IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2009 | Volume:45 | Issue:2 (178)|Papers Count:8

An investigation was carried out to determination fertility status and mating type of Cochliobolus miyabeanus, the causal agent of brown spot of rice disease, in Guilan province. A total of one hundred and forty-seven isolates of Cochliobolus miyabeanus were collected in spring and summer of 2007-2008 from different rice growing areas of Guilan province. The pathogen was isolated from infected leaves and seeds on potato dextrose agar and purified by monoconidial isolation. Isolates were selfed and mated in all possible combinations. According to the result, all of the isolates were self-sterile and only 23.8% of isolates were fertile. Thirty-five isolates were placed in two arbitrary mating type A and a that 17 isolates were female-fertile and 18 isolates were male-fertile. Ascospores germination ability was examined on water and water agar under laboratory condition. Ascospores from all of the fertile isolates were able to germinate.

Gaeumannomyces graminis (Sacc.) Arx & Olivier is one of the most important soilborne plant pathogens, and the causal agent of take-all disease of cereals and grasses world wide. In a survey conducted during 2005-06 wheat growing seasons, 52 isolates were obtained from diseased samples collected from different provinces of Iran including Fars, Golestan, Markazi, Mazandaran and Tehran. Pathogenicity tests indicated that all isolates were pathogenic on wheat but only ten isolates (out of 52) were pathogenic on oat. Disease severity among isolates and pathogenicity on two hosts (wheat and oat) were significantly different. Disease severity of 64% of the isolates was over 60% on the wheat seedling. Except for one isolate from Naghsh-e-Rostam, Fars province, all produced simple hyphopodia. Average length of ascospores produced on wheat and oat were measured 67-85 mm and 66-88 mm, respectively. These isolates were identified as G. graminis var. tritici Growth rates of isolates at 25oC on PDA ranged between 1.81-5.35 mm/day. There was no correlation between mycelial growth rate and virulence isolates on wheat. In this study for molecular identification of isolates of G. graminis var. tritici specific primers were used. These primers revealed that with the exception of three isolates which belonged to the type B, all the remaining 49 isolates were of the type A. The Ggt A and B-type isolates produced PCR products consistent with the predicted size of 93 and 132 bp, respectively. These primers did not amplify any product in G. graminis var. graminis and Magnaporthe grisea as control.

In the framework of study of rust fungi of Fars province, southern Iran, the province visited during 2006-2008 and many infected plant specimens were collected. Fourty five rust taxa were identified. Of these, 33 taxa are reported here. Twenty two taxa viz. Puccinia absinthii, P. acarnae, P. cynodontis, P. hieracii, P. kermanensis, P. majoricensis, P. punctata, P. tanaceti, Phragmidium kamtschatkae, Ph. sanguisorbae subsp. mediterraneum, Uromyces anthyllidis, U. inaequialtus var. ecbatanesis, U. acantholimonis var. zagrosica, U. junci, U. lineolatus, U. muscari, U. ononidis, U. polygoni-avicularis, U. punctatus, U. thellungi, U. tinctoriicola and Miyagia pseudosphaeria are new to the Fars mycobiota. Three taxa viz. P. coronata var. himalensis, P. persistens subsp. persistens and P. polypogonis are believed to be new recordes to the Iranian mycobiota. The aecial state of P. stapfiana is newly reported from Iran. The aecial state of Melampsora euphorbiae-gerardianae is newly described based on a collection of this species on Euphorbia microsciadia. Several hosts new to the rust taxa are also indicated.

