First Report of Watermelon Wilting Caused by Fusarium brachygibbosum in Sonora, Mexico

Abstract

fields in the Coast of Hermosillo and two of the Guaymas Valley, the major producing areas of watermelon in Sonora, Mexico, were sampled. Symptomatic watermelon plants exhibiting a cortical rot at the base of the stem and the upper portion of the taproot were observed and collected. Wilting and death was observed in approximately 50% of ungrafted watermelon plants in the sampled fields. One-centimeter pieces from the edge of lesions on stems and roots were superficially disinfected with 1% sodium hypochlorite, rinsed with sterile distilled water, placed onto petri dishes containing potato dextrose agar (PDA), and incubated at 25°C for 3 days. Mycelia from 46 isolates were used for morphological and molecular identification. After DNA extraction, the rDNA-ITS region was amplified using PCR with the universal fungal primers ITS1 and ITS4 (White et al. 1990). The purified products were separately sequenced in both directions using the same primer pair. A five species fungi complex, potentially pathogenic, was identified: Rhizoctonia solani, Ceratobasidium sp., Fusarium oxysporum, Fusarium solani and Fusarium brachygibbosum. F. brachygibbosum has not previously been reported as pathogenic in watermelon. Four different isolates of this fungal species were obtained. Two of them showed 100% nucleotide similarity with the GenBank accession No. KF985966 (Mirhosseini et al. 2014) and another two with 99% similarity to KF028369 both corresponding to F. brachygibbosum. The morphology of growth for this fungus showed white colonies with abundant aerial mycelium, which became pink, with yellow-orange spots, and red pigmentation in the agar. Few spores and oval microconidia were observed. Macroconidia were hyperbolically curved, with 3-5 marked septa, wide central cells, slightly sharp apexes, and basal cells with foot shape. Terminal and intercalary chlamydospores, alone or in chain, usually unicellular and globose were also recorded. The pathogenicity was tested under growth chamber conditions. Sets of seven healthy watermelon seedlings of the Sugar Red variety were inoculated with the isolates of F. brachygibbosum. Three disks (8 mm in diameter) of mycelia grown on PDA were placed around the roots of each plantlet. Pots were maintained at 27 ± 0.1°C for 14 days with a photoperiod of 12 h. Seven uninoculated seedlings were used as a control. After 10 or 14 days, all inoculated seedlings showed the typical disease symptoms as lesions of variable size and light brown-colored at neck and root, causing wilting of leaves or the whole plant. Seedlings without inoculum were free from infection and disease symptoms. The fungus was re-isolated from the inoculated seedlings, confirmed as F. brachygibbosum by sequencing of rDNA-ITS and confirmed by morphological characteristics as described by Padwick (1945). To our knowledge, this is the first description of this pathogen causing wilting on watermelon. Mexico is the world's eleventh largest producer of watermelon and the main exporter of watermelon in the world, providing 22.9% of thi...

Análisis filogenético multilocus del complejo fúngico asociado a pudrición radicular de sandía en Sonora, México

“…The characteristics of the colonies coincide with the first description published (Padwick, 1945), they present abundant white to pink aerial mycelia white to amber sclerotia of up to 2.0 mm in diameter, oval or fusiform conidia, hyperbolically curved macroconidia, terminal or alternated chlamydospores, single or in chain, generally unicellular. As a preliminary product of this investigation, F. brachygibbosum was reported for the first time as a pathogenic agent, causing this wilting in watermelon seeds (Rentería-Martínez et al, 2015). It has recently been recorded as a causal agent of rotting in the stem of maize plants (Shan et al, 2017), wilting and regressive death in Euphorbia larica and olive trees (Al-Mahmooli et al, 2013;Trabelsi et al, 2017) and of rotting and cankers in almond and chestnut trees (Stack et al, 2017;Marek et al, 2013).…”

“…Las características de las colonias coinciden con la primera descripción publicada (Padwick, 1945), presenta micelio aéreo abundante de blanco a rosa, esclerocios de blanco a ámbar de hasta 2.0 mm de diámetro, conidias ovoides a fusiformes, macroconidias hiperbólicamente curveadas, clamidosporas terminales o intercaladas, sencillas o en cadenas, generalmente de una célula. Como producto preliminar de esta investigación, F. brachygibbosum fue reportado por primera vez como agente pató-geno, causante de marchitez en plantas de sandía (Rentería-Martínez et al, 2015). Recientemente se ha registrado como agente causal de podredumbre del tallo del maíz (Shan et al, 2017), marchitez y muerte regresiva en Euphorbia larica y olivo (AlMahmooli et al, 2013;Trabelsi et al, 2017) y de podredumbre y cancros en almendro y nogal (Stack et al, 2017;Marek et al, 2013).…”

Pest categorisation of Fusarium brachygibbosum

“…F. brachygibbosum was also isolated from asymptomatic almond rootstocks (Seidle, 2016). In artificially inoculated watermelon, F. brachygibbosum produced light-brown lesions variable in size at collar and root level, causing wilting of leaves or whole plants (Renter ıa-Mart ınez et al, 2015). The 1 An EPPO code, formerly known as a Bayer code, is a unique identifier linked to the name of a plant or plant pest important in agriculture and plant protection.…”

Root and crown rot pathogens causing wilt symptoms on field-grown marijuana (Cannabis sativa L.) plants

“…Fusarium brachygibbosum has also been reported to cause a stalk rot of corn in China (Shan et al, 2017), characterized by a dark brown disintegration of internal stalk tissues. Watermelon wilt and plant death due to F. brachygibbosum was also reported from Sonora, Mexico, which caused a cortical rot on the upper portion of the taproot (Renteria-Martinez et al, 2015). Other plant species on which stem die-back and wilt were reported to be caused by F. brachygibbosum include olive in Tunisia (Trabelsi et al, 2018) and Euphorbia in Oman (Al-Mahmooli et al, 2013).…”