Development of a fungal biological control agent for potato cyst nematodes in Jersey
The production of Jersey Royal potatoes is an important industry for the island of Jersey. The crop is grown annually, and sometimes biannually, so there is no opportunity to practise crop rotation in order to control potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis. Control of these pests in Jersey has traditionally relied on the use of nematicides, but with increased public pressure to reduce the use of pesticides and the intention of the Government of Jersey to eventually ban them, there is a desire for an alternative methods of control to be developed. Three nematophagous fungi, Plectosphaerella cucumerina, Paecilomyces lilacinus and Verticillium chZamydosporium, were isolated from PCN cysts taken from potato fields in Jersey. The efficacy of these fungi for the control of PCN was studied to determine their suitability for use in an integrated pest management programme. The radial growth rates of the nematophagolls fungi were reduced when grown on media amended with the fungicides Gambit and Rizolex, commonly used for the control of Rhizoctonia solani, another major pathogen of potatoes. Radial growth of V. chlamydosporium was also inhibited by Monceren and the nematicide Vydate. Growth of R. solani was inhibited by P. lilacinus at 20°C and 10°C in vitro and by V. chlamydosporium at 20°C, but the strain of V. chlamydosporiurn used did not grow at 10°c. Plectosphaerella cucumerina was a poor saprophytic competitor when grown against R. solani, P. lilacinus and V. chlamydosporium, therefore it may not be a suitable soil applied agent as it is out grown by other fungi in the soil. Paecilomyces lilacinus in a pelleted support matrix made from an alginate, gave better control of R. solani than non-formulated P. lilacinus alone. Of the different formulations of nematophagous fungi tested in pots, P. lilacinus incorporated into alginate pellets reduced the numbers of peN by the most (79.5%) and when applied in a field trial, reduced PCN population increase by approximately 60%. Plectosphaerella cucumerina, when incorporated into alginate pellets, also reduced field population increase by approximately 60%. A combination of these two formulated fungi tested in a plunge trial gave a poorer level of control than the fungi added individually. The fungi remained viable in alginate pellets for at least 18 months. The population composition of PCN in Jersey was previously unknown. Using an ELISA technique, this study has shown both PCN species are present, but the proportions were not determined. To ascertain whether the early lifting of Jersey potatoes was selectively reducing levels of one of the species of PCN, DNA was extracted from nematodes stained in situ in the roots of potatoes. The results were inconclusive and further work is required.