Stimulatory effects of defective and effective 3-indoleacetic acid-producing bacterial strains on rice in an advanced stage of its vegetative cycle.

The production of 3-indoleacetic acid (IAA) by plant growth-promoting bacteria (PGPR) stimulates root development and plant growth. In addition, morphological changes such as an increased root ramification and root hair production improves nutrient absorption and biomass accumulation. The objective of this work was to evaluate the effect of IAA-producing strains on rice in an advanced stage of its vegetative cycle. Rice was inoculated with Gluconacetobacter diazotrophicus PAL 5 and its lao- mutant, deficient in auxin production, Azospirillum baldaniorum Sp 245, and Escherichia coli DH10b. Both the mutant and wild-type G. diazotrophicus stimulated root elongation, area, volume, and diameter. However, the lao- mutant strain was the only one capable of increasing the number of roots. In turn, inoculation with A. baldaniorum had no significant effect on plant development. The inoculation with E. coli led to changes in root volume, area, and diameter, and a response that may be related to the stress caused by its presence. We conclude that the inoculation with G. diazotrophicus stimulates the root system's growth independently of their IAA production ability, suggesting that a metabolite other than IAA is responsible for this effect at advanced stages of the rice's vegetative cycle.

Germinação e vigor de sementes de arroz inoculadas com bactérias diazotróficas / Rice seed germination and vigour as affected by the inoculation with diazotrophic bacteria

Objetivou-se, neste trabalho, avaliar a germinação e o vigor das sementes de arroz inoculadas com bactérias diazotróficas. Foram instalados dois experimentos, sendo que no primeiro o delineamento experimental adotado foi o inteiramente casualizado em esquema fatorial, com dois lotes de sementes arroz da cultivar IC4440 x 10 tratamentos, com quatro repetições. Os tratamentos foram representados pela inoculação com oito estirpes de bactérias diazotróficas (AR1122, M130, BF1358, ZAE94, AR3122, AR2112, CD e BR2113), bem como pelo recobrimento das sementes com a turfa umedecida com o meio de cultivo esterilizado e pelas sementes não inoculadas. No segundo experimento, o delineamento experimental adotado foi o inteiramente casualizado, em esquema fatorial, com dois lotes de sementes recém-colhidas das cultivares IR42 e Zebu Branco x oito tratamentos, com quatro repetições. Os tratamentos foram representados pela inoculação das sementes com seis estirpes de bactérias diazotróficas (BF1358, AR3122, AR1122, ZAE94, M130 e AR2112), bem como pelo recobrimento das sementes com a turfa umedecida com o meio de cultivo esterilizado e pela não realização do procedimento de inoculação. As bactérias AR1122, M130, BF1358, ZAE94 e AR3112 podem ser selecionadas para formular inoculante para sementes de arroz. A inoculação com as bactérias diazotróficas aumenta a velocidade de germinação das sementes das cultivares IR42 e Zebu Branco, com menor contaminação por fungos.

The objective of this work was to evaluate the germination and vigour of rice seeds affected by inoculation with diazotrophic bacteria. Two experiments were conduced. In the first one, a completely randomized design with four replications arranged in a factorial scheme (2 lots x 10 treatments) was used. For this, rice seeds of cultivar IC4440 were inoculated with eight strains of diazotrophic (AR1122, M130, BF1358, ZAE94, AR3122, AR2112, CD e BR2113), submitted to coating with peat soil humidified with a sterile medium and not inoculated. In the second study, a completely randomized design with four replications arranged in a factorial scheme (2 lots x 6 treatments) was used. For this, recently harvested seeds of cultivars IR42 and Zebu Branco were inoculated with six strains (BF1358, AR3122, AR1122, ZAE94, M130 e AR2112), submitted to coating with peat soil humidified with a sterile medium and not inoculated. The bacteria AR1122, M130, BF1358, ZAE94 and AR3112 can be selected for inoculation of rice seeds. The inoculation of diazotrophic bacteria increases the speed of germination of rice seeds of cultivars IR42 e Zebu Branco, with low contamination by fungi.

Occurrence and diversity of nitrogen-fixing Sphingomonas bacteria associated with rice plants grown in Brazil.

So far, the occurrence of nitrogen-fixing Sphingomonas bacteria has been restricted to three strains of Sphingomonas azotifigens. In this work, a group of 46 Sphingomonas-like isolates, which originated from two rice varieties grown in two soils in Brazil, were characterized based on morphological, physiological and genetic analyses. The PCR genus specifically applied indicated that all 46 isolates belonged to the Sphingomonas genus and confirmed the results based on the yellow pigment of the colonies grown on potato agar medium and the BIOLOG data. It was also observed that 22 isolates are nitrogen-fixing bacteria as determined by the acetylene reduction method and confirmed by nifH gene detection. The genetic diversity based on the 16S rRNA analysis (amplified rDNA restriction analysis) showed that the isolates formed two distinct groups at a similarity value of 60%. Furthermore, five clusters at 60% similarity were observed with the 16S-23S intergenic space (ribosomal intergenic space analysis) analysis. Sequencing of the 16S rRNA gene and nifH fragments showed that most of the 22 nitrogen-fixing isolates formed clusters apart from that of the S. azotifigens. This is the first report on the occurrence of nitrogen-fixing Sphingomonas bacteria associated with rice grown in Brazil.