First Report of Neofusicoccum parvum Associated with Dieback of Mango Trees in Peru.

Abstract

Mango (Mangifera indica L) is one of the most important cash crops of northern Peru. Since 2003, adult mango trees (cvs. Criollo and Kent) located in Piura Province developed symptoms of dieback characterized by the death of twigs and branches in the tree canopy. Additional disease symptoms involved darkened, elongated lesions on the peduncle, causing an early maturation of the fruit, and in advanced symptoms, stem-end rot of fruits. Symptoms were frequent in the spring months (September to November) when the lesions expand rapidly. Diseased tissues from branches and fruits were collected and small pieces of necrotic tissues were surface disinfected and plated onto potato dextrose agar (PDA) with 0.5 g L-1 streptomycin sulfate. Plates were incubated at 25°C in the dark. All affected tissues consistently developed colonies with a white mycelium, moderately dense, and becoming olivaceous gray after 5 to 6 days. Pycnidia were produced on sterile mango twigs placed on the surface of potato carrot agar (PCA) after 10 days. Conidia were hyaline, guttulate, aseptate, measuring (15-) 18.5 (-22.5) × (4-) 5.2 (-7.5) μm. Conidia became olivaceous and developed one or two septa before germination. Isolates were identified as Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers, & A.J.L. Phillips (1). DNA sequences of the rDNA internal transcribed spacer region (ITS) and part of the translation elongation factor 1-alpha (EF1-α) genes were used to confirm the identification through BLAST searches in GenBank (ITS: 99% identity to Accession No. EU080928; EF1-α: 98% identity to Accession No. AY343367). Representative sequences of the studied DNA regions were deposited at GenBank (ITS: Accession No. FJ528596; EF1-α: Accession No. FJ528597). Pathogenicity tests were conducted on 18-month-old potted mango plants cv. Kent with two N. parvum strains (A4 and A5). A mycelial plug (3 cm in diameter) taken from the margin of an actively growing colony of each isolate was put in a wound made with a cork borer of the same diameter on the stem of each plant. Inoculation wounds were wrapped with Parafilm. Controls were inoculated with sterile PDA plugs. Ten replicates for each isolate were used with an equal number of control plants. Plants were maintained in a greenhouse with a temperature range of 22 to 28°C. After 4 weeks, mango plants showed necrotic stem lesions originating from the inoculation point affecting also the branches of the inoculated plants. No differences in lesion area between strains were obtained. No lesions developed in the control plants. Reisolations from necrotic tissues were successful and both isolates were morphologically identical to those used for inoculations. N. parvum was isolated from all symptomatic trees in all surveyed areas. This pathogen has already been reported on mango (2) and currently represents a serious problem in the mango-producing areas of Peru. To our knowledge, this is the first report of N. parvum affecting mango in Peru.