Browsing by Author "Van Coller, Gerhardus Johannes"

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    Identification and management of toxigenic fusarium species associated with fusarium head blight and fusarium crown rot of wheat in South Africa
    (Stellenbosch : Stellenbosch University, 2018-03) Van Coller, Gerhardus Johannes; Viljoen, Altus; Lamprecht, Sandra, C. ; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Fusarium head blight (FHB) and Fusarium crown rot (FCR) are important diseases of wheat. FHB, which is caused by members of the Fusarium graminearum species complex (FGSC), reduces yields and grain quality, and contaminates grain with mycotoxins (toxic secondary fungal metabolites) like deoxynivalenol (DON), nivalenol, and zearalenone (ZEA). FCR, caused by Fusarium pseudograminearum, infects the lower stem and causes stem rotting, which also results in yield losses. Fusarium pseudograminearum can also cause FHB. Management of FHB involves integrating agronomical practices (crop rotation, tillage), host resistance and chemical control. In the irrigation regions of South Africa, however, producers rotate wheat with summer crops like maize, which also hosts the FGSC, while crop rotation and minimum/no-till is common in the Western Cape. These practices necessitates the use of host resistance and chemical control to manage FHB in South Africa. Accurate identification of pathogens causing FHB and FCR in South Africa is needed to determine their distribution and to assist breeders in developing resistant wheat cultivars. Comprehensive surveys were thus conducted over 2 years to identify Fusarium species and their chemotypes in the country. The FGSC with the 15-cetyldeoxynivalenol chemotype predominated in the irrigation regions of South Africa, while F. pseudograminearum was the dominant species in the Western Cape region. Commercial irrigation and dryland wheat cultivars, as well as test lines with different quantitative trait loci (QTL), were evaluated for resistance to FHB by field-inoculation with F. graminearum s.s. and F. pseudograminearum. Among the irrigation cultivars, Krokodil, SST843, SST866, and SST884 performed the best. The Fhb1 QTL had a marked effect on the percentage Fusarium-damaged kernels, and reduced DON content in most test lines. One test line, BFUS2011-17, with no QTLs from Sumai 3, grouped among the top performers. Disease levels were low in dryland trials, but DON and ZEA levels were high in the first year, with the resistant control and SST027, SST056 and SST087 containing low mycotoxin levels. The efficacy of three commercial fungicides (Abacus, Amistar Xtra and Prosaro) and two chemical seed treatments (Galmano Plus and Vitavax Plus) to manage FHB and increase grain quality was determined in field trials over 2 years. All foliar treatments reduced disease and DON levels, while significantly improving grain quality and yield. Seed treatments had little effect on FHB, but Abacus combined with seed treatments reduced disease incidence more than Abacus alone. Prosaro combined with Galmano Plus reduced yields compared to Prosaro alone. This study provided the first comprehensive report of Fusarium species and their type B trichothecene chemotype associated with FHB and FCR in South Africa. Irrigation cultivars, test lines and dryland cultivars with improved resistance to FHB and DON contamination were identified, while fungicides reduced FHB and DON, and improved grain quality. Future studies should determine the natural occurrence of mycotoxins in wheat fields throughout South Africa, develop resistant irrigation and dryland cultivars, determine the efficacy of chemical control of FHB in different environments over multiple years, and optimise chemical control of FHB through timing of application, different nozzles and adjuvants.