Jiaojiao Ren, Penghao Wu, Gordon M. Huestis, Ao Zhang, Jingtao Qu, Yubo Liu, Hongjian Zheng, Amos E. Alakonya, Thanda Dhliwayo, Michael Olsen, Felix San Vicente, Boddupalli M. Prasanna, Jiafa Chen & Xuecai Zhang

Theoretical and Applied Genetics; May 2022; vol. 135: 1551–1563 

Key message

A major QTL of qRtsc8-1 conferring TSC resistance was identified and fine mapped to a 721 kb region on chromosome 8 at 81 Mb, and production markers were validated in breeding lines.

Abstract

Tar spot complex (TSC) is a major foliar disease of maize in many Central and Latin American countries and leads to severe yield loss. To dissect the genetic architecture of TSC resistance, a genome-wide association study (GWAS) panel and a bi-parental doubled haploid population were used for GWAS and selective genotyping analysis, respectively. A total of 115 SNPs in bin 8.03 were detected by GWAS and three QTL in bins 6.05, 6.07, and 8.03 were detected by selective genotyping. The major QTL qRtsc8-1 located in bin 8.03 was detected by both analyses, and it explained 14.97% of the phenotypic variance. To fine map qRtsc8-1, the recombinant-derived progeny test was implemented. Recombinations in each generation were backcrossed, and the backcross progenies were genotyped with Kompetitive Allele Specific PCR (KASP) markers and phenotyped for TSC resistance individually. The significant tests for comparing the TSC resistance between the two classes of progenies with and without resistant alleles were used for fine mapping. In BC₅ generation, qRtsc8-1 was fine mapped in an interval of  ~ 721 kb flanked by markers of KASP81160138 and KASP81881276. In this interval, the candidate genes GRMZM2G063511 and GRMZM2G073884 were identified, which encode an integral membrane protein-like and a leucine-rich repeat receptor-like protein kinase, respectively. Both genes are involved in maize disease resistance responses. Two production markers KASP81160138 and KASP81160155 were verified in 471 breeding lines. This study provides valuable information for cloning the resistance gene, and it will also facilitate the routine implementation of marker-assisted selection in the breeding pipeline for improving TSC resistance.

See: https://link.springer.com/article/10.1007/s00122-022-04053-8

Fig. 4: Fine mapping of qRtsc8-1 with a progeny test strategy. The genetic structure of each recombinant type is shown in different colors on the left. White and black bars represent homozygous La Posta Sequia C7 F64-2-6-2-2-B-B-B genotype and heterozygous La Posta Sequia C7 F64-2-6-2-2-B-B-B/CML495 genotype, respectively. Significant differences (P < 0.05) in resistance to tar spot complex (TSC) between the two groups of genotypes indicate that qRtsc8-1 is in the heterozygous region, and their corresponding recombinants are deduced as resistant (R). No significant differences (P ≥ 0.05) in resistance to TSC between the two groups of genotypes indicate that qRtsc8-1 is not in the heterozygous region, and their corresponding recombinants are deduced as susceptible (S). The QTL qRtsc8-1 was finely mapped between markers KASP81160138 and KASP81881276 within a  ~ 721 kb interval