Plantlets of sugarcane cultivars L62-96 (susceptible), CL 73-239 (moderately susceptible) and CP73-21 (resistant) were generated by in vitro apical meristem tissue culturing.Plantlets were then inoculated with mixture of two types of sporidia and/ or dikaryotic mycelial suspension. Ratoons of the same cultivars were also inoculated and planted in the field. In the field, infected whips were developed in 33.8% and 15.9% of the plants of the susceptible and moderately susceptible cvs., respectively. No symptoms were observed in the resistant cvs. However DNA of Ustilago scitaminea was detected by PCR, - in tissue extracts from below and above the site of inoculation and also from suckers,-in all cvs.(susceptible as well as resistant) of the in vitro inoculated plantlets. Based on the results of this study, detection of the fungus in the tissue cultured plantlets by PCR cannot be used for assessment of resistance or susceptibility to U. scitaminea of sugarcane cvs in vitro.

Watermelon mosaic virus (WMV) is one of the most economically important and widespread viruses of cucurbitacous plant in the world. To study geographical distribution of WMV in Golestan province, 179 samples of pumpkin, watermelon, melon and cucumber were collected in six regions of the province and subjected to DAS-ELISA using WMV antiserum. four ELISA positive samples plus two other isolates from Shiraz and Mashhad were subjected to RTPCR to clone and sequence the CP region of the genome. These and 41 isolates from the GenBank were analyzed to determine their phylogenetic relationship. The results showed that all WMV sequences can be placed into 6 clades.Iranian isolates fall into two distinct clades. Golestan and Mashhad isolates were grouped with isolates from Europe, Mediterranean and Australia, while Shiraz isolate was grouped with two isolates from Japan. Genetic distance between and within groups confirmed the phylogenetic results. Genetic diversity (Õ) calculation showed that, in spite of presence of remarkable variation in the isolates of WMV in the world, the genetic diversity in the distinct regions such as Europe is very low. Analyses of genetic diversity within different populations of WMV in the world showed that the diversity increases from the West to the East. Maximum molecular and host variation occur in Eastern Asia.

Lime witches’-broom (LWB) caused by Candidatus Phytoplasma aurantifolia is one of the most destructive diseases of lime in the southern Provinces of Iran. To prepare LWB polyclonal antibody, midribs of the infected plants were homogenized using GMS buffer. After low and high speed centrifugations, the extract was incubated with an antiserum previously prepared against healthy lime extract. Differential centrifugation was repeated and the final extract was emulsified in equal volume of freund’s incomplete adjuvant and injected into New Zealand white rabbits. After purification of gamma globulin, the best reaction was found between the 1/100 dilution of the gamma globulin and the 1/500 dilution of infected plant extract in indirect ELISA. Furthermore, the 1/100 dilution of the gamma globulin was reacted with the 1/100 and 1/500 dilutions of infected plant extract in DIBA test. Whereas no reaction was found between the antiserum and healthy lime extracts. The results indicated that antibody raised against Candidatus Phytoplasma aurantifolia could be used for monitoring LWB disease in the field.

Aspects of biology of common root lesion nematodes, Pratylenchus thornei and P. neglectus in the irrigated fields of wheat and corn of Marvdasht (Fars province) were studied under laboratory and greenhouse. Preliminary pathogenicity test of these nematodes on wheat, cultivar Falat, in irrigated and dry farming condition, with or without fertilizers were performed. In addition, the responses of common field crops of Marvdasht to P. thornei and P. neglectus were studied under greenhouse conditions. Moreover, the time it takes to complete the life cycle and temperature effects on laying eggs, hatching and the rate of reproduction of P. thornei were investigated. The result of pathogenicity test showed that two species put the effect on growth indicators and yield of wheat, such as root dry weight, shoot fresh and dry weight, number of spikes and tillers of plants. Negative effects of nematodes on plant indices in treatments of dry farming and without fertilizers were more than the other are. Study of effects of different field crops under greenhouse condition showed that wheat, barely and rapeseed are sensitive to P. neglectus, and wheat and beans to P. thornei, and the nematode population were increased. While the nematode population decreased under tomato, sugar beet and fallow condition. Biology study of P. thornei in laboratory and growth chamber also showed that the best temperature for laying eggs, hatching and reproduction of this species is 25oC. In this temperature, the nematode life cycle was completed in a period of 25 to 26 days.