A New Concept for Multiple Resistance Breeding in Wheat to Leaf and Ear Diseases

Abstract

A selection strategy was developed in wheat to screen for improved multiple resistance to Fusarium culmorum (FC), Septoria nodorum (SN) and Septoria tritici (ST) simultaneously during breeding in segregating generations from F-2-F-8 after quantitative accumulation of resistance genes from donors of varying sources under recurring crossing procedures. The selection for improved levels of resistance occurred under field infection techniques with highly homogenic inoculations, using well-tested aggressive mixtures of inoculum twice for setting the appropriate infections. Disease values on leaves and spikes were scored 3-5 times during epidemic development in plots inoculated separately to each disease and simultaneously to combined mixtures of all three pathogens. For comparison a control plot was planted to each genotype tested. In addition yield loss values were measured as differences between inoculation and control plots. From all field data a total resistance value was calculated using multiple regression procedures, which allowed also for corrections to confounding factors like earliness and culm length. Resistance and aggressivity effects were defined by a general factorial host-parasite interaction model and for aggressivity a basic aggressivity value was defined to demonstrate broad genetic variability within all pathogen populations used. From 20 years selection, summarized results demonstrate a significant increase of multiple resistance at close to constant levels of yield and morphological traits. This gain through selection was achieved under quantitative selection procedures, including a toxicity trait in harvested grains at the final stage of selection by measuring the Fusarum intoxication with a bioluminescence test. Selection progress was speeded up by appliction of an improved single-seed-descent technique including all infection tests under greenhouse conditions during 5 generations within 2 years.