Résumé
Sugarcane yellow leaf was diagnosed for the first time in Guadeloupe in 1996 and in Martinique in 1997. Affected plants show early leaf yellowing, which starts from the leaf midrib. This emerging disease, transmitted by aphids and cane cuttings, is caused by a polerovirus called Sugarcane yellow leaf virus (SCYLV). SCYLV is distributed worldwide and occurrence of at least seven genotypes has been reported, three of which were identified in the French West Indies. In order to control epidemics of this disease, which affected almost 30% of sugarcane plants in commercial fields in Guadeloupe in 2010, we need to understand its local spread. Previous studies showed that (i) spread of yellow leaf by the vector in virus-free fields is regulated by rainfall that impacts primary infection due to immigrant aphids, and (ii) virus genotypes vary in virulence and infection capacity. Based on these results, spread of the disease since its emergence in commercial fields in the French West Indies was characterized using SCYLV diagnosis by tissue blot, computing of climate data, and identification of virus genotypes with genotype specific primers. In Guadeloupe, SCYLV incidence in fields has increased progressively over the last decade, from 0.6% in 2000 to 1.7% in 2003, 14% in 2005, and 28% in 2010. On the other hand, in Martinique, virus incidence has been high from the early years of emergence (30% in 1999) and it has remained at this level (32% in 2005). Data analyses showed that rainfall, impacting vector dynamics, is one of the key factors in disease epidemics. Resistance of sugarcane varieties to yellow leaf and interactions between sugarcane varieties and SCYLV genotypes also affect disease incidence. Spread of an emerging vectored disease such as yellow leaf appears, therefore, to be regulated by vector dynamics, as well as host and pathogen genetics. (Résumé d'auteur)