Agronomic studies on the population dynamics of Verticillium dahliae

Verticillium dahliae reduces crop yields by causing early senescence. The fungus survives in the soil as microsclerotia formed on senescing tissue of colonised plant parts. V.dahliae is endemic in many soils because of the high potential survival of its microsclerotia and its wide host range. The primary aim of the research was to investigate the feasability of reducing the inoculum density in the soil by stimulating the microsclerotia to germinate. A second aim was to quantify the formation of microsclerotia on various crop species and cultivars, and various parts of potato plants. Haulm treatments to control the formation of microsclerotia on potato were tested and finally a theoretical model describing the long-term dynamics of the inoculum density in the soil was developed and tested.

All crops investigated stimulated the germination of microsclerotia in the soil. Host plants such as potato and field bean induced more microsclerotia to germinate than a non-host such as barley, but none of the crops was able to reduce the soil inoculum density effectively.

The highest total microsclerotial yield occurred in flax, followed by potato cultivars; the other crops lagged far behind. In potato, the mature aerial parts had the highest numbers of microsclerotia.

Potato cv. Element and field bean proved to be most sensitive to their own isolate. In plots cropped with good hosts, soil inoculum density increased very rapidly. Removing the debris of potato, field bean and flax from the field was effective in reducing the increase of the inoculum density. Mechanical haulm treatments reduced the formation of microsclerotia more than a chemical treatment.

A theoretical model built on the basis of biological and ecological principles gave a very high correlation when it was fitted to the data obtained in a long-term field experiment.

This study provides a quantitative basis on the interactions between crops and V.dahliae that deserves to be expanded in further research.