Mango nurseries as sources of Fusarium mexicanum, cause of mango malformation disease in central western Mexico

Malformation is the most important disease of mango in Mexico. It affects floral and vegetative shoots, and reduces fruit production. Although several species of Fusarium cause the disease worldwide, F. mexicanum is most important in Mexico. To better understand epidemiology of disease in Mexico, we studied mango nurseries as a source of infected planting material. In 2011, 2012 and 2014, 20 mango nurseries in the states of Colima (1 nursery), Jalisco (1 nursery), Guerrero (6 nurseries) and Michoacan (12 nurseries) were examined for floral and vegetative symptoms of the disease. Although malformed plants were not observed in Colima, Guerrero and Jalisco, malformed mango seedlings and grafted plants were observed in 10 commercial nurseries in Michoacan in 2011 and 2012. Thirty-three isolates from a total of 197 symptomatic plants were identified as F. mexicanum, based on morphological and genetic criteria. Analyses of partial sequences of the EF-1 alpha and beta-tubulin genes and mating type indicated that isolates of F. mexicanum from mango nurseries are mostly a single clonal population, identical to F. mexicanum isolates previously described from mango orchards in Michoacan. Thus, mango nurseries in Michoacan could be a significant source of inoculum when new mango orchards are established in the state. Efforts should be made to produce and utilize pathogen-free planting material during orchard establishment.