Abstracts |
Three non-systemic (Rizolex [tolclofos-methyl], Orthocide (captan) and Botec [dicloran/ captan]) and three systemic fungicides (Benlate (benomyl), Tecto (thiabendazole) and Vitavax (carboxen) [carboxin]/captan) at various rates (1, 2, 3, 4 and 5 g/kg) were used as seed dressings for lupin (Lupinus termis [L. albus] cv. Giza 2) plants in pot experiments in 1996 and 1997. The plants were grown in the presence of a standard inoculum ofvesicular arbuscular mycorrhizal (VAM) inoculum Glomus and Gigaspora spp. (900 spores/pot). In a second study, with fungicides applied at the recommended rate of 3 g/kg, the VAM inoculum was applied at 600, 750, 900, 1050 and 1250 spores per pot. The effects of fungicides on VAM colonization and on vegetative growth and yield were also studied in 2 further experiments with fungicides at 3 g/kg and a VAM inoculum of 900 spores/pot. VAM development was monitored at different stages of plant growth (up to 120 days after planting), and yields were recorded at harvest. Increasing the spore level increased the root infection percentages in both fungicide-treated and untreated seeds. Systemic fungicides induced higher reductions in mycorrhizal infection percentage than non-systemic ones. The reduction in mycorrhizal infection by fungicides at different levels of mycorrhizal inoculum was alleviated by increasing the number of mycorrhizal spores from 600 to 1250 spores per pot. The fungicide application rate had a marked adverse effect on root colonization percentage with VAM fungi. The extent of mycorrhizal infection reduction was proportional to the fungicide rate. The reduction was more pronounced at the early growth stage (30 days from planting) than at later stages. Root infection with VAM fungi increased with progressive aging of the host seedlings developed from fungicide-treated or untreated seeds. The systemic fungicides were more effective than non-systemic ones in reducing mycorrhizal infection at different plant growth stages. |