Study on phenotypic variation for aggressiveness and fungicide sensitivity of the rice sheath blight pathogen under high temperature of Global warming condition

Global warming will have impacts on agriculture including severity of plant disease, probably population structure of pathogen and its chemical treatment. This study was designed to determine of phenotypic variation for aggressiveness and fungicide sensitivity of three populations of rice sheath blight pathogen, Rhizoctonia solani AG-1 IA (each population with 10 SSR genotypes) from Rasht, Tonekabon and Amol counties by changes in temperature. Disease severity caused by each genotype was measured on detached rice leaves under temperatures from 26 to 30 and 34 °C. At these temperature levels radial growth of each genotype was measured on PDA plats amended separately with Azoxystrobin and Propiconazole at the 3 and 6 concentration levels (a.i.) respectivly. Data analyses showed that the highest and lowest disease severity from each population was developed at the 26 and 34 °C respectively. No disease incidence was observed due to 40, 60 and 20% of genotypes from Rasht, Tonekabon and Amol respectively at 34 °C, whereas, all genotypes were able to grow on PDA medium at this temperature. Therefore, this temperature is the first high stressful temperature for R. solani AG-1 IA populations to cause rice sheath blight disease in northern Iran. According to these findings two suppositions are under consideration: 1. as a new variety of biodiversity or evolutionary lines, R. solani AG-1 IA populations will divided in tow pathogenic and nonpathogenic groups, or 2. nonpathogenic genotypes will decline because of inability to cause disease and reproduction. Therefore, if global warming continues as expected, it is estimated that genetic diversity within this species may reduce in rice fields of northern Iran. Results from temperature changes on fungicides effectiveness showed that, Tilt was more effective at 26 °C temperature than 34 °C to reduce mycelial growth of each pathogen population at all tested concentrations. While the results from Azoxystrobin revealed the opposite of this cause.