EFFECTS OF SEED-BORNE MICRODOCHIUM-NIVALE ON ESTABLISHMENT AND POPULATION-DENSITY AT HARVEST OF WINTER-SOWN OATS

The relationship between seed-borne levels of Microdochium nivale and establishment, development and subsequent population density at harves t of winter-sown oats under field conditions was examined. Six varieti es of oats were sown in a field trial at three seeding rates (400 seed s, 480 seeds, and 560 seeds m(-2)) using untreated seed in October 199 1. Plant establishment in November 1991 was variable between varieties and ranged from 40% to 82%. Samples of seed from each variety were te sted on potato dextrose agar and found to have levels of M. nivale ran ging from 5% to 61% significantly correlated with plant establishment. Laboratory work showed seedbone M. nivale was effectively transmitted to seedlings. At harvest, plant population density ranged from 360 to 470 ears m(-2) and was significantly correlated with establishment. G rain yield ranged between 6.9 t to 8.2 t ha(-1) and was related to est ablishment but was also influenced by a number of variety-specific fac tors including susceptibility to Erysiphe graminis. observed reduction s in emergence, ears m(-2) and grain yield indicate the importance of effective control of seed-borne M. nivale infection in winter-sown oat s.