Morphological and molecular characterization of Fusarium spp. associated to the regional occurrence of wilt and dry bud rot in Agave tequilana

Abstract

Wilt and dry bud rot of the agave (Agave tequilana var. azul) are diseases of high economic impact for this crop. The implication of Fusarium spp. in both diseases at a regional context was determined in this research. Root and soil samples were collected from 40 commercial plantations located in 13 counties at Los Altos, Jalisco an important cultivation region of agave azul in Mexico; Inoculum charge, as a Fusarium Index was obtained base on colony units (Fusarium vs total fungi) and its relationship with pH and organic matter were estimated from each sampling plantation. A total of 109 isolates were morphologically characterized as Fusarium spp. of which 25 were selected for molecular identification with ITS and EF-1a. The selection considered symptomatology, macro and microscopic characters and prevalence of colony types observed in vitro in Komada, Sabouraud, SNA and CLA media. The cultural and morphological characters evaluated were mycelial coloration, size, shape and septation of macro and microconidia, and length and number of phialides. Five species were associated with wilt and/or dry bud rot within three phylogenetic complexes: F. oxysporum of the Fusarium oxysporum species complex (FOSC) with 56% (46.2 % soil y 66.7 % root) regional representation; F. solani, F. falciforme and Fusarium sp. of Fusarium solani complex (FSSC) (40%); and Fusarium sp. of Fusarium fujikuroi complex (FFSC) (4%). MO and pH correlated inversely with Fusarium Index (r2=0.680.70). It is postulated that wilt and dry bud rot of blue agave constitute a syndrome in which several Fusarium species are associated and parasitically specialized. A single isolate per each species complex was found associated specifically to each or both symptoms. Most isolates were associated to wilting with prevalence of F.oxysporum.