Molecular mapping of Cg1, a gene for resistance to anthracnose (Colletotrichum sublineolum) in sorghum

Abstract

Anthracnose, caused by the fungus Colletotrichum sublineolum is one of the most destructive diseases of sorghum and has been reported in most areas where the crop is grown. Several control strategies have been developed but host plant resistance has been regarded as the most eVective strategy for disease control. Here, we describe the search for molecular markers that co-segregate with Cg1, a dominant gene for resistance originally identiWed in cultivar SC748-5. To identify molecular markers linked with the Cg1 locus, F 2:3 plants derived from a cross to susceptible cultivar BTx623 were analyzed with 98 AFLP primer combinations. BTx623 was chosen as the susceptible parent because it is also one on the parents used in creating RFLP and AFLP maps and BAC libraries for sorghum. Four AFLP markers that cosegregate with disease resistance were identiWed, of which Xtxa6227 mapped within 1.8 cM of the anthracnose resistance locus and all four AFLP markers have been previously mapped to the end of sorghum linkage group LG-05. Sequence scanning of BAC clones spanning this chromosome led to the discovery that Xtxp549, a polymorphic simple sequence repeat (SSR) marker, mapped within 3.6 cM of the anthracnose resistance locus. To examine the eYcacy of Xtxa6227 and Xtxp549 for marker-assisted selection, 13 breeding lines derived from crosses with sorghum line SC748-5 were genotyped. In 12 of the 13 lines the Xtxa6227 and Xtxp549 polymorphism associated with the Cg1 locus was still present, suggesting that Xtxp549 and Xtxa6227 could be useful for marker-assisted selection and for pyramiding of Cg1 with other genes conferring resistance to C. sublineolum in sorghum.

Quantitative Trait Loci Associated with Anthracnose Resistance in Sorghum

“…Thus, it is inconclusive if the same QTL for anthracnose resistance on chromosome 5 was identified in the two studies despite their overlapping genomic locations. Perumal et al (2009) andBurrell et al (2015) used resistant genotype SC748-5 to map an anthracnose-resistance QTL to chromosome 5, but this QTL at ~70 Mbp was ~5 Mbp away from the chromosome 5 QTL identified in SC414-12E in this study. Additionally, the segregation of F 2:3 progeny derived from a cross between SC748-5 and SC414-12E indicated the presence of different sources of resistance in these genotypes (Mehta et al, 2005).…”

“…Hence, a focus of applied breeding programs is to identify multiple genetic resistance sources and then pyramid resistance genes into elite cultivars. Both dominant and recessive sources of genetic resistance to anthracnose have been reported, and resistance loci have been mapped with molecular techniques that include random amplified polymorphic DNA (Boora et al, 1998;Singh et al, 2006), amplified fragment length polymorphisms (AFLPs) (Perumal et al, 2009), simple sequence repeats (Klein et al, 2001;Murali Mohan et al, 2010), complementary DNA-AFLP transcript profiling in combination with virus-induced gene silencing (Biruma et al, 2012), and single-nucleotide polymorphisms (SNPs) Burrell et al, 2015).…”

Genetic diversity and pathotype determination of Colletotrichum sublineolum isolates causing anthracnose in sorghum

“…From intercrosses between 11 different anthracnose resistant sorghum lines, Mehta et al (2005) found evidence for five different resistance genes, one of which (SC748-5) was effective in all test locations. Crosses between resistant and susceptible lines have been used to develop molecular markers for three different resistance genes, at least one of which is recessive (Boora et al 1998;Singh and Boora 2008;Ramasamy et al 2009;). The recessive gene in SC326-6 was tagged using short PCR primers to randomly amplify polymorphic DNA.…”

“…A dominant gene (Cg1) conferring anthracnose resistance to sorghum line SC748-5 (resistant to all 18 C. sublineolum isolates tested in this study) was also identified in a cross to BTx623. In that case, a specific highly virulent isolate was used with artificial inoculation to determine disease response after several attempts to rely on natural field infection proved inadequate for accurate classification due to a high rate of escapes (Ramasamy et al 2009). Although the genomic sequence of C. sublineolum has yet to be determined, it is reasonable to predict that numerous potential Avr genes are present.…”

Sorghum

“…Gene-forgene relationships have not been conclusively demonstrated and, therefore, assignment of races or pathotypes has been difficult [108]. However, genetic variation for resistance has been reported [109,111].…”