Response of sorghum accessions from Chad and Uganda to natural infection by the downy mildew pathogen, Peronosclerospora sorghi in Mexico and the USA

In this study, 78 accessions from Chad, Central Africa and 20 photoperiod insensitive accessions from Uganda, East Africa were evaluated for downy mildew resistance in Ocotlan, Mexico in 2004 and 2005. Ninety-four of these accessions were also evaluated at two locations in Wharton County, Texas, USA, in 2005. Accessions were planted in a randomized complete block design with each sorghum accession replicated three times. Disease incidence was determined from natural infection. Disease incidence varied between locations, with the highest mean disease incidence observed for the Mexican evaluation. Germplasm from Chad also showed a higher mean disease incidence than germplasm from Uganda. Several sources of downy mildew resistance were identified. Three accessions PI282860, PI282864, and PI563505 from Chad were shown to possess high levels of downy mildew resistance in Mexico and Texas, whereas PI282843, PI282877, PI549196, and PI563438 also from Chad exhibited high levels of resistance to the disease in Texas. Accessions PI297210, PI576386 and PI576395 from Uganda also showed downy mildew resistance in Mexico and Texas. These sorghum accessions from Chad and Uganda can be utilized in breeding for downy mildew resistance in Mexico and Texas.