نشریه مهار زیستی در گیاه پزشکی
سال هشتم شماره 2 (پاییز و زمستان 1399)

Rice blast caused by Pyricularia oryzae is the most important disease of rice worldwide. Although application of chemical pesticides can control the disease, but they cause harmful effects on environment and human health. The objective of the current study was to isolate and identify the fungal endophytes of rice as the effective and safe alternatives to chemical fungicides for controlling rice blast disease. Fungal endophytes obtained from leaf, stem, sheath and root samples of rice plants in paddy fields of Mazandaran and Guilan provinces. The antagonistic activities of the fungal endophytes was evaluated in dual culture test in vitro and the most effective strains were selected accordingly for greenhouse experiments. Rice seedlings were treated with the fungal endophytes and p < /em>. oryzae P274 isolate. Disease severity and growth parameters were measured. The lowest blast severity were recorded for Fusarium sp. NR–L645 strain and Microdochium bolleyi NR–L182 strain as 91.67% disease control. In addition, these two fungal endophytes significantly promoted the growth parameters of rice seedlings compared to the control. According to the results of this study, fungal endophytes of rice could be applied as the potential biocontrol agents of rice blast disease and plant growth promoters, but more research is needed for developing them in the future.

The rice blast disease caused by Pyricularia oryzae is one of the most important fungal diseases in Iran and worldwide. From 150 samples of healthy and infected rice seedlings, leaves and spikes collected from paddy fields of Guilan province, 68 fungal isolates were obtained. Eleven isolates identified based on morphological and molecular methods that were not able to cause disease on rice in pathogenicity test including Ulocladium alternariae, Ulocladium cf. alternariae, Ulocladium cf. consortiale, Ulocladium sp., Curvularia pallescens, Preussia sp., Trichoderma harzianum, Trichoderma virens, Trichoderma viride, Alternaria citriand Epicoccum sp. were selected for rice blast disease biocontrol studies. In the laboratory, we useddual culture, culture filtrate, slide culture and volatile metabolites methods and based on results, T. harzianum, T. virens, T. viride, A. citri and U. cf. consortialeisolates had highest percentage of mycelial growth inhibition of P. oryzae. These fungal isolates were inoculated in a four–leaf stage on rice plant of Hashemi cultivar under greenhouse conditions. All inoculated fungi except U. cf. alternariae, reduced leaf blast disease rating, among them T. harzianum with 27.36% reduction in disease rating was the most effective antagonist in greenhouse studies followed by T. virens, T. viride and A. citri. Comparison of data average in least significant difference (LSD) method showed that there was significant difference betweenbiocontrol fungi (T. harzianum, U. cf. alternariae and Preussia sp.)in terms of efficiency in rice blast control. Also, there was a statistically significant difference between the fungi in terms of effect on height, fresh weight and dry weight of rice plants in the greenhouse andamong these fungi, T. harzianum showed the highest efficiency in improving these traits.The results of the present study showed that there are different fungi in microflora of rice plants which are considered as potential biological control of rice blast disease.

Beneficial bacteria protect the plants against pathogens in various strategies. Some of these strategies are included the production of secondary metabolites such as antibiotics, volatile organic compounds and siderophores, plant resistance induction and promoting the plant growth parameters. In recent years, biofilm production has been considered as one of the important features in the survival of plant beneficial bacteria. A biofilm is a community of one or more bacterial species surrounded by polymeric materials. In addition to bacteria, fungi, algae and protozoa may be found in the biofilm. Living in biofilms has many benefits for antagonistic bacteria. Biofilm protects bacteria against adverse nutritional conditions, shortage of available oxygen, high osmotic pressure, sudden changes in temperature and pH, drought stress and antimicrobial compounds such as antibiotics and chlorine compounds. In addition to enhancing the production of effective secondary metabolites in disease biocontrol in biofilm, its matrix provides complete protection of these compounds. Concerning the importance of forming complete and three–dimensional biofilms by beneficial bacteria, and its positive effects on increasing their biocontrol capability, it is suggested that this feature be considered in the screening of beneficial bacteria to select effective strains in biocontrol of plant diseases and their use in commercial production.

