نشریه کنترل بیولوژیک آفات و بیماری های گیاهی
سال پنجم شماره 2 (پاییز و زمستان 1395)

As the host plants based on their physical and chemical characteristics can affect virulence of microbial control agents on the target pest and its natural enemies, therefore in the current study, the virulence of Beauveria bassiana TV isolate at concentration 107 conidia/ml was evaluated against T. urticae female adults, on three different host plants; tomato, cucumber and strawberry. Spray tower method with five replications was used in this research. In control, the spider mites were not treated by B. bassiana. Afterward, the sensitivity of fifth instar nymphs and six-day olds adult females of predatory bug, O. niger was investigated to the fungus at concentration of 107 conidia/ml on these three host plants with five replications. The experiments were conducted in a completely randomized design. Variance analysis revealed that the effect of this isolate was different statistically against T. urticae on three plants. Mean comparisons using F-LSD demonstrated that the highest mortality of mites with 63% was observed on cucumber compared to tomato and strawberry which were 57% and 50%, respectively. Based on the results, these three host plants did not affect the virulence of isolate TV on O. niger female adults and nymphs. Our findings showed, isolate TV is highly toxic to spider mite population tested in laboratory. Also, obtaining a good control result for a biological agent against a particular pest on a specific host plant, does not necessarily mean that the agent is effective on the same target pest but different host plant.

Salinity stress is one of the most important abiotic factors that restrict the growth and yield of many plants. Salinity can increasingly influence the host susceptibility, occurrence and development of plant diseases due to its negative effects on the host plants. Mycorrhizal fungi are able to increase the tolerance of some plants to salinity. In this study, the biological effects of Glomus mosseae were studied against cucumber damping off caused by Pythium aphanidermatum. Subsequently the effects of different concentrations of salinity in the presence of AM fungus were assessed on the plant growth, the mineral nutrient uptake and also, the disease severity of cucumber damping off on seedlings. The results showed that G. mosseae significantly (P≤0.05) decreased the disease severity. The mean of disease severity caused by the pathogen was 56%, while in treatments inoculated to mycorrhizal showed a reduction to 28%. Furthermore, the plant growth parameters including root length and plant hight increased in treatments inoculated with mycorrhizal fungus as compared with non-mycorrhizal roots in salinity soil. It can be a consequence of more nutrient uptake by roots. Content of P and K was significantly reduced by increasing salinity, whereas the level of Na increased. The plants inoculated with mycorrhizal fungus increased the nutrient content of P and K as compared to non-inoculated treatment in all levels of salinity, but the content of Na decreased. These results showed that the colonization of cucumber seedling roots by G. mosseae can reduce the deterimental effects of salinity and damping off disease caused by Pythium.

Pectobacterium carotovorum is one of the most important bacterial pathogens of potato in the world.The expression of numerous genes including those involved in the production of virulence determinants in this bacterium are regulated by quorum sensing (QS). The signal molecules involved in QS in P. carotovorum belong to the group of N-acyl homoserine lactones (AHLs). Recently, several soil bacteria were found to degrade AHLs, thereby interfering with the QS system. In this research, 1280 bacterial strains were isolated from potato rhizosphere in Iran. For the screening of isolates for AHL-inactivating, Chromobacterium violaceum CV026 and Escherchia coli pSB401 was used as biosensors. The 69 isolates have highly AHL-degrading potential. The AHL degradation measurement by HPLC showed that residue of C6-HSL was not detected in some isolates that means completely degradation of it by antagonists. The screened isolates tested for protect potato tubers against soft rot. 40 strains reduced tuber soft rot more than 50 percent. 16 of the best isolates were used for inhibition of stem tissue maceration. Bacillus toyoensis 2L, Escherchia coli 1M and Acinetobacter calcoaceticus 32P reduced stem maceration more than 70 percent. These strains were identified by 16s rDNA sequencing. These results showed that interference with P. carotovorum quorum sensing system can be considered as an attractive target for development of biological control method of this disease.

