Study on DNA diversity of Iranian populations of Erysiphe betae causal agent of sugar beet powdery mildew.

107 samples of E. betae were collected on infected leaves from all over Iranian beet cultivation areas. Their choosing were based on geographical and host origin(sugar beet, red beet, fodder beet and wild beet). 30 isolates were single colonized and grown on sugar beet susceptible genotype 7233. 107 specimens were analyzed by restriction fragment length polymorphism (RFLP) of the ribosomal internal transcribed spacers (ITS) and 5.8s DNA which previously amplified by the polymerase chain reaction (PCR) with 2 universal primers, ITS1 and ITS4. PCR product was affected by 9 different restriction enzymes. PCR product was a 645 bp band for all of the isolates. 3 restriction enzymes; CfoI, MspI and HaeIII could cut this fragment into smaller bands, but electrophoretic patterns were identical for all of the isolates. 30 single colonized isolates were used in RAPD experiments. In RAPD-PCR experiment genetic diversity was investigated with 30 isolates from different parts of the country. 59 random primers were used and then 21 primers that displayed good consistency and reproducibility were selected. Most of the primers revealed identical patterns between 3 to 14 bands. 5 primers that showed more polymorphism were selected to analyze 30 isolates. For these 5 primers 61 distinct bands were obtained which 62% of these bands were polymorphic. Results indicated that there is no relationship between cluster grouping and geographical origin and the isolates showed a high similarity.

Study on the overwintering of cleistothecia and conidia of Erysiphe betae causal agent of sugar beet powdery mildew in Iran.

Sugar beet leaves covered by sexual (cleistothecia) and asexual forms (mycelia and conidia) of Erysiphe betae were gathered at harvest time and maintained under natural outdoor conditions. In order to determine the function of cleistothecia and also conidia in the overwintering of E. betae some experiments were performed. The results showed that ascospores were unable to be released in petri dishes but their release under natural conditions occurred after 4 months. Under In vitro conditions ascospores did not germinate but on the leaves germination was rarely possible, however these ascospores were degraded after 7 days and didn't have pathogenicity. Conidia could induce pathogenicity after 3 but not 4 months. The period after inoculation until appearance of disease symptoms increased with aging of conidia. The results for conidial germination showed that fresh conidia had 80 percent germination on glass slides but it decreased sharply after 2 weeks and reached to 0 percent after 4 weeks. Although their germination on the leaves was not more than 46 percent of fresh conidia but they had good germination after 2 and 4 weeks. The results for the experiment to observe the first appearance of the disease in the field suggested that the first conidia were trapped by spore-trap in early June and the first symptoms appeared 20 days later. The conclusive results showed that ascospores had no function in the survival of the fungus and air-borne conidia are the main source of primary infections.

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.