INCIDENCE AND SURVIVAL OF RHIZOBIOPHAGES IN BACTERIAL CARRIERS AND LIQUID CULTURE MEDIA UNDER STRESS CONDITIONS AS WELL AS RESPONSE OF SOME LEGUMES TO INO-CULATION WITH RHIZOBIAL PHAGE-RESISTANT ISOLATES

Document Type : Original Article

Authors

1 Department of Microbiology, Faculty of Agriculture, Cairo University, Giza

2 Agricultural Microbiology Research Department, Soil, Water and Environment Research Institute, Agricultural Research Center, Giza, Egypt

Abstract

Occurrence of rhizobia phages in some rhizobial carriers were investigated. The effects of stress conditions in liquid cultures e.g. heat shock, pH and UV irradiation on the survival of rhizobiophages was examined. The response of four leguminous plants to inoculation with phage-resistant rhizobial isolates and their homologous strains was also evaluated. The phages were detected and isolated from both fine peat and Irish peat carriers but not from vermiculite after enrichment with YEM broth medium. Tho number of phages ranged be-tween 9 to 18 and 12 to 25 PFU g carrier-1 for both fine peat and Irish peat, respectively. When the three carriers were inoculated with rhizobial strains, the Irish peat showed higher values of phage plaques as compared to fine peat. while the vermiculite carrier exhibited no plaques.The numbers ranged from 1.8x102 to 4.6x102 and 1.6x102 to 2.8x102 PFU g carrier.' for Irish peat and fine peat, respectively. The isolated phages specific for rhizobial strains showed no lysis for phage-resistant rhizobial isolates. R.leguminosarum by. Wok iso-lates (ARC102 and TAL112) and R.leguminosarum by. viceae isolates (ARC 207Fand ICARDA 441) did not differ in appearance and showed no variations in their colony morphology as compared to their parent strains, while the others were different All tested phages were highly sensitive to high temperatures. When phages J and M were incubated at 60°C for 15 min only 40% of their population survived while it was only 10% for phage T and V.The phages were rap-idly affected by increasing time of irradiation. The phage activity decreased gradually when the phew was exposed for 30 min but it was completely lost after 35 min. All phages survived very well at pH 4 -10, however, at pH a or 11 the phages did not survive at all. Inoculation of soybean, alfalfa, berseem clover and faba bean with their susceptible strains (parents) enhanced nodulation, bio-mass and N-content yields. In contrast. inoculation of the four legumes with their corresponding phage-resistant isolates reduced the values of all plant per-meters measured. Moreover, soybean and fan bean plants inoculated with their phage-resistant isolate tailed to form any nodules on the root system of the growing plants, which indicated loosing its infectivity character. These data suggest that rhizobial carriers should be tested for rhizobiophage infection be-fore using, employing the detrimental factors to minimize rhizobiophage effect and selecting for superior and effective phage-resistant rhizobial strains for in-oculation to maximize legumes productivity specially for bioagriculture farms.

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