IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2003 | Volume:39 | Issue:3-4|Papers Count:17

Talaromyces flavus a fungal antagonist of Verticillium dahliae was isolated from ‎rhizosphere in the cotton fields. In this study antagonistic effects of T. flavus against ‎V. dahliae was investigated in invitro and in vivo. Soil samples from cotton fields in ‎Karkendeh and Araghimahalleh Experiment Stations of Golestan province, were ‎cultured on selective medium. T. flavus colonies were recovered after three weeks. In ‎invitro experiments, volatile and non- volatile extracts of T. flames caused 95 and ‎‎73% growth reduction in V dahliae respectively. In greenhouse experiments, the ‎incidence of Verticillium wilt of cotton was reduced by 91 % in plants treated with T. ‎flavus ascospores‏.‏

Phytotoxin (Zearalenone) production by Fusarium graminearum isolates, the causal ‎agent of head blight disease of wheat was evaluated using an accurate and sensetive ‎bioassay ethod. The chemical nature of active compounds was determined by TLC ‎and HPLC techniques using pure ZEA as checks. In this study the sensitivity of four ‎yeast species including accharomyces cerevisiae, S carlesbergensis, Kluyvermyces ‎marxianus and Rhodotorula minuta as well as two bacterial species Bacillus subtilis ‎and B. cereus to ZEA was examined. We have stablished a reproducible in vitro ‎system fir toxin production in the laboratory by artificially infecting rice in the husk. ‎To optimize the system, a combination of experiments were conducted using various ‎media (NA, CZ, YPD. YMA), different volume of agar media/ petri dish (4, 6,8 and ‎‎10 ml), various pH (4.5, 5, 5.5, 6. 6.5, 7, 7.5 and 8), pre - incubation temperatures ‎‎(4,8, 20, 35) °C and its duration (0,2 ,4 and 8 hr) and incubation temperatures ‎‎(20.23,25, 30 and 35) °C. On the basis of these experiments, optimum sensivity of ‎tested microorganisms to toxins was obtained when petri dishes contained 6-8 ml of ‎media with a pH of 7.5 and pre-incubated at 4°C. for 2 -4 hours prior to transferring to ‎‎25°C Twenty four hours after incubation, inhibition zone of the cultures containing ‎Z.EA was measured and analysed‏. ‏ Based on the results obtained, Iranian isolates of F. graminearum produced a high ‎amount of ZEA. This was not to be expected since F. graminearum is the most ‎important Fusarium species known to produce this toxin. Results also indicated that of ‎six icroorganisms tested, B. cereus was the most sensitive one to ZEA in which its ‎growth was inhibited at the lowest concentration of 0.2 ppm (pure ZEA toxin from ‎Sigma inhibited the growth of the same organism at 2.5 ppm). This supports the ‎reliability of our bioassay system specially in detecting naturally infected kernels. All ‎four yeasts tested in the present study were highly resistant to ZEA. This is the first ‎report on a sensitive bioassay method for evaluation of zearalenone production by F. ‎graminearum isolates in Iran‏.‏

In order to study species of Meloidogyne in Iran, affected roots of different plants including field crops, orchard trees, weeds and ornamentals were collected from different areas based on symptoms such as wilting, dwarfing, chlorosis and presence of galls on roots. White females of Meloidogyne were extracted from galls on roots. The second stage juveniles and males were also extracted from egg masses and soil samples. Perineal  patterns were prepared from females in lactic acid and glycerin. The second stage juveniles and males were fixed and mounted in glycerin. Morphological and morphometerical characteristics of females, perinea l patterns, the second stage juveniles and males were studied. In addition to four previously reported species Viz. M. javanica, M. incognita, M. hapla and AL arenaria, three other species of Meloidogyne namely AL cruciani, M. microcephala and A7 thamesi were identified as new plant parasitic nematodes fauna for Iran. The first species was isolated from the roots of Cucurbita moschata, Coleus blumei, Lycopersicon esculentum in Karaj and Mashhad, also from the roots of Cucumis sativus in Hashgerd, Dianthus caryophyllus in Mahallat and Olea europaea in Roodbar. The second species was isolated from roots of Phaseolus vulgaris in Ramjin - Karaj and the third from roots of Lycopersicon esculentum in Jiroft. Their morphological and morphometerical characters are described in this study.

