2007. Sensitivity of field populations of Ascochyta rabiei to chlorothalonil, mancozeb, and pyraclostrobin fungicides, and effects of strobilurin fungicides on the progress of ascochyta blight of chickpea. Can. J. Plant Sci. 87: 937-944. Chickpea production faces a major challenge from ascochyta blight (Ascochyta rabiei), a devastating disease that can cause total crop loss. To assess the effect of repeated fungicide application on disease progress, strobilurin fungicides, primarily alternating pyraclostrobin and azoxystrobin treatments, were applied up to five times per year in each of 2 yr. A single application or two early applications reduced blight severity. A third application resulted in additional benefits in 1 of 2 yr, but additional applications did not reduce severity further. To monitor for fungicide tolerance in populations of A. rabiei, 66 single-spore isolates were collected and grown on growth media amended with chlorothalonil, mancozeb, or pyraclostrobin. Insensitivity to one or more of the fungicides was detected in 49 (74%) of the isolates. Based on the effect on conidial germination, insensitivity to pyraclostrobin or chlorothalonil was observed in 26 of 37 isolates (70%). Repeated fungicide application may be selecting for insensitive isolates of the pathogen; fungicide application should be combined with cultural measures to control ascochyta blight. des populations naturelles de Ascochyta rabiei au chlorothalonil, au mancozèbe et à la pyraclostrobine, et incidence des fongi-cides à la strobilurine sur la progression de la brûlure ascochytique chez le pois chiche. Can. J. Plant Sci. 87: 937-944. La brûlure ascochytique (Ascochyta rabiei), maladie dévastatrice pouvant détruire complètement une culture, pose un sérieux prob-lème aux producteurs de pois chiches. Afin d'évaluer l'incidence d'un usage répétitif de fongicide sur la progression de la mal-adie, les auteurs ont appliqué des fongicides à la strobilurine, principalement de la pyraclostrobine et de l'azoxystrobine en alternance, jusqu'à cinq fois par année pendant deux ans. Une seule application ou deux applications précoces de fongicide atténu-ent la gravité de la maladie. Une troisième application a eu des effets bénéfiques additionnels une année mais pas l'autre. Les applications supplémentaires n'ont pas réduit la gravité de la maladie davantage. Pour déterminer la tolérance de A. rabiei aux fongicides, les auteurs ont recueilli 66 isolats d'une spore qu'ils ont cultivés sur un milieu de croissance contenant du chlorothalonil, du mancozèbe ou de la pyraclostrobine. Quarante-neuf (74 %) des isolats étaient insensibles à un ou à plusieurs fongicides. D'après la germination des conidies, on a décelé l'insensibilité à la pyraclostrobine ou au chlorothalonil chez 26 des 37 isolats (70 %). L'application répétitive de fongicide pourrait favoriser la sélection d'isolats insensibles du pathogène; il con-viendrait de combiner le traitement antiparasitaire à des méthodes de lutte culturales pour combattre la brûlure ascochytique.
Coleoptile length under soil compaction as a percent of length under no compaction was used to measure coleoptile strength. Varieties that produced long coleoptiles under no compaction produced the longest coleoptiles under compaction. Correlations were found between cell diameter and several morphologic structures of the coleoptile. As soil compaction increased, coleoptile length was reduced; total plants emerged and rate of emergence also decreased.
Fusarium root rot (Fusarium spp.) is one of the most important seedling diseases of coneflower (Echinacea spp.) in Alberta greenhouses. Effects of microbial antagonists (Trichoderma spp.) and fungicides, including difenoconazole, fludioxonil, and a mixture of fludioxonil, metalaxyl and difenoconazole, on the management of this disease, were investigated in Alberta. Twenty Trichoderma isolates demonstrated antagonistic activity to Fusarium in agar plate bioassays, with inhibition rates ranging from 44 to 65%. Some Trichoderma isolates significantly ( p £ 0.05) reduced disease incidence and severity on seedlings in greenhouse experiments. An in vitro bioassay indicated that difenoconazole and the mixture equally inhibited the growth of both Fusarium and Trichoderma, but, while fludioxonil strongly inhibited the growth of Fusarium, it had little effect on Trichoderma, according to the dose-response models developed ( p £ 0.01, R 2 ¼ 0.902)0.998). Two Trichoderma isolates, T1 and T13 were applied singly or in combination with a low rate of fludioxonil in greenhouse evaluations. The results suggested that fludioxonil and Trichoderma could be integrated into a disease management program for fusarium root rot in coneflower.
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