Using plant probiotic bacteria, which can induce systemic tolerance in plants, is one of the most important strategy to reduce the damage of drought stress in plants. In this study the effect of four fluorescent strains (T17-4, VUPF5, 428, CHA0) was investigated on resistance of two pistachio cultivars (Badami-Rize-Zarand and Sarakhs) against the drought stress. A completely randomized design was applied with a factorial arrangement at three replications in a greenhouse trial. In order to evaluate the effects of bacteria on reduction the effects of drought stress, some parameters such as prolin, soluble sugars, chlorophyll a, chlorophyll b, P, Zn, Fe content of shoot and root were measured. The results showed that drought stress increased the prolin and soluble sugars content in both inoculated and non-inoculated seedlings, although the content of prolin and soluble sugars in inoculated seedlings were higher than non-inoculated seedlings. The result also indicated that the drought stress reduces growth parameters, photosynthesis pigments and mineral element content in both cultivars under inoculated and non-inoculated conditions. The most reduction of these traits were recorded in non-inoculated seedlings. The cultivars of pistachio showed different responses to drought stress, so that sarakhs cultivar was recognized more sensitive to drought stress than badami-Rize-zarand cultivar.

The functional response and predation rate of Hippodamia variegata (Goeze)(Col.: Coccinellidae) were studied under laboratory conditions at 25 and 27.5oC, 65 ± 5 RH and a photoperiod of 16:8 (L:D). In order to study the predation rate, newly first instar larvae were chosen and each age stage were fed by three and four instars of pomegranate green aphid, Aphis punicae (Hem.: Aphididae). According to the results, predation rate at 25 and 27.5°C were 11.4 and 10.3% for larval stage, and 86.8 and 89.7 % for female adult stage, respectively. The consumption value in females compared to males is 1.5 times. The net predation rate (C0) at 25 and 27.5 °C were 1725.14 and 1870 three and four instars of pomegranate green aphid respectively. The result showed that all age stages of the predator at 25 and 27.5 oC exhibited type II functional response. Thus, based on the searching efficiency at 25°C, 3th and 4th larval instars and at 27.5°C 4nd larval instar and adults of H. variegate are the most effective as predators on A. punicae. So in both temperatures, fourth instar larvae showed a better searching efficiency. The results indicated that the H. variegata may be a useful candidate for the biological control of A. punacae in pomegranate gardens.

The greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hem., Aleyrodidae) is a cosmopolitan and polyphagous insect that attack a wide range of crops. In this study, the biological parameters of parasitoid wasp, Eretmocerus delhiensis Mani (Hym., Aphelinidae) on T. vaporariorum were evaluated. The experiments were conducted at 25±1°C, 65±5% RH and a photoperiod of 16: 8 h (L: D) in growth chamber. Based on the results of our studies, all of parasitoid progeny were female and there was no male progeny. Adult emergence, pre-oviposition, oviposition and post-oviposition period, developmental time and longevity of female parasitoid were 71 %, 15.03±0.32, 0.46±0.06, 4.2±0.12, 1.04±0.08, and 5.71±0.13 and 20.74±0.5 days, respectively. Also, other parameters such as; daily fecundity, total fecundity, daily host feeding, and total host feeding were 3.04±0.11 and 17.43±0.17 eggs 1.07±0.05, and 6.40±0.35 nymphs, respectively. Regression analysis revealed that host feeding had a significant effect on oviposition of this parasitoid. Therefore, the parasitoid wasp E. delhiensis not only parasitize their hosts but also kill them through host feeding. These results suggest E. delhiensis has the potential to be used as a biological control agent in greenhouse whitefly management.

