BIO CONTROL IN PLANT PROTECTION
Year:2018 | Volume:6 | Issue:1 (11) |Papers Count:8

Aspergillus flavus grows on a wide range of agricultural and food products and causes contamination with aflatoxin. One of the suitable methods for controlling aflatoxin is the use of biological agents, which is possible by the application of effective bacterial antagonists. The objectives of the present study were to isolate and characterize a superior biocontrol agent against the above-mentioned fungus on pistachio, to develop an industrial culture medium and to optimize its growth conditions for enhancing maximum biomass production for Bacillus amyloliquefaciens UTB96. According to the results, this strain was capable of significant growth inhibition of A. flavus and reducing aflatoxin concentration in the pistachio up to 98. 38%. Moreover, its VOCs showed growth inhibition as well. The most effective environmental factors were screened using the Bremenplacket design, in terms of their effects on the biomass production of the antagonistic bacterium and optimizing the production of bacterial biomass in culture medium designed using the screened factors. The results showed that sugarcane molasses and corn steep could be used as the industrial sources of carbon (C) and nitrogen (N) in production at 10 and 2 g/l respectively. Optimum conditions for maximum production of biomass in this culture medium included pH=7, 30° C and C/N ratio 1: 23. Using the optimized culture medium and conditions in a semi-industrial method, the amount of biomass was reached up to 0. 17 g/l, and the antagonistic effects increased by 8%. Bacillus species used in this work shows some similarities with B. velezensis that needs to be validated by further molecular analysis.

Trichoderma spp. can reduce the severity of the disease caused by plant parasitic nematodes by parasitizing the eggs and juveniles and induction of plant resistance responses. The effects of solid nutrient substrates (millet, grain and wheat bran) on the sporulation of Trichoderma harzianum Tr6, chitinase enzyme production and the ability to control of Meloidogyne javanica were studied. Results showed that the substrates had different effect on sporulation of the fungi and also control of the target nematodeand that the best substrate was wheat bran. Using this substrate, spore production of T. harzianum a rate of about 1. 5×1011 per gram of medium. Furthermore, a great control of the second stage juveniles was observed with 87. 66% of mortality of the second stage juveniles and reduction of 13. 66% eggs hatching by. Chitinase enzyme assay showed that Trichoderma cultured on wheat bran exhibited a U / min per ml enzyme enzyme production. In addition, the antagonistic fungi that is cultured on wheat bran showed a major effect on control of nematode in comparison with other solid substrates and the Gall index in this treatment was 0. 6.

Cucumber is one of the most important crop in Iran. Pests and pathogens are the most important factors limiting its cultivation and lead to reduced yields. Biological control is condiderd as the best control method for soil-borne disease including Fusarium stem and root rot. In this study, antagonistic effects of Pseudomonas fluorescens strains on the important root rot pathogens of cucumber with dual culture method was examined in vitro. Strain VUPf760 showed the highest inhibition zone against Fusarium oxysporium and Fusarium solani with 9 and 7 mm, respectively. Inhibitory effects of these isolates on the disease was evaluated in the greenhouse. The results showed that seeds treatment with T17-4 and VUPf5 isolates reduced the severity of disease caused by F. oxysporum and F. solani by 58 and 60%, respectively. In addition, all three isolates alone increased peroxidase activity, total phenols and polyphenol oxidase in cucumber seedlings. However, the activity of these enzymes were higher in treatments with combination of antagonist and pathogen.

Fusarium root rot of common beans is an important economic disease in Iran. It is broadly suggested that farmers use ecofriendly methods of plant disease management, compatible with the sustainable agriculture to minimize the application of pesticides in the fields. The current study was conducted to investigate the effectiveness of native rhizobium, mycorrhiza and chemical treatment. The experiment was carried out in a randomized complete block design in a field experiment at Sarab Changaie Research Station in 2017 with Ofogh red-bean cultivar. The trial treatments exerted as follow, superior native rhizobium isolate Rhizobium etli b. v. phaseoli (CCSM_B011401)(R), Rhizophagus irregularis(M2), Rhizophagus irregularis + Funneliformis mosseae (M1+M2), R. irregularis + F. mosseae + R. etli b. v. phaseoli (R+M1+M2), R. irregularis + R. etli b. v. phaseoli (R+M2), fungicide treatment and control. Rhizobium powder was applied as seed treatment and mycorrhiza was added directly in seedbed during the sowing of seeds. The best result was achieved from coinoculation of arbuscular mycorrhiza fungi and indigenous rhizobium, which showed a significant increase of the number of seeds per pod, 100 seeds weight, grain yield and biomass yield as 34, 24. 9, 51. 6 and 38 percent compared to control. In addition, the co-inoculation treatment reduced the incidence of bean root rot disease up to 89%. Results indicated that the synergism of indigenous rhizobia and arbuscular mycorrhiza could be useful for managing of common bean root rot disease, reducing the use of pesticides and producing the crop in a sustainable and optimized manner.

