نشریه مهار زیستی در گیاه پزشکی
سال یکم شماره 1 (بهار و تابستان 1392)

Cabbage aphid, Brevicoryne brassicae is one of the major pests of Cruciferae plants, especially cabbages and canola. In order to investigate the effect of plant essential oils to control of cabbage aphid, the contact effect of essential oils of laurel, Laurus nobilis and eucalyptus, Eucalyptus camaldulensis leaves was evaluated on apterous morph adults of cabbage aphid. Bioassay experiments were carried out with essential oil concentrations causing 20-80% mortality to determine LC50 by Topical application. The experiment was done in a Germinator with 25±1ºC, 60±5% RH and photoperiod of 16:8 (L­:­D) at five replications and 10 aphid adults were placed on cabbage leaf disc in each Petri dish as one replication. According to the results, essential oils derived from the studied plants had contact effect on cabbage aphid. LC50 of laurel andeucalyptus essential oils on cabbage aphid wereestimated as high as 11563 and 16835 ppm, respectively, and so laurel essential oil was more effective than eucalyptus one. Results of the experiments conducted as completely randomized design with five replications also revealed that tested essential oils reduced the aphid's fecundity and longevity in comparison to the control, but laurel essential oil was more effective. Application of laurel essential oil caused up to 45.47% and 32.78% reduction in fecundity and longevity of cabbage aphid, respectively. Repellency activity of essential oils of laurel and eucalyptus was evaluated using an Olfactometer (model RZR). An increased repellency percentage was observed at higher concentration of the studied essential oils. Repellency of laurel’s essential oil was more than that of eucalyptus, so that repellency percentage was 86.67% for laurel and 10% for eucalyptus essential oils in LC50. Plant essential oils were extracted by Distillation method and their compounds were identified by GC-MS. Results showed that 1,8-cineole (a component with insecticidal effect) was the major component in L. nobilis (25.5%) and E. camaldulensis (35.14%) essential oils, respectively.

Verticillium wilt is one of the most important diseases of cotton, tomato, potato and greenhouse cucumber that causes serious losses in these crops. Biological control could be an effective strategy for controlling this disease. In this study, for the investigation of antagonistic mechanisms of Talaromyces flavus, first, pathogenic agents and antagonistic fungus were isolated from cultivated regions of above-mentioned crops using Komada and TF culture media respectively. In next step, antagonistic mechanisms of T. flavus including mycoparasitism, volatile metabolites production and non-volatile metabolites production were studied separately. In this study, sixty T. flavus isolates were used from which 23, 15, 14 and 8 isolates belonged to cotton, tomato, potato and greenhouse cucumber respectively. For cotton and potato wilt disease caused by V. dahliae and V. albo-atrum respectively, maximum inhibitory percents (81.51 and 64.93%) were mediated by TF-Co-G-1 and TF-Po-V-48 respectively. Non-volatile metabolites played the most important role in their antagonistic activity. However, for tomato and greenhouse cucumber wilt disease caused by V. albo-atrom, maximum inhibitory percents (73.67 and 54.78%) were mediated by TF-To-V-31 and TF-Cu-V-60 respectively. According to the results, the most effective antagonistic mechanisms of these isolates was volatile metabolites production.

Plant diseases severity is presently evaluated using manual tools such as ruler, digital ruler or by scaling. Extending the great potential of computer science in accurate and rapid determination of disease severity, this study was conducted to evaluate biological control potential of two yeasts, Pichia guilliermondii (A6) and Candida membranifaciens (A4) in combination with silicon (Si) at 0.1%, 0.3% and 0.5% for controlling Penicillium expansum P1 and P2 at 20 ˚C. The results showed that antagonistic yeasts controlled blue mold of apple significantly. Combination of the yeasts with Si improved the control of blue mold in comparison with yeasts alone. Statistical information obtained from the infected area in RGB channels showed that blue average (R2=0.70) was the most important and green standard deviation (R2=0.43) was the least important factors in recognition of disease severity. Linear discrimination analysis using blue average, green average, blue standard deviation, red standard deviation, green kurtosis and green standard deviation separated the disease severity statistical groups with the accuracy of 80%. The overall results of this study suggest that the color could be a powerful descriptor which could be applied for determination of disease severity in apple blue mold.

