The assessment of the rice cultivars/lines resistance to blast disease in Mazandaran province, Iran.

Blast, caused by Magnaporthe grisea, is one of the most important diseases in rice production regions of the world including Iran. To determine progress of rice blast disease on the selective cultivars and lines also to assay some components of partial resistance, a set of Iranian rice cultivars (Local and breeding) along with near-isogenic lines (NILs) and breeding lines from International Rice Research Institute (IRRI) were tested with some field races of the fungus in blast nursery and five of selective races in greenhouse. These experiments were conducted in a Randomized complete Block Design (RCBD) with three replications (except greenhouse experiment on the leaves). Traits in this study consisted of Infection Neck Number (INN), Neck Lesion Size (NLS), Infection Type (IT), percent Diseased Leaf Area (DLA) and Area Under Disease Progress Curve (AUDPC); also IT, Sporulation Lesion Number (SLN), Sporulating Region Diameter (SRD) and percent DLA were measured in leaf blast in greenhouse (one replication). The Iranian local cultivars and NILs i.e. Co-39 and C104-PKT located as susceptible group for AUDPC, IT, INN and NLS. Iranian breeding cultivars, breeding lines from IRRI and NILs (except Co-39 and C104-PKT) were resistant or indicated hypersensivity reaction (HR). Some cultivars (Fujiminori, Onda, and Hassan Saraii) were semi susceptible to leaf blast in nursery. The main point is correlation in 1% (a = 0.0001) between the traits in greenhouse and blast nursery. Neck node infection of Haraz cultivar in greenhouse experiment to IA-89 race is very important, because Haraz is a resistant cultivar to blast disease in Iran.

Sheath rot of rice in Iran.

Sheath rot of rice occurs in most rice-growing regions of the world. It usually causes yield losses from 20 to 85%. Sheath rot was reported from Iran in 1993. Year after year, the number of diseased plants increased in the Northern Iran. In summer of 2001, these symptoms were observed in most fields: lesions occur on the upper leaf sheaths, especially the flag leaf sheath. As the disease progresses, lesions enlarge and coalesce and may cover most of the leaf sheath. Panicle may fail to completely or at all. Brown or partially brown not filled or partially filled grain is also associated with infection of the panicle. A whitish powdery growth may be found inside affected sheaths. Infected plants were collected and trasferred to laboratory. Small pieces of diseased tissues were washed under tap water for one hour. Then tissues were placed on WA and incubated at 25 degrees C. These isolates were purified and identified as: Sarocladium oryzae, Fusarium udum, F. semitectum, F. avenaceum, F. flocciferum, F. graminearum, Bipolaris oryzae, Alternaria padwickii, Rhizoctonia solani, Paecilomyces sp., Nigrospora sp. and Trichoderma sp. This is the first report of F. udum in Iran. Also this is the first report that rice is the host for F. semitectum, F. avenaceum and F. flocciferum in Iran. Pathogenicity tests were conducted in glass house. Following species were found to be associated with sheath rot of rice: S. oryzae, F. graminearum, F. udum, F. avenaceum, B. oryzae, A. padwickii. This is the first report in the world that F. udum and A. padwickii are the causal agents of the sheath rot on rice plants.