First Report of Mango Malformation Disease Caused by Fusarium pseudocircinatum in Mexico

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. After 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, the USA (Florida), Egypt, South Africa, Oman, and elsewhere; F. sterilihyphosum in South Africa and Brazil; F. proliferatum in China; F. mexicanum in Mexico; and recently, F. tupiense in Brazil (1,2,3,4). Besides F. mexicanum, F. pseudocircinatum, not yet reported as a causal agent of MMD, was isolated in Mexico from affected inflorescences and vegetative malformed tissues (4). Symptoms of vegetative malformation caused by F. pseudocircinatum included hypertrophied, tightly bunched young shoots, with swollen apical and lateral buds producing misshapen terminals with shortened internodes and dwarfed leaves. Infected inflorescences of primary or secondary axes on affected panicles were shortened, thickened, and highly branched, while the peduncles became thick, remained green and fleshy, and branches profusely resembled a cauliflower in shape and size (3). Ten isolates of F. pseudocircinatum were recovered from cultivars Ataulfo, Criollo, Haden, and Tommy Atkins in Guerrero, Campeche, and Chiapas states and characterized. Isolates produced mostly 0-septate but occasionally 1- to 3-septate oval, obovoid, or elliptical aerial conidia (0-septate: 4 to 19 [avg. 8.7] × 1.5 to 4 [avg. 2.6] 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 to 58 [avg. 41] × 2 to 3.3 [avg. 2.9] μm; 5-septate: 33.5 to 76.5 [avg. 56.7] × 2.5 to 6 [avg. 3.5] μm). Circinate sterile hyphae were rarely formed. Two representative isolates, NRRL 53570 and 53573, were subjected to multilocus molecular phylogenetic analyses of portions of five genes: nuclear large subunit 28S ribosomal RNA, β-tubulin, calmodulin, histone H3, and translation elongation factor (TEF)-1α (GenBank GU737456, GU737457, GU737290, GU737291, GU737371, GU737372, GU737425, GU737426, GU737398, and GU737399). Two pathogenicity tests were conducted with NRRL 53570 and 53573 on healthy 2-year-old nucellar seedlings of polyembryonic Criollo; 20 μl conidial suspensions (5 × 10⁶ conidia/ml) of each isolate and water controls were inoculated separately on 15 buds on 3 different trees, as described previously (1). The following conditions were used in experiment 1: 24 to 27°C with light intensity of 16.2 to 19.8 •Mol m^-2s^-1 in the range of 400 to 700 nm, and photoperiods of 14 h light and 10 h dark. Typical vegetative disease symptoms were discernible in plants inoculated with NRRL 53570 (20%) and 53573 (7%) after 8 months. In experiment 2, after 3 months growth under the above conditions, seedlings were transferred to an outdoor nursery in Iguala, Guerrero. 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 9 months. Isolates from typical symptomatic vegetative buds were confirmed as F. pseudocircinatum by sequencing a portion of their TEF-1α gene, thus fulfilling Koch's postulates. This is the first report of F. pseudocircinatum as a causal agent of MMD. References: (1) S. Freeman et al. Phytopathology 89:456, 1999. (2) C. S. Lima et al. Mycologia 104:1408, 2012. (3) W. F. O. Marasas et al. Phytopathology 96:667, 2006. (4) G. Otero-Colina et al. Phytopathology 100:1176, 2010.