6.6
EPIDEMIOLOGY OF THE CARROT MOTLEY DWARF VIRUS COMPLEX IN PARSLEY

P VERCRUYSSE1 , F MEERT1, P BLEYAERT2, L TIRRY3 and M HÖFTE1

1Laboratory of Phytopathology, and 3Laboratory of Agrozoology, University of Ghent, Belgium; 2POVLT, Beitem (Rumbeke), Belgium

Background and objectives /b>
For more than 15 years carrot motley dwarf (CMD) has been one of the important parsley diseases in Belgium [1]. The virus disease is transmitted in a persistent way by the willow-carrot aphid (Cavariella aegopodii). There is no rapid and sensitive detection technique for the CMD viruses (carrot red leaf virus and carrot mottle virus) in parsley, and there are still a lot of difficulties in controlling the disease. In this epidemiological study the aphid vector of the CMD disease, as well as the presence of CMD symptoms on parsley (red and yellow discoloration of the leaves, stunting), were investigated.

Materials and methods
Aphid captures in parsley were performed with yellow pan traps. The population of C. aegopodii on parsley was studied using a sampling procedure and an extraction method for aphids, which were first evaluated. Two different planting dates for parsley were sampled during the growing season. Symptoms of CMD were rated using a visual scale for both parsley plantings.

Using the extraction method, the presence of the aphid vector was investigated on other secondary hosts (umbelliferous weeds) surrounding the parsley fields.

Results and conclusions
A clear C. aegopodii flight pattern with three peaks was observed. The early flights in May and June were the most important for the colonization of the parsley plants by the vector of CMD. A more important parameter is the number of viruliferous aphids, for which a sensitive detection method for the CMD viruses is necessary. A detection method using cocktail ELISA and hybridization with DIG-labelled cDNA-probes is being developed [2].

The extraction method for aphids proved to be very efficient and could be performed within a short period of time. The parsley samples were representative for the whole plant. In the early planting, C. aegopodii was present in large numbers on the sampled parsley plants from the beginning of June. In the late planting of parsley, the population of C. aegopodii initially was smaller than in the early planting, but its development later in the growing season was analoguous. There was no correlation between the presence of C. aegopodii on the parsley plants and the appearence of CMD symptoms. The CMD symptoms developed later in the late planting, and the number of plants showing symptoms was considerably lower than in the early planting. Further tests are being done to determine the influence of environmental factors on CMD symptom development.

For the control of CMD, several insecticides are being evaluated in toxicity tests with the aphid vector and in field tests. Until the end of July, C. aegopodii was present on most sampled flowerheads of Anthriscus sylvestris and Aegopodium podagraria surrounding the parsley fields. Later in the growing season, Daucus carota subsp. carota was the most important umbelliferous weed that was infested with the CMD-vector.

References
1. Dunn JA, 1965. Annals of Applied Biology 56, 429-438.
2. Watson MT, Falk BW, 1994. Plant Disease 78, 477-481.