JWSS - Journal of Water and Soil Science

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Systemic properties of pyroquilon, an anti-blast systemic chemical, used in controlling rice blast disease caused by Pyricularica grisea, was investigated through in vivo tests. Rice plants were treated with pyroquilon as granules in soil. Leaf and stem tissues were collected at different times after treatment and pyroquilon was extracted from tissues and detected by gas chromatography. Treated rice plants were also exposed to disease infection in blast nursery at different times and disease incidence was evaluated one week later. Pyroquilon was detected in leaf tissue one day after treatment (DAT), reached maximum during 4-7 DAT, and then reduced gradually to a nondetectable level after 28 DAT. In stem tissue, change in pyroquilon content was similar to but its quantity was less than that of leaf tissue. On inoculated plants, disease was controlled up to 60% at 2 DAT and completely controlled during 4-28 DAT. The results indicated that pyroquilon could be taken up and systemically translocated in rice plants after applying as granules in soil. Extent of disease control was a good function of pyroquilon content in leaf tissue (R²=0.93) and 2 ppm of compound in leaf could provide 90% control of the disease. In contrast, disease control was not a good function of pyroquilon content in stem tissue (R²=0.30).

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  Blast, caused by Magnaprthe grisea, is often an important fungal disease in the production of rice in temperate and tropical areas including Iran. To determine reaction of rice cultivars against blast disease, 40 rice genotypes from Iran and other sources from Asia were selected. Four blast isolates from different races were used to test all rice genotypes in different greenhouse tests. In blast nursery, experiments were conducted in a Randomized Complete Block Design (RCBD) with three replications. In different experiments inoculated plant materials were evaluated for Infected Neck Number(INN), Neck Lesion Size(NLS), Infection Type(IT), Diseased Leaf Area(DLA), Area Under the Disease Progress Curve(AUDPC), Lesion Number(LN), and Sporulating Region Diameter(SRD). Most of the Iranian traditional cultivars together with CO-39 and C104-PKT showed susceptible reaction for AUDPC, IT, INN and NLS. Performance of improved cultivars from Iran, IRRI and NILs (except C104-PKT) was resistant. Some cultivars including Fujiminori, Onda , Hassan saraii were moderatly susceptible to leaf blast in blast nursery. All components of resistance in both growing stages in greenhouse and nursery tests were significantly correlated. In some cases such as cultivar Haraz different reaction was observed in seedling and flowering stages, indicating that genetics of resistance in two stages could be different.

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A comprehensive study is underway now to determine the predicting factors of rice blast and its loss assessment in Guilan province. In a preliminary study, the effect of climatic factors on spores population and forecasting the disease were considered. So, during cultivation season of 2006 and 2007, some fields were chosen five kilometers away from weather stations in three regions of Guilan, including, Rasht, Lahijan and Anzali, and the daily spore population was measured on slides. Climatic data including precipitation (mm), maximum and minimum daily temperature, maximum and minimum daily humidity and sunny hours were obtained from weather stations. Then the relation between spore population and weather data was analyzed, and the most important climatic factors affecting spore population and predicting of rice blast were determined. It was concluded that climatic factors such as precipitation (mm), maximum daily temperature, minimum daily humidity and sunny hours are the most important factors for predicting rice blast in Guilan province. Spore population was positively correlated with precipitation, increase of daily minimum humidity, decrease of daily maximum temperature and decrease of sunny hours. The blast disease occurred in the fields during next 7 to10 days.

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