Phylogeny and pathogenicity of soilborne fungi associated with wilt disease complex of tomatillo (Physalis ixocarpa) in northern Sinaloa, Mexico

Abstract

Wilt disease complex is one of the most important diseases of tomatillo (Physalis ixocarpa) in the production areas of Mexico. Disease symptoms include wilting, poor growth, discoloration of vascular tissues, root rot, and death of plants. The aims of this study were to identify the fungi associated with wilt disease complex of tomatillo by the combination of phylogenetic analyses and morphological characterization, as well as to determine their pathogenicity and virulence on tomatillo seedlings. A total of 88 fungal isolates were obtained from symptomatic plants from 19 tomatillo fields distributed in northern Sinaloa, Mexico. Subsequently, a subset of 37 isolates representing the range of geographic origin was selected for further morphological and molecular characterization as well as pathogenicity tests. Phylogenetic analyses using Maximum Likelihood were used to identify 15 isolates of Rhizoctonia (ITS sequence data), 14 isolates of Fusarium (EF-1α sequence data), five isolates of Macrophomina (ITS, EF-1α, BT, and ACT sequence dataset) and three isolates of Neocosmospora (EF-1α sequence data) to species level. Pathogenicity tests were performed on tomatillo seedlings (cv. Gran Esmeralda) under greenhouse conditions. Phylogenetic analyses of 37 fungal isolates allowed the identification of Rhizoctonia solani AG 4-HGI (40.5%), Fusarium oxysporum (29.8%), Macrophomina phaseolina (13.5%), F. nygamai (8.1%) and Neocosmospora falciformis (8.1%). All fungal species were found to be pathogenic on tomatillo seedlings but a significant difference in disease severity was observed. To our knowledge, F. nygamai, M. phaseolina and N. falciformis were recorded for the first time infecting tomatillo in Mexico and worldwide.