Resumen. El estado de Sonora es uno de los principales productores de sandía en México. Cada año, los productores locales enfrentan problemas fitosanitarios, provocados principalmente por hongos del suelo. En el presente estudio se analizó la presencia de hongos patógenos asociados con pudrición de raíz en plantas de sandía en las dos zonas de mayor producción en Sonora. Abstract. The state of Sonora is one of the main producers of watermelons in Mexico. Each year, agricultural producers deal with phytosanitary issues like soilborne pathogens. In this study the presence of phytopathogenic fungi associated to watermelon root rot was analyzed in the main production regions of Sonora. Morphological analysis revealed three genera: Fusarium (73%), Ceratobasidium (20%) and Rhizoctonia (6%). Through a multilocus phylogenetic analysis (ITS1, TEF and RPB2 for Fusarium; ITS1 and RPB2 for Rhizoctonia and Ceratobasidium), the following species were identified: Fusarium falciforme, F. brachygibbosum and F. oxysporum. In addition to this, two anastomosic groups for Ceratobasidium sp. (AG-F y AG-A) and two for Rhizoctonia spp.(AG-4 y AG-6) were identified. Pathogenicity assays showed that the representative isolates from these five different species caused root rot wounds and wilting in watermelon plantlets 21 234Fully Bilingual

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...

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Recientemente se ha identificado a Fusarium brachygibbosum, F. falciforme y F. oxysporum como causantes de marchitez y muerte en plantas de sandía en Sonora, México. Debido a la escasa información morfológica acerca de F. brachygibbosum y con el fin de establecer las características macroscópicas y microscópicas distintivas entre las especies, en el presente trabajo se realizó la descripción de cuatro morfotipos F. brachygibbosum y su comparación con tres de F. falciforme y dos de F. oxysporum. La categorización de los morfotipos se realizó, con base en la forma de crecimiento, tonalidades del micelio y el color desarrollado en agar-dextrosa-papa, a partir de 32 aislados de Fusarium patogénicos en sandía. Los cuatro morfotipos de F. brachygibbosum presentaron clamidosporas sencillas o dobles, de pared gruesa, intercalares y terminales. Monofiálides cortas y escasas polifiálides. Macroconidios con células apicales en ligera forma de gancho y células basales con forma típica o ligera forma de pie. El mayor grosor de paredes fue distintivo en las clamidosporas de F. brachygibbosum. La morfología de los macroconidios fue diferente en las tres especies. Una característica distintiva en los morfotipos de F. falciforme fueron las monofiálides largas y delgadas; mientras que en los de F. oxysporum fue la ausencia de septos en los microconidios. El tamaño de los macroconidios y microconidios fue significativamente diferente entre los morfotipos, pero no entre las especies.