BIOLOGICAL CONTROL OF PESTS AND PLANT DISEASES
Year:2021 | Volume:9 | Issue:2|Papers Count:8

Verticillium wilt disease caused by Verticillium dahliae is one of the most important diseases of tomato, for this reason, the control of this disease, including biological control is of serious interest. Endophytic fungi are one of the biological control agents that in addition to controlling plant diseases, improve growth in the host plant. In this study, the biocontrol potential of several isolates from plant endophytic fungi against tomato verticillium wilt was evaluated by dual culture methods in PDA, various laboratory and greenhouse test, respectively. Base on the results, three species of Nigrospora oryzae, Chaetomium globosum and Coniolariella limonispora selected from dual culture test, in addition to reducing the germination rate of microscelerotia of V. dahliae, they were able to produce cellulase and chitinase enzymes as well as the production of auxin. N. oryzae produced the highest amount of auxin with a production of 17. 625 mg/l. In greenhouse studies and under conditions of artificial contamination in potting soil, N. oryzae endophytic fungus caused the greatest reduction in the severity of symptoms of verticillium wilt (67. 61%) in tomato seedlings of sensitive Falat cultivar compared to the control. Comparison of the means of some growth indices showed that this fungus (N. oryzae) had a significant effect on increasing stem and root length, and fresh weight of the plant compared to other treatments. Nigrospora oryzae endophytic fungus was selected as the superior endophytic fungus in this study with the greatest effect on reducing the severity of V. dahliae disease and increasing stem and root length and fresh weight of the plant.

Wheat is one of the most important agricultural products in Iran, that plays an important role in ensuring food security. Crown and root rot disease by F. pseudograminearum is one of the most important pathogens that cause economic damages every year. In this study, 80 isolates of Bacillus were isolated from wheat rhizosphere. In dual-culture test, 3, 11, 22, 4 and 7 isolates with 60, 55, 37. 5, 22. 5 and 20% maximum ability, respectively. In effect test of volatile metabolites on inhibination the growth of F. pseudograminearum, 3, 7 and 11 with 54, 52 and 49% showed the highest percentage of inhibition of fungal growth. These isolates were also capable of nitrogen fixation, production of siderophore and extracellular enzymes involved in biological control (protease, lipase and chitinase), but none of the isolates were able to produce phosphatase enzyme. Greenhouse studies by treating wheat seeds with selected isolates showed that 3 was able to control crown and root rot of wheat by 80. 33% compared to the control treatment. Also, this isolate could increase the growth indices of wheat (stem length and root dry weight) in the presence and absence of pathogenic fungi. Therefore, this isolate, after further studies can be introduced as a superior isolate to control crown and root rot disease and promote wheat growth.

Plant growth-promoting rhizobacteria have great potential for increasing plant biomass and controlling plant diseases. Therefore PGPRs can be a good substitute for the use of pesticides and chemical fertilizers in agriculture. For evaluation of the effects of antagonistic activities of several PGPRs against Pseudomonas syringae pv. lachrymans the causal agent of cucumber angular leaf spot disease in laboratory and greenhouse conditions. Several bacteria isolated from different cucumber rhizosphere soil in Kerman province and a number of bacterial strains in the collection of Vali-e-Asr University of Rafsanjan were used. After in vitro screening, four isolates with the ability of growth inhibitory effect were selected for further studies in vitro and in planta. Antibacterial activity characteristics of biocontrol agents such as the production of secondary metabolites and some of their plant growth promoting traits were evaluated in vitro. During in planta study, the ability of bacterial strains to prevent the development of symptoms using the area under disease progress curve (AUDPC) and increasing the biomass of cucumber plants were evaluated. Greenhouse study showed that Pseudomonas fluorescens VRPF 54 strain has high biocontrol efficacy. During in planta study, this strain, both alone and in the interaction plant-pathogen in comparison with the control plant, significantly increased biomass and controlled cucumber leaf spot disease. After the selection of this strain, some of its antagonistic activities, biochemical properties and molecular identification were screened in vitro. Also, the assay of antioxidant enzyme activity such as peroxidase, guaiacol peroxidase, phenylalanine ammonia lyase, polyphenol oxidase and total phenol content were considerably increased.

Chickpea Fusarium yellowing and wilting disease, caused by Fusarium redolens (Fr) and Fusarium oxysporum f. sp. ciceris (Foc) is one of the most common diseases of this plant in Iran. In this study, the effect of bacterial and fungal probiotic strains received from different sources belonging to Alcaligenes, Bacillus, Delftia, Pseudomonas, Stenotrophomonas and Trichoderma genera was investigated on mycelial growth of the plant pathogens in the laboratory and chickpea growth and disease indices in the greenhouse. The volatile compounds of all probiotics prevented the growth of pathogens mycelium. In dual-culture test, all probiotics had an inhibitory effect on Foc growth, but only the effect of Bacillus pumilus INR7 and Trichoderma harzianum T33 on Fr growth inhibition was significant. In the greenhouse, Delftia tsuruhatensis PIIR and Alcaligenes faecalis 1624 were among the best treatments in reducing Fr disease indices and increasing growth factors. In contrast, T. harzianum T33 and Pseudomonas putida RUP1 were the best strains in decreasing disease indices and improving plant growth from Foc infected plants. Overall, the probiotics had the potential for promoting plant growth and biocontrol of these pathogens and after the necessary studies, can be recommended in integrated management of Fusarium disease of chickpeas.

