Distribution of blight diseases and characterisation of phytopthora infestans of tomato in selected agro-ecological regions of Uganda

Abstract

Blight diseases are among the most devastating biotic stresses of tomato in Uganda, causing yield losses of up to 95.8% in susceptible varieties in East Africa. Blights impact on both the quality and quantity of tomato produced, and hence constitute a threat to food security, nutrition and income generation. Scarcity of information on the severity and incidence of blight diseases constrain effective monitoring as well as management attempts to combat blight diseases. This study investigated the incidence, severity of both early, and late blight diseases in four agro-ecological zones of Uganda; i.e., Northern, Eastern, Central and Western agro-ecological zones and evaluated genetic variability of Phytopthora infestans isolates across agro-ecological zones and districts. Tomato plants from farmer fields infected with late or early blight diseases were identified, followed by collection of leaf samples for pathogen isolation, DNA extraction in the laboratory. Sequencing of P. infestans was out-sourced from Macrogen, UK. There were significant differences in the incidence and severity of both blight diseases (P<0.05) across agro-ecological zones, districts and farms. The highest incidence of late blight (23%) was recorded in Central Uganda and lowest in Northern Uganda (5%). For early blight, Northern Uganda had highest disease incidence (76%) and lowest in Western zone (8%). The development of these diseases is linked to varieties, crop development stages, environmental factors, cultivation and field management. Isolates of P. infestans showed high nucleotide diversity (Pi = 0.41) and high level of genetic differentiation, indicating infrequent gene flow (FST = 0.55). There was significant difference (P < 0.05) in the genetic variability of P. infestans isolates across districts as revealed by the analysis of molecular variance but not across agro-ecological zones. High genetic variation of a pathogen can lead to severe disease symptoms in plants and rapid disease transmission in populations. To manage blight diseases effectively, continuous monitoring of the diseases across Uganda is essential and understanding how P. infestans population has changed over time can enhance the effectiveness of current management strategies.