Pythium root rot of sugar beet caused by Pythium aphanidermatum is an important yield reducing disease in Iran and so far its chemical control has not been achieved successfully, therefore, alternative control measures including biological control might be effective in managing this disease. A green house study was conducted to investigate the efficacy of some native Trichoderma isolates in controlling this disease in Agricultural Research Center, Shahrood, Iran during 2007- 2008. Out of 22 Trichoderma isolates collected from sugar beet fields, seven isolates belonging to four species (Trichoderma harzianum, T. longibrachatum, T. erinaceum and T. koningii), among which T. erinaceum is a new species for Iran mycoflora and had previously performed effective in inhibiting mycelial growth of the pathogen through dual culture and production of volatile and non-volatile metabolites were selected for green house evaluations using seed and soil treatment methods. Results of green house experiments during two years evaluations indicated significant reduction in seedling damping-off in potted plants treated with Trichoderma isolates either as seed or soil treatment (compared with untreated control). Plant growth promotion was also observed in plants treated with Trichoderma isolates in comparison with untreated control. Based on the overall results of this study, T. harzianum 2736 demonstrated the highest disease reduction (70%) in both methods.

Citrus blast caused by Pseudomonas spp. is one of the most important diseases in the northern citrus growing provinces of Iran which causes considerable losses to citrus orchards in conducive climatic conditions. In this study, we tried to isolate and introduce some yeast strains from citrus orchards with acceptable biological control potential against the disease. The evaluations were performed under green house conditions on sour orange seedlings. Yeast cell suspensions were sprayed three times with two-days intervals on seedlings before pathogen inoculation. Statistical analysis of the results was carried out using Randomized Complete Block experimental design and comparison of disease severity means was performed by Duncan's Multiple Range Test. For the identification of the effective yeast strains, ITS regions of their rRNA operon were amplified using universal primers (ITS1 and ITS4) by PCR and the amplified fragments were sequenced. Based on the above procedures and comparison of the sequences with those deposited in the GenBank, the effective yeasts were identified as Sporobolomyces ruberrimus, Cryptococcus albidus, C. magnus and Rhodotorula sp.According to the results, S. ruberrimus, was the most effective yeast and controlled the disease more efficiently than other species.

Trichogramma wasps (Hym., Trichogrammatidae) are frequently used as egg parasitoid and biological control agent of lepidopteran pests. These haplodiploid wasps display two reproductive modes, including thelytoky and arrhenotoky. The thelytoky (unisexuality) are often associated with the presence of endosymbiotic Wolbachia bacteria (α-proteobacteria). The use of thelytokous parasitoids has long been considered as a way to enhance the biocontrol efficacy. In this study a series of experiments were conducted to compare the behavioral aspects, dispersal potential and parasitism of thelytokous (BW+) and bisexual (B) Trichogramma brassicae strains (Baboulsar ecotype) at 25◦C in laboratory conditions. By using Y-tube olfactometer, it was observed that the Wolbachia infection in the Baboulsar strain (mixed population) neither affected the wasp's response to volatile odors of honey water solution and factitious host eggs nor did it interfere with female wasp's sex pheromone emission. Greenhouse release tests on corn plants, resulted in non significant differences between the strains taking the number of parasitized eggs per one female wasp into consideration. However, based on releasing 100 wasps (male and female in the case of bisexual), the number of egg masses parasitized by thelytokous T. brassicae (6.01) was significantly higher than B strain (2.88). Therefore, this thelytokous line of Trichogramma might be superior to bisexual conspecifics under more natural conditions and hence have a higher potential in pest control.

Root rot and vine decline disease caused by Monosporascus cannonballus and charcoal root rot disease caused by Macrophomina phaseolina are important diseases of melon plants in Iran. In this study, the efficacy of wood vinegar on the mycelial growth of these pathogens as well as the integrated effect of wood vinegar and compost tea were examined on the control of root rot and vine decline disease. To test the antifungal activity of wood vinegar, mycelial disks (3 mm in diameter) of M. cannonballus and M. phaseolina were placed on PDA culture media amended with different concentrations of wood vinegar (0.025, 0.05, 0.37, 0.5, 0.75 v/v). Wood vinegar inhibited the mycelial growth of both pathogens at 0.05 probability level. In green house condition, muskmelon seeds were sown into pot-soil containing 15% v/v of compost tea and infested with M. cannonballus. Three concentrations of wood vinegar (0.125%, 0.25%, 0.5%) which had shown the maximum inhibitory effect on mycelial growth in the laboratory were then drenched into the soil. Results showed that disease severity was significantly reduced in all concentrations used (α= 0.05). The integration of compost tea and wood vinegar reduced the pathogenicity of M. cannonballus up to 94% compared with untreated control. Roots and shoots weights increased by 8% and 25% respectively in the presence of wood vinegar and compost tea (α= 0.05).

During sampling of Apricot branches in several locations in Fars province (in Bavanat and Khorram-Bid) (Iran) at February and March 2012, a larval parasitoid of long horned beetle Cerambyx dux (Col.: Cerambycidae) was found. The ichneumonid parasitoid, Dolichomitus kriechbaumeri (syn. subglabratus), was reared from the larvae of Cerambyx dux, which infests the trunks and twigs of apricot in orchards. Cerambyx dux is a new host for D. kriechbaumeri.