Anastatus acherontiae is the native egg parasitoid of Streblote siva and Acherontia atropos in Bushehr, southern Iran. The life table parameters and demography of A. acherontiae was studied on S. siva based on the age-stage, two-sex life table under laboratory conditions (a light/temperature cycle of L16h/26° C, D8h/18° C and 65± 5% RH) using TWO SEX-MS Chart program. The mean and standard errors of the life table parameters were estimated using paired bootstrap method with 200, 000 iterations. Results showed that A. acherontiae was able to complete its development on S. siva eggs. The intrinsic rate of increase, the finite rate of increase, the mean generation time and the net reproductive rate of A. acherontiae on host eggs were 0. 059 day-1, 1. 06 times per day, 65. 48 days and 47. 72 offspring per generation, respectively.

Frost stress is one of the most important factors limiting the crop production, especially horticultural products and pistachio plant in Kerman region. Because of the economic value of pistachios, the frost management of this product is very necessary. One of the novel methods is the use of anti-ice nucleating bacteria on the surface of plants, including pistachios. Some of these epiphytic bacteria can produce antifreeze proteins that bind to water molecules in order to suppress crystal formation in the target sites. In this study, 100 epiphytic pistachio bacteria were assessed in anti-freeze activity, out of which, four isolates were effective both in vitro and wheat seedling bioassays. These were identified by biochemical and molecular tests. PCR primers 63f and 1387r were used for amplification of 16SrDNA genes sequencing. Sequences were then compared with other isolates in NCBI GenBank using blast methods. With 99% sequence similarity, the bacteria were identified as Serratia sp, Pseudomonas sp., Erwinia iniecta and Escherichia fergusonii. Sequences recorded at GenBank under the accession numbers MH704448, MH704263, MH703583 and MH703535 respectively. Obviously this study could open up a new horizon in the management of frost damage of agricultural products.

The fungi related to the genus Trichoderma are of important biological control agents that although their direct and indirect effects on insect and mite pests have vastly been studied but less is known about their interactions with host plant and its effects on the predators. Here, we used Tetranychusurticae infested been plant as host, treated with T. harzianum Tr6, in order to investigate bahavioural characteristics of the predatory mite, Phytoseiulus persimilisi. e. the predation, oviposition and establishment rate. Besides, the olfactory response of the predator was studied. Using the paired patches, treated and untreated with Trichoderma, we recorded a higher predation rate of P. persimilis. Conducting the oviposition experiment performed with same-aged bean potted plants, with adhesive banned stems, we recorded no significant difference in the predator oviposition rates between the plants treated and untreated with fungi. In the establishment experiment, performed with connecting the leaf patches with a plastic bridge, the number of predator presence time on fungi treated patches was significantly more than that on control ones. The olfactory experiments were performed considering three starvation status, no starvation, three hours and six hours and two states of T. urticae infestation period (two and four days) and five minutes critical time. None of the treatments showed predator attraction towards plants treated with fungi. The significant increase in the establishment and predation rates on patches treated with fungi is due to the quantitative or qualitative promotion of herbivore induced plant volatiles that needs further investigations regarding the results related to olfactory and oviposition tests.

The present study aimed to investigate root colonization percent and spore population of Arbuscular mycorrhizal fungi (AMF) in soils of 9 regions of Rafsanjan city. Also, the effect of climate and some physical and chemical properties of soil including pH, EC, organic carbon, amount of absorbed P and B soil and amount of silt, sand and clay on these two factors were evaluated. Samples were collected from the rhizosphere of different plants and AMF spores were isolated from the soil samples using the wet sieve method. After root staining and spore extraction of spores from the soil, root colonization and spore population were determined. As a result, all samples have arbuscular mycorrhizal symbiosis. The average root colonization percent ranged from 17. 7% in Western suburbs ( sandy loam soil, PH: 8. 72, Ec: 8. 82 and organic carbon %0. 13) to 83. 3 % in Raviz (sandy loam soil, PH: 8. 39, Ec 1. 44 and OC 3. 99%). The average spore population per 10 gr of soil samples ranged from 5. 68 in Western suburbs to 139. 2 in Davaran. There was a significant and positive correlation between the spore population and root colonization percent (α = 0. 01). There was a significant and positive correlation between the percent of sand and organic carbon with spore population and root colonization percent (α = 0. 01). correlation of measured indices with pH, EC, P, B, silt and clay showed significant and negative correlation(α = 0. 01). furthermore, the results showed that the root colonization percent and spore population in each region is related to the host plant and climate as well.