Screening of sorghum (sorghum bicolor) genotypes for resistance to covered kernel smut disease (sporosorium sorghi) for western kenya

Abstract

Sorghum is an important food security crop for arid and semi-arid tropics but its production is hampered by covered kernel smut disease (CKSD) which is a seed borne panicle disease caused by fungus Sporosorium sorghi. The fungus attacks susceptible sorghum genotypes causing yield losses estimated at 43% in Western Kenya posing a major threat to sorghum production. The current control measures involve the use of chemical, cultural and biological methods but they are costly, and environmentally unfriendly, laborious and ineffective and hence not sustainable. Most researchers have proposed the use of resistant genotypes which is affordable and sustainable to small scale farmers, but such varieties are not available. Thus, a study was conducted in 2019 growing seasons in order to determine the response of selected sorghum genotypes to CKSD under field and greenhouse conditions, and determine heterosis for agronomic traits in sorghum single crosses developed from tolerant and susceptible varieties to control CKSD as a first step to initiate introgression breeding for tolerance to the disease. A total of 15 genotypes were evaluated in two disease hotspot areas of Migori and Homa Bay counties in a Randomized Complete Block Design (RCBD) replicated thrice. Each genotype was planted in a 2.25 X 4m plot at spacing of 75 X 20cm. For controlled experiment in the greenhouse, the 15 genotypes were planted in pots in a Completely Randomized Design (CRD) also replicated thrice. In both cases, data on disease incidence, severity and grain yield was collected per genotype and analyzed using R for windows (version 3.6.2) and means separated using Tukey’s test. Resistant genotypes were identified then crossed with the susceptible lines to incorporate covered kernel smut disease resistance through hand emasculation. Results showed significant differences among genotypes for disease incidence, severity and yield parameters. The disease incidence was evenly distributed and it varied significantly (p<0.001) between the sorghum genotypes per location. A range of 0-60% and 0-69% disease incidence was recorded under field and greenhouse conditions with Nyadundo2 and C26 having 60% and 69% respectively, while T53, T30, IS3092, N4 and N68 had 0% incidence. Similarly, severity also followed the same trend with Nyadundo 1 having a score of 5 while T53 scored 1. T53 produced the highest mean grain yield of 3.63t/ha while Seredo had the lowest mean grain yield of 0.20t/ha. Significant heterosis for seed weight, panicle traits, plant height and 50% days to flowering were observed on the eight F1 crosses. Various crosses showed significant heterosis in different traits. For instance, MUK60 X N13 had negative heterosis and heterobeltiosis for 50% days to flowering and plant height while NYADUNDO1 X IESV92038/SH had a positive heterosis and heterobeltiosis for panicle traits. This study has identified and developed six crosses which are potential sources of resistance for covered kernel smut disease that can be utilized to significantly improve yields in hotspot areas of western Kenya or for further breeding.