronomically elite parental lines viz., ICMB 841 and 863B, which were known to differ for important traits like downy mildew resistance, drought and salinity tolerance, straw ruminant nutritional quality, grain Fe and Zn concentration, and grain and stover yield components. One thousand four hundred and ninety-two progenies (derived from BC5F3, BC5F2 and BC6F1 families) expected to provide coverage across most of each of the seven pearl millet linkage groups were selected for genotyping at 74 marker loci (48 SSR, 21 SSCP-SNP and 5 STS). Based on this genotyping, a total of 124 segmental introgression lines (12 for LG1, 10 for LG2, 10 for LG3, 41 for LG4, 32 for LG5, 12 for LG6 and 17 for LG7) were identified. Among them, 56 were unique introgression segments from 863B in the ICMB 841 genetic background. These contiguous segmental substitution lines (CSSL) provide a nearly ideal set of genetic stocks for fine mapping the multitude of traits for which their parents differ, and use in unraveling the genetic and physiological mechanisms of several agronomically important but complexly inherited traits. The productivity of major crops is severely constrained by biotic stresses and drought stress is a regular occurrence in pearl millet production environments. Hence identification of quantitative trait loci (QTLs) responsible for grain and stover yield, and their maintenance under stress conditions, has become an essential component in pearl millet improvement. To understand the genetic basis of grain and stover yield-related traits of pearl millet, testcross hybrid agronomic performance of selected homozygous introgression lines (ILs), along with their donor and recurrent parents, and a set of sample of recurrent parental allele homozygotes, was evaluated using three genetically diverse, elite inbred pollinators (H 77/833-2, PPMI 301 and RIB 3135-18) under three moisture regimes (fully-irrigated control, late-onset drought stress, and early-onset drought stress conditions) during the summer and kharif seasons at ICRISAT-Patancheru. Twelve phenotypic characters related to grain and stover yield were recorded and line × tester analysis was performed to estimate general combining ability (gca) of each line in each of these environments and across these environments. Several ILs had significant positive gca for grain yield and stover yield, with hybrids showing better performance than that of recurrent parent ICMB 841. Introgression of the 863B-P2 segment between SSR markers Xpsmp2069 and Xpsmp2273 on LG1 for grain yield and Xpsmp2270 and Xpsmp2213 on LG6 for panicle harvest index showed better gca effects than recurrent parent ICMB 841.The present results validate these QTLs which were detected in earlier studies using testcrosses of an F2-derived F4 mapping population based on the same parental lines.