| Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schwein) Petch) isan important pathogen to wheat, rice and maize---the three most important crops in theworld. The fungus can infect many plant parts during the life cycle of the host and thuscause a range of diseases. F. graminearum can cause seedling blight, brown foot rot, andscab (also known as ear or head blight) of cereal, and both stem rot and ear rot of maize.After the harvesting of wheat. F. graminearum can also infect the ear and the basalsheath of rice. In addition to causing yield losses, infection by F. graminearum can leadto contamination of grains by mycotoxins which pose a serious health threat to humansand animals. With the innovation of cultivation system in China and the climate changesworldwide, crop diseases caused by F. graminearum is more and more serious in China.Moreover, F. graminearum has been divided into 9 clades and these clades have beenrenamed. But less research work have been done for the Chinese F. graminearumpopulation. Therefore, it's important to understand the pathogen composition associatedwith Fusarium head blight (FHB) and maize ear rot, the population and genetic diversity,phylogenetic development and the type of mycotoxin produced by Chinese F.graminearum. Knowledge of F. graminearum population and chemotype distribution andtheir relationship with pathogenicity and morphological characters is helpful forintegrated control of wheat and maize Fusarium diseases and mycotoxin detection ofinfected grains.In this study, 1229 Fusarium strains were isolated from Fusarium head blightsamples collected from Hebei, Heilongjiang and Hubei provinces and maize ear rotsamples from Hebei and Gansu provinces. After single spore purification andidentification by morphological and molecular methods, nine Fusarium species---F.graminearum, F. equiseti, F. verticillioides (formerly known as F. moniliforme), F.subglutinans, F. proliferatum, F. chlarnydosporum, F. culmorum, F. semitectum and F.acuminatum were confirmed to be associated with Fusarium head blight; five Fusariumspecies---F. graminearum, F. equiseti, F. verticillioides, F. subglutinans and F.proliferatum were associated with maize ear rot. Among them, F. graminearum is predominant for Fusarium head blight and maize ear rot; F. graminearum, F.verticillioides, F. subglutinans and F. proliferatum were obtained from both wheat andmaize samples and had higher proportion among the isolates. However, the compositionand frequency of other Fusarium species were variable among sample sites and years.Three hundred and thirty-seven F. graminearum isolates were tested for SCAR andmycotoxin production analysis using Fg16F/Fg16R primers and the primers contrivedfrom the related sequence of Tri13 and Tri3 gene. 7C1, 6A5 and another unknownpopulation were confirmed to exist in China. By phylogenetic analysis using elongationfactor-1αgene sequences and genetic diversity analysis by RAPD method, three F.graminearum populations were further confirmed to be F. graminearum lineage 7(Fusarium graminearum), F. graminearum lineage 6 (Fusarium asiaticum) and F.graminearum lineage 3 (Fusarium boothii). The three F. graminearum lineages havedifferent geographical distribution and host origin in China. F. graminearum lineage 7widely exists in all the regions; F. graminearum lineage 6 is mainly distributed in Hubeiand Heilongjiang provinces in China and F. graminearum lineage 3 was isolated frommaize only. It was also the first time to find F. graminearum lineage 3 isolates exist inChina. Moreover, highly genetic diversity was found among geographical isolates in eachlineage. The results of F. graminearum mycotoxin production analysis indicated thatthree mycotoxin chemotypes 3-ADON, 15-ADON and NIV existed in China. TheNIV-producing strains were mainly distributed in the FHB prevalent area in Hubei andHeilongjiang provinces. 3-ADON chemotype-producing isolates mainly came from thewanner wheat-growing area of Hubei province and 15-ADON was mainly present insome colder regions, e.g., Heilongjiang, Gansu and Hebei provinces. It's also the firsttime for quickly detecting of NIV, 3-ADON and 15-ADON chemotypes produced by F.graminearum in China.Seventy-five F. graminearum isolates from different geographical and host originswere tested for the growth rate, production of conidia and perithecia, and also theirsensitivity to carbendazim. Variation in the biological characters between isolates fromthe same origin was found. Comparing between the F. graminearum populations ofdifferent origins, the strains isolated from maize had higher mycelial growth rate andconidia production than the isolates from wheat. The mycelial growth rate and conidiaproduction of isolates from spring wheat in Hebei and Heilongjiang were quicker andhigher than that of isolates from barley in Hubei. For the perithecia production, isolatesfrom wheat and maize in Hebei produced more perithecia than isolates from spring wheatin Heilongjiang and barley in Hubei, whereas isolates from maize in Gansu had the leastperithecia production. Three hundred and thirty-seven F. graminearum isolates weretested for the resistance to carbendazim at the concentration of 10μg·mL-1. None resistance strain was detected. Further tests by using 75 F. graminearum strains showedthat the sensitivity to carbendazim at the concentration of 2μg·mL-1 had differencebetween strains from the same origin, but there had no obvious difference between thepopulations from different regions. Among them, the isolates from barley of Hubei andspring wheat of Heilongjiang were less sensitive to carbendazim.The pathogenicity of F. graminearum to wheat was tested by using coleoptile, stemand spike inoculation methods. Results of three inoculation methods were consistent andthe aggressiveness of F. graminearum to wheat was different among populations fromdifferent geographical and host origins. The strains isolated from maize had loweraggressiveness to wheat and the isolates from wheat in Hebei and Heilongjiang hadhigher aggressiveness than the isolates from barley in Hubei. Comparing theaggressiveness of strains with the lineage and biological characters, the aggressiveness ofstrains was mainly related to the F. graminearum lineage type. Moreover, theaggressiveness might also have relationship to the character of mycelial growth rate andconidia production.
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