Occurrence of Vine Decline Diseases of Muskmelon in Guatemala

Central American countries have become major production areas of melons (Cucumis melo L.) destined for export to Europe and the United States during the winter months. Double cropping in the same fields year after year has created serious vine decline diseases in melons grown in the Capco area of Guatemala. Vines typically appear healthy until the fruit are approaching maturity, when the crown leaves begin to turn yellow and collapse and the decline gradually radiates outward. There was evidence of slightly water-soaked lesions in the crown of some plants; however, the symptoms were not similar to charcoal rot or gummy stem blight. The roots exhibited some decay, lesions, and discoloration, but were not macerated and rotten. A minimum of 10 affected plants were collected from each of nine fields in the Capco area of Guatemala. Isolations were made from the crown area, primary root, and secondary roots of selected plants by excising 3- to 5-mm pieces and surface sterilizing them for 30 to 60 s with 0.5% sodium hypochlorite. The isolations were made on 2% water agar plus 0.1 g of streptomycin sulfate per liter. Plates were examined for fungal growth daily for 5 days with hyphal tips from all colonies transferred to potato dextrose agar and Synthetischer nährstoffärmer agar (2) and allowed to sporulate. Isolations revealed the presence of several fungi capable of causing vine decline or suspected of being involved in the vine decline complex. Rhizoctonia solani Kühn and Fusarium semitectum Berk. & Ravenel were isolated from more than 50% of plants in some fields. F. semitectum, R. solani, and a Stagonospora-like fungus were isolated from 38, 18, and 17% of the total plants, respectively. R. solani was isolated from the crown more often than from the roots, but its role is not understood. With one exception, F. semitectum was always isolated from the crown area, which may suggest a more significant role in the vine decline complex than suspected previously. The Stagonospora-like fungus, isolated from 30% of the plants from one field, has been reported as a pathogen of cantaloupe that may contribute to the vine decline complex (1). Monosporascus cannonballus Pollack & Uecker and Fusarium oxysporum Schlechtend.:Fr. emend. W. C. Snyder & H. N. Hans. were isolated from 60% of the plants from one field. It was the only field in which M. cannonballus was isolated. Plectosporium tabacinum (van Beyma) M. E. Palm, W. Gams et Nirenberg, a cucurbit pathogen, was isolated infrequently. This is the first report of M. cannonballus, P. tabacinum, and the Stagonospora-like fungus in Guatemala. References: (1) M. E. Miller et al. Phytopathology 86:S3, 1996. (2) H. I. Nirenberg. Mitt. Biol. Bundesanst. Land Forstwirtsch. Berlin-Dahlem. 169:1, 1976.