Verticillium dahliae, the causal agent of verticillium wilt, is a soil-borne fungus which infects both woody and herbaceous plants. It is spread over a very wide area, occurring notably in Europe, the USA, North Africa and Asia. Infected plants generally show leaf necroses which develop into generalised wilting (Fig. 1). Black spots may occur in the vascular tissue of the stem or roots (Fig. 2). V. dahliae forms resting bodies, called microsclerotia, which can survive in the soil for many years. Root exsudate from the host plant causes the microsclerotia to produce mycelial hyphae which penetrate the cortex of young roots. The fungus produces conidia which travel through the plant via the xylem. The disease rapidly becomes systemic. The plant reacts by forming plugs in the xylem vessels and producing substances that are toxic to the fungus.
Objectives
Verticillium wilt mainly occurs at nurseries on plots heavily stocked with susceptible host plants. Due to the microsclerotia’s life span (between 20 and 30 years) and the polyphagous nature of the pathogen, once a plot becomes infected it is very hard to eradicate the disease. This makes it important to check plant health prior to planting and to determine the infectious potential of the soil in the plot to be planted. Also, if the disease does break out, it must be possible to disinfect the soil. Metam-sodium can be used. However, its use is restricted to authorised professional users. Moreover, handling involves a certain health hazard. The use of a biological soil disinfection method thus offers an attractive alternative.
Description of tasks
1)Characterisation of isolates collected in Belgium This study aims to compare the phenotypic and genetic characteristics of Belgian isolates of Verticillium dahliae with those of reference isolates from other countries (comparison of VCGs in particular). 2)Development of a PCR tool for identification of Verticillium dahliae in plant tissues The project includes the development of specific PCR (Polymerase Chain Reaction) primers for detecting Verticillium dahliae from infected plant tissues. 3)Validation of a biological soil disinfection method One of the project tasks is to validate a soil disinfection method developed in the Netherlands. This involves sowing rye-grass in the plot to be disinfected. After three months the organic matter is ploughed into the soil. The soil is well watered and a waterproof sheet spread over the plot for ten weeks. The decomposing organic matter releases methane which is toxic to the fungus. 4)Service activities Another aspect of the project involves carrying out tests to assess the infectious potential of the soil. The method consists of spreading a soil suspension on a semi-selective culture medium (core sampling on a systematic basis and placing in a water/agar suspension). After twenty-one days’ incubation in the dark, the germinated microsclerotia are counted with the aid of a binocular magnifying glass.
Expected results
This project will enable nurserymen to control the disease more effectively: - by checking plant breeding material health before planting; - by determining the infectious potential before planting a potentially susceptible crop; - by reducing the infectious potential of infected plots by means of biological disinfection.
Contribution
1)Characterisation of Verticillium dahliae isolates collected in Belgium on the basis of morphological criteria, vegetative complementation (VCG) and molecular analysis (using RAPD and RAMS methods). 2)Selection of PCR primers specifically to detect Verticillium dahliae 3)Validation of a biological soil disinfection method 4)Establishing of procedure for assessing the infectious potential of nursery plots (sample and analysis method).
Partners
This study is being carried out in cooperation with nurserymen at Lesdain.
