Status of Northen Leaf Blight, Phaeosphaeria maydis Leaf Spot, Southern Leaf Blight, Rust, Maize Streak Virus and Physiologic Specialization of Exserohilum turcicum in Kenya

Abstract

Exserohilum turcicum, Phaeosphaeria maydis, Bipolaris maydis, Puccinia polysora, Puccinia sorghi and maize streak virus were the most serious maize pathogens found in Kenya during a 1995/96 survey of 65 farms representing all the agro-ecological zones. Exserohilum turcicum - induced blight was observed in all maize producing areas with disease incidence reaching over 45%. Lesions were sometimes over 400 mm long by 25 mm in width. Southern leaf blight caused by Bipolaris maydis was most severe in the Kenyan maize granary located in the highlands west of the Rift Valley where it occurred alone or with Phaeosphaeria maydis leaf spot. Incidences of over 75% were recorded for southern leaf blight and Phaeosphaeria maydis leaf spot in western Kenya and over 85% for Phaeosphaeria maydis leaf spot in Thika, Nyeri, Muranga and Kirinyaga Districts of Central Province. Common rust caused by Puccinia sorghi was equally severe in the areas of Molo, Njoro and Bahati in Nakuru District with severity levels of over 65%. Lowland rust caused by Pucinia polysora was important in the coastal region with over 75% disease severity in Kwale District. Traces of lowland rust were observed in Kirinyaga District. Maize streak virus was severe in the Lake Victoria region of western Kenya, central areas of Kenya and in the Coast. This disease was severe where Napier grass (Pennisetum purpureum) with streak like symptoms was near the infected maize plots. Individual cultures of Exserohilum turcicum were not appreciably different in appearance but varied in growth rates at 22oC. A total of nineteen isolates of Exserohilum turcicum were classified into races using the Ht gene bearing maize differential inbred lines. Three isolates were race 0, three were race 1, one was race 2, one was race 3, two isolates were race 12, and eight did not fit in the known classification. These were named and grouped as k1, k2 and k3. The k3 race was virulent to HtN gene only. Four Kenyan and two American lines were inoculated with eight isolates of Exserohilum turcicum. All the Kenyan lines were susceptible to the isolates used. Tables of means comparisons and figures for disease occurrence and severity are provided. This is the first time disease prevalence and severity has been documented for maize in Kenya.