Identification of Quantitative Trait Loci for Alfalfa Forage Biomass Productivity during Drought Stress

Large portions of the world's arable acreage experience water stress on a regular basis. Improving crop productivity in such drought‐prone environments is a critical breeding objective. The goal of this study was to detect quantitative trait loci (QTL) associated with alfalfa (Medicago sativaL.) forage productivity during drought stress. Two first‐generation backcross (BC1) mapping populations (n= 253) derived from a cross between M. sativasubsp. sativaand M. sativasubsp. falcatawere used to develop an updated tetraploid (2n= 4x= 32) genetic linkage map constructed from 600 single‐dose allele molecular markers. Map lengths associated with the two populations were 1293 and 1049 cM, with an average marker density of 3.8 and 3.9 cM, respectively. Half‐sib families derived from 206 BC1individuals were evaluated for forage yield in seeded plots in seven water‐stressed environments in New Mexico and Oklahoma, USA. Significant genotype effects were detected within each population and environment. Interval mapping analysis identified 10 and 15 QTL that, respectively, improved or reduced forage yield during drought. Average phenotypic effects of each QTL on biomass yield ranged from 3 to 6% and the direction of these effects were generally consistent over environments. Desirable alleles identified in these parents may be suitable for marker‐aided introgression into elite populations to incrementally improve their forage productivity in water‐limited environments.