Etiology, Effect of Soil pH and Sweetpotato Varietal Reaction to AlternariaLeaf Petoile and Stem Blight in Kenya

Abstract

Leaf petiole and stem blight disease is commonly encountered on sweetpotato in Kenya. A study was carried out to confirm the causal agent of the disease in different agro-ecological zones of Kenya and determine the importance of soil pH as well as field conditions on disease development. Diseased leaf and vine tissues were collected and pathogen isolated. The Kabete, Kakamega, Busia (Alupe), and Kabondo isolates were identified as Alternaria bataticola while the Kisii isolate was identified as Alternaria alternata. Pathogenicity and virulence of different isolates of A. bataticola and A. alternata were investigated under greenhouse conditions. Within 4 - 6 days following artificial inoculation, and depending on sweetpotato cultivar, the fungus produced characteristic symptoms typical of Alternaria leaf petiole and stem blight. All the isolates were pathogenic and differences in virulence depended on isolate source and conidial concentration. The Kabete isolate was more virulent than Kakamega, Kabondo and Alupe isolates, whose virulence did not differ significantly from each other (P<0.05). In a greenhouse study the different pH levels did not influence disease severity (P<0.05). However, there were significant differences in disease severity among the cultivars evaluated. Alternaria leaf and stem blight caused by Alternaria bataticola was monitored in field plots of sweetpotato accessions selected from the CIP germplasm collection field. Cultivars Viola (440046) and Yanshu 1 (440024) were more susceptible than other entries. The lowest disease levels were observed on cultivar Jayalo.