Rice sheath blight and its causal agent Rhizoctonia solani AG-1 IA are associated with intensive and high input production systems. To our knowledge, resistant varieties have not been introduced for this disease, thus good crop management is expected to be among viable disease control methods. The aims of the present study were to determine the effect of different rates of nitrogen fertilizer, planting spaces and inoculum densities on sheath blight incidence and severity, including grain yield loss. Additionally we aimed to identify those developmental stages that are more susceptible to the disease. Field experiments were conducted over two consecutive years, in 2017 and 2018 in the Guilan province of Iran. Results indicated that higher N rates, denser planting and higher initial inoculum density resulted in greater disease development. Among five different growth stages, inoculation of plants at booting and flowering stages, resulted in maximum disease severity and grain yield loss. Taken together, reasonable use of nitrogen fertilizer, optimum planting space and reduced inoculum density obtained by spraying fungicide at the booting and flowering stages of rice are suggested as the best options to control sheath blight epidemics in rice.

To evaluation of pathogenicity and race classification of Xanthomonas oryzae pv. oryzae agent bacterial leaf blight of rice, 153 isolates of X. oryzae pv. oryzae were collected from different rice-growing cities of Guilan province-Iran. All of isolates were inoculated to assess the differential characteristics of 26 near isogenic rice lines containing a single resistance gene or two to five genes. Inoculation was done 21 days after sowing in the greenhouse. Scoring of inoculated plants was done 18 days after inoculation. The level of infection was not so clear among pyramiding lines, expect IRBB53 and IRBB61. Therefore, the pyramiding lines can not be used as differentials for pathogenicity evaluation of X. oryzae pv. oryzae The 12 rice lines with a single resistance gene were used further to establish a system of races classification of X. oryzae pv. oryzae IRBB14, IRBB21and IRBB7 were resistance to the most isolates. Whereas, IRBB1, IRBB2, IRBB4 and IRBB10 were susceptible to all isolates. Based on the interactions between the isolates X. oryzae pv. oryzae and the 12 nearisogenic rice lines, seven single-gene rice lines were chosen as differentials, and the 153 tested isolates were classified into four races. Except for cultivar types, different terrain, climate, period of rice planting and other factors may be associated with the population diversity and virulent variation of X. oryzae pv. oryzae.

The reactions of rice bacterial leaf blight races were identified in Guilan province-Iran on 12 near-isogenic lines and 14 pyramiding lines from International Network for Genetic Evaluation of rice (INGER) and 8 local and improved Iranian varieties were evaluated under natural photoperiod condition in the field. Inoculation was done at panicle initiation by clipping the sterilized scissors in the bacterial suspension to booting stage. Scoring of inoculated plants was made 21 days after inoculation. Infection levels of pyramiding lines containing two to five resistance genes, expect, IRBB53 and IRBB61 with respectively resistance gene combination, Xa5 + Xa13 and Xa4 + Xa5 + Xa7, were not so clear. Among near-isogenic lines IRBB1, IRBB2, IRBB4 and IRBB10 carrying resistance gene Xa1, Xa2, Xa4 and Xa10 were susceptible; IRBB8, IRBB11, IRBB3, IRBB5 and IRBB13 were moderately susceptible; (having resistance gene Xa8, Xa11, Xa3, Xa5 and Xa13) IRBB14, IRBB21 and IRBB7 with respectively resistance gene Xa14, Xa21 and Xa7 were moderately resistance to bacterial blight. Furthermore, most of the time gene combinations support the strategy of pyramiding appropriate resistance gene. Local varieties were more susceptible than improved varieties to leaf blight disease. Among local varieties, Tarom was the most susceptible. And also, there were no significant differences among improved varieties and all of them were moderately resistance.

Dariush S., Ebadi A.A., Khoshkdaman M., Rabiei B., Elahinia A. (2012): Characterising the genetic diversity of Pseudomonas syringae pv. syringae isolated from rice and wheat in Iran. Plant Protect. Sci., 48: 162-169.Sheath rot of rice and leaf blight of wheat caused by Pseudomonas syringae pv. syringae are the important bacterial pathogens of rice and wheat in Iran. The randomly amplified polymorphic DNA (RAPD) method was used to investigate the genetic diversity of 60 strains of P. s. pv. syringae obtained from rice and wheat in different growth stages. Cluster analysis by UPGMA method showed that strains were grouped into two clusters. The AMOVA analysis indicated that about 18% of the total genetic variation existed between two populations of rice and wheat, which showed the lack of host specialization in P. s. pv. syringae strains among rice and wheat. We confirmed that high genetic heterogeneity existed in the P. s. pv. syringae strains which are detectable by RAPD analysis, and that molecular and statistical analysis of RAPD fragments can be used both to distinguish between strains and to determine relatedness between them.