JOURNAL OF RESEARCH IN PLANT PATHOLOGY
Year:2011 | Volume:1 | Issue:1|Papers Count:8

Two root endophytic fungi (Piriformospora indica Varma and Sebacina vermifera Warcup), as well as two species of Trichoderma (T. viride and T. harzianum (T-100)) were used against Macrophomina phaseolina. Antagonistic ability of root endophytic fungi and Trichoderma species against the pathogen in dual culture, volatile metabolites and colonization were evaluated. Assays in dual culture revealed that antagonistic fungi produced a good zone of inhibition. Interaction of root endophyte fungi and Trichoderma species in combination resulted in maximum inhibition of mycelial growth and microsclerotia formation of the pathogen. The volatile metabolite studies revealed that endophytic fungi did not act by producing volatile metabolites but possibly by other mechanisms of competition or parasitism. As for mechanism of colonization, it was revealed that antagonistic fungi were able to overgrow the colony of the pathogen and lyse its mycelia.

Determining the pathogenicity factors of barely powdery mildew casual agent is the first step in identifying and producing resistant cultivars. During growing season 2008, ten isolates of barely powdery mildew were collected from different parts of Fars province (Iran). Mass propagated on a barely susceptible cultivar. Seedlings of 19 near-isogenic barley lines, obtained from Palas base type and containing various resistance genes, were inoculated with the collected isolates. A susceptible cultivar (cv. Afzal) was used as positive control. Later on, reactions of lines were recorded according to latent period, type and severity of disease. The detected pathogenicity factors in Fars province seemed to have variable frequencies. Virulence factors against Ml-a3 and Ml-a23 resistance genes were the most abundant in the tested area, while for Ml-K, Ml-a7+Ml-(NO3), Ml-h and Ml-a12+Ml (Em2) genes were the second most abundant. For the Ml-a22 and Ml-a6+Ml-a14 the least frequency of pathogenic potential was observed. There are no pathogenicity factors against Ml-05, Ml-g-Ml-(Cp), Ml-(La), Ml-a8, (Ml-a1, Ml(A12)), Ml-a9, Ml-a10+Ml-(DU2), Ml-a13+Ml-(Ru3), Ml-K(1), Ml-P and Ml-at resistance genes in Fars province. Almost all barley lines followed a similar pattern in their latent period.

The cucurbit damping off, root and crown rot caused by Rhizoctonia solani Kuhn are the most important diseases of these crops. In a survey of fields and greenhouses during 1384-1385 samples of cucumber, pumpkin, watermelon and melon, suspected of being infected by Rhizoctonia in Tehran, Mazandaran, Khouzestan and Isfahan provinces were collected and the fungus was isolated. In this study, 59 isolates of R. solani were recovered from soil, crown and roots of cucumber, pumpkin, watermelon and melon. Hyphae width ranged from 4.46 to 6.86 mm, and all of them were multinucleate. Anastomosis grouping showed that 81% of samples belonged to AG4 and the rest of isolates did not anastomose with either of the standards AG2 and AG7. The results of pathogenicity test showed that of the 59 recovered isolates, 97% were pathogenic, which in turn were classified in 10 separate categories based on their virulence. In this investigation two isolates of pumpkin and cucumber belonging to AG4 from Isfahan province appeared to be non pathogenic. This is considered to be the first report AG4 on pumpkin in Iran.

To investigate the diversity and the range of genetic differences and similarities of isolates of pseudo-fungus Pythium spp., different regions of Hamadan province were searched, 150 isolates were collected and thereafter 12 species were identified based on morphological characters. Eight Pythium isolates with spherical sporangium were selected and compared using RFLP marker. Finally, restricted digestion of amplified ITS1-5.8S-ITS2 region resulted in 36 bands with a length ranging 350 to 600 kpb. Accordingly the isolates were placed in 3 groups and 7 clades. Pythium group G and P. tracheiphilum were identical thereby implying common ancestry. The most intraspecific distances were observed in P. pyrilobum and P. irregulare measuring 80 percent and 65 percent respectively.

To determine fungal contamination of rape seeds, samples were taken of harvested seed consignments from different regions viz, Saadatshahr, Zarghan, Arsanjan. Ghir-Karzin, Biza and Zafar abad of Fars province during 2008. Seeds were surface sterilized for 2.5 and 5 min. in 1% sodium hypochlorite, and plated on PDA or WA supplemented with 50% Lactic acid, incubated at 25±2oC. Growing colonies that developed during 4 to 15 days of incubation were isolated, purified and indentified morphologically using available keys. Aspergillus species were the dominant mycoflora recovered ranging from 20 to 40% in different seed samples. In addition to Aspergillus species, other fungi were also isolated and identified as follows: Penicillium sp., Alternaria sp., Fusarium sp., Cladosporium sp., Rhizoctonia sp., Phoma sp., Botrytis sp., and Rhizopus sp. Knowledge of seed contamination and its severity in different areas will help in decision making on planning for healthy seed production.

During the years 2009-2010, a survey was conducted in Marvdasht region (Fars province), to identify the casual agents of root and crown rot in tomato plants. Symptomatic and healthy looking samples collected from different fields were surface sterilized and cultured on potato dextrose agar. Eighty isolates belonging to 17 genera were separated from infected roots. Isolates of Pythium aphanidermatum, Phytophthora nicotiana, Rhizoctonia solani, Macrophomina phaseolina, Phoma betae and Fusarium oxysporum were able to cause root rot on tomato plants in pathogenicity tests. R. solani and P. nicotiana were most (26%) and least (2%) frequently isolated species, respectively. Pathogenicity tests on tomato plants also showed that R. solani and M. phaseolina were most severe pathogens. On tomato plants, this is the first report of M. phaseolina from Iran and P. nicotiana from Fars province.

In this study, antibiotic resistant mutants of antagonistic bacteria to Rifampicin and Nalidixic acid using spontaneous mutation were obtained. Antagonistic activity of three isolates belonging to Pseudomonas fluorescens were tested in vitro against a virulent isolate of Rhizoctonia solani, the causal agent of cotton seedling damping-off, using dual culture method. It was shown that two isolates had better antagonistic traits against fungus in comparison with their wild types. The above isolates were also evaluated for their inhibitory mechanisms against fungal pathogen and the results showed that all three mutants were different than their wild types in volatile metabolites production. There were no differences between the mutants and wild types in production of non-volatile metabolites. However, some mutants (Pf-C-1, Pf-W-2) produced more siderophores than their wild types. Results of this study suggest that spontaneous mutation may affect and enhance the activity and performance of antagonistic bacteria.

The Pythium species were studied in Hamedan province during 2007-2009. Samples were collected from various parts of the province including Hamedan, Nahavand, Malayer, Asadabad, Ghahavand, Touiserkan, Serkan, Razan and Joraghan. Species were identified based on morphological characters of sexual and asexual stages. Of the total of 150 isolates of Pythium recovered, the following 12species P. aphanidermatum, P. deliense, P. hydnosporum, P. irregulare, P. macrosporum, P. oligandrum, P. perplexum, P. pyrilobum, P. salinum, P. tracheiphilum, P. ultimum var ultimum and Pythium group G. were identified. Pythium group G was the dominant species, representing 28% of isolates. According to our knowledge this is probably the first report of isolation of Pythium hydnosporum from Plumbago europaea in the world, while P. hydnosporum, P. macrosporum, P. perplexum and P. pyrilobum are new records for mycoflora of Iran.