A Fusarium sp. different from Fusarium oxysporum and F. mangiferae is associated with mango malformation in Michoacán, Mexico

Malformation of mango has a pantropical distribution. In 1958, it was first reported in México where it now limits production in several southern states. Fusarium oxysporum, F. proliferatum and F. sterilihyphosum have been associated with the disease worldwide, but Koch's postulates have been completed only with F. mangiferae (Marasas et al., 2006).

A Fusarium sp. was recovered in 2004 and 2005 in Michoacán, México from 27 mango trees with typical symptoms of malformation. All 147 isolates differed from F. oxysporum, F. proliferatum and F. mangiferae, noneof which were found in affected trees. Fourteen representative, single-spored isolates from eight production areas were dark pink to salmon-colored on PDA. On carnation leaf agar chlamydospores were absent, three- to five-celled macroconidia rare (29-42 μm long) but microconidia copious on mono- and polyphialides. Of the above taxa, only F. oxysporum produces chlamydospores, only F. proliferatum, F. sterilihyphosum, and F. mangiferae produce polyphialides, and only F. sterilihyphosum produces coils of sterile hyphae. A F. mangiferae-diagnostic PCR primer pair (1-3F/R) did not amplify DNA from the Michoacán strains, but a primer pair that amplifies DNA from F. sterilihyphosum but not F. mangiferae (61-2F/R) amplified the reported 445 bp-fragment (Zheng and Ploetz, 2002). The Michoacán strains grew more than 50% faster than F. sterilihyphosum (Rodrí­guez-Alvarado et al., 2006), and possessed a 625 bp sequence of the translation elongation factor-1α that differed at 18 nucleotide positions from a F. sterilihyphosum sequence in GenBank (Accession No. DQ452858.1).

Malformation symptoms were produced after 12 weeks on nucellar, 9-month-old 'Ataulfo' mango seedlings inoculated separately with four isolates of the Fusarium sp. using standard protocols (Freeman et al., 1999), but not on water-inoculated control plants. Inoculated strains were re-isolated. It is clear that a taxon other than F. mangiferae causes mango malformation in Michoacán. Our findings challenge previous reports that F. oxysporum causes mango malformation in Michoacán, though isolates from mango were not available. Further work is also needed to compare this Fusarium sp. and F. sterilihyphosum.