P. Champoiseau, Cirad, UPR Multiplication Végétative, Petit-Bourg, Guadeloupe, F-97170 France;
P. Rott, Cirad, UMR Cirad-Inra-Montpellier SupAgro Biologie et Génétique des Interactions Plante-Parasite (BGPI), TA A-54/K, Campus International de Baillarguet, Montpellier Cedex 5, F-34398 France; and
J.-H. Daugrois, Cirad, UPR Multiplication Végétative, Petit-Bourg, Guadeloupe, F-97170 France
Three separate field trials were established in Guadeloupe under different agronomic and rainfall conditions to study phyllosphere contamination and infection of sugarcane plants by Xanthomonas albilineans, the causal agent of sugarcane leaf scald. Disease-free and leaf scald susceptible cv. B69566 was planted and monitored during three 1-year crop cycles. Presence of leaf scald contaminated sugarcane fields in the proximity of the disease-free trials appeared critical in early contamination of the sugarcane phyllosphere. Later on, particular meteorological events, such as tropical storms, were also important in aerial spread of the pathogen. A positive correlation was found between epiphytic populations of X. albilineans and severity of leaf necrotic symptoms, but occurrence of leaf symptoms was not always related to subsequent stalk infection. However, when the data of the three crop seasons were considered together, a high correlation was found between rainfall and maximum epiphytic populations of X. albilineans, and between rainfall and subsequent stalk infections. Consequently, rainfall is a key factor to be considered in evaluation of risks of leaf scald epidemics, and protocols for propagation of healthy sugarcane material and screening methods for leaf scald resistance may have to be revised in humid tropical locations.