IDENTIFICATION AND MAPPING OF ANTHRACNOSE RESISTANCE GENES IN SORGHUM [SORGHUM BICOLOR (L.) MOENCH]

Colletotrichum sublineolum is the causal agent of sorghum anthracnose, a very common and destructive fungal disease in warm and humid areas, especially in West and Central Africa. Use of host plant resistance is considered as the most important and effective control option for sorghum diseases. To achieve this goal, identification and mapping resistance genes is essential. In this study, we used an isolate of C. sublineolum, CsGL1, to screen our sorghum germplasm and identified a resistant inbred line, P9830. We developed a mapping population from a cross between P9830 and a susceptible line, TAM428, for this research. The population was advanced to the F₆ generation. Progenies were phenotyped at F₂, F₃ and F₆ generations for disease resistance against the pathogen, CsGL1. In the F₂ generation, 460 individuals showed resistance and 149 individuals showed susceptibility to CsGL1. This result fits the 3:1 segregation pattern expected for resistance controlled by a single gene. Bulked segregant analysis with next generation sequencing was used on selected F₆ recombinant inbred lines. A significant peak containing 153 SNPs was observed on the distal end of the long arm of chromosome 8. To verify resistance to CsGL1 was controlled by genes in this region, indel and SNP markers were used between 59.4Mbp and 60.6Mbp on chromosome 8 to fine map the resistance locus. One SNP marker located in the gene Sobic.008G166400 co-segregated with resistance, and another two indel markers were discovered to be tightly linked to the resistance locus. These three PCR-based SNP markers would be useful for marker-assisted selection for improving anthracnose resistance against CsGL1. Two candidate genes, Sobic.008G166400 and Sobic.008G166550, were found in the locus. Both of the genes encode LRR proteins implicated in plant disease defense response. The identity of DNA sequence between these two candidate genes is 94.1%, possibly the result of tandem duplication. Another possible ortholog in the region is Sobic.008G167500. Quantitative PCR analysis showed that the expression level of Sobic.008G166400 didn’t change significantly in a resistant RIL, 17-12 but was induced in a susceptible RIL, 13-31, after CsGL1 infection. In conclusion, we mapped two candidate genes conferring resistant to CsGL1 on chromosome 8, and Sobic.008G166400 is more likely of the two to be determined as the gene controlling resistance to CsGL1.