نشریه تحقیقات بیماری های گیاهی
سال یکم شماره 2 (تابستان 1392)

The biocontrol activity of T. harzianum BI on root-knot nematode M. javanica and its ability to induce some biochemical defense responses on tomato were investigated. The roots of tomato seedlings were inoculated with suspension (106 conidia/ml) of the antagonistic fungus and 2000 second-stage juveniles (J2) per plant. Enzymatic activity of peroxidase, polyphenol oxidase and levels of phenolic compounds were measured on days1 to 8 after inoculation. In addition to significant reductions in disease incidence and the number of nematode galls on the roots of plants in green house, T. harzianum BI increased the death percent of second stage juveniles (J2), and at the same time decreased the percent of egg hatch in the laboratory assays. It also increased peroxidase and polyphenol oxidase activities that reached their maximum levels 4 days after nematode inoculation. The highest level of phenolic compounds was observed on the 5th day after nematode inoculation in treatments of T.harzianum BIand nematode compared with control. The ability of T. harzianum BIto increase activities of peroxidase, polyphenol oxidase and levels of phenolic compounds and plant defense induction may be some of the mechanisms responsible for its biocontrol activity.

Sheath blight, caused by Rhizoctonia solani AG1-IA, is an important disease of rice in Northern provinces of Iran, including Mazandaran. In order to study the status of the disease in the province, 53 fields in 5 regions (Amol, Sari, Qaemshahr, Savadkuh and Behshahr) were evaluated during 2008 and 2009 seasons. Statistical analyses of disease data were performed based on disease incidence (I), mean severity (S), (Lesion height / plant height) and (S2), (Number of diseased tillers / number of tillers in a diseased hill) of the fields. The results revealed that the regions were significantly different based on the I, S and S2 (P<0.01). Minimum and maximum of disease amounts were observed in Behshahr (with I, S and S2 values of 10.92, 6.55 and 9.9 %,) and in Amol (with I, S and S2 values of 42.87, 28.66 and 34.99 %,) respectively.

Thirty five original and fifteen complementary soil samples each consisting of 500 gm soil and 100 gm roots of pistachio trees were collected randomly. The soil samples were washed by centrifugal method (Jenkins, 1964) and nematodes were extracted from roots by Coolen and De Herde (1972) technique, nematodes were transferred to glycerin by De Grisse (1969) method and permanent slides were prepared. Drawings and measurements were made and the species were identified. Totally 23 species belonging to 16 genera were identified. Meloidogyne javanica was found in 40% of the samples and is recorded as the dominant pathogenic species in the region. The list of nematodes from different localities of Sirjan and their percent occurrence is shown in table1. Rotylenchus whiteheadi (Ganguly & Khan, 1987) Castillo et al, 1994 is a new record for Iran and is reported for the first time from Sirjan in (Kerman province) south of Iran.

In order to identify and evaluate the pathogenicity of Fusarium species associated with root and crown rot of contalupe and melon, several fields in different regions of Khorasan including Mashhad, Kashmar, Mahvelat, Khaff, Torbat Jam, Fariman, Neyshabour and Sarakhs were sampled during 2009-2010 growing season. After disinfection with sodium hypochlorite (1%), pieces of infected tissues were cultured on potato dextrose agar (PDA) medium. Grown fungal isolates were then purified and were identified based on their morphological characteristics as different Fusarium species. To test pathogenicity of Fusarium isolates, 12-day-old cantaloupe seedlings grown in the green house were inoculated with fungal spore suspension (106/ ml) by root dip inoculation method. The disease symptoms appeared after 4- 21 days. To fulfill Koch’s (pathogenicity) postulates, disease causal agents were re-isolated from the symptomatic plants. The pathogenic isolates were identified as F. solani, F. oxysporum and F. equiseti of which the first species was dominant. The results also showed that F. equiseti and F. acuminatum were mostly isolated from mature plants while F. solani and F. oxysporum were present in all growth stages of plants (seedling up to fruit stages). Results of distribution studies showed that these species were widely spread throughout the province and apparently their distribution is not affected by weather conditions. According to our findings, the above-mentioned Fusarium species seem to be the causal agents of root and crown rot of cantaloupe and melon and consequent wilting and vine decline which is an important disease in arid and semiarid areas.

In this study, Rhodotorula mucilaginosa isolate A1 was recovered from healthy apple surface and Penicillium expansum was isolated from infected apple. The yeast isolate was evaluated as a potential biological control agent for apple blue mold caused by P. expansum. Dual culture, extracellular metabolite and volatile compounds tests were used in in vitro assays. The yeast inhibited growth of P. expansum, the inhibition by yeast was 60.97%, in dual culture, 90.57% in volatile gases and 83.36% in cell free metabolite tests. Apple fruit were wound-inoculated using 40 µl of yeast cell suspension (107cell/ml) followed 24 h later by P.expansum (105 conidia/ml). The apples were then incubated at 20 and 5°C. The yeast reduced the decayed area at both (20 and 5 °C) temperatures. In the second section of this study, the ability of yeast to induce catalase, peroxidase and phenolic compounds in apple tissue was investigated. The apples were first treated with the yeast, then inoculated with the pathogen and incubated for 10 days at 20 °C. Peroxidase, catalase activities and levels of phenolic compounds were measured 2, 4, 6, 8 and 10 days after inoculation with P. expansum. R. mucilaginosa A1 caused increase in peroxidase and catalase activities that reached their maximum level 6 days after inoculation with pathogen. The highest level of phenolic compounds was observed at 6 days after pathogen inoculation in treatments of R. mucilaginosa A1and Penicillium compared with control (apple treated with distilled water). The ability of R. mucilaginosa to increase activities of peroxidase, catalase and levels of phenolic compounds may be some of the mechanisms responsible for its biocontrol activities.

Seventy nine isolates of Fusarium solani were obtained from crown and root rotted parts of tomato plants collected from different regions of Khuzestan province during autumn 2009 using Nash-Snyder medium. Pathogenicity of isolates was tested on potted tomato seedlings of cultivar Primo at 2-leaf stage, under field conditions. Genetic diversity among F. solani isolates was also studied using vegetative compatibility groups (VCGs). Pathogenicity tests revealed that all the isolates were pathogenic. In order to determine VCGs, nit mutants were generated on culture medium CDAC supplemented with 5% KClO3 and Rose Bengal. Using this medium collectively 631 nit mutants were recovered. Nit mutants were divided into 3 phenotypic classes, nit1 (68%), nit3 (18%) and NitM (14%) according to their growth pattern on basal media containing one of four nitrogen sources: sodium nitrate, sodium nitrite, hypoxantine and ammonium tartrate. Complementation test among nit mutants placed isolates into 25 vegetatively compatible groups. In this investigation no relation was observed between VCGs and geographic regions.

Eleven isolates of Macrophomina phaseolina, isolated from various hosts (soybean, sunflower, cantaloupe, muskmelon, wheat) in different provinces were assayed for reaction to potassium chlorate on nutrient medium. The isolates were grown on minimal medium amended with 120 mM potassium chlorate. The results showed that isolates were separated into two groups of which 54.5 % were chlorate-resistant and showed dense phenotype. The results of pathogenicity tests on soybean plants in green house showed that there was positive correlation between soybean root rot and reaction to potassium chlorate. The M-21 and M-30 isolates with chlorate-resistant reaction and dense phenotype were recognized as the most virulent isolates.