Registration of sorghum backcross‐nested association mapping (BC‐NAM) families in a BTx623 or RTx436 background

Two sorghum [Sorghum bicolor (L.) Moench] backcross‐nested association mapping (BC‐NAM) populations (Reg. no. MP‐5, NSL 546724 MAP) have been developed, composed of 30 families totaling 2189 BC1F4 lines using an elite maintainer (B) or restorer (R) line as the recurrent parent. The families were derived from unadapted founder lines that were backcrossed to BTx623 and/or RTx436 based on the fertility reaction score and phylogenetic analysis of the founder lines. These unadapted founder lines were selected based on agronomic fitness, breeder desirability, and genetic diversity and represent a range of races and working groups. The 30 families were developed from 27 founder parents—three of the founder parents were backcrossed to both recurrent parents to provide a genetic relationship across all 30 families. Each family consists of 45–100 BC1F4 lines selected for standard agronomic fitness, and each population was genotyped using genotype‐by‐sequencing. To identify families that possess (or segregate for) traits of interest, 13 lines from each population were randomly selected and phenotyped for a range of agronomic and stress tolerance traits. These BC‐NAM populations, which are adapted to US production regions and possess novel genetic diversity, have application in genetic research as a mapping resource for traits of interest and for sorghum breeding programs to diversify R and B line parental heterotic pools. Core Ideas Sorghum improvements are based on access to genetic diversity within elite, adapted germplasm. Access to diversity in sorghum genetics is limited by maturity and plant height requirements. The development of backcrossed‐derived nested association populations provides both a genetic and breeding resource. These populations are available for both research and breeding purposes.