Cucurbit Genetics Cooperative Report 23:114-116 (article 38) 2000
Zucchini Yellow Mosaic Virus in Cucurbita pepo var. styriaca: Epidemiology, Strategies of Control
Federal Office and Research Institute for Agriculture, Spargelfieldstrase 191, 1226 Vienna, Austria; email@example.com
In 1997 a severe outbreak of Zucchini Yellow Mosaic Virus (ZYMV) (3) caused serious damage and yield losses in oil pumpkin, cucurbita pepo var. styriaca all over austria. In 1998 and in 1999 the economic impact of the disease was lower, nevertheless the virus was againfound in oil pumpkin crops all over the country. From infected oil pumpkins the virus was transmitted to melons, cucumbers and zucchini and severely ffected the harvest.
In Cucurbita pepo var. styriaca symptoms usually become visible in the middle of June 3-4 weeks after germination. On leaves severe yellowing and mottling, mosaic symptoms, vein banding, or vein clearing, darker green blistersm deformations and more or less intense reductions of size can be observed (Fig. 1). Shoots are stunted and stand out from the crop. Early infected plants develop no or very small fruits, later infecttions lead to malformations and to reduced fruit size (Fig. 2). Infections before flowering period may diminish the number of pistillate flowers.
In concurrence with results obtained for Cucurbita maxima (2) preliminary studies by our institute indicate that oil pumpkin seed from old fruits does have the potential to act as a disease reservoir between seasons. Virus tests of weeds showed latent ZYMV infections in a few cases. Infected weeds, however, were only observed in or adjacent to ZYMV-infected cucurbit crops. No evidence for over-wintering of ZYMV in perennial weeds has been found. Thus it must be presumed that at present infected oil pumpkin seed plays the most important role for over-wintering of ZYMV in Austria.
From a few primary infection sites the virus spreads rapidly to the whole crop. During mechanical weed control plants are wounded thus transmitting the virus from plant to plant. Usually only a few aphids can be observed in oil pumpkins. Nevertheless it must be presumed that aphids from neighboring crops play an important role as virus vectors both within and between fields. Sometimes virus particles are also carried by vertebrates like deer or rabbits.
Several measure are necessary to control ZYMV in oil pumpkin crops and to reduce economic losses. The production and the exclusive use of healthy seed are imperative.
In order to reduce mechanical virus transmission mechanical weed control can only be carried out as long as the plants are not in contact with the working equipment.
In oil pumpkins virus sources can normally be found within the crop, the virus is not brought in from the outside. Thus, seed treatment with imidacloprid preventing aphid multiplication on the pumpkin plants has been tried through its influence on the non-persistent virus transmission is controversial (1). Its effect on spread of ZYMV in cucurbita pepo var. styriaca cannot yet be estimated. It is, however, obvious that a partial use of treated seed does not reduce virus spread. In this case virus contaminated aphids from neighboring fields transmit the virus into the insecticide-treated crop.
The mentioned measure, especially the improvement of seed quality might reduce the spread of ZYMV. In order to avoid yield losses like in 1997, however, they must be combined with the use of a ZYMV-tolerant oil pumpkin variety. In contrast to other varieties of cucurbita pepo , for oil pumpkins only one or two fruits per plant are needed to achieve a satisfactory harvest.Thus even a ZYMV-tolerance allowing the first fruits to develop without major damage should be sufficient to insure acceptable yields.
- Collar, J,L., Avilla, C., Duque, M. and A. Ferres, 1997. Behavioral response and virus vector ability of Myzus persicae probing on pepper plants treated with aphicides. J. Econ. Entomol. 9-0, 1628-1634.
- Fletcher, J.D., Nott., H.M., Wallace, A.R., Rogers, B.T. and J.B.Herman, 1998. Potyviruses in New Zealand buttercup squash. 9th Conference of the ISHS vegetal be virus working group, --. 24-25, Turin 2-27, August 1998.
- Lisa, V. and H. Lecoq, 1984. Zucchini yellow mosaic virus. CMI/AAB Descriptions of Plant Viruses no. 282.