Reaction of improved maize (Zea mays L.) varieties to grey leaf spot (Cercospora zeaemaydis) in South and Southwest Ethiopia

Abstract

Grey leaf spot (GLS) is one of the most important diseases that constrain maize production and productivity in maize-growing areas of Ethiopia where a warm humid environmental condition prevails. Thus, this study was conducted to evaluate the reaction of 12 maize varieties to maize grey leaf spot under field conditions in Hawassa and Jimma, south and southwest Ethiopia, in 2014 and 2015 cropping seasons. The treatments consisted of twelve maize varieties. The experiment was laid out as a randomized complete block design (RCBD) and replicated three times per treatment. Disease severity was assessed as the proportion of leaf area affected by the disease on 10 randomly tagged plants in the middle two rows. The area under disease progress curve (AUDPC) and disease progress rates were estimated from the percent severity index (PSI). Similarly, grain yield was determined after harvest and converted into yield per hectare. The results revealed that the final disease severity varied from 37.33 to 84.83 PSI and 39.5 to 81.83 PSI at Jimma; 35.67 to 78.12 PSI and 35.67 to 78.12 PSI at Hawassa in 2014 and 2015 main cropping seasons, respectively. AUDPC varied from 1426.67 to 3281.67%-days in Jimma and from 1476.67 to 3225%-days in Hawassa in 2014 main cropping season; 1176.17 to 3031.67%-days in Jimma and 1226.67 to 2975%-days in Hawassa in 2015 main cropping season. The varieties Gibe-2, BH-543 and Local-K exhibited high disease severity, high AUDPC and high infection rate and were categorized as highly susceptible maize varieties. The results also indicated that BH-660 and BH-670 were considered resistant to grey leaf spot across the two locations and had low disease severity as well as low AUDPC values. It is concluded that under field conditions, different maize varieties responded differently to grey leaf spot and the disease severity was strongly affected by the use of different resistance levels of maize varieties and difference in the environmental conditions. It is therefore, promising to use the two maize varieties, such as BH-660 and BH-670, were considered as resistant under field conditions and that are recommended to be used by farmers in the study areas and elsewhere with similar agro-ecologies in Ethiopia.

Keywords: AUDPC, disease progress rate, disease severity index, grey leaf spot, grain yield, Zea mays