Inheritance of adult plant resistance to mildew in oats

SUMMARY Adult plant resistance of a durable nature in oat cv. Maldwyn was studied in a cross with the very susceptible cv. Selma, using a replicated F3 population grown under field conditions. Segregation was found to be continuous, with no discrete classes, and a preponderance of segregants showing intermediate values between the two parents indicating additive genetic control. The number of effective genetic factors segregating in this cross was estimated to be four when material was at the ‘boot stage’ (G.S. 45) and eight or nine at the stage when flowering was complete (G.S. 69). At this latter stage Maldwyn was estimated to be contributing about seven factors for resistance, and the susceptible Selma one or possibly two. Further improvement, through accumulation of factors from both parents, could be expected and this has subsequently been achieved. The possible effects, on the durability of resistance in highly resistant transgressive segregants, from increased selection pressure on the pathogen are discussed.