Induced resistance is one of the ways by which plants cope with the biotic stress. Phenylalanine ammonialyase (PAL) and lipoxygenase (LOX) as inducible defense enzymes, are synthesized by plant in response to biotic stress. This research was carried out with the aim of investigating the effect of Pseudomonas sp. isolates (antagonistic and inducer bacteria) and potassium silicate treatment on expression changes and production of enzymes at 0, 6, 12, 24, 48 and 72 hours after rice seedling contamination of Fajr cultivar to R. solani, the causal agent of rice sheath blight disease. Analysis of gene expression showed that the maximum expression was observed in 72 hours after plant inoculation, and the combination of antagonistic bacteria and potassium silicate as an inducer had the highest expression during the first 6 hours of infection. Analysis of enzyme content showed that the use of treatment compounds in the initial time interval of zero to 6 hours were caused a significant increase in protein content, which was more than the phenylalanine ammonia-lyase in the combination of the antagonistic bacteria and the potassium silicate as an inducing agent for the lipoxygenase enzyme. In general, by attacking the pathogens, the plant increases the amount of these enzymes due to the important role of these genes in defense against the pathogen. Increasing the expression level of these genes directly increases the activity of the enzymes which indicate direct role of these gens in plant defense system, that, it is possible to increase their expression by applying potassium silicate and antagonistic and inducer bacteria on the plant.

Phthorimaea operculella Zeller (PTM) is one of the most destructive pests of potato both in the field and store. The present study was conducted to assay lethal and deterrent activities of methanolic extracts of Maclura pomifera (Raf. ) Schnied, Cotinus coggygria Scop and Valeriana officinalis L. on different growth stages of P. operculella. The most effective extract was also investigated on parasitism rate of Trichogramma brassicae Bezdenko. The experiments were carried out under laboratory conditions at 26 ± 1 ° C, 65 ± 5 RH and a photoperiod of 8: 16 (L: D). V. officinalis exhibited the highest efficacy against eggs and neonate larval penetration of potato tuber moth, which elicited LC50 values equivalent to 262. 28 and 170. 74 ppm, respectively. The most repellent extract against neonate larval penetration was V. officinalis followed by C. coggygria and M. pomifera (% repellency= 92. 33, 90. 66 and 83. 33%, respectively). Oviposition preference trials after 24, 48 and 72 h demonstrated that the three methanolic extracts showed anti-ovipostional activity against PTM females and they preferred to oviposit their eggs on non-treated tubers. Additionally, there was no adverse effect of sub-lethal dose of V. officinalis on percent parasitism of T. brassicae (66. 66%).

In parasitoids, host recognition and host preference strongly affect offspring fitness. These behavioral features are important in biological control when using the banker plant method. The use of banker plants (Vicia faba infected by Aphis fabae) in the presence of Lysiphlebus fabarum (Braconidae: Aphidiinae) was investigated as a way to control Aphis gossypii on cucumber plants. Synchronous wasp cohorts were produced on A. fabae or A. gossypii, then the mated females emerging from each aphid species were individually released into a petri dish containing 15 A. fabae and 15 A. gossypii (second-instar), to determine the impact of the host species of the parents on the fitness of the emerging adult parasitoids. The female wasps parasitized a larger percentage of available A. gossypii than A. fabae, and in addition, the females reared on A. gossypii were significantly larger than females reared on A. fabae. The results revealed that reducing the preference of A. fabae as an alternative host by L. fabarum led to an increase in parasitism of the pest aphid A. gossypii.

The widespread use of chemicals and pesticides has always led to risks to the human health, animals, ecological changes and imbalances in environmental sustainability. During this study, sampling was followed by collecting samples of rhizosphere of Helianthemum ledifolium and desert truffle surrounding soils in Golestan province, selected 7 strains of gram-positive Lactobacillus and catalase-negative which was isolated and identified on PDA, NA and MRS medium. Biochemical tests showed some of the bacterial strains were able to grow in acidic condition from pH 3 to 8 and they were able to tolerate up to 8% salt. Strains were also able to grow at minimum 15  C and maximum 45  C and the fermentation of the sugars were tested by the carbohydrate fermentation test. Using the 16S rDNA gene sequence, different strains of R11, R12, R21, R22, R31, S11 and S12 were identified as L. plantarum. In agar well-diffusion test, the highest inhibitory level was significantly observed in Pseudomonas syringae and Staphylococcus aureus with a diameter of 11 mm by R31 and S11 isolated from H. ledifolium root and desert truffle soil, respectively. In antifungal activity, the maximum growth inhibitory for P. expansum and F. solani were 69. 37 and 66. 69 percent, respectively. Sporulation reduced in P. expansum in comparison to the control. The results based on SAS system and completely randomized design showed that lactic acid bacteria with plant and soil origin could inhibit the growth of pathogenic fungi and bacteria with high spectrum and can be used as safe biocontrol bacteria in post-harvest crop contamination.