Fusarium graminearum species complex (FGSC) composition in South African wheat and maize grown in rotation
Date
2016-03
Authors
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Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
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.
AFRIKAANSE OPSOMMING: Fusarium graminearum is 'n belangrike patogeen van ekonomies belangrike graan gewasse. Die morfo-spesie is onlangs geherklassifiseer as 'n spesie kompleks wat bestaan uit 16 filogenetiese spesies, naamlik die Fusarium graminearum spesie kompleks (FGSK). FGSK spesies veroorsaak belangrike graan siektes, insluitend Fusarium aarskroei van koring en Gibberella kopvrot van mielies. Infeksie deur hierdie patogene veroorsaak swak graan opbrengte en kwaliteit, en besoedel graan met giftige sekondêre metaboliete wat bekend staan as mikotoksiene. FGSK spesies produseer tipe-B trichothecenes (TCT-B); veral nivalenol (NIV), fusarenon-X (FX), deoxynivalenol (DON), 15-asetiel-deoxynivalenol (15-ADON) en 3-asetiel-deoxynivalenol (3-ADON); en zearalenone (ZEA). Die inname van mikotoksien-besmette graan gaan gepaard met ernstige menslike en diere gesondheid risiko's. Die diversiteit en verspreiding van die FGSK is al wêreldwyd geëvalueer, maar daar is slegs 'n enkele studie in Suid-Afrika gedoen. Tot op hede is ses van die 16 filogenetiese spesies gedokumenteer op koring, mielies en gars in Suid Afrika. Koring en mielies is die twee belangrikste verboude grane in Suid-Afrika en word algemeen geroteer in wisselbou. Wisselbou is van kritiese belang vir siekte ontwikkeling en mikotoksien besmetting van hierdie twee gewasse. Die koring en mielies in Suid-Afrika, waarvandaan die FGSK spesies geïdentifiseer is, was nie geroteer met mekaar nie. Die doel van hierdie studie was dus om die FGSK spesiesamestelling op koring en mielies, wat saam in wisselbou stelsels in Suid-Afrika gebruik word, te ondersoek. Die identifisering van Fusarium spesies was uitsluitlik gebaseer op morfologiese kenmerke, maar was onvoldoende vir die effektiewe onderskeid tussen naverwante spesies. Die eerste doelwit van hierdie studie was dus om “matrix-assisted laser desorption ionization–time of flight mass spectrometry” (MALDI-TOF MS), Polimerasie Ketting Reaksie beperkings fragment lengte polimorfisme (PKR-RFLP) en spesie-spesifieke PKR te evalueer as vinnige en betroubare identifikasie tegnieke vir die FGSK spesies, wat voorheen in Suid-Afrika berig is. Verskillende proteïn massa spektra was verkry met MALDI-TOF MS en was in staat om die FGSK spesies te onderskei. Dubbel restriksie ensiem vertering met BfaI en BsaHI kon F. graminearum s.s., F. cortaderiae en F. acaciae-mearnsii van mekaar onderskei, terwyl die oorblywende twee FGSK spesies met ʼn verdere enkel restriksie ensiem vertering onderskei kon word. Die profiel wat geproduseer is met Earl, waar die histoon (H3) geen verteer is, onderskei F. boothii van die FGSK spesies wat geëvalueer is. Hierdie tegnieke kan dus gebruik word om FGSK spesies in Suid-Afrikaanse graangewasse te identifiseer. Die tweede doelwit van hierdie studie was om FGSK spesies en hul chemotipes, wat voorkom op koring en mielies wat in wisselbou gebruik word met mekaar, te identifiseer. Die in vitro produksie van NIV, FX, DON en 15-ADON is ook bepaal. Die mees geïsoleerde FGSK spesies van koring en mielies was F. graminearum s.s. Slegs een isolaat van koring is geïdentifiseer as F. boothii. Geen ander FGSK spesies was geïsoleer vanaf mielies nie, maar verskeie nie-FGSK spesies was geassosieer met besmette mielies. 15-ADON was die oorheersende chemotipe van die FGSK spesies wat geïdentifiseer is in Suid-Afrika. Sewe isolate produseer die NIV chemotipe, maar nie een van hierdie isolate is FGSK spesies nie. Kulturele praktyke, soos wisselbou met gashere van die FGSK spesies, moet verder geëvalueer word siende dat rotasie met graan gewasse die voorkoms van F. graminearum s.s bevorder het.
