First Report of Leaf Scald Disease and Ratoon Stunting Disease of Sugarcane in French Guyana.

In December 1995, leaf scald symptoms were observed in sugarcane (Saccharum sp.) cultivar B64277 in French Guyana. Symptomatic plants occurred both in a sugarcane germplasm collection near the road between Sinnamary and Saint-Elie and in a nursery near Sinnamary. Sugarcane imported from Martinique had been used to establish the germplasm collection that in turn had been used to establish the nursery. Ten-month-old mature plants in the germplasm collection had abnormal side shoots on the lower part of the stalks and suckers (nonmillable stalks) with white scalded areas on leaves. Leaves on 1-month-old shoots in the nursery exhibited chlorosis and white, pencil-line streaks. Samples prepared from symptomatic stalks from the two locations were plated on a selective medium (1), and two isolates of Xanthomonas albilineans were recovered. Both of these isolates caused leaf scald symptoms on leaves of sugarcane cultivar B69566 inoculated by a decapitation technique, and belong to serovar 3 previously reported in the Caribbean from Guadeloupe, Martinique, and St. Kitts. The RFLP (restriction fragment length polymorphism) pattern of these two isolates was different from the 54 patterns among 218 other strains collected throughout the world (2), but similar to the pattern of a strain of serovar 3 from Martinique. This indicated that the pathogen might have been introduced with cuttings imported from Martinique. Three stalks of mature cane from varieties B5992, B64277, and R570 from the germplasm collection were tested for the presence of Clavibacter xyli subsp. xyli, causal agent of ratoon stunting disease. Immunofluorescence tests on sap (3) revealed the presence of the pathogen in the three stalks of B64277. All sugarcane plants in the nursery and the germplasm collection were destroyed by the use of glyphosate sprays in January 1996 in an attempt to arrest the spread of the two bacterial pathogens. In order to obtain healthy seed cane for future planting, a new germplasm collection of 0.6 ha and consisting of 11 cultivars was planted in January 1996 with disease-free, tissue-cultured plants provided by the CIRAD sugarcane breeding station in Guadeloupe. References: (1) M. J. Davis et al. Plant Dis. 78:78, 1994. (2) M. J. Davis et al. Phytopathology 87:316, 1997. (3) M. J. Davis and J. L. Dean. Plant Dis. 68:896, 1984.