Daugrois, J.-H., Champoiseau, P. and Rott, P. 2005. Epiphytic colonization and infection by Xanthomonas albilineans of two sugarcane cultivars differing in resistance to leaf scald disease. Proceedings International Society of Sugarcane Technologists Congress. 25:678-685.

Abstract: Colonization of the sugarcane leaf canopy by Xanthomonas albilineans appears to be an important step in the epidemiological cycle of leaf scald disease in Guadeloupe. Previous studies showed that healthy sugarcane plants can be infected by X. albilineans after aerial transmission of the pathogen. Variation in colonization of the leaf canopy of sugarcane cultivars differing in resistance to leaf scald and progress of pathogen populations during consecutive crops is, however, unknown. A trial was set up in Guadeloupe with two sugarcane cultivars differing in resistance to leaf scald, B69566 (susceptible) and B8008 (resistant). Disease-free tissue-culture propagated sugarcane was planted in the field in 1999. Epiphytic populations of X. albilineans were regularly monitored for 3 crops (plant cane and two ratoons) by measuring bacterial populations in water droplets sampled on sugarcane leaves at sunrise. Infection of sugarcane stalks by X. albilineans was determined by isolating the pathogen from the stalk sap after 11-12 months of growth in each crop cycle. In plant cane, the pathogen was first detected on the leaf canopy of both cultivars after three months of plant growth. Once the canopy was colonized by X. albilineans, bacterial populations increased more rapidly on cultivar B69566 than on cultivar B8008. However, once the leaf canopy was entirely colonized, epiphytic population size of the pathogen on both cultivars was similar, whatever the crop cycle. Highest epiphytic populations varied between crop cycles and reached 5 x 10^6, 4 x 10^4 and 6 x 10^5 bacteria per mL of water droplet in plant cane, first and second ratoon crops, respectively. Percentage of stalk infection by X. albilineans varied according to cultivar and, in cultivar B69566, concurrently with epiphytic populations of the pathogen. The size of epiphytic populations appears therefore critical, but not sufficient, for stalk infection after aerial transmission of the leaf scald pathogen.