الفهرس 
Soil-borne pathogensOnly 14 pages are availabe for public view
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Abstract
Legumes are subjected to the attack of several soil-borne pathogenic fungi. Chemical control of those pathogens using fungicides poses risks to the environment and human health, and drastically affects the symbiotic N7-- fixation between rhizobia and le,o;umes. Therefore, the present study was conducted to exploit the nature’s biological potency to reach effective biocontrol against soil-borne pathogenic fungi of le,oumes with no toxic residues and in the same time biologically compatible to rhizobia. Isolation trials carried out on diseased soybean and pea plants collected from different locations in Egypt, as well as the pathogenicity and identification tests revealed, that Sclel-otizrm rolfsii, Fztsai-iztrn solani, and Marcrophomina phaseolina are the major soil borne pathogenic fungi of soybean, whereas those of pea were Rhizoctonia solani, Pythiuin debaryanum and Fzmarizrm oxyspomm f. sp. pici. These pathogens are implicated in damping-off, root rotting and wilting of soybean and pea. The preliminary screening of several hundreds samples from the rhizosphere-soil of healthy legumes resulted in the isolation of 72 bacterial and 5 fungal isolates exhibiting marked antifungal activity against the tested pathogens. The predominant antifungal bacterial isolates were belonging to Bacilli, Pseudomonads and Actinotnycetes, whereas the Fungal isolates were belonging to Trichoderma. These antifungal isolates obtained in the preliminary screening were s~~bjectetod standardized test to select those having the highest efficiency against the pathogenic fungi under investigation. Results indicated that the bacterial isolates B 10 and Ps4 as well as the fungal isolate TG were the most efijcient antifungal agents against the tested pathogens. They were identified as Bacillrrs subtilis (B 1 O), Pseudon2onm sp. (Ps4) and Trichoderrna harrianzrm (T6). The antifungal isolates B 10, Ps4 and T6, which proved in viti-o to be most efficient against the pathogenic fungi, were tested in vivo. Results of pot experiments confirmed the efficiency of these antifungal isolates. Highly significant levels of protection of soybean and pea plants against each of pathogens were achieved by soil application of B 10 (I 08cfu/g of soil), Ps4 (108cfu/g of soil) or T6 (2% of soil weight) at the time of planting. Levels of protection achieved were comparable to those obtained by the recommended dose of benlate. However the effect of BlO and Ps4 and T6 was less pronounced in soil infested with mixtures of pathogens. Results of esperiments carried out in vitvo and in vivo to test the biological compatibility of the antifungal isolates BIO, Ps4 and T6 indicated that the growth and symbiotic nitrogen fixing ability of Bradyrhizobizim japonicziln with soybean or Rhizobiz~nz le,aminosanm biovar viceae with pea were not negatively affected. Nodulation and accumulation of nitrogen in plants were not significantly different from those of control treatments inoculated with Rhizobia alone. Results also revealed that application of Benlate at the recommended dose reduced the N7-- fixation parameters to levels not significantly different from those of plants not inoculated with Rhizobia. It practically deprives legumes from any beneficial effect of Jdxzobial inoculation. Results of experiments conducted to evaluate the performance of the antifungal isolates B 10, Ps4 and T6 in the presence of both the pathogen(s) and I-hizobia reconfirmed their efficiency as biocontrol agents against soilborne fungal pathogens of leagums. Soil application of B 1 0 (1 08cfdg of soil), Ps4 (108cfdg of soil) or T6 (2% of soil weight) at the time of planting in soil infested with fungal pathogen(s) and inoculated with rhizobia achieved significantly high levels of protection against each of the tested pathogens, and permitted meanwhile reasonable N2-fisation. Levels of protection achieved were not significantly different form those obtained by recommended dose of Benlate. Total N of soybean and pea plants recorded 90 days after planting was two to five times larger than that of un-protected plants and one to two times larger than that of plant protected by Benlate.