Molecular characterization of phytoplasmas associated to sugarcane yellow leaf syndrome (YLS) in Cuba. | Caracterización molecular de fitoplasmas asociados al síndrome del amarillamiento foliar de la caña de azúcar (YLS) en Cuba.

Sugarcane is the main crop in Cuba. Among diseases affecting this crop in our country, Sugarcane Yellow Leaf Syndrome (YLS) is one of the most important. YLS was first informed in Hawaii in 1988 and recently, typical symptoms of the disease have been observed in Cuban sugarcane growing areas. According to the few information about YLS and the considerable losses it causes in susceptible varieties, the aims of this work were: to detect the presence of phytoplasmas associated with YLS in Cuba, to determine the genetic variability of phytoplasmas associated with the disease and their relationship with those informed in other countries, to establish a molecular diagnostic method for the detection of phytoplasmas with efficacy levels over 90%, to evaluate a field diagnostic method for the detection of the disease with a high porcentage of coincidence with the detection of phytoplasmas by molecular methods, and lastly, to determine the presence of phytoplasmas in the main commercial varieties of the country. The association phytoplasmas-YLS was strongly demonstrated in Cuba. The disease is associated with at least 3 genetically different phytoplasmas. The predominant one belongs to subgroup I-A from Aster Yellows Group (AY), which is a new isolate of AY-27 phytoplasma from Canada and it was named ScYPIII-Cu (AY-27 Cuban isolate). A new subgroup from AY which was named Subgroup I-J: Cuban Sugarcane Yellow Leaf Phytoplasma, CScYLP was selected. The presence of ScYPI-Afr phytoplasma, from Western X Group (WX) was also found. The combination of nested PCR (polymerase chain reaction) and the digestion of nPCR products with the restriction enzyme HaeIII resulted an efficient system for the detection of phytoplasmas, including latent and multiple infections. A molecular system for the specific detection of phytoplasmas with validation parameters over 98%, as well as a field diagnostic method based on leaf brix values, with a compared efficacy of 90.68 and 90.34% related to the presence of symptoms and the detection of phytoplasmas by nPCR/HaeIII were validated. Surveys demonstrated the presence of YLS in all Cuban provinces, affecting commercial and seed areas with a 23% of national propagation. The major infection percentages were found in Cienfuegos (34.11%), and Central and Oriental regions (26.81% and 23.90% respectively). The disease mainly affects plants of 13 months old or more, although its early presence was evidenced in the first 3 months of age corresponding to a 12.92% infection percentage. Results related to the presence of YLS and the genetic variability of phytoplasmas associated with the disease are very new aspects for Cuba and the world.