Anthracnose field evaluation of sorghum germplasm from Botswana

Sorghum anthracnose is a disease of worldwide importance and host-plant resistance is the most practical method of disease management. In this study, 154 sorghum accessions from the Botswana collection maintained by the United States National Plant Germplasm System were inoculated with Colletotrichum sublineolum and evaluated for disease resistance at the Tropical Agriculture Research Station in Isabela, Puerto Rico during 2007 and 2008. A resistant response was observed for 69 accessions in 2007 and for 48 accessions in 2008 with no acervuli development observed on inoculated leaves. The low frequency of resistant germplasm is expected from a region of low annual rainfall. However, disease severity was low for the susceptible accessions with a mean severity of 11% for the 85 susceptible accessions observed in 2007 and 17% for the 106 susceptible accessions identified in 2008. The highest frequency of resistant accessions was observed for the Ngamiland district with 58% of the accessions rated as resistant, whereas the frequency of resistant accessions ranged from 22% to 36% for the other districts. The lowest mean disease severity was also observed for the susceptible accessions from the Ngamiland district with the highest mean disease severity observed for susceptible accessions from the Kgatleng district. The resistant accessions identified in this study would be useful for the development of disease resistant varieties and the results indicated an ecogeographic association with disease resistance.