Submitted to: Plant Disease
Publication Type: Research notes
Publication Acceptance Date: 7/11/2014
Publication Date: 10/15/2014
Citation: Freeman, S., Otero-Colina, G., Rodriquez-Alvarado, G., Fernandez-Pavia, S., Maymon, M., Ploetz, R.C., Aoki, T., O'Donnell, K. 2014. First report of mango malformation disease caused by Fusarium pseudocircinatum in Mexico. Plant Disease. 98(11):1583. Interpretive Summary:
Technical Abstract: Mango (Mangifera indica L.) malformation disease (MMD) is one of the most important diseases affecting this crop worldwide, causing severe economic loss due to reduction of yield. Subsequent to the first report in India in 1891 (3), MMD has spread worldwide to most mango-growing regions. Several species of Fusarium cause the disease, including F. mangiferae in India, Israel, USA (Florida), Egypt, South Africa, Oman, and elsewhere; F. sterilihyphosum in South Africa and Brazil; F. proliferatum in China; F. mexicanum in Mexico, and most recently, F. tupiense in Brazil (1,2,3,4). We conducted an extensive survey of putative MMD pathogens in Mexico (4). Besides F. mexicanum, F. pseudocircinatum, not yet reported as a causal agent of MMD, was isolated from affected inflorescences and vegetative malformed tissues. Ten isolates of F. pseudocircinatum were recovered from cultivars Ataulfo, Criollo, Haden, and Tommy Atkins in three states (Guerrero, Campeche, and Chiapas) and characterized employing morphological and multilocus molecular phylogenetic data, and by pathogenicity tests. Isolates produced mostly 0-septate but occasionally 1(-3)-septate oval, obovoid, or elliptical aerial conidia (0-septate: 4-8.7-19 × 1.5-2.6-4 µm) in false heads in the dark and in short false chains under black light, unbranched or sympodially branched prostrate aerial conidiophores producing mono- and polyphialides, and sporodochia with straight or falcate conidia that were mostly 3-to-5-septate, but sometimes up to 7-septate (3-septate: 25-41-58 × 2-3.3-2.9 µm; 5 septate: 25-41-58 x 2-3.3-4 µm). Circinate sterile hyphae were rarely formed. Two representative isolates, NRRL 53570 and 53573, were subjected to multilocus molecular phylogenetic analyses of portions of the following five genes: nuclear large subunit 28S ribosomal RNA, ß-tubulin, calmodulin, histone H3 and translation elongation factor 1a (GenBank accessions GU737456, GU737457, GU737290, GU737291, GU737371, GU737372, GU737425, GU737426, GU737398, and GU737399). Two pathogenicity tests were conducted with NRRL 53570 and 53573 on healthy 2-yr-old nucellar seedlings of cv. polyembryonic Criollo; 20 µl conidial suspensions (5 × 106 conidia per ml) of each isolate and water controls were inoculated separately on 15 buds on three different trees, as described previously (1). The following conditions were used in the first experiment: 24 to 27oC with light intensity of 16.2 to 19.8 'Mol m-2 s-1 in the range of 400 to 700 nm, and photoperiods of 14 h light and 10 h dark. Typical disease symptoms including swollen axillary buds were discernible in plants inoculated with NRRL 53570 (20%) and 53573 (0.07%) after 8 months. In the second experiment, after three months growth under the conditions described above, seedlings were transferred to an outdoor nursery with unregulated weather, located in Iguala, Guerrero. In this experiment, typical vegetative symptoms of MMD were observed in 86.7 and 13.3% of the buds inoculated with F. pseudocircinatum NRRL 53570 and 53573, respectively, after nine months but not in the water controls (Fig. 1). Isolates from typical symptomatic vegetative buds were confirmed as F. pseudocircinatum by sequencing a portion of their translation elongation factor 1a gene, thus fulfilling Koch´s postulates. This is the first report of F. pseudocircinatum as a causal agent of MMD. Currently, the relative importance of the F. mexicanum and F. pseudocircinatumas MMD pathogens in Mexico is not known.