Identification and characterization of a novel etiological agent of mango malformation disease in Mexico, Fusarium mexicanum sp. nov.

The primary objective of this study was to characterize Fusarium spp. associated with the economically devastating mango malformation disease (MMD) in Mexico. In all, 142 Fusarium strains were isolated from symptomatic mango inflorescences and vegetative tissues in eight geographically diverse Mexican states from 2002 through 2007. Initially, all the Mexican isolates were screened for genetic diversity using appolymerase chain reaction and random amplified polymorphic DNA markers and were grouped into seven distinct genotypes. Based on results of these analyses, evolutionary relationships and species limits of the genetically diverse MMD-associated Fusarium spp. were investigated using multilocus DNA sequence data and phylogenetic species recognition. Maximum parsimony analyses of a five-locus data set comprising 5.8 kb of aligned DNA sequence data indicated that at least nine phylogenetically distinct Fusarium spp. within the Gibberella fujikuroi species complex are associated with MMD, including one species within the African clade (Fusarium pseudocircinatum), two species within the Asian clade (F. mangiferae and F. proliferatum), and at least six species within the American clade (F. sterilihyphosum and five undescribed Fusarium spp.). Molecular phylogenetic analyses indicate that a novel genealogically exclusive lineage within the American clade was the predominant MMD associate in Mexico. This new Fusarium sp. caused MMD and could be distinguished from all other known species morphologically by the production of mostly sterile, coiled hyphae which are typically associated with sporodochial conidiophores together with unbranched or sparsely branched aerial conidiophores. Koch's postulates were completed for isolates of the new species on nucellar seedlings of mango cv. Ataulfo. This pathogen is formally described herein as F. mexicanum.

Characterization of colletotrichum isolates from tamarillo, passiflora, and mango in Colombia and identification of a unique species from the genus.

ABSTRACT This study was conducted to identify the species of Colletotrichum infecting tamarillo, mango, and passiflora in Colombia and to assess whether cross-infection between host species is occurring. Isolates of Colletotrichum spp. from tamarillo (n = 54), passiflora (n = 26), and mango (n = 15) were characterized by various molecular methods and by morphological criteria. Morphological characterization grouped the tamarillo isolates as C. acutatum and the passiflora and mango isolates as C. gloeosporioides. Species-specific primer analysis was reliable and confirmed grouping of the tamarillo isolates (besides Tom-6) as C. acutatum and the mango isolates (besides Man-76) as C. gloeosporioides. However, DNA of the passiflora isolates was not amplified by either C. acutatum- or C. gloeosporioides-specific primers, but reacted with a new primer, Col1, designed according to the internal transcribed spacer (ITS) 1 region of these isolates. Isolates Tom-6 and Man-76 also reacted positively with the Col1 primer. All the isolates reacting with the C. acutatum- and C. gloeosporioides-specific primers failed to react with primer Col1. Isolate Pass-35 from passiflora did not react with any of the taxon-specific primers. Arbitrarily primed polymerase chain reaction (ap-PCR), random amplified polymerase DNA (RAPD)-PCR, and A+T-rich DNA analyses delineated representative isolates into subgroups within the designated species. Molecular analyses indicated that the C. acutatum tamarillo isolates were uniform or clonal, whereas the C. gloeosporioides mango isolates and Colletotrichum passiflora isolates were heterogeneous. Likewise, sequence analysis of the complete ITS (ITS1-5.8S-ITS2) region identified certain isolates to their respective species: tamarillo isolates as C. acutatum; mango isolates as C. gloeosporioides; passiflora, Tom-6, and Man-76 isolates as a Colletotrichum sp. as yet undefined; and the Pass-35 isolate as an additional undefined Colletot-richum sp. Molecular analyses of the population of Colletotrichum isolates from passiflora, Tom-6 from tamarillo, and Man-76 from mango indicate that this population may not be host specific.