Occurrence of plant growth-promoting traits in clover-nodulating rhizobia strains isolated from different soils in Rio Grande do Sul state

Abstract

SUMMARYIn the last decades, the use of plant growth-promoting rhizobacteria has become an alternative to improve crop production. Rhizobium leguminosarum biovar trifolii is one of the most promising rhizobacteria and is even used with nonlegume plants. This study investigated in vitro the occurrence of plant growthpromoting characteristics in several indigenous R. leguminosarum biovar trifolii isolated from soils in the State of Rio Grande do Sul, Brazil. Isolates were obtained at 11 locations and evaluated for indoleacetic acid and siderophore production and inorganic phosphate solubilization. Ten isolates were also molecularly characterized and tested for antagonism against a phytopathogenic fungus and for plant growth promotion of rice seedlings. Of a total of 252 isolates, 59 produced indoleacetic acid, 20 produced siderophores and 107 solubilized phosphate. Some degree of antagonism against Verticillium sp. was observed in all tested isolates, reducing mycelial growth in culture broth. Isolate AGR-3 stood out for increasing root length of rice seedlings, while isolate ELD-18, besides increasing root length in comparison to the uninoculated control, also increased the germination speed index, shoot length, and seedling dry weight. These results confirm the potential of some strains of R. leguminosarum biovar trifolii as plant growth-promoting rhizobacteria.Index terms: rhizobacteria, siderophore, indoleacetic acid, phosphate solubilization, antagonism, rice.(

Diversity of native rhizobia isolated in