Status of sugarcane yellow leaf virus in commercial fields and risk assessment in Guadeloupe

Sugarcane yellow leaf virus (SCYLV), the causal agent of sugarcane yellow leaf disease, is present in Guadeloupe, but its incidence and distribution in commercial fields was unknown. Therefore, five sugarcane cultivars located in 48 plant cane fields in seven sugarcane growing areas in Guadeloupe were analysed for virus infection and populations of Melanaphis sacchari, the aphid vector of SCYLV. Twenty one of the 48 fields were also analysed in the first ratoon crop. Depending on the area of the field, 200 to 400 leaf samples per field were tested by tissue blot immunoassay to detect the virus, and presence of aphids was determined on 10% of sampled plants. In addition, virus incidence in five fields of second and third propagations of nursery stocks produced from tissue cultured plants was determined. Mean virus incidence in plant cane crops was 6.4%, and it ranged from 0% to 21% according to cultivar and geographical location. M sacchari was widespread in all areas. Mean virus incidence increased to 11.2% in the first ratoon crop, and it increased in all cultivars except in cultivar B69566. Cultivar B69566 consistently had the lowest virus incidence, whereas virus incidence was consistently high in cultivar R579, even if cultivar B69566 was more colonised by aphids. In the second stage nursery fields, virus incidence ranged from 2.5% to 17.3%. Overall, virus incidence did not increase in the third stage nursery step that derived from the second stage nurseries. SCYLV genotype REU was found in all commercial fields, whereas genotypes BRA and CUB were found only in a few samples from five fields. In Guadeloupe, SCYLV appears to be spread by aphid vectors and infected cuttings. Presence of a major virus genotype suggested that this genotype was more adapted to the local environment, or that the two other genotypes were only recently introduced and have not spread yet on the island. Yield losses may occur in extending cultivars such as R579, as it was shown in Reunion Island. Because variation in virulence exists between SCYLV genotypes, disease impact may vary in Guadeloupe in the future. (Résumé d'auteur