Blast is one of the most important and destructive rice diseases in the world. Nanoparticles are antimicrobial agents used as biological and non–biological stimulants and can induce resistance in plant against pathogens. Effects of different biological and non–biological nanoparticles on inhibition of various plant fungal pathogens has been proved. However, no study has been done about the effect of biological nanoparticles on control of this disease through induction of resistance and expression of defense genes. In this study, in addition to direct effect of biological silver nanoparticles synthesized using Trichoderma harzianum fungus in vitro, its indirect effect was investigated by inducing systemic resistance in susceptible local Tarom cultivar on pathogenic fungus Magnaporthe oryzae under greenhouse conditions. For this purpose, expression of several important defense genes investigated in biological silver nanoparticle–treated plants in comparison with control plant (without biological silver nanoparticle) using real–time qPCR technique at different times after pathogen inoculation. The results showed a positive effect of different concentrations of biological nanoparticles in reduction of pathogen growth in comparison with the control treatment so that the amount of inhibition of pathogen growth in different concentrations (36, 27, 18, 9, 4.5 ppm) was 92, 81, 56, 28 and 7 percent compared to the control treatment, respectively. Phenotypic study of rice plant interaction with the fungus causing blast disease in presence of biological nanoparticle showed that there was no significant difference between the disease severities in biological nanoparticle–treated plants compared to control plants. Also, accumulation of transcripts of NPR1, PR2, PR3 and LOX genes between two mentioned treatments did not show significant increase. Therefore, indirect effect of biological silver nanoparticle on pathogenic fungus by induced resistance and increasing the rice plant defense genes is not considerable.

The endoparasitic wasp, Aenasius bambawalei Hayat (Hym.: Encyrtidae), is one of the most effective parasitoids of cotton mealybug, Phenacoccus solenopsis Tinsley (Hem.: Pseudococcidae), in Iran. Since natural enemies alone are not able to keep the population of mealybug under economic injury level, the use of chemical insecticides is inevitable. In this study, the effects of sublethal concentrations of 0.5, 1 and 25 ppm of dimethoate, thiodicarb and imidacloprid were investigated on the life table parameters and survival of the parasitoid in laboratory conditions. The results showed that the fertility of the female parasitoids decreased in insecticidal treatments and the length of the total preoviposition period (TPOP) increased. However, the length of the adult preoviposition period (APOP) and the longevity of females did not change. Moreover, the intrinsic rate of increase (rm), the finite rate of increase (λ), and the net reproduction rate (R0) in dimethoate and thiodicarb treatments were significantly lower than control, but in imidacloprid treatment, the difference was not significant. According to these results, imidacloprid had less negative effects than the other two inecticides on the growth parameters and the life table of A. bambawalei.

Feeding Aculops lycopersici (tomato russet mite) on tomato leaves and stems change color to fawn color, plant dryness and fruits nars of infested plants. An investigation carried out with three botanical pesticides, i.e. GC–mite (1ml/l), Biomite (2 ml/l), Neem 1.8 EC (3ml/l) and 25% lower than – recommended doses in compared with 0.5ml/l dose of Bifenazate 24% SC, Cyflumetofen 20% SC, Spirodiclofen 24% SC, Spiromesifen 24% SC, 0.75 ml/l of Milbemectin 1% EC on tomato under field and greenhouse conditions in Tehran and Varamin, respectively. A completely randomized design and randomized complete block design used in greenhouse and the field with three replications. Water sprayed in control treatment. Effects of each treatment determined by random 30 tomato leaves collected at one day before and 3, 7 and 15 days after treatments. Active mite stages on lower surface of tomato leaf counted and collected data by Abbott and Henderson–tilton formulas in greenhouse and field converted to mortality percentage, respectively. Mean mite mortality percentage analysis showed a significant (p<0.05) for 3rd day interval only under greenhouse and minimum 94.70 % control received among treatments at 15th day of sampling. While least of mean of mite control among treatments after 15 days under field condition recorded 89%. Mite mortality percentage found significant (p<0.05) between 3rd and 15th days sampling time among treatments under field conditions. Higher effects of botanical recorded 92.39% for 0.75 ml/l GC–mite, Biomite (93.23, 97.22%), Neem (97.11, 95.15%) doses, respectively. Least of mite pest controlled recorded 80.98% by spirodiclofen among synthetic acaricidal under field conditions. This finding suggested that through application of botanical pesticides in rotation with other pesticides, tomato production and natural enemies almost remained safe under field conditions.

