Submitted to: Plant Protection Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 11, 2011
Publication Date: November 11, 2011
Citation: Erpelding, J.E. 2011. Anthracnose field evaluation of sorghum germplasm from Botswana. Plant Protection Science. 47:149-156. Interpretive Summary: The breeding of disease resistant sorghum varieties is hindered by variation in the pathogen population resulting from frequent genetic changes, which reduces the effectiveness and longevity of available sources of host-plant resistance. Combining multiple resistance genes into a single variety is one method to prevent disease epidemics. However, new sources of resistance are needed to develop these varieties. Anthracnose is a fungal disease of sorghum that occurs worldwide; therefore, screening germplasm collections should identify new sources of anthracnose resistance. The USDA-ARS, National Plant Germplasm System maintains 157 sorghum accessions from Botswana of which 154 accessions were evaluated for anthracnose resistance at the USDA-ARS, Tropical Agriculture Research Station in Isabela, Puerto Rico. Approximately 30% of the sorghum accessions from Botswana showed resistance when inoculated with the anthracnose pathogen and evaluated during the 2007 and 2008 growing seasons. Annual rainfall is less than 700 mm in Botswana and previous research has shown that regions receiving less than 800 mm of annual rainfall are associated with a lower percentage of anthracnose resistant accessions. Wet and humid climatic conditions will result in greater disease development, which will contribute to greater selection pressure for disease resistance. Thus, in regions with a drier climate, such as Botswana, selection pressure will be lower resulting in fewer accessions showing anthracnose resistance as was observed in this study. However, a greater percentage of the accessions collected from villages near the Okavango Delta in the northern region of Botswana showed resistance to anthracnose. From this region, 58% of the accessions were rated as resistant. Whereas, the frequency of resistant accessions collected from villages in the southern regions of Botswana ranged from 22 to 36%. Annual rainfall is similar across the regions; however, the Okavango Delta is a large reservoir of water that would influence climatic conditions in the region. The occurrence of more favorable climatic conditions for the pathogen in this region of Botswana would contribute to greater disease pressure resulting in more anthracnose resistant accessions from the region. Additionally, the resistant accessions identified in this study should provide new genetic variation for the development of disease resistant sorghum varieties.
Technical Abstract: 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 the 2007 and 2008 growing seasons. A resistant response was observed for 69 accessions in 2007 and for 48 accessions in 2008 with no acervuli development observed on inoculated leaves. Infection severity was low for the susceptible accessions with a mean infection severity of 11% for the 85 susceptible accessions observed in 2007 and 17% for the 106 susceptible accessions identified in 2008. The low frequency of resistant germplasm is expected from a region of low annual rainfall, such as Botswana. The majority of the accessions were collected from the Central, Kgatleng, Kweneng, and Southern districts, where the frequency of accessions rated as resistant ranged from 22 to 36%. The highest frequency of resistant accessions was observed for the Ngamiland district with 58% of the accessions rated as resistant. The lowest mean infection severity was also observed for the susceptible accessions from the Ngamiland district; whereas, the highest mean infection severity was 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.