Today, the use of essential oils and extracts of medicinal plants in food and pharmaceutical industries is growing because of their medicinal, antifungal, antibacterial and antioxidant properties. In this way, the effects of various extracts of Scrophularia striata, a medicine plant, were studied for inhibiting Aspergillus flavus mycelial growth and reducing aflatoxin B1-level in culture liquid potato-dextrose (PDB) as well as the pistachio nut. Aflatoxin B1 (AFB1) was evaluated by high performance thin layer chromatography (HPTLC) method. Application of different concentrations of the extracts (250, 500, 1000, 2000 mg/L) in order to inhibit the growth of Aspergillus flavus and also Aflatoxin B1 production in PDB medium demonstrated that the aqueous extract at a concentration of 2000 mg/L could significantly inhibit the A. flavus growth (41.02% loss in dried weight). Ethyl acetate, methanol and aqueous extracts had amazing effect (92-100%) to inhibit toxin production. The results of AFB1 degradation assay indicated that the application of aqueous and methanolic extracts led to significant degradation of aflatoxin by 33.7 and 29.2%, respectively. It is shown that only aqueous extract at concentrations of 2000 and 4000 mg/L could significantlly inhibit (37.14- 58.91%) fungal sporulation on pistachio nuts, while both  methanol and aqueous extracts showed the strongest impact on inhibiting toxin production and caused a reduction of 96.85% and 75.48%, respectively, in AFB1 content. At the concentration of 2000 mg/L only methanol exract was able to reduce AFB1 (40.35%) on the pistachio nuts. Finally, the use of Scrophularia striata can possibly inhibit the aflatoxin contamination on agricultural products.

The European corn worm, Ostrinia nubilalis (Hübner) is an important pest of corn in Iran. In this research, the influence of corn monoculture and also, three strip-intercropping systems including three, six and nin rows of corn with three rows of clover were evaluated on the natural enemies diversity of O. nubilalis, the proportion of predators/prey density and finally, the percentage of parasitized eggs and larvae in experimental fields in Ardabil region in 2014 and 2015. In this study, eight predator species, five larval parasitoid species and one egg parasitoid species were collected and identified which amongst them, Orius niger (Wolff), Lydella thompsoni Herting, Bracon hebetor Say and Trichogramma brassicae Bezdenko had the high relative abundance in the tested cropping systems. The Shannon diversity index (H) in each of the three intercrops was significantly greater than in corn monoculture. The values of Morisita–Horn index (CMH) between corn monoculture and each of the three intercrops (CMH ≤ 0.893) were lower in comparision with the values of this index among the three intercrops (CMH ≥ 0.977). In two years, the proportion of predators/prey, and the percentage of parasitized eggs and larvae of O. nubilalis in each of the three intercrops were significantly higher than in corn monoculture. Implementation of these cultivation systems in the corn fields is an important step in the management of O. nubilalis.

The ability of four bacterial strains include Pseudomonas fluorescens VUPF5, VUPF52 and Bacillus cereus IPRI95, Bacillus subtilis IPRI96 on increase of growth parameters of two cultivars of pistachio in presence and absence of Meloidogyne incognita was evaluated. The experiment was a factorial design in a complete randomized design with the three factors including cultivar (Badami and Sarakhs), disease (presence and absence of nematode) and probiotic bacteria (Pseudomonas fluorescens strains VUPF5, VUPF52, Bacillus cereus strain IPRI95, Bacillus subtilis strain IPRI96 and water) in three replications. All of measured parameters showed considerable increases following treatment with bacterial strains in both cultivars. However, this increase in Sarakhs cultivar was higher than Badami cultivar. The maximum increase in treated pistachio seedlings was recorded for shoot height by 75.1, 12.1, root height by 50.63, 29.6, fresh shoot weight by 115, 34, fresh root weight by 63, 31, dry shoot weight by 34.41, 18.52 and for dry root weight by 1, 17.1 percent in Sarakhs and Badami cultivars respectively as compared with control. The number of galls and number of egg masses four month after inoculation was significantly decreased by 49.7 and 30.5%, for cv. Sarakhs and 64.4 and 71%, for cv. Badami respectively as compared with nontreated seedlings.

Pseudomonas fluorescens strains producing 2,4-diacetylphloroglucinol (DAPG) contribute to the biological control of many fungal plant diseases. Tomato Fusarium wilt is one of the most important diseases of this plant that causes considerable damage to the crop. In the current study, 35 strains of P. fluorescens were screened for the presence of phlD and hcnAB genes and it was revealed that nine strains harbored the target genes. Antagonistic ability of phlD+ and hcnAB닚� was tested against pathogen under in vitro conditions using dual culture method and five strains including PGU, PGU1, PGU2, PGU3 and CHA0 were selected for further studies. Strains were checked for production of antimicrobial metabolites and plant growth promoting traits and then, their potential to control Fusarium wilt and promoting tomato growth was investigated under greenhouse conditions. Laboratory results showed that bacterial strains were capable of producing antimicrobial compounds like DAPG, pyoluteorin and monoacetylphloroglucinol, hydrogen cyanide, indole-3-acetic acid, protease and solubilization of mineral phosphate. Strains were also able to control the disease and stimulate tomato plants growth significantly under greenhouse conditions and PGU strain performed better in comparison to other strains. This study suggests that the production of antimicrobial metabolites and/or metabolites stimulating plant growth plays a key role in effective disease control and increasing plant growth parameters under greenhouse conditions.