AFRIKAANSE OPSOMMING: Fusarium graminearum is 'n belangrike patogeen van ekonomies belangrike graan gewasse. Die morfo-spesie is onlangs geherklassifiseer as 'n spesie kompleks wat bestaan uit 16 filogenetiese spesies, naamlik die Fusarium graminearum spesie kompleks (FGSK). FGSK spesies veroorsaak belangrike graan siektes, insluitend Fusarium aarskroei van koring en Gibberella kopvrot van mielies. Infeksie deur hierdie patogene veroorsaak swak graan opbrengte en kwaliteit, en besoedel graan met giftige sekondêre metaboliete wat bekend staan as mikotoksiene. FGSK spesies produseer tipe-B trichothecenes (TCT-B); veral nivalenol (NIV), fusarenon-X (FX), deoxynivalenol (DON), 15-asetiel-deoxynivalenol (15-ADON) en 3-asetiel-deoxynivalenol (3-ADON); en zearalenone (ZEA). Die inname van mikotoksien-besmette graan gaan gepaard met ernstige menslike en diere gesondheid risiko's. Die diversiteit en verspreiding van die FGSK is al wêreldwyd geëvalueer, maar daar is slegs 'n enkele studie in Suid-Afrika gedoen. Tot op hede is ses van die 16 filogenetiese spesies gedokumenteer op koring, mielies en gars in Suid Afrika. Koring en mielies is die twee belangrikste verboude grane in Suid-Afrika en word algemeen geroteer in wisselbou. Wisselbou is van kritiese belang vir siekte ontwikkeling en mikotoksien besmetting van hierdie twee gewasse. Die koring en mielies in Suid-Afrika, waarvandaan die FGSK spesies geïdentifiseer is, was nie geroteer met mekaar nie. Die doel van hierdie studie was dus om die FGSK spesiesamestelling op koring en mielies, wat saam in wisselbou stelsels in Suid-Afrika gebruik word, te ondersoek. Die identifisering van Fusarium spesies was uitsluitlik gebaseer op morfologiese kenmerke, maar was onvoldoende vir die effektiewe onderskeid tussen naverwante spesies. Die eerste doelwit van hierdie studie was dus om “matrix-assisted laser desorption ionization–time of flight mass spectrometry” (MALDI-TOF MS), Polimerasie Ketting Reaksie beperkings fragment lengte polimorfisme (PKR-RFLP) en spesie-spesifieke PKR te evalueer as vinnige en betroubare identifikasie tegnieke vir die FGSK spesies, wat voorheen in Suid-Afrika berig is. Verskillende proteïn massa spektra was verkry met MALDI-TOF MS en was in staat om die FGSK spesies te onderskei. Dubbel restriksie ensiem vertering met BfaI en BsaHI kon F. graminearum s.s., F. cortaderiae en F. acaciae-mearnsii van mekaar onderskei, terwyl die oorblywende twee FGSK spesies met ʼn verdere enkel restriksie ensiem vertering onderskei kon word. Die profiel wat geproduseer is met Earl, waar die histoon (H3) geen verteer is, onderskei F. boothii van die FGSK spesies wat geëvalueer is. Hierdie tegnieke kan dus gebruik word om FGSK spesies in Suid-Afrikaanse graangewasse te identifiseer. Die tweede doelwit van hierdie studie was om FGSK spesies en hul chemotipes, wat voorkom op koring en mielies wat in wisselbou gebruik word met mekaar, te identifiseer. Die in vitro produksie van NIV, FX, DON en 15-ADON is ook bepaal. Die mees geïsoleerde FGSK spesies van koring en mielies was F. graminearum s.s. Slegs een isolaat van koring is geïdentifiseer as F. boothii. Geen ander FGSK spesies was geïsoleer vanaf mielies nie, maar verskeie nie-FGSK spesies was geassosieer met besmette mielies. 15-ADON was die oorheersende chemotipe van die FGSK spesies wat geïdentifiseer is in Suid-Afrika. Sewe isolate produseer die NIV chemotipe, maar nie een van hierdie isolate is FGSK spesies nie. Kulturele praktyke, soos wisselbou met gashere van die FGSK spesies, moet verder geëvalueer word siende dat rotasie met graan gewasse die voorkoms van F. graminearum s.s bevorder het.
Description
Thesis (MScAgric)--Stellenbosch University, 2016.
Keywords
Fusarium graminearum species complex, Molecular identification techniques, Chemotyping, Mycotoxins, Fusarium diseases of plants, Crop rotation, Wheat -- Diseases and pests -- South Africa, Corn -- Diseases and pests -- South Africa, Maize -- Diseases and pests -- South Africa, Pathogenic microorganisms, UCTD