الفهرس 
Chemical fungicidesOnly 14 pages are availabe for public view
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Abstract
Rhizoctonia solani is a soil borne fungal pathogen that causes major economic losses by inducing root rot symptoms in many crop plants. This fungus induces root rot disease of Phasoelus vulgaris. Root rot is now widespread where it could be detected in most bean growing area. Moreover, Phaseolus vulgaris yield losses caused by root rot occurs regularly and intensively.
Fungal disease can be controlled by synthetic fungicides. Fungicide flutolanil used to control root rot disease. However, the development of fungicide resistance by pathogens and increasing environmental concern over fungicidal residue in fruits and vegetables has stimulated a search for alternative measures for disease control.
Recently, many reports have shown that induced disease resistance in plants by biotic and abiotic elicitors is very effective method for restricting spread of fungal infection.
Thus, the objective of the present work was carried out to control root rot disease and study the possible action of the chemical fungicide (flutolanil), biocontrol agents (biozaid and mycorrizal fungi AM) and chemical inducers (jasmonic acid JA and benzothiadiazole BTH) in the induced defence mechanisms in Phaseolus vulgaris plants against Rhizoctonia root rot disease.
The results obtained are summarized as follow:
• The pathogenic fungus, Rizoctonia solani appeared root rot symptoms in bean plants after 15 days. Treatments with fungicide flutolanil, bioagents (biozaid & AM fungi) or chemical elicitors (BTH & JA) alleviated the effect of R. solani by reducing root rot disease of bean plants under the same conditions as compared with infected control.
• Growth parameters (Plant height, fresh and dry weights) in bean plants significantly decreased in infected plants by pathogen fungi R. solani and increased with increasing time of infection. Treatments of fungicide flutolanil, bioagents (biozaid, AM fungi) or chemical elicitors (BTH, JA) increased growth parameters. Bioagents-treated plants were more effective in increasing growth parameters.
• Yield parameters (mean number of pods/ plant, fresh and dry weights of seed/pod) were significantly reduced in response to the infection by R. solani as compared with non-infected control. Application of flutolanil, bioagents or chemical inducers markedly increased yield parameters as compared with infected control. The highest response was recorded in AM and BTH-treated bean plants. However, treatment with JA showed the lowest response, compared with other treatments.
• Photosynthetic pigments (chl. a, chl. b, carotenoids and total pigments) were significantly decreased in leaves of bean plants in response to R. solani. Treatments of flutolanil, bioagents or chemical inducers markedly increased chl. a, chl. b, carotenoids and total pigments in leaves of infected plants at 14, 28 old days comparing with infected control. Plants treated with AM had the highest value in photosynthetic pigments as compared with biozaid. However, the most registered higher value was obtained when BTH was used.
• The infection with R. solani markedly decreased some elements (N, P, Ca, Zn and Mn) contents and increased K content in roots of bean plants at two stages of growth as compared with healthy control. Treatments with fungicide, bioagents or chemical inducers markedly increased element contents. The most nutrient contents increased by chemical inducers treatments compared with bioagents treatments.
• Total soluble sugars (TSS) significantly decreased in roots and shoots of bean plants infected with R. solani at 14 days old but increased in roots and shoots of 28 days after sowing as compared with control. Total soluble sugars markedly increased in both roots and shoots at 14 and 28 days of treated with flutolanil, bioagents or chemical inducers.
• Total soluble proteins (TSP) significantly decreased in roots and shoots of 14 and 28 days old bean plants infected with R. solani as compared with non-infected control. TSP significantly increased in roots and shoots treated with fungicide, bioagents or chemical inducers comparing with infected control.
• Reactive oxygen species (ROS) (superoxide anion O2.- and H2O2) significantly increased in both roots and shoots of 14 and 28 days old of bean plants in response to pathogen infection by R. solani. Application of chemical fungicide, bioagents and chemical inducers significantly decreased production of O2.- and levels of H2O2 in both roots and shoots of R. solani infected bean plants. JA-treated plants showed the lowest O2.- in roots at two stages and in shoots at 28 days old. The highest level of O2.- was recorded in AM-treated bean shoots.
• R. solani infected bean plants caused highly increased in lipid peroxidation (MDA) and lipoxygenase activity (LOX) in both roots and shoots of 14 and 28 days old of compared with healthy control. Level of MDA significantly decreased in response to fungicide, bioagents or chemical inducers treatments compared with infected control. These treatments highly increased LOX activity in infected bean plants compared with infected or non-infected control. AM-treated plants had the lowest content of MDA in roots and shoots of bean plants, but the highest MDA content was found in BTH-treated plants. AM fungi was more effective than biozaid for increasing LOX activity in infected bean plants. The highest LOX activity was found in BTH-treated plants in shoots at 28 old days.
• Activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) increased in roots and shoots of 14, 28 days old bean plants infected by R. solani as compared with non-infected control. Application with flutolanil and both bioagents (biozaid or AM fungi) decreased activity of SOD comparing with R. solani infected plant. BTH and JA were more effective for inducing SOD activity in infected bean tissues, but the best result was noticed in JA-treated plants. Three different treatments significantly decreased CAT, and GR activities in roots and shoots of infected bean plants comparing with infected plants. The highest activity of CAT was foundin roots of flutolanil-treated plants and in shoots of AM-treated plants at 14 and 28 days old. Hormonal inducer JA significantly increased activity of GR in roots and markedly decreased in shoots of bean plants. Treatments with flutolanil decreased activity of APX in roots and shoots compared with infected bean plants. bioagents and chemical inducers markedly increased APX activity at 14, 28 days old in roots and shoots.
• Plants infected with R. solani significantly induced accumulation of phenolic compounds in roots and shoots of 14 and 28 days old as compared with healthy control. Application of flutolanil increased phenolic compound in roots but decreased in shoots as compared with infected plants. Unlike the trend of flutolanil, total phenolics highly increased in shoots and decreased in roots of biozaid and AM-treated plants. Application of BTH, JA inducers highly significant increased total phenolics in roots and shoots of infected bean plants compared to R. solani.
• Activities of lignifications enzyme (Peroxidase POX, polyphenol oxidase PPX and phenylalanine ammonia lyase PAL) significantly increased in both tissues of bean plants in response to R. solani comparing with non-infecte. Flutolanil treated plant decreased activity of peroxidase in roots and shoots as compared with infected control. Bioagents and chemicals inducers were significantly POX activity in roots of bean plant as compared with infected or non-infected plants. Treatments with bioagents and chemical inducers induced activity of PAL in roots and shoots comparing with infected plants.
• Total flavonoid significantly increased in roots but decreased in shoots of 14 and 28 days old of bean plant infected by pathogenic R. solani treated or non-treated with flutolanil, bioagents (biozaid and AM fungi) and chemical inducers (BTH, JA).
• Content of anthraqueinon (AQ) in roots and shoots of R. solani infected bean plants at two stages of growth significantly increased as compared with healthy control. Plants treated with flutolanil, the content of AQ, slightly decreased in roots at 14 and 28 days old and significantly decreaed in shoots as compared with infected plants. Application of bioagents and chemical elicitros recorded markedly increased AQ content in roots of bean plants but decreased in shoots at 14, 28 days old as compared with infected plants.
• Activity of β-1,3 glucanase significantly increased in roots but slightly decreased in shoots of bean plants infected with R. solani as compared with healthy control. Application of flutolanil, bioagents and chemical inducers highly increased activity of β-1,3 glucanase in both tissues of infected bean plants comparing with infected or healthy plants.
• Pathogenic fungi R. solani, bioagents (biozaid and AM fungi) and chemical inducers (BTH and JA) increased activity of chitinase in both roots and shoots of bean plants at different stages, compared with non-infected control.
• Changes in protein profile
- The relative molecular weights and the percentage of the polypeptide bands are 4 polypeptide bands of molecular weights 122, 51, 36 and 29 KDa appeared in shoot of healthy control and disappeared in other treated plants.
- The protein band of molecular mass 61 KDa detected only in roots of non infected bean plants.
- Shoots of infected plants with R. solani induced the appearance of novel proteins having (56, 35 KDa), 100 KDa appeared only in infected plants treated with flutolanil , 34 KDa appeared with bizaid treatment, 50 and 13 KDa were induced in AM treatments. Chemical inducers, BTH induced protein band of M.wt 57 KDa, 120 and 62 KDa were induced in response by JA.
- Inoculation with R. solani induced the appearance of new proteins bands in roots having M.wt 62 KDa, protein bands having molecular weights 117 KDa (induced by fungicide flutolanil), 60, 81 KDa (induced by AM fungi) and 27, 50 KDa (induced by BTH). However, a set of four new protein bands having molecular mass (42, 44, 46, 47 and 49 KDa) were recorded in proteins extracted from roots of plants treated with JA.