The present study was conducted to determine the efficacy of Trichoderma asperellum Volatile Organic Compounds (VOCs) in suppression of mycelial growth and conidial germination of Botrytis cinerea and also in control of Botrytis fruit rot of strawberry. Significant reduction in colony diameter, percent of conidial germination and length of germ tubes of B. cinerea was observed in treatments exposed to VOCs of 5-days old T. asperellum compared control. The incidence and severity of Botrytis fruit rot of strawberry was also significantly reduced by exposure to the VOCs of 5-day old T. asperellum cultures. VOCs profile of T. asperellum was identified using solid phase microextraction coupled to gas chromatography–mass spectrometry (SPME-GC-MS) technique. Six compounds out of 34 VOCs identified in this including isobutyric acid, 1,3,5,7-cyclooctatetraene, dimethyl sulfide, para-menta-6,8,dien-2-ol-acetate, phenyl ethyl alcohol and 1-butanol, 3-methyl-, acetate were the most abundant. Synthetic compounds of isobutyric acid and dimethyl sulfide were the most effective compounds among these compounds in suppression of mycelial growth and conidial germination of B. cinerea with IC50 of 26.5 and 10 μl/ liter, respectively.

The cabbage aphid, Brevicoryne brassicae (L.), is a major pest of cruciferous crops all over the world that causes a considerable damage on different products by direct sap feeding and transmission of pathogenic viruses. Use of chemical pesticides is the most common control method of this pest but the adverse effects of these pesticides have shifted considerations to other environmental-friendly agents. In this study, the virulence of two isolates (DEMI001 and V245) of the fungus, Metarhizium anisopliae (Metch.) Sorokin was investigated against the adults of cabbage aphid in laboratory conditions. Adult aphids were treated with (103-107 conidia/ml) concentrations of fungus. Moreover, life table parameters of aphid were evaluated when treated with sub-lethal (LC30) concentration of the effective isolate, DEMI001. Results showed that the adults of cabbage aphid were completely sensitive to the isolates of fungus. LC50 values was scored 1.5×105 and 2.3×106 conidia/ml respectively for DEMI001 and V245 isolates. The shortest time needed for the mortality of 50% of the population was 6.67 days belonging to DEMI001 isolate at 107 conidia/ml concentration. Moreover, results showed that a sub-lethal (LC30) concentration of DEMI001 isolate, had significant effect on fertility of treated aphids. The values of rm and λ parameters were 0.28 female/female/day and 1.32 female/day, respectively. Our results showed that M. anisopliae can be used as an effective biocontrol agent in cabbage aphid control.

To evaluate the efficiency of head flies Urophora xanthippe (Dipt.: Tephritidae) in control of knapweed through the destroying of seed, three experiments was conducted separately in the field, greenhouse and laboratory condition at University of Birjand in 2010. The first experiment was conducted for evaluation of the ability of U. xanthippe to the destroying of seed andreducing of the number of knapweed seed. Other experiments carried out to determination of host range and preference of insect. The results showed that the average of seeds in attacked boll (6.35 ± 0.01) had significant difference with no attacked boll (11.83±0.01), in treated plants. Also, the mean number of seeds (including seeds intact and damaged) had significant difference between the treated plants (11.82±1.02) and the control (29.77±1.02). The results of this study showed that the attack of U. xanthippe causes 64.00±0.01 destroying of knapweed seeds in natural conditions. Due to the high potential of U. xanthippe in reducing the number of seeds and also, a limited host range, it can be used as a biological control agent of knapweed in the integrated management of this weed species.