Crown gall is a very destructive plant disease caused by Agrobacterium radiobacter. The most important symptom of this disease is abnormal growth like tumors or galls at or below the soil surface on the crown of plants and sometimes the trunks of seedlings and trees, as well as reduced growth and weakness of infected plants. This disease is one of the most damaging bacterial diseases economically infected at least 40 species of plants, including fruit and non–fruit trees, crops and ornamental plants. Failure of chemicals in the management of this disease indicates special attention focused on the biological control of plant diseases as an alternative to chemical control. This article is a comprehensive summary of new discoveries and advances in our understanding of the application of biological control agents in the control of crown gall disease.

Whiteflies and thrips are important pests that active in cotton fields and in addition to direct damage, they alsoindirectly reduce quantity and quality of oilseeds. Orius niger (Wolff) (Hem.: Anthocoridae) is one of theoptimal biocontrol agents for thrips and whiteflies, which is abundant in oilseed fields, especially cotton fields ofGolestan province. In order to evaluate the predatory efficiency of O. niger, this insect was collected from cottonfields and grown in laboratory conditions. In experiments related to the study of predatory; for each predator(female), whitefly densities of 5, 10, 20, 30 and 40 nymphs, 5, 10, 20, 30 and 50 eggs and 5, 10, 20, 30 and 40thrips nymphs were placed in the Petri dish. The results of logistic regression showed that the functionalresponse model is type III for both egg and nymph stages of whitefly and type II for nymphs of thrips. For thripsnymphs, eggs and nymphs of whitefly, according to Roger's equation, calculated searching efficiency parameter(a′) was 0.0697, 0.01193 and 0.01072 /h, and handling time (Th) was 0.3802, 0.2686 and 4.1042 hours,respectively. Prey preference experiments were calculated using the Manley's formula. Manley index of thripslarvae (prey I) and whitefly eggs (prey II) were 0.92 and 0.08, respectively, and for thrips larvae (prey I) andwhitefly nymphs (prey II) were 0.85 and 0.15 which shows that this predator significantly prefers thrips larvae tothe other two preys. In general, the results showed that O. niger can be used as a favorable biological controlagent for thrips in cotton fields.

Plant growth–promoting rhizobacteria (PGPR) release polysaccharides extracellularly into the environment called exopolysaccharides in the form of capsules or slime, protecting them from biotic and abiotic stress conditions and enabling them to survive in the rhizosphere. Bacillus amyloliquefaciens is well known for producing wide spectrum of biopolymers and antimicrobial compounds.  On the other hand, take–all is one of the most important diseases of wheat caused by the fungus Gaeumannomyces graminis var. tritici. Biological control of this disease depends on the colonization of bacterial population in rhizosphere under stress conditions. In present study we targeted one of the most important genes in the production of exopolysaccharide polymer called eps E gene showed that bacterium has. The eps E gene expression analysis by Real Time PCR technique showed that bacteria in the treatment of culture medium prepared with sucrose and glucose compared with the control treatment had a 60–fold increase in eps E expression. The results of disease control showed that there was a significant difference in the disease incidence when seeds were treated with bacterium plus the maximum exopolysaccharide and bacterium with minimum exopolysaccharide, in comparison with a control treatment. The percentage disease inhibition recorded for the treatments of Baran cultivar 88 and 64% and Ouhadi cultivar 88 and 56% related to culture medium containing EPS with maximum amount and nutrient broth culture medium with minimum amount of EPS, respectively. The overall results of this study demonstrated that the B. amyloliquefaciens with high production of exopolysaccharide had a strong ability to control take–all disease in comparison with treatment of NB culture medium.

