Browsing by Author "Gokul, Anushka"

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    Fusarium graminearum species complex (FGSC) composition in South African wheat and maize grown in rotation
    (Stellenbosch : Stellenbosch University, 2016-03) Gokul, Anushka; Rose, Lindy J. ; Viljoen, Altus; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Fusarium graminearum is an important pathogen of economically important cereal crops. Recently, the morpho-species has been reclassified as a species complex consisting of 16 phylogenetic species, called the Fusarium graminearum species complex (FGSC). FGSC species cause a number of important plant diseases, including Fusarium head blight (FHB) of wheat and Gibberella ear rot (GER) of maize. Infection by these pathogens results in poor grain yield and quality and contaminates grain with noxious secondary metabolites, called mycotoxins. FGSC species produce Type B-type trichothecenes; such as nivalenol (NIV), fusarenon-X (FX), deoxynivalenol (DON), 15-acetyl-deoxynivalenol (15-ADON) and 3-acetyl-deoxynivalenol (3-ADON); and zearalenone (ZEA). The consumption of mycotoxin-contaminated grain has been associated with serious human and animal health risks. The diversity and distribution of FGSC species have been evaluated globally, but only a single study has been conducted in South Africa. To date, six of the 16 phylogenetic species have been documented on wheat, maize and barley produced in the country. Wheat and maize, the two most important cereals grown in South Africa, are commonly rotated with each other. This is of particular concern to disease development and mycotoxin contamination of the two crops. While FGSC species have been identified on wheat and maize in South Africa, these crops were not grown in a rotational system. The aim of this study, therefore, was to investigate FGSC species composition on wheat and maize grown in a rotational cropping system in South Africa. Identification of Fusarium species based exclusively on morphological characteristics has proven to be inadequate for the effective differentiation between closely related species. Therefore, the first objectives of the study was to evaluate matrix-assisted laser desorption ionization – time of flight mass spectrometry (MALDI-TOF MS), PCR – restriction fragment length polymorphism (PCR-RFLP) and species-specific PCR for the rapid and reliable identification of FGSC species previously reported in South Africa. Different protein mass spectra obtained with MALDI-TOF MS were able to separate the FGSC species reported in South Africa. Double restriction digestion of the translation elongation factor α-1 (EF-1α) gene region of local FGSC species with BfaI and BsaHI was able to distinguished F. graminearum s.s., F. cortaderiae and F. acaciae-mearnsii from each other and from the remaining two FGSC species in a single restriction digest. The restriction profile produced by EarI, when the histone (H3) gene region was digested, distinguished F. boothii from the FGSC species evaluated. These techniques, thus, could be used to identify FGSC species present on cereal crops in South Africa. The second objective of the study was to identify FGSC species on wheat and maize grown in rotation and their chemotypes. The in vitro production of nivalenol (NIV), fusarenon-X FX, deoxynivalenol DON and 15-acetyl-deoxynivaleno 15-ADON was also determined. The most isolated FGSC species from wheat and maize was F. graminearum s.s. Only one isolate from wheat was identified as F. boothii. No other FGSC species were isolated from maize, but several non-FGSC species were associated with diseased maize ears. 15-ADON was the predominant chemotype of the FGSC identified in South Africa. Seven isolates produced the NIV chemotype, but none of these isolates were FGSC species. Cultural practices, such as crop rotating with hosts of the FGSC species, needs to be further evaluated as crop rotation in combination with other variables potentially favoured the occurrence of F. graminearum s.s.