J.H. Daugrois1 , V. Dumont1, P. Champoiseau1, L. Costet2, R.
Boisne-Noc1 and P. Rott3(1) Station de Roujol, CIRAD-CA, 97170,
Petit Bourg, Guadeloupe, French West Indies
(2) Laboratoire de Phytopathologie, CIRAD, BP 180, 97455 Saint
Pierre Cedex, Réunion Island, France
(3) UMR 385 ENSAM-INRA-CIRAD Biologie et Génétique des Interactions
Plante-Parasite, TA 71/09, Avenue Agropolis, 34398 Montpellier
Cedex 5, France
Abstract Two sugarcane plots were set up in Guadeloupe with
disease-free tissue cultured plants in a banana growing location
distant from sugarcane fields. Thirteen weeks after planting
sugarcane in the field, a Xanthomonas albilineans strain belonging
to serotype 3 (strain XaS3) was detected in water sampled at
sunrise on the leaves in the first plot. This strain randomly
invaded the sugarcane canopy. Seven weeks later, a new strain
belonging to serotype 1 (strain XaS1) appeared on leaves and
populations of strain XaS1 progressively increased on the leaf
surface, whereas populations of strain XaS3 progressively
decreased. Leaf scald symptoms were first noted 26 weeks after
sugarcane planting. However, only strain XaS1 was isolated from
leaves and a few sugarcane stalks showing symptoms. Both strains
also colonized the second field plot, which was studied at the end
of the experiment to avoid human interference of aerial
contamination of sugarcane. After inoculation of three sugarcane
cultivars by the decapitation technique, strain XaS1 was as
virulent or more virulent than five other strains of X. albilineans
isolated from diseased sugarcane plants in Guadeloupe. Although
strain XaS3 colonized a few stalks, it failed to produce any
symptoms and was the least virulent strain. Leaf surface
colonization by X. albilineans was reproduced in a greenhouse trial
by spraying the pathogen on sugarcane foliage. After 8 weeks, the
pathogen was isolated from disinfected leaf blades. Although the
leaf scald pathogen is thought to be mainly transmitted by infected
cuttings, aerial transmission of X. albilineans is also known to
occur. These results indicate the importance of sugarcane
phyllosphere colonization by virulent strains in the
epidemiological cycle of leaf scald disease in Guadeloupe.
