Anthracnose resistance genes in sorghum: Characterization and molecular markers

Anthracnose resistant sorghum germplasm were crossed among each other to classify them according to the source of resistance. Analysis of the progeny of these crosses revealed at least seven different sources of anthracnose resistance were present in this germplasm. Segregating progeny from the cross of a representative germplasm from each group to the susceptible parent BTx623 indicated that four sources are controlled by different dominant single gene or tightly linked genes and three sources are inherited by different single recessive gene or tightly linked genes. Four populations representing different resistance groups, along with a set of differentials, were selected for studying effectiveness of the resistance sources across locations and for identifying molecular markers for selected resistance sources. A set of progeny from these populations was evaluated in six locations: College Station, Texas; Rohwer and Pine Tree. Arkansas; Cairo, Georgia; Mansa, Zambia; and Bamako, Mali. Only SC748-5 derived progeny were resistant at all the locations, while SC991-14E resistant progeny were moderately resistant. Progenies of SC414-12E identified as resistant at College Station, were susceptible at two locations known to have highly virulent isolate(s) of Colletotrichum graminicola. Reversal of resistance was observed in one population of SC155-14E*BTx623 (1999), however resistant F_2:3 progeny of the cross evaluated in 2000 and reciprocal cross were consistently resistant across years and locations. The basis for this observation has not been determined, but two complementary linked recessive resistance genes is a possibility. Amplified fragment length polymorphism DNA fingerprinting and modified bulk segregant analysis techniques were used to determine markers linked to resistance sources, and MAPMAKER/EXP (v 3.0b) was used to establish the linkage groups. For the SC155-14E derived population, separate marker analysis was carried out for 1999 and 2000 populations. No linkages could be identified for the BTx623*SC155-14E (1999) population. Putative linkages were identified for SC748-5 and SC155-14E (2000) derived populations. Expansion of population size to confirm the markers and for further fine mapping is required to be able to perform marker-assisted selection. Several crosses have been made for gene pyramiding and for transferring anthracnose resistance into the elite germplasm.