RELATIVE OCCURRENCE OF PHAEOSPHAERIA-NODORUM AND MYCOSPHAERELLA-GRAMINICOLA ON SPRING WHEAT IN SASKATCHEWAN

The relative occurrence of Phaeosphaeria nodorum, causal agent of septoria nodorum blotch, and Mycosphaerella graminicola, causal agent of septoria tritici blotch, on spring wheat cultivars planted into wheat stubble varied with cultivar, location, and year. Little difference in the number of lesions of M. graminicola occurred on Kenyon, Katepwa, and Pembina. However, these lesions were found only rarely on Oslo, suggesting that Oslo possesses resistance to this pathogen. In 1987 and 1988, P. nodorum produced lesions on seedlings within three weeks of emergence (early June), while M. graminicola lesions were not observed until early to mid July. P. nodorum produced more lesions than M. graminicola on all leaves sampled at Paddockwood in 1987. At Shellbrook, P. nodorum, was predominant on the penultimate leaf, but both pathogens were equally prevalent on the flag leaf. In 1988, P. nodorum was the predominant pathogen on all leaves at both Shellbrook and Weirdale, whereas M. graminicola produced only few lesions. Temperature and duration of leaf wetness periods appeared to have less effect on septoria nodorum blotch than on septoria tritici blotch. Septoria nodorum blotch developed at all temperatures recorded, whereas both high (above about 25-degrees-C) and low (below 7-degrees-C temperatures delayed development of septoria tritici blotch. Septoria nodorum blotch also developed when most leaf wetness periods were less than 11 h in duration, whereas septoria tritici blotch required longer periods. Thus, in the Parkland region of Saskatchewan if inoculum is present septoria nodorum blotch will be a problem in most years, whereas septoria tritici blotch will be a problem only in years with moist conditions and moderate temperatures.