نشریه کنترل بیولوژیک آفات و بیماری های گیاهی
سال چهارم شماره 2 (پاییز و زمستان 1394)

In this study, biocontrol effect of some strains Pseudomonas fluorescent surveyagainst Pythium aphanidermatum the causal agent of cucumber root rot disease. First biocontrol ability of bacteria against the fungal pathogen evaluated by cross-culture method. Results showed that inhibition zone of strain T17-4 (7.5 mm) was more than others. Seven strains including T17-4, CHA0, CHA89, VUPf52, VUPf506, VUPf760 and VUPf5 that had the best effect on control of some disease were selected for greenhouse conditions. The result of this experiment showed VUPf52, VUPf5 and T17-4 strains with 50, 49 and 43% (toward infected treatment) had the highest inhibition of cucumber root rot disease, respectively. These strains promote plant growth parameters such as height, dry and wet weight of shoot and root, too. The defense changes showed the highest increasing in peroxidase activity, total phenolic content and polyphenol oxidase after nine days inoculation and then decreased. The rate of increase in peroxidase activity, total phenolic content and polyphenol oxidase in treatments combined with bacteria and fungi compared with control treatment was significant.

The predatory bug Orius niger Wolff is an important predator of the onion thrips, Thrips tabaci Lindeman in the potato fields of Ardabil region. In this study, preference for prey, predatory rate, body size, and some life history parameters of O. niger were studied on seven potato genotypes (including Savalan, Agria, Morene, Kondor, Diamant, PI397082-2, and PI397097-2)infested to T. tabaciunder laboratory conditions. In preference test, the predator females were more attracted to the onion thrips-infested leaves of Savalan after 24, 48 and 72 hours from release. In test, prey consumption by O. niger nymphs on Savalan was significantly higher than on the other tested genotypes. Moreover, the predator females reared on the onion thrips-infested leaves of Savalan had higher body mass and greater body size among the seven tested genotypes of potato. The development time of predator nymphs on the onion thrips-infested leaves of Savalan was significantly shorter compared with Kondor, Diamant and PI397097-2. Furthermore, the survival rate of predator nymphs on the onion thrips-infested leaves of Savalan was significantly greater than on Kondor, Diamant, PI397082-2 and PI397097-2. Therefore, it can be concluded that the preference and performance of O. niger was more significant on Savalan amongst the tested potato genotypes.

Trichoderma spp. are known as efficient plant growth promoting agents. Hence, enrichment of soil by appropriate population of Trichoderma is useful and important for effective plant growth promote. Present study aimed to investigate the plant growth promoting effects of five strains of the genus Trichoderma species include: Trichoderma harzianum Tr6, T. harzianum T22, T. asperellum T34, T. atroviride P1 and T. harzianum on cucumber and select the most efficient candidate under greenhouse conditions. Then this superior strain was applied in various soils including normal, phosphorus-defective soil, potassium-defective soil, alkaline soil, soil with two levels of salinity and acidic soil to evaluate the detailed effects on cucumber growth parameters under greenhouse conditions. The results showed that Trichoderma strain Tr6 led to statistically significant improvement in examined growth indices in soils suffering from salinity and potassium- and phosphorus deficiency. In view of stability of Trichoderma population in different soils, comparison of means showed that the highest population was achieved in acidic and normal soil and the lowest population occurred in the soils with high level of salinity and alkaline soils. Generally, we concluded that low Trichoderma population under some soil conditions is likely due to the lack of optimum condition for its growth and it can improve plant growth under these stressed soils by restoring its population by adding successful strains of Trichoderma to the soils.

Citrus blast caused by species of Pseudomonas spp. is one of the most important citrus diseases in north of Iran. This disease causes considerable losses to citrus orchards in conducive climatic conditions. Due to restrictions on the use of antibiotics and chemical compounds, biological control and use of plant antimicrobial compounds can be an effective way to control citrus blast disease. In this study, performance of several epiphytic yeasts isolates and Golpar seed extract on bacterial blast of citrus were studied under in vivo and in vitro conditions. Antagonistic yeasts collected from citrus leaf samples were isolated from different regions of the Northern provinces. Also, Golpar seeds were collected from the highlands of the city of Babol (Mazandaran, Iran). The seed extract of Golpar showed significantly inhibited the growth of two pathogens on KB medium but none of the yeasts show significant growth inhibition. The results of greenhouse studies indicated that one of yeast isolate (Pichia sp.) reduces the severity of disease with average 78.8 percent. Also Golpar extract was able to reduce the pathogen populations by 60 percent in citrus fruit. The results showed that Pichia sp. and Golpar extract are effective for controlling the disease.

Predatory damsel bug, Nabis pseudoferus Remane has a high density in the alfalfa fields and feeds on different types of prey. In this study, biological properties and life table statistics of N. pseudoferus by feeding on melon aphids have been determined under controlled conditions (at 25±1˚C, 60±10% relative humidity and under a photoperiod of 16h light/ 8h dark). Data analysis carried out based on age-stage two sex life table program. The results indicated that the mean duration of eggs, 1st instar, 2nd instar, 3rd instar, 4th instar, 5th instar nymphs and adult longevity was 9.00±0.05, 2.89±0.02, 2.86±0.02, 3.10±0.03, 3.67±0.03, 5.87±0.05 and 19.47±0.52, days respectively. Life table statistics include r, R0, GRR, λ and T were estimated as 0.06±0.002 day-1, 16.39±1.99 eggs/individual, 59.58±6.16 eggs/individual, 1.07±0.002 day-1 and 43.97±0.31days, respectively. The death and birth rates for this predator by feeding on melon aphid were determined 0.02 and 0.08, respectively. With regard to predatory habit of most life stages of N. pseudoferus and longevity of adults, this predator could be considered as a potential candidate for reducing cotton aphid populations.

