Infestation-damage relationship for the host-parasite system wheat-Septoria nodorum Berk.

It was the aim of these investigations to elucidate the relationship between infestation by Septoria nodorum Berk. and the damage caused thereby to the winter wheat varieties grown in the GDR. In 1983 and 1984 the varieties Alcedo and Taras were tested, and for the identification of typical varietal reactions, another 4 cultivars (Arkos, Compal, Mironovskaya 808 and Ilyitshovka) were included, in 1984. Artificial inoculation was carried out when the ears were emerging, using spore suspensions of barying density to achieve various degrees of infestation. For each variety, ear and flag leaf infestations were recorded on 800 culms and these were then grouped into th1913e categories 1, 2 and 3 according to the number of points they had received (9 without any infestation, 7 and 5 = number of points decreasing as infestations increased). Altogether 5-6 assessments were made, with the points given at the growth stage 'beginning of the milky ripeness' being used as the basis for the calculation of the infestation-damage relationship. The most important criterion for each group was the mean single ear weight, the 1000-grain weight and the number of grains per ear, were also taken into consideration. Comparing ear infestation with yield it can be stated that the variety Compal and the early ripening Soviet varieties Mironovskaya 808 and Ilyitshovka showed relatively low losses. The variety Taras ranked in the middle. Alcedo and Arkos suffered the highest yield losses. Depending on the variety, an infestation level rated with 7 points at the beginning of milky ripeness implied yield losses of 5-13 per cent, whereas a 5 rating point would represesnt losses of 13-23 per cent. The results obtained make it clear that the wheat cultivars tested were not damaged by S. nodorum to the same degree, indicating differing varietal susceptibility, which does not allow a generalization with respect to the infestation-damage relationship for the host-parasite pair wheat-S. nodo