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Viral Etiology of Diseases Detected in Melon in Guatemala

At the beginning of 1999, 30 melon (Cucumis melo L.) plots on several farms (1,500 ha) in the Zacapa Valley of Guatemala were visited, and melon plants with two different symptomologies were observed. One group of plants exhibited stem necrosis at the crown level, and less frequently, small necrotic spots on leaves. Some plants exhibited necrosis of veins and yellow areas that evolved into interveinal necrosis and often expanded into large necrotic interveinal lesions. Roots were poor and lacked secondary rootlets. In some cases, wilt and plant death were detected. Affected plants appeared as localized patches in various areas of the plots on farms that were visited. Double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) serological analyses were carried out with 34 symptomatic plants. In these plants, a mixture of the crown and root were analyzed with two repetitions and two lots of different Melon necrotic spot virus (MNSV) polyclonal antisera (Loewe No. 07097 and Sanofi No. 70217). All 34 plants were positive for this virus. These results were confirmed using reverse transcription-polymerase chain reaction (RT-PCR) with specific MNSV primers (1). Spores of Olpidium bornovanus, the vector of MNSV, were seen on all ELISA-positive plants after staining rootlets with potassium hydroxide and neutralization with hydrochloric acid. In the same fields, another group of melon plants showed yellowing, curling, and mottling of leaves. Leaves collected from five symptomatic plants gave positive results in triple-antibody sandwich-ELISA using a Tomato yellow leaf curl begomovirus antiserum (DSMZ AS-0421 and DSMZ AS-0546/2). In 2001, these results were confirmed using PCR with degenerate primers that amplify the core region of most begomovirus coat protein genes (P. Martínez-Culebras, M. I. Font, and C. Jordá, unpublished). A 560-bp DNA fragment was amplified in these symptomatic melon samples. Three of the PCR products were sequenced and each showed 99% identity with the Melon chlorotic leaf curl virus isolate from Guatemala (GenBank Accession No. AF325497). Only one mixed infection of MNSV and MCLCV was found. During the four years subsequent to 1999, the number of melon plants showing both types of symptoms has increased. This study provides information on the current status of virus diseases in melon crops in Guatemala, and to our knowledge, this is the first report of MNSV in Guatemala.

Reference: (1) B. Gosalvez et al. J. Virol. Methods 113:87.