The inheritance of host plant effect on latency period of wheat leaf rust in spring wheat. II: Number of segregating factors and evidence for trangressive segregation in F3 and F5 generations

Summary The dry matter yields of four varieties of Lolium perenne with similar flowering dates (Ba 10761, cv. Talbot, cv. S.321 and cv. Tove) were compared during two harvest years in an orthogonal plot trial with two contrasting harvesting frequencies, three levels of applied nitrogen (200, 400 and 600 kg N/ha/yr) and two wear treatments (with and without wear). Frequent harvesting, reduction of applied nitrogen from 600 to 200 kg/ha, and wear reduced mean annual yield by 6.49, 5.13 and 0.65 t/ha respectively. Differences between varieties in mean annual dry matter yields over all treatments were 0.52 t/ha in the first harvest year and 1.49 t/ha in the second harvest year. Over both harvest years, Ba 10761 outyielded Talbot by 15% under frequent harvesting but by only 5% under infrequent harvesting. This variety/harvesting frequency interaction was due to relatively poor growth of Ba 10761 during the reproductive phase of growth, reproductive growth accounting for a larger proportion of total annual yield under infrequent harvesting than under frequent harvesting. Talbot gave relatively low yields at the lowest level of nitrogen. Genotype/harvesting management interactions arising from genetic independence of productivity during vegetative and reproductive growth can be predicted from results of single-management trials but such predictions of genotype/nitrogen level interaction are not yet possible.