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Fungal nonribosomal peptide synthetases (NRPSs) are responsible for the biosynthesis of numerous metabolites which serve as virulence factors in several plant-pathogen interactions. The aim of our work was to investigate the diversity of these genes in a Fusarium graminearum sequence database using bioinformatic techniques. Our search identified 15 NRPS sequences, among which two were found to be closely related to peptide synthetases of various fungi taking part in ferrichrome biosynthesis. Another peptide synthetase gene was similar to that identified in Aspergillus oryzae which is possibly responsible for the biosynthesis of fusarinine, an extracellular iron-chelating siderophore. To our knowledge, this is the first report on the identification of a putative NRPS gene possibly responsible for the biosynthesis of fusarinine-type siderophores. The other NRPSs were found to be related to peptide synthetases taking part in the biosynthesis of various peptides in other fungi. Transcription factors carrying ankyrin repeats were observed in the vicinity of four of the identified peptide synthetase genes. Additionally, NRPS related genes similar to putative long-chain fatty acid CoA ligases, acyl CoA ligases, ABC transport proteins, a highly conserved putative transmembrane protein of Aspergillus nidulans, and a-aminoadipate reductases have also been identified. Further studies are in progress to clarify the role of some of the identified NRPS genes in plant pathogenesis.

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The presence of double-stranded RNA (dsRNA) elements in Fusarium culmorum and F. graminearum isolates of different origin, and the possible effect of these elements on pathogenicity and toxin production of the isolates were examined. Altogether 40 F. culmorum and 38 F. graminearum isolates were involved in this study, together with F. cerealis and F. pseudograminearum strains. Double-stranded RNA elements indicative of mycovirus infection were detected for the first time in 5 F. culmorum isolates. The isolates originated from the United States, The Netherlands, Australia and Israel. The dsRNA nature of the fragments was proved by RNase, DNase and S1 nuclease treatments. The sizes of the dsRNA elements varied between 0.6–3.95 kbp. A dsRNA element of 3.0 kbp in size was also detected in a F. graminearum isolate came from South Africa. None of the Central-European isolates examined were found to carry such elements. We also examined the mycotoxin producing abilities and pathogenicity of the dsRNA infected isolates. Four of the mycovirus infected F. culmorum isolates produced deoxynivalenol and zearalenone (chemotype I), while one of the isolates came from the USA produced nivalenol and fusarenone X (chemotype II). The dsRNA-containing F. graminearum isolate produced deoxynivalenol and zearalenone. In general, dsRNA-containing isolates were found to be as pathogenic to two wheat cultivars as dsRNA free isolates. RAPD analysis and sequence analysis of a putative reductase gene fragment indicated that dsRNA-containing isolates are scattered among dsRNA free isolates. Further work is in progress in our laboratory to characterize these dsRNA elements by sequence analysis.

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Fusarium head blight (FHB) is a devastating disease of wheat ( Triticum aestivum L.) world-wide. The objective of this study was to identify FHB resistance QTLs of the Brazilian spring wheat cultivar Frontana through molecular mapping. Frontana has small and medium effective QTLs. These types of QTLs are sensitive for the environmental factors and for the problems of heterogeneity. 206 DH lines from Frontana/Remus (IFA-Tulln) /2005–2006/ and 105 DH lines of Mini Mano/Frontana (CRC Szeged) /2006–2007/ were inoculated with isolates of F. graminearum and F. culmorum . The Frontana/Remus DH population had wide differences in flowering time and plant height. MM/Frontana was created by CRC, Szeged so that too early and late DH lines were discarded and the remaining lines flowered within five days. Lines with extra plant height were also discarded, so differences were kept within 20–30 cm. In the Frontana/Remus population QTLs were identified on the chromosomes 3B, 5A, 6B. In the MM/Frontana population chromosomes 3B and 5B gave positive signal. Although in both populations Frontana was the resistant parent no QTL markers were identical for them. It seems that the more homogeneous population increases the accuracy of the QTL analysis. An increased morphological homogeneity seems to be necessary to decrease „background noise“ in QTL analyses and increase precision. Until now no QTL were found that gave positive signs for all epidemic situations. As QTLs are not validated, it is early to apply MAS in breeding.

