Study on the Relationship between Rate of Rice Blast Disease (at its Different Growth Stages) and its Yield Loss under Natural Infection Conditions in Guilan (Rasht)

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To determine rice yield loss resulting from blast disease (Magnaporthe grisea) at the corp's different growth stages, a field experiment was conducted at the Rice Research Institute of Iran, Rasht. Rice local cultivar Hashemi was transplanted to 3×4m plots for the experimental treatments (time of disease evaluation) Each treatment was replicated 4 times. Under natural infection conditions, percentage of diseased leaf area and panicle blast incidence on each sample were scored 40 and 50 days following transplanting, 15 and 25 days after panicle appearance and as well at harvest time. Fungicide (Tricyclazole) was applied to prevent blast development after each time of disease scoring, until harvest time. Linear regression analysis was employed to calculate percentage yield loss due to leaf and panicle blast at each appearance time. Only the equation y= -0.74 + 0.5x (R2= 0.91*) was found significant to predict yield loss (y) from panicle blast (x) at harvest from the treatment in which no fungicide had been applied at the development stages. This treatment had also been more effected than the others in its increase of unfilled grains. Differences of blast disease rate and its development were not significant at the different levels of urea fertilizer application due to the high temperatures occuring at the most susceptible stages of rice growth.

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