Cucurbit Genetics Cooperative Report 12:40-41 (article
Transmission of the Causal Agent of Muskmelon Yellowing Disease
C. Soria and M.L. Gomez-Guillamon
Estacion Experimental "La Mayora", Algarrobo-Costa, (Malaga), Spain
Since 1982, a yellowing disease has seriously affected muskmelon (Cucumis melo L.) crops cultivated under polythene greenhouses on the southeast coast of Spain. It now seriously affects the profitability of muskmelon growing in this area because it considerably decreases the numbers of fruits per plant and the average fruit weights.
The symptomology of the affected plants is of two types: one starts with small yellow spots on the leaves; the other shows up as an intense yellow stain at the base of the leaf stalk. In each case, the disease spreads until the whole of the leaf, except the veins, is yellowed (1). In both cases, the symptoms start on the old leaves and progress to the younger ones.
The observation that there is a close relationship between the presence of greenhouse white-fly Trialeurodes vaporariorum and the appearance of the disease and the symptoms described suggests that muskmelon yellowing disease may be the same as that previously described in Japan (5), Holland (4), France (3) and Bulgaria (2). In each of these works, the cucumber yellows virus (CuYV) is ascribed as the causal agent of the yellowing in spite of the fact that no virus particle was isolated.
To determine the optimum conditions for carrying out controlled infections in experiments in order to select genotypes which might be used to introduce resistance to this yellowing disease into commercial varieties usually cultivated in this area, the three following possible types of disease transmission were studied: a) transmission by Trialeurodes vaporariorum, b) mechanical inoculation and c) seed transmission.
The experiments were carried out at temperatures between 25°C (max) and 11°C (min), with a relative humidity of 70% and a 16:8 hr light:dark cycle. The vegetable material employed was Cucumis melo var. Piel do Sapo.
The conclusions arrived at from the results were that the greenhouse white-fly Trialeurodes vaporariorum acts as the vector causal agent of this yellowing disease. Under the conditions in which the experiments were carried out, at least 40 days were required to confirm transmission. The symptoms observed in the infected plants were identical to those described above. The disease was not transmitted by mechanical inoculation of the infected extract.
No case of seed transmitted disease was observed in the 100 plantings obtained from seeds of diseased muskmelon plants which were previously inoculated using T. vaporariorum as vector.
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