In order to indicate the effect of duck's presence, Anas platyrhynchos in paddy fields on rice (Oryza sativa L.) yield, yield components and its effect on weed density, an experiment was carried out in Baz Ghaleh Dezh village, located in Sangar, Guilan, Iran in 2013. This experiment was performed based on factorial split-plot analysis conducted in a randomized complete block design (RCBD). Each treatment was applied in three replications. In this experiment the main factor (duck) had two levels (in the presence of duck and in the absence of duck) and the minor factor was the factorial combination of weeding levels (weeding on the releasing day of ducks and not weeding on the releasing day of ducks) and also the planting spaces were 20×20, 25×25, 30×30 cm. The results of variance analysis of rice data showed that duck's presence on paddy field causes 17.28% filled grain per panicle, 6.19% one thousand grain weight, 11.13% harvest index (HI), and 9.5% grain yield. Also, the results of variance analysis of weeds data showed that duck's presence on paddy field can make a significant effect on number and biomass of weeds Echinochloa crus-galli, Scirpus maritimus, Paspalum distichum, and weeds density at harvest time. The results showed that duck's presence causes reduction of 38.93% of Echinochloa crus-galli, 58.29% of Scirpus maritimus, 47.48% of Paspalum distichum at the harvest time, 34.58% of biomass Echinochloa crus-galli, 40.88% of Scirpus maritimus biomass, 62.69% of Paspalum distichum biomass, and 53.77% of weeds at the harvest time in comparison with treatment by duck's absence on paddy fields.

The biological control ability of fluorescent Pseudomonas spp. results from competition for space and untrient, antibiosis and colonization in the rhizosphere. Biocontrol fluorescent pseudomonads produce a wide variety of antibiotics. In this study, the biocontrol ability of 39 strains of biocontrol Pseudomonas fluorescens, was examined against Fusarium graminearum the causal agent of wheat Fusarium Head Blight in vitro. Growth inhibition of F. graminearum was examined by a dual culture test and the antifungal activity of bacterial volatile and nonvolatile metabolites. In all experiments, four strains of Pseudomonas fluorescens P13, UTPf127, UTPf125 and UTPf105 were the most effective in controlling the pathogen. These strains were evaluated for screening the phlD and hcnAB genes and their ability to colonize ectorhizosphere of wheat under greenhouse conditions in 14, 28 and 42 days after planting. hcnAB gene was detected in all strains while phlD was detected in all bacteria except for P13. Wheat seeds were inoculated with the same concentration (108 cfu/ml) of each strains and sterile distilled water as a control and bacterial populations were enumerated on selective KB medium. The results showed that there are significant differences among strains in different days. Bacterial population colonizing the ectorhizosphere was decreased by the time. P13 and UTPf125 strains couldn’t be detected in 42nd day, on the other hand, they could be detected in 28th days more than 1.8×104 Cfu/g (fresh weight of root). UTPf127 population remained in ectorhizosphere at 1.1×104 CFU/g (fresh weight of root) in 48th day.

Biofilm formation in bacteria is an important survival strategy. Biofilm of probiotic Bacillus subtilis consist of long chains of cells that are covered by a polymeric matrix of exopolysaccharides. This bacterium is known as one of the most effective biocontrol agents against plant pathogens and has a high ability in biofilm formation. This study was aimed to investigate the effect of some environmental conditions including temperature, pH and osmotic pressure; nutritional elements such as sugars and amino acids secreted from wheat root and important soil elements like Ca2, Mn2, Mg2, Fe 2, Zn2, Mo6, Co2, B3 and Cu2 on biofilm formation of mentioned bacterium using polystyrene plate. Results of this study indicated that the most amount of biofilm in three studied strains produced at 30°C, pH 7 and the osmotic pressure using concentration of 75% sucrose. Cations of magnesium, calcium, zinc, iron, manganese and copper increased but cations of molybdenum, cobalt and boron decreased biofilm formation. All sugars and amino acids secreted from wheat root increased biofilm formation of studied strains. Among sugars, arabinose and glucose; and among amino acids, lysine and asparagine showed the greatest increasing effect on biofilm formation. According to our results, environmental conditions and the content of nutrient can influence on biofilm formation and consequently, the survival and establishment of probiotic bacteria in their environments, host colonization and biological control against plant pathogens.

Regarding the importance of Bacillus thuringiensisisolates in microbial control, we attempted to collect native isolates and study their virulence on diamondback moth, Plutella xylostella. More than 148 samples were collected from Guilan, Mazandaran, West Azarbaijan and Alborz Provinces. Experimental samples including soil samples from forest, fruit gardens, agricultural fields, diseased and dead larvae, were transferred to laboratory in sterile plastic containers. The soil samples, after sieving, were processed by acetate sodium selective method at two concentrations 0.25 and 0.35 M. Insect cadaver samples were surface sterilized and dissected and body contents were placed on Nutrient agar with sterile loop. Microscopic observations, Catalase test and Gram staining were carried out for all samples. For evaluating virulence of B. thuringiensis isolates, a cabbage leaf dip method with 106 cell/ml concentration of various Bt isolates was applied. Larval mortality was recorded 72 hours after treatment. According to the results, Bt isolates varied based on morphological characteristics. All isolates were Gram-positive and catalase positive. Spores and crystals were observed in 155 Bt isolates obtained from soil and insect host. In addition, this research introduced ten strains that are highly virulent to P. xylostella and would be valuable as the potential biocontrol agents for controlling lepidopteran pests.