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- Author or Editor: Ákos Mesterházy x
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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.
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.
Fumonisins were extracted from a rice culture which had been inoculated with Fusarium verticillioides isolated from maize stalk. The culture extracts were analysed by a hyphenated technique: reversed-phase high-performance liquid chromatography/electrospray ionization ion-trap mass spectrometry (RP-HPLC/ESI-IT MS 2 ). Besides already known fumonisins, a new type of fumonisin series (PHFB4OSA belonging to the formerly described FBX)-containing four new compounds-was detected. At these compounds, one of the OH groups attached to the fumonisin backbone was esterified by carboxylic acid (oxalylsuccinic acid, OSA) other than tricarballylic acid (TCA). The masses of the protonated molecules and of the characteristic product ions and the characteristic neutral mass losses from the protonated molecules suggested their structure. The relative quantities of the new minor compounds were expressed as percentages of FB1 toxin.
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.
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.
