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Evaluation of bacteria isolated from rice for plant growth promotion and biological control of seedling disease of rice

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Abstract:

Of 102 rhizoplane and endophytic bacteria isolated from rice roots and stems in California, 37% significantly (P 0.05) inhibited the growth in vitro of two pathogens, Achlya klebsiana and Pythium spinosum, causing seedling disease of rice. Four endophytic strains were highly effective against seedling disease in growth pouch assays, and these were identified as Pseudomonas fluorescens (S3), Pseudomonas tolaasii (S20), Pseudomonas veronii (S21), and Sphingomonas trueperi (S12) by sequencing of amplified 16S rRNA genes. Strains S12, S20, and S21 contained the nitrogen fixation gene, nifD, but only S12 was able to reduce acetylene in pure culture. The four strains significantly enhanced plant growth in the absence of pathogens, as evidenced by increases in plant height and dry weight of inoculated rice seedlings relative to noninoculated rice. Three bacterial strains (S3, S20, and S21) were evaluated in pot bioassays and reduced disease incidence by 50%–73%. Strain S3 was as effective at suppressing disease at the lowest inoculum density (106 CFU/mL) as at higher density (108 CFU/mL or undiluted suspension). This study indicates that selected endophytic bacterial strains have potential for control of seedling disease of rice and for plant growth promotion.Key words: biological control, plant growth promotion, endophytes, rice, seedling disease.

Parmi 102 bactéries endophytes et du rhizoplan isolées à partir de racines et de tiges de riz en Californie, 37% on inhibé significativement (P 0,05) la croissance in vitro de deux pathogènes, Achlya klebsiana et Pythium spinosum, causant la maladies des semis chez le riz. Quatre souches endophytiques se sont avérées particulièrement efficaces contre la maladie des semis selon des analyses de croissance en pochettes. Le séquençage des gènes amplifiés de l'ARNr 16S nous a permis d'identifier celles-ci comme étant Pseudomonas fluorescens (S3), Pseudomonas tolaasii (S20), Pseudomonas veronii (S21) et Sphingomonas trueperi (S12). Les souches S12, S20 et S21 étaient porteuses du gène de la fixation de l'azote, nifD, mais seule la souche S12 fut capable de réduire l'acétyène en culture pure. Les quatre souches ont significativement augmenté la croissance végétale en l'absence de pathogènes, comme l'ont indiqué des augmentations dans la hauteur des plantes et dans le poids sec de semis de riz inoculés par rapport à du riz non inoculé. Trois souches bactériennes (S3, S20 et S21) ont été soumises à des bioessais en pots et ont diminué de 50%–73% l'incidence de la maladie. La souche S3 fut en mesure de supprimer efficacement la maladie à la densité d'inoculation la plus faible (106 CFU/mL) aussi bien qu'à une densité plus élevée (108 CFU/mL ou suspension non diluée). Cette étude indique que des souches de bactéries endophytes sélectionnées démontrent un potentiel dans le contrôle de la maladie des semis et dans la stimulation de la croissance végétale.Mots clés : contrôle biologique, stimulation de la croissance des plantes, endophytes, riz, maladies des semis.[Traduit par la Rédaction]
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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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