The Rosaceous long–horned beetle (Osphranteria coerulescens) attacks a range of fruit trees belonging to Rosaceae family. Starting from May to February 2012, samples of branches infected with O. coerulescens were collected from almond and apricot orchards in South Khorasan province of Iran and subsequently the fungal pathogens were isolated and identified. Based on the morphological characteristics of the isolated fungus, it was identified as Paecilomyces formosus and in the phylogenetic study the representative isolate was located in clade of P. formosus. In evaluating the efficiency of fungal arrays, the mean mortality rate of larvae at concentrations of 104, 105 and 106 spores per ml of was 44, 72 and 86, respectively. The LC50 for beetle larvae were calculated as 2×104 spores per ml. In the present study, isolation and pathogenicity of P. formosus on this insect is reported for the first time both in Iran and worldwide based on morphological and molecular data. Due to the high mortality rate of this fungal array on the larvae of the beetle pest, the potential of its application in the integrated pest control program can be considered.

Postharvest diseases cause a lot of damage to grapes and reduce the quality and marketability of the product. These infections are mainly caused by the fungal species Penicillium expansum and Botrytis cinerea, which are the most important pathogen of postharvest grape rot worldwide. Biological control has become important to control these postharvest diseases due to the recent global awareness of the side effects of chemical agents. In this study, the biocontrol ability of yeasts isolated from Urmia Lake basin against postharvest diseases of grapes has been investigated. We used 11 yeasts belonged to Pichia guilliermondii species isolated from Urmia Lake basin. The results of inhibitory activity of 11 P. guilliermondii isolates against two postharvest pathogens of grape, P. expansum and B. cinerea, showed that three yeast isolates can considerably inhibit both fungi in dual culture method on PDA medium. Three promising isolates were selected to reduce postharvest decays of grape at the storage period.  The results exhibited that three yeast isolates could significantly reduce grape decays. The yeast isolate 8 by reducing 82.3% of grape decays, showed the strongest activity against P. expansum. The yeast isolate 10 was found the most effective isolate to suppress B. cinerea decay on grape by 78.5%.

Microbial biopesticides because of their less environmental impact ensure the management of agro–ecosystems. Among the microbial biopesticides, baculoviruses have been interested. Because of the low stability of baculoviruses against sunlight, preparation of UV protectant formulations is being focused in this study. Accordingly, the ultraviolet protective effect of some natural and chemical additives (green tea, black tea, coffee, cocoa, Tween 80, sodium lignin sulfonate and titanium dioxide) at two concentration levels (0.5% and 3% w/v) for the Helicoverpa armigera nucleopolyhedrovirus was evaluated. The investigation was expanded to include three natural polymers (sodium alginate, gelatin, starch) which have recently been used for microencapsulation of biopesticides. Results are based on larval insecticide bioassays to test original activity remaining (OAR). The results showed that titanium dioxide (3% w/v) had no protective effect after 8 hours exposure to UVA (26.66± 3.33). After 48 hours exposure, although titanium dioxide (3% w/v) provided a very little protection against UVA radiation (30.00± 6.35), it still remained the less effective additive. Unlike some reports, titanium dioxide did not provide adequate protection against UVA radiation in our study. In addition, it reduced the activity of occlusion bodies (OBs) in the absence of UV rays. After eight hours exposure to UVA radiation, sodium alginate (3% w/v) was an excellent UVA protectant (93.33± 3.33), whereas the mentioned polymer provided inadequate protection, 48 hours post UVA radiation (50.00± 3.46). The other applied polymers provided medium protection against UVA radiation. After 48 hours, the concentrations of 3% w/v of green tea and coffee provided significant UV protection on stability of Helicoverpa armigera nucleopolyhedrovirus activity at 80.00± 1.54 and 83.33± 3.33, respectively. Lignin at both concentration levels was a proper UV protectant after 48 hours (83.33± 6.66).