Fine-mapping of qRfg2, a QTL for resistance to Gibberella stalk rot in maize.

Stalk rot is one of the most devastating diseases in maize worldwide. In our previous study, two QTLs, a major qRfg1 and a minor qRfg2, were identified in the resistant inbred line '1145' to confer resistance to Gibberella stalk rot. In the present study, we report on fine-mapping of the minor qRfg2 that is located on chromosome 1 and account for ~8.9% of the total phenotypic variation. A total of 22 markers were developed in the qRfg2 region to resolve recombinants. The progeny-test mapping strategy was developed to accurately determine the phenotypes of all recombinants for fine-mapping of the qRfg2 locus. This fine-mapping process was performed from BC(4)F(1) to BC(8)F(1) generations to narrow down the qRfg2 locus into ~300 kb, flanked by the markers SSRZ319 and CAPSZ459. A predicted gene in the mapped region, coding for an auxin-regulated protein, is believed to be a candidate for qRfg2. The qRfg2 locus could steadily increase the resistance percentage by ~12% across different backcross generations, suggesting its usefulness in enhancing maize resistance against Gibberella stalk rot.