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

Abstract

Of 102 rhizoplane and endophytic bacteria isolated from rice roots and stems in California, 37% significantly (P < or = 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 (10(8) 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.

Protection of Arabidopsis thaliana against Leaf-Pathogenic Pseudomonas syringae by Sphingomonas Strains in a Controlled Model System

“…Likewise, studies report on Sphingomonas spp. as producers of plant growth-stimulating factors (2,10,46).Another way in which plants could benefit from their commensal bacteria is by protection against invading pathogens. In the past, several efforts to find natural agents for the control of foliar plant pathogens have been made (20).…”

“…Likewise, studies report on Sphingomonas spp. as producers of plant growth-stimulating factors (2,10,46).…”

Design of Sphingomonad-Detecting Probes for a DNA Array, and Its Application to Investigate the Behavior, Distribution, and Source of RhizospherousSphingomonasand Other Sphingomonads Inhabiting an Acid Sulfate Soil Paddock in Kalimantan, Indonesia

“…1,16) Taken together, certain contributions of the rhizospheous sphingomonads to rice production were tentatively inferred. 16,37) In fact, in ammonia-assimilating Melastoma malabathricum, it has been found that S. rosa EC-K013 promotes the growth of saplings under nitrogen-starving and strongly acidic (pH 3.0) nursery conditions. 38) Our sphingomonad-detecting DNA array probes made it possible to investigate and pursue microfloral succession in the rhizosphere of several acid-tolerant plants, since the rhizospherous sphingomonads are most likely to be a mediator in the rhizosphere of acid-tolerant plants in South and Central Kalimantan.…”

Requirement of a Relatively High Threshold Level of Mg 2+ for Cell Growth of a Rhizoplane Bacterium, Sphingomonas yanoikuyae EC-S001

“…This is likely a reason why Sphingomonas spp. are often found as plant-associating bacteria, particularly on the surfaces of roots (24), leaves (10), flowers (10), and seeds (10,17), and even in inner tissues as endophytes (1,5). Another unique property of Sphingomonas spp.…”