Septoria tritici blotch

Authors: Goodwin, Stephen - Steve

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 3/7/2018
Publication Date: 10/29/2018
Citation: Goodwin, S. B. 2018. Diseases affecting wheat: Septoria tritici blotch. Pages 47-68 in Integrated Disease Management of Wheat and Barley (R. P. Oliver, ed.). Burleigh Dodds Science Publishing, Cambridge, UK.

Interpretive Summary: Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is one of the most economically important diseases of wheat worldwide. Despite its importance, relatively little is known about its mode of infection or the genetic basis of resistance. To address this deficiency, the primary literature was reviewed. Resistance genes have now been found on all 21 wheat chromosomes, giving a rich resource for marker-assisted selection for increased resistance. However, despite much recent progress, we still know very little about what the pathogen is doing during its symptomless, early growth phase, how it switches from one mode of nutrition to another, or whether toxins are involved in its growth and disease etiology. The first STB resistance gene has now been cloned but the mechanism of resistance remains a mystery. Despite the huge progress made during the past 20 years STB remains a difficult disease that is likely to require substantial future efforts by fungal geneticists, plant pathologists and plant breeders for its control.

Technical Abstract: Septoria tritici blotch (STB), caused by the haploid, ascomycete fungus Zymoseptoria tritici (synonyms: Mycosphaerella graminicola; Septoria tritici), is one of the most common and economically important diseases of wheat worldwide. Despite its importance, compared to other wheat diseases relatively little was known about its mode of infection or the genetic basis of resistance. This review of the literature shows where the disease is most prominent worldwide and the measures that have been taken for its control. Fungicides have been the primary means of disease management, but resistance to all single-site mode of action fungicides developed rapidly and has rendered some compounds ineffective; the rest may fail in the near future. Using fungicides with different modes of action together will minimize disease-control failures. Qualitative or quantitative resistance genes have now been found on all 21 wheat chromosomes, giving a rich source of genes for plant improvement. The major, qualitative genes are likely to break down so should only be used in combination or preferably within a strong background of quantitative resistance. Molecular markers are now available for many resistance genes making marker-assisted selection for increased resistance an achievable goal for the future. Recent analyses have begun to elucidate the molecular basis for the host-pathogen interaction. One effector involved in pathogenicity has been identified and numerous other candidates have been identified from the genome sequence and by mining RNA sequencing results through bioinformatics analyses. However, we still know very little about what the pathogen is doing during its symptomless, early biotrophic phase, how the switch from biotrophy to necrotrophy is triggered, or whether toxins are involved in necrotrophic growth and disease etiology. Wheat can sense and respond to the pathogen very quickly, within three hours after inoculation, but later host responses at the time when the pathogen is switching from biotrophic to necrotrophic growth most likely determine whether the outcome of the interaction is resistance or susceptibility. The first STB resistance gene has now been cloned but the mechanism of resistance remains a mystery. Despite the huge progress made during the past 20 years STB remains a difficult disease that is likely to require substantial future efforts for its control.