Factors affecting development of covered kernel and long smut diseases and yield losses of grain sorghum

Sorghum plants ( Sorghum bicolor linn. Moench) is the important grains crop for human being and animals in Upper Egypt, grain sorghum are attacked by certain smut diseases causing considerable losses in the grain yield. Covered kernel smut (CKS) caused by Sporisorium sorghi and long smut (LS) caused by Sporisorium ehrenbergii are one of the most significant diseases in sorghum production especially where untreated seed is planted. Results of this study showed that the high rates of inoculum of S. sorghi and S. ehrenbergii teliospores playing a great factor to increasing the infection with CKS and LS diseases and yield losses, while they reduced the yield of grains. Sorghum cultivars Giza-15 and Dorado differed in their ability to infection with these two types of CKS and LS respectively. Results revealed that due to infection by CKS disease Giza-15 (highly susceptible) recorded the lowest yield and highest yield losses (2.30 kg and 51.78%, respectively) and (2.25 kg and 52.22%, respectively) in both 2014 and 2015 seasons, respectively. While Shandweel-305 cv. (highly resistant) recorded the highest yield and lowest yield losses (3.11 kg and 12.39%, respectively) and (3.15 kg and 11.26%, respectively) in both 2014 1nd 2015 seasons, respectively. Also, due to infection by LS disease, Dorado cv. (highly susceptible) recorded the lowest yield and highest yield losses (2.53 kg and 29.72%, respectively) and (2.56 kg and 30.99%, respectively) in both 2014 1nd 2015 seasons, respectively. While Shandweel-305 cv. (moderately resistant) recorded the highest yield and lowest yield losses (3.35 kg and 6.42%, respectively) and (3.33 kg and 3.47%, respectively) in both 2014 1nd 2015 seasons, respectively. Different planting dates (1 st May, 1 st June and 1 st July of the early, optimal and late planting, respectively) also affected on the response of grain sorghum to infection by both smut diseases and yield losses. Therefore, adjustments to time of sowing often make it possible for sorghum to escape from smut diseases by ensuring that the crop is not in the most disease susceptible stage when smut inoculum is abundant and the weather favorable for infection and disease spread.