Evaluation of A1, A2, A3, A4(M), A4(G) and A4(VZM) cytoplasms in iso-nuclear backgrounds for grain mold resistance

Breeding for resistance to grain mold, an economically important disease of sorghum, has been only partially successful. Hybrid technology is well developed in sorghum due to availability of the cytoplasm male sterility (CMS) system and at present almost all commercial hybrids are based on the A₁ CMS system. To compare the available alternate CMS systems for grain mold resistance, 72 hybrids were produced by crossing 36 A-lines (six CMS systems; A₁, A₂, A₃, A_4(M), A_4(G), A_4(VZM) each in six nuclear backgrounds) with two common restorers, and were evaluated during the 2006 and 2007 rainy seasons in grain mold nursery at ICRISAT. Data analyses indicated influence of cytoplasm on the responses of hybrids to grain mold infection as measured by panicle grain mold resistance (PGMR) score. The A₁ cytoplasm seemed to contribute to grain mold resistance followed by A_4(VZM) and A₂ cytoplasms. The A_4(M) cytoplasm had superior general combining ability (GCA) effects while the A₁ and A_4(VZM) cytoplasm based hybrids had superior specific combining ability (SCA) effects on the PGMR score. Almost all hybrids had significant mid-parent heterosis. The A₁ cytoplasm is the best suited for the development of sorghum hybrids for the rainy season adaptation with grain mold resistance. However, use of alternate cytoplasms (A₂ and A_4(VZM)) for hybrid development will not increase susceptibility to grain mold in commercial grain production.