Septoria iritici (teleomorph: Mycophaerella gram Nicola) the cause of Septoria leaf blotch of wheat is a major wheat disease in mars and other provinces in Iran causing economic loss periodically. To evaluate the reaction of wheat cultivars to the pathogen, ten isolates of S. tritici collected from different whet growing areas in Fan province were used. Wheat seedlings and detached leaves of different wheat cultivars were inoculated with conidial suspenision of S. tritici respectively in greenhouse and Petri plates containing water agar amended with benzimidazole and incubated at 20° C in growth chamber. The results of host pathogen interaction in both conditions showed that there was significant differences among wheat cultivars in respect to isolates. On the other hand, the isolates were in the same statistical group but the wheat cultivars divided into 6 and 7 categories for wheat seedlings and detached leaves respectively. Under both conditions, it was found that, wheat cultivars Darab2 and Falat had highest and cultivar Cross Azadi (Marvdasht) the lowest percentage of pycnidial coverage by S. tritci isolates.

The allelopathic potential of hairy vetch aqueous extracts was investigated under ‎laboratory conditions. Germination and seedling growth of redroot pigweed, ‎velvetleaf, common lambs quarters and barnyard grass decreased when exposed to ‎increased concentrations (8.3 to 33.2 g debris/1) of aqueous field-grown hairy vetch ‎extract, but this was not true for soybean and corn. Hairy vetch allelochemicals ‎inhibited germination more than seedling growth of redroot pigweed, velvetleaf, and ‎common lambs quarters. Beside allelochemical effect, hairy vetch aqueous extract also ‎had an osmotic effect on seedling growth and germination. In some cases allelopathic ‎and osmotic properties together and in other cases each one separately affected ‎germination and seedling growth. This bioassay indicated a promising potential for ‎controlling weeds in corn mid soybean‏.‏

Grapevine fan leaf is the most destructive viral disease of grapevine worldwide. The ‎causal vines, Grapevine fanleaf virus (FLV), is a Nepovirus transmitted by Xiphinema ‎index. While Old Persia has been regarded as the original site of GFLV, little ‎information is available on the incidence and prevalence of this virus in Iran. In the ‎present work, geographical distribution, rate of incidence and symptomotology of ‎GFLV in this country were studied. Random samples were taken from various ‎vineyards of Fars, Kohgiluyeh-Boyrahmad and West Azarbaijan provinces and the ‎rate of disease incidence was determined. Samples were tested by ELISA using IgG to ‎an American isolate of GFI, V. F (ab')2 was used to improve sensitivity of the ‎reactions. A number of samples were also tested by polymerase chain reaction (PCR) ‎using GFLV-specific primers to verify ELISA results. The results showed wide ‎distribution of GFLV in vineyards in various parts of the country. Bavanat, a city in ‎northern Fars, with 54 percent infection was regarded as the region of the highest ‎incidence. The rate of incidence in other regions varied between 21% and 37%. The ‎symptoms in infected vines consisted of mosaic, leaf malformation, opening of ‎petiolar sinus, vein banding, yellow mosaic, short internode, stunting, presence of ‎double node, thin fruit cluster and decline. However many GFLV-infected vines ‎showed no particular symptoms. PCR results showed presence of the expected 320 hp ‎hand in the ELISA positive vines. The results of this work confirm the idea GFLV is ‎native to the region and has spread from it is origin to other regions in the world‎‏.‏

Seven strains of Streptomyces obtained from soil surrounding the roots of capsicum ‎were evaluated in vitro and in the greenhouse as potential biological control agents of ‎pink- rot of potato and root and stem rot of tomato. Cell - free metabolites of all ‎strains of Streptomyces inhibited growth of the pathogen, Phytophthora ‎erythroseptica, in vitro. The lesion size on Pontiac potato plant in treatment P. ‎erythroseptica +mixing of all Streptomyces strains (13.25mm) was significantly less ‎than that of P.erythroseptica only (54.75uun). The yields of tubers from Pontiac plants ‎treated with P.erythroseptica and combined Streptomyces isolates (mean of 1(.5 g ‎fresh weight/pot) were significantly greater than in controls inoculated with the ‎pathogen alone (mean of 6.77 g/pot). Control of damping-of of tomato was achieved ‎by inoculating potting mix with Streptomyces strain S2 at the time of planting in a ‎greenhouse‏.‏

Ascochyta blight incited by Ascochyta rabid is one of the most important diseases of chickpea crop causing great losses in Western provinces of Iran. the disease is effectively controlled by cultivating resistant varieties. For this regard, pathotyping of pathogen isolates is of primary importance. In present study, 30isolates of Ascochyta rabiei were obtained from diseased samples collected in different areas of Kermanshah province, through 1993-9G. Each isolate was inoculated on differential chickpea cultivars in the greenhouse, and then disease severity was scored two weeks after inoculation. Twelve different virulent from among the 30 isolates were identified by categorizing the disease rating from highly (H) to weakly virulent (W). They were classified in to 4 groups based on their virulences on the 4 differential chickpea cultivars and into 3 groups by cluster analysis. The results showed high variability of pathogenicity among the isolates tested. Therefore efforts should be focused on accessibility of multigenic chickpea resistant lines.