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Variovorax sp. Has an Optimum Cell Density to Fully Function as a Plant Growth Promoter

United Graduate School of Agricultural Sciences, Iwate University, 18-8 Ueda-sanchome, Morioka, Iwate 020-8550, Japan
Department of Life and Food Science, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan
Institute of Food Science and Technology, College of Agriculture and Food Science, University of the Philippines Los Baños, Laguna 4031, Philippines
Department of Science and Technology Philippines-Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development, Los Baños, Laguna 4030, Philippines
Hokkaido Agricultural Research Center, National Agriculture and Food Research Organization, 9-4 Shinsei-minami, Memuro-cho, Kasai-gun, Hokkaido 082-0081, Japan
Author to whom correspondence should be addressed.
Microorganisms 2019, 7(3), 82;
Received: 18 February 2019 / Revised: 6 March 2019 / Accepted: 13 March 2019 / Published: 15 March 2019
(This article belongs to the Special Issue Plant Control of Symbiotic Microbe Behavior and Reproduction)
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Utilization of plant growth-promoting bacteria colonizing roots is environmentally friendly technology instead of using chemicals in agriculture, and understanding of the effects of their colonization modes in promoting plant growth is important for sustainable agriculture. We herein screened the six potential plant growth-promoting bacteria isolated from Beta vulgaris L. (Rhizobium sp. HRRK 005, Polaromonas sp. HRRK 103, Variovorax sp. HRRK 170, Mesorhizobium sp. HRRK 190, Streptomyces sp. HRTK 192, and Novosphingobium sp. HRRK 193) using a series of biochemical tests. Among all strains screened, HRRK 170 had the highest potential for plant growth promotion, given its ability to produce plant growth substances and enzymes such as siderophores and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, respectively, concomitantly with active growth in a wider range of temperatures (10–30 °C) and pH (5.0–10.0). HRRK 170 colonized either as spots or widely on the root surface of all vegetable seedlings tested, but significant growth promotion occurred only in two vegetables (Chinese cabbage and green pepper) within a certain cell density range localized in the plant roots. The results indicate that HRRK 170 could function as a plant growth promoter, but has an optimum cell density for efficient use. View Full-Text
Keywords: plant growth-promoting bacteria; Variovorax; bioinoculant; GUS staining plant growth-promoting bacteria; Variovorax; bioinoculant; GUS staining

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Natsagdorj, O.; Sakamoto, H.; Santiago, D.M.O.; Santiago, C.D.; Orikasa, Y.; Okazaki, K.; Ikeda, S.; Ohwada, T. Variovorax sp. Has an Optimum Cell Density to Fully Function as a Plant Growth Promoter. Microorganisms 2019, 7, 82.

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