Cucurbit Genetics Cooperative Report 13:29-30 (article 11) 1990

Host Range of the Causal Agent of Melon Yellowing Disease

V. Cura, C. Soria, and M. L. Gómez-Guillamón

Estación Experimental "La Mayora". Algarrobo-Costa, (Málaga), Spain

Breeding melon (Cucumis melo L.) plants with genetic resistance to melon yellowing disease is a long-term objective of extended research. Therefore, there is a serious need for short- or medium-term solutions that will permit the control of the disease or reduce its incidence. One approach to the problem is to seek and identify those wild or cultivated species that could act as reservoirs of the causal agent in the periods between consecutive melon crops. Once these other host plants are known, growers can carry out selective destruction of weeds in and around the greenhouse and to use cultivation strategies to avoid identified periods of growth.

The following are the plant species examined to date: Tropaeolum majus L., Cucurbita spp., Cucumis sativus L., Phaseolus vulgaris L., Cichorium endivia L., Lactuca sativa L., Pisum sativum L., Lycopersicon esculentum Mill., Taraxacum officinale Weber, and Capsella bursa-pastoris (L); the disease symptoms in the last two species have already been described and the species have been used as indicators of the presence of disease in experiments with Cucumis melo (3,4).

In the first experiment, non disease-carrying whitefly (Trialeurodes vaporariorum Westwood) are allowed to feed for 48 h on melon plants showing clear symptoms of yellowing. Then, these whiteflies were transferred in groups of 40 flies to 10 seedlings of each species and allowed to feed for 72 h. Five melon seedlings were used as indicators.

In the second experiment, numerous specimens of T. vaporariorum were allowed to feed for 48 h on plant species showing clear or suspected symptoms of disease. Then, for each species to be tested, groups of 40 flies were transferred to 10 seedlings of the same species and 10 melon seedlings, and left to feed for 72 h. In both experiments, whiteflies were then destroyed and the plants were transferred to an insect-proof and fly-free greenhouse to await the development of symptoms.

Table 1 shows that Cucurbita spp., C. sativus, Ch. endivia and L. sativa are hosts of the causal agent of melon yellowing disease and also efficient infection sources of nearby melon crops. These four species develop a mosaic yellowing that, in Cucurbita spp. and C. sativus, starts with a spotting which progresses until all the leaf, except the veins, is yellow.

Ph. vulgaris develops a slight chlorotic staining of the leaves, but in attempts to transmit the infection to other seedling of the same specie, this symptomology could not be reproduced, nor was melon yellowing produced in the melon plants and thus, Ph. vulgaris cannot be considered an infection source. T. majus showed a progressive yellowing of the leaves in some plants, but these symptoms could not be reproduced in plants of the same specie nor did melon yellowing appear in the melon plants infected with whiteflies that had previously been allowed to feed on symptom-showing leaves of T. majus.

P. sativum and L. esculentum never showed any symptoms.

Table 1. Possible range of hosts of the causal agent of melon yellowing disease. A incidence of yellowing in plants inoculated by whitefly previously allowed to feed on melon plants with clear symptoms of disease. B incidence of yellowing in plants of each species inoculated by whitefly previously allowed to feed on plants of the same species showing symptoms. C incidence of yellowing in melon plants inoculated by whitefly previously allowed to feed on plants of each species showing symptoms.

	A	B	C
Cucurbita spp.	2/10z	4/10	7/10
Cucumis sativus	8/10	8/10	8/10
Phaseolus vulgaris	9/10	0/10	0/10
Cichorium endivia	3/10	3/10	9/10
Lactuca sativa	5/10	8/10	7/10
Tropaeolum majus	4/10	0/10	0/10
Pisum sativum	0/10	-	-
Lycopersicon esculentum	0/10	-	-
Taraxacum officinale	6/10	-	-
Capsella bursa-pastoris	9/10	-	-

^za/b; a no. of plants with symptoms, b total of plants inoculated.

These results suggest that the causal agent of melon yellowing disease observed in the greenhouses of S.E. Spain could be the beet pseudo yellows virus (BPYV) whose range of hosts has been described by Duffus (1). The symptomology of the hosts described by Van Dorst et al. (5) and Hristova and Natskova (2) also coincides with our results. Yamashita et al. (6) describe the cucumber yellowing virus (CuYV) that produces the same yellowing symptoms in melon, but which can only be transmitted to Cucurbitaceae.

Literature Cited

1. Duffus, J. E. 1965. Beet pseudo yellows virus, transmitted by the green-house whitefly (Trialeurodes vaporariorum). Phytopathology 55(4): 450-453.
2. Hristova, D. P. and V. T. Natskova. 1986. Interrelation between Trialeurodes vaporariorum W. and the virus causing infectious chlorosis in cucumbers. Comptes Rendus de L'Academie Bulgare de Sciences 39:105-108.
3. Soria, C. and M. L. Gómez-Guillamón. 1988. Transmission of muskmelon yellowing disease by Trialeurodes vaporariorum Westwood. Eucarpia. Cucurbitaceae 88. Avignon-Montfavet. (France).
4. Soria, C. and M. L. Gómez-Guillamón. 1988. Posibles vías de transmisión del virus del amarilleamiento del melón. III Congreso de la S.E.C.H. Puerto de la Cruz, Tenerife. (España).
5. Van Dorst, H. J. M., N. Huijberts, and L. Bos. 1980. A whitefly-transmitted disease of glasshouse vegetables, a novelty for Europe. Neth. J. Pl. Path. 86:311-313.
6. Yamashita, S., Y. Doi, K. Yora, and M. Yoshino. 1979. Cucumber yellows virus: its transmission by the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and the yellowing disease of cucumber and muskmelon caused by the virus. An Phytopathol. Soc. Japan 45:484-489.