The influence of disease complexes involvingLeptosphaeria (Septoria) nodorumon detection of resistance to three leaf spot diseases in wheat

摘要

In controlled inoculation studies withSeptoria nodorumandPyrenophora tritici-repentis, estimates of the relative proportion of each pathogen demonstrated differences in the responses of cultivars to pathogen mixtures that were not apparent from measurements of diseased leaf areas. Under field conditions estimates of the relative proportion ofS. nodorum, P. tritici-repentisandS. triticivaried between field screening locations in Western Australian but also between lines within locations. Lines with known resistance toP. tritici-repentisandS. tritici, but susceptible toS. nodorum, could not be distinguished from susceptible lines on the basis of leaf area diseased or grain weight depression whenS. nodorumwas present in the disease complex. Such conditions, while suitable for the selection of combined resistance to these pathogens, were unsuitable for identifying resistance to individual pathogens. As symptoms were similar, the proportion of diseased leaf area sporulating with each pathogen provided a means of measuring the variation in disease development induced on lines varying in resistance. Knowledge of the components of disease and their relative importance were essential in understanding varietal response information under mixed infections of these leaf spot pathogens.