SOME VIRUSES INFECTING CUCURBITS IN KWAZULU-NATAL: THEIR DISTRIBUTION AND CONTROL
KR CRADOCK, JV DA GRArvA and MD LAING
Department of Microbiology and Plant Pathology, University of Natal, Private Bag X01, Pietermitzburg, ScottsVilie, 3209, South Africa
Background and objectives
Viruses which have been recorded as being important pathogens of cucurbits were zucchini yellow mosaic potyvirus (ZYMV), watermelon mosaic potyvirus - Morocco strain (WMV-M) and cucumber mosaic cucumovirus (CM011]. Of these, WMV-M was the most common virus found infecting plants in the field . A field study of these aphid-borne viruses of the Cucurbitaceae, as well as watermelon mosaic 2 potyvirus (V 2), was conducted in KwaZulu-Natal from February to May, 1997, months during which virus symptoms are usually severe.
Materials and methods
Samples of a variety of cucurbits were collected from both commercial farms and community gardens around the province. Some weed samples were collected from within and around fields to determine whether any were acting as reservoirs for the viruses. The presence of viruses in a sample was tested using DAS ELISA for the potyviruses and indirect ELISA for CMV.
Results and conclusions
ZYMV (69.8%) and WMV-M (30.2%) were found to be the prevalent viruses, followed by CMV (1 1.6%) and WMV 2 (9.3%). These last two viruses were only present in samples collected from April and May. It is interesting to note that WMV 2 was only found in samples from the north coast region. The other viruses were found in all the regions that were sampled. Multiple infections were common, occurring in 44.2% of the samples. A number of samples gave borderline results which may be due to low virus titre. Weed species found to be infected were Cucumis myriocarpis (striped wild cucumber) (WMV-M), Galinsoga parviflora (small-flowered quickweed) (ZYMV; WMV-M), and Datura stramonium (common thornapple) (V-M; CMV). A number of methods were considered as means of control of these pathogens. The controls were aimed at repelling the aphid vectors of the viruses, and included a garlic repellent, white reflective mulch, straw mulch, and companion planting with fennel.
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