Inheritance of Resistance to Turcicum Leaf Blight in Sorghum

Abstract

Sorghum (Sorghum bicolor) has global socio-economic importance and is as model plant species for many tropical grasses with complex genomes. It is frequently devastated by Turcicum leaf blight, caused by Exserohilum turcicum, leading to considerable grain and fodder yield losses. Developing varieties with resistance against E. turcicum is the most cost-effective way to manage the disease. However, inheritance of resistance to E. turcicum in sorghum is poorly understood. Studies were carried out in Uganda to investigate the mode of inheritance of resistance to E. turcicum in sorghum under greenhouse and field conditions. Segregating families derived from a cross of MUC007/009 (a local resistant accession) and Epuripuri (susceptible, an elite sorghum variety) were used along with the two parents in the study. Evaluations of families also included four checks, namely GAO6/106 (moderately resistant), Lulud (susceptible), MUC007/010 (resistant) and GAO6/18 (moderately susceptible). Disease severity of F₂ plants in the greenhouse were skewed toward resistance. In the field, the resistant parent had much lower disease severity than the susceptible parent. However, there was no difference between both parents under greenhouse conditions. Under field conditions, F2:3 progeny disease scores were skewed towards resistance, suggesting quantitative inheritance of resistance. In maize resistance to Turcicum leaf blight is both qualitative and quantitative. This study shows that resistance in sorghum to Turcicum leaf blight is quantitative suggesting that quantitative resistance in both maize and sorghum, close relatives, predates speciation. Breeding for such complex traits is often compounded by genotype by environment interactions and as such, marker assisted selection could hasten the process. Further characterisation of resistance loci and mapping of quantitative trait loci will support effective more resistance breeding.

Keywords: Exserohilum turcicum, Sorghum bicolor, transgressive segregation, Uganda

African Crop Science Journal, Vol. 20, Issue Supplement s1, pp. 155-161