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Abstract

The acreage of English walnut (Juglans regia L.) is constantly expanding in Hungary, due to the favorable climatic conditions and economic importance. Last years, serious damage was reported from several orchards with high percentage of rotted, moldy kernels. The aim of this research was to identify the pathogens at different growth stages. Fungi were cultured from the spotty, shriveled and rotted kernels, and monosporic isolates were identified based on morphological characters and molecular markers (ITS region and tef1 locus sequences). Botryosphaeria dothidea and Diaporthe eres were identified in high proportion from symptomatic kernels. These species were also isolated from different parts of walnut trees in different seasons. D. eres was detected in a high proportion from asymptomatic buds in March, while the presence of both species was observed in symptomatic husks with Overnight Freezing-Incubation Technique (ONFIT) in June. Their optimal growth temperature defined to be between 20–25 °C, and the growth of D. eres isolates was completely inhibited at 35 °C.

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Cereal Research Communications
Authors:
Beáta Tóth
,
János Varga
,
Ágnes Szabó-Hevér
,
Szabolcs Lehoczki-Krsjak
, and
Ákos Mesterházy

Fusarium head blight caused mainly by Fusarium graminearum and F. culmorum is the most important disease of wheat in Central Europe. While F. graminearum is homothallic, no sexual cycle has been observed in F. culmorum . Knowledge regarding the species distribution and population structure of these pathogens is important to estimate their significance for breeding. There are two fundamental means by which fungi and other organisms transmit genes to the next generation: through clonal reproduction or by sexual recombination. To clarify the population structures of F. culmorum and F. graminearum in Central Europe, RAPD and IGS-RFLP data sets of the isolates were subjected to both the index of association tests and tree length tests. Our data indicate that the world-wide F. graminearum and F. culmorum populations have recombining structures, while both the Hungarian F. culmorum and F. graminearum populations reproduce clonally. The frequent occurrence of F. graminearum perithecia on corn residues indicates that this species undergoes a sexual cycle. Both mating type genes have been identified in each examined F. graminearum isolate, while the heterothallic distribution of mating type genes in F. culmorum indicates that this species lost its sexual cycle relatively recently.

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Cereal Research Communications
Authors:
Szabolcs Lechoczki-Krsjak
,
Beáta Tóth
,
Csaba Kótai
,
Imre Martonosi
,
László Farády
,
László Kondrák
,
Ágnes Szabó-Hevér
, and
Ákos Mesterházy

Four nozzle types were tested on large scale trials with 2500 m 2 plot size. The AIC TeeJet, the TeeJet XR, the Turbo FloodJet and the Turbo TeeJet Duo nozzles were tested in 2006 and 2007. 250 l/ha spray amount was used for all nozzles at 7–8 km/hr speed. Nine fungicides generally used to control FHB were tested. Across nine fungicides the mean reduction in symptoms was 60 % for both AIC TeeJet and XR TeeJet nozzles, but the more effective fungicides performed better with the XR TeeJet nozzle. The Turbo TeeJet Duo nozzles reduced the symptoms by 70 % and the Turbo FloodJet nozzle by 80 %. Among the fungicides the Prosaro 1 l/ha was the most effective. The coverage was controlled by water sensitive paper stripes and UV sensitive color mixed into the spray. Data show better uniformity by paper stripes, the UV pictures show that the all-side protection by the Turbo FloodJet nozzle is not perfect, the coverage is less than anticipated. Therefore, further work is necessary for improve the coverage being necessary to an even more effective control. However, the existing improvements allow 80 % or higher reduction with the best fungicides giving a chance for a better protection. Small plot tests with the same fungicides gave highly similar results achieved with the large-scale farm application. Farm efficacy could be forecasted with r = 0.90 correlation based on small plot hand sprayed tests.

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