نشریه تحقیقات بیماری های گیاهی
سال چهارم شماره 1 (بهار و تابستان 1395)

Effects of date and depth of sowing on incidence of chickpea wilt incited by Fusarium oxysporum f. sp. ciceri and crop yield were evaluated on three chickpea cultivars in Lorestan, Kohdasht during 2014, using a factorial experiment based on RCBD design with four replications. Sowing date with three levels of early November, early December and early March were used as main plots. Planting depth including 5, 9 and 13 cm depth were used as sub plots and three chickpea cultivars including Adell, Hashem and Arman were used as sub sub plots. Rows were 30 cm apart and distance between seeds in a row was 10 cm. The rate and severity of disease symptoms were recorded every 7 to 10 days. The results showed that the effect of planting date on all the indicators, yield & disease severity was significant. Statistical analysis showed that sowing in March resulted in highest infection and lowest yield compared with the earlier sowing dates. Advancing the sowing date from early March to early October doubled the crop yield and decreased disease by 41 percent. Different depths of sowing did not show significant differences in yield nor disease incidence. Interaction of sowing depth × cultivars, however, revealed that highest yield was obtained in the third sowing depth in Adell cultivar.

In order to identify the species and the races of root knot nematodes in the air-cured tobacco fields of Mazandaran province, 102 soil and root samples from tobacco fields were collected during 2014. Nematodes were extracted from soil and roots using Jenkins and Coolen and DHerde methods, respectively. The number of nematodes were counted, and the species and races were determined by studying perineal patterns obtained from adult females and the reaction of differential host plans (cotton Deltapin 16, tobacco NC-95, watermelon Charleston grey, tomato Rutgers, Peanut Florunne, pepper Early California Wonder) to nematode infection. This study revealed that 59.52 percent of the samples were infected with M. incognita Race 2, 40.47percent M. javanica, 14.28 percent M. arenaria Race 2 and 7.14 percent M. hapla. About 21 percent of samples were infected with two species where M. incognita was always one member of the mixed populations, the other members were M. javanica, M. arenaria or M. hapla. These species were distributed in Sboukola, Velashed and Kharkesh tobacco fields in Mazandaran province, Iran.

In recent years studies on the use of plant essential oils and extracts against pathogenic fungi have attracted much attention because of rising resistance against a large number of chemical pesticides. Essential oils are antifungal materials which are renewable and compatible with environment. In this study, essential oil and ethanol extracts of watermint (Mentha aquatica) were obtained from aerial parts using distillation and ethanol solvent methods, respectively. The inhibitory effect of different concentrations (0, 100, 200 and 300 ppm / 9 cm Petri dish) of watermint essential oilswith fumigation and contact methods and their extracts on mycelium growth of Botrytis cinerea, Fusarium oxysporum, Rhizoctonia solani, Phytophthora capsici were investigated in a factorial experiment based on completely randomized design. Fungi showed different sensitivity to watermint essential oils and extract. None of watermint concentrations of essential oils and extract had any inhibitory effect on growth of F. oxysporum but all concentrations inhibited the growth of B. cinerea, R. solani and P. capsici significantly. Increase in concentration enhanced the inhibitory effect significantly. The highest percentage of inhibition was related to concentrations 200 ppm and 300 ppm in R. solani (%91.06 and %97.77 respectively) and also concentration 300 ppm in P. capsici (%91.89). Therefore, watermint essential oils and extract can be considered as natural fungicide for control of pathogenic fungi.

In this research some metabolites of Pseudomonas tolaasii the causal agent of mushroom bacterial blotch disease and Pseudomonas reactans associated with it were investigated. Characteristic features of P. tolaasii included brown pit formation on button mushroom caps, tolaasin production, lysis of erythrocytes, and white line induction in agar plate in presence of Pseudomonas reactans. Further, the metabolites of P. tolaasii and mushroom-associated bacteria were extracted and their effects were evaluated against the blocks of the mushroom A. bisporus. It was noticed that the strains of P. reactans also produced a lipodepsipeptide, WLIP. Certain complementary tests were also conducted to confirm the presence of these compounds in products extracted. The rpoB gene of a pathogenic strain of Pseudomonas sp. p2 isolated from the same mushroom was amplified using the primer pair of LAPS and LAPS27 and sequenced and deposited in Genebank at NCBI. Effect of impure WLIP of the strain P. reactans Pr 5 and standard strain of P. reactans NCPPB1311 were examined on blocks of A. bisporus and potato tubers. In bioassays, the tolaasin of strain P. tolaasii Pt 6 created both brown blotch and slight pitting symptoms. Whereas, WLIP of the P. reactans Pr 5 could only induce slight discoloration. Another important finding was that simultaneous application of P. reactans A6 in combination with tolaasins of P. tolaasii Pt 6 or P. tolaasii NCPPB2192 resulted in suppression of brown blotch symptoms on treated blocks with P. tolaasii. Results indicate the importance of associated bacteria in suppression of disease by P. tolaasii.

Today, the application of molecular methods is a common and necessary part of many routine researches. DNA extraction is the foundation for most of such research studies. As a result, it is of great significance to discover and select proper techniques that are productive, inexpensive, straightforward, safe and rapid at the same time. Agricultural research and experiments are no exception in this respect. C-TAB, phenol-chloroform and DNA extraction kits are conventional techniques in agriculture for extracting DNA from filamentous fungi. Each of these methods has its advantages and disadvantages. In this study, we have developed a novel, straightforward and effective method to extract the DNA from antagonistic-, saprophytic- and plant pathogenic-filamentous fungi. This method is a composition of the aforementioned techniques and is used to avoid the application of liquid nitrogen and phenol. It is called squish with grinder and is a safer, more affordable and quicker method that results in relatively pure DNAs. The purity of obtained DNA was assessed by spectrophotometry. The ITS region and β-tubuline gene was amplified by PCR. The results of this assessment justify this method as a practical and reliable technique to extract filamentous fungal genomic DNA.

Fusariumwilt of tomato is a worldwide disease causing significant damage in more than 32 countries. In this experiment the antagonistic effects of locally isolated strains of Bacillus subtilis and Pseudomonas fluorescens against the pathogen were studied in the laboratory and greenhouse. Results showed that in dual culture tests the isolates P. fluorescens (P1), P. fluorescens (P2) and Bacillus subtilis inhibited growth of Fusarium by 28/8, 25/74 and 10/52 percent respectively. In the greenhouse experiments roots of tomato seedlings were separately dipped in the bacterial suspensions before transplanting into pots, the top one-third soil of which was inoculated with the pathogen. The interaction between antagonists and pathogen in the greenhouse, 60 days after inoculation of seedlings was evaluated by measurement of growth factors, root and shoot wet and dry weights, of tomato plants and the severity of Fusarium wilt disease. Both P. fluorescens and B. subtilis decreased disease incidence and increased growth factors of tomato plants in the presence of the pathogenic fungus but, in contrast to results of dual culture tests, Bacillus subtilis was more effective in reducing disease severity.