Association of Pythium aphanidermatum with Root and Crown Rot of Melons in Honduras.

Abstract

Approximately 10,000 ha of melon (Cucumis melo L.), primarily cantaloupe and honeydew types, are grown in Honduras for export to U.S. markets. In 2004 and 2005, several soil surveys were conducted in areas with a history of vine decline. Twenty-nine soil samples from six farms were collected from the rhizosphere of wilted plants. Thirty-six melon plants were planted in a mixture of each rhizosphere sample and vermiculite (1:6 v/v). The plants were maintained in a growth chamber at 23 to 25°C with a 16-h photoperiod. The first symptoms, which appeared at the one- or two-true-leaf stage, were girdling of the lower stem, leaf chlorosis, and wilting. Affected plants exhibited necrotic crowns and roots and half of all plants died less than 3 days after wilting. Isolations from washed and dried crown and roots pieces from affected plants were placed on malt extract agar. Colonies were transferred to potato carrot agar and into dishes of sterile water and immature carnation petals to aid in the identification of recovered fungi. Nearly 500 isolates of Pythium species were cultured, and approximately 60% were identified as P. aphanidermatum (Edson) Fitzp. on the basis of their toruloid sporangia, aplerotic oospores, terminal and smooth oogonia, monoclinous sac-shaped antheridia (one to two per oogonium), and abundant appressoria. The pathogenicity of nine isolates was confirmed in a growth chamber. Ten plants of melon cv. Amarillo Canario, grown in sterilized vermiculite, were inoculated at the two- or three-true-leaf stage by drenching pots with 100 ml of a suspension of each isolate (103 CFU ml-1). Noninoculated plants served as controls. There were three replicates per isolate. Plants began to die 7 days after inoculation and the incidence of the affected plants reached an average of 70%. P. aphanidermatum causing decline of melon plants has been previously reported in hot and semi-arid areas in Israel and Spain (1,2). To our knowledge, this is the first report of P. aphanidermatum pathogenic to melon plants in Honduras.