V.K. Chebotar1, U.G. Kang2, H.M. Park2, N.M. Makarova1, T.A. Popova1, S. Akao3
1 All-Russia Research Institute for Agricultural Microbiology, Shosse Podbelskogo 3, St. Petersburg - Pushkin 8, 196609, Russia
2National Yeongnam Agricultural Experiment Station, P.O. Box 6, Milyang 627-130, Korea
3National Institute of Agrobiological Resources, Tsukuba, Ibaraki, 305, Japan
Concern about possible health and environmental consequences of using increasing amounts of mineral fertilizers and chemical pesticides have led to strong interest in alternative strategies to ensure competitive yields and protection of crops. This new approach to farming, often referred as sustainable agriculture, seeks to introduce agricultural practices that are more friendly to the environment and that maintain the long-term ecological balance of the soil ecosystem. The main objective of our study was to isolate strains with high root colonization activity possessing beneficial properties: biological nitrogen fixation, biocontrol activity and plant growth promotion. An original method for isolation of rhizobacteria inhabiting roots of rice grown in South Korea and Russia has been used. Among 256 isolated strains, 8 promising strains with high root colonization activity possessing beneficial properties (biological nitrogen fixation, biocontrol activity and plant growth promotion) were selected. These strains showed high motility and enzyme activity compared with other tested isolates. Acetylene reduction activity in pure cultures showed that tested strains demonstrated higher activity than reference strain of Herbaspirillum seropedicae BR11175 after 24 and 48 hours of incubation. Promising isolates demonstrated strong plant growth stimulation as was shown by two methods. It is interesting to note that in cell suspension at 1:1 dilution inhibition of growth of maize seedling roots was observed while a dilution 1:50 showed significant stimulation. Tested strains produce growth-promotion substances as was shown by HPLC analysis (data not shown). KR076 and KR083 strains, but not Herbaspirillum seropedicae showed very high biocontrol activity against major phytopathogens Fusarium culmorum, Fusarium solani, Pythium spp., Phytophtora capsici, Rhizoctonia solani in plate tests. Colonization of the plant roots by soil-borne or introduced bacteria is a very important step in the establishment of effective plant-bacteria interactions. Success in introduction of beneficial bacteria to the plant seeds or seedlings usually depends on the colonization potential of introduced strains. We studied colonization of rice roots cv. Keumobyeo by promising isolates in competition with reference gus-marked strain Pseudomonas fluorescens WCS365 known as active root colonizer. Some tested strains demonstrated high colonization ability. Pot experiments with promising isolates showed that only strain KR181 has increased yield of rice by 26.5% comparing with uninoculated control. The effect of this strain on number of panicles per hill, chlorophyll content and rice yield was the same as in variant with NPK 100%. Other tested strains did not show any positive effect on growth parameters of rice even though they demonstrated some beneficial properties. However the pot experiments with lettuce and radish have shown high efficiency of KR076 and KR083 strains. Seed inoculation of barley and sorghum in field tests with strain KR076 has been increased yield by 11% and 99% respectively. So, it is not clear what mode of action is responsible for success of inoculation and further pot and field experiments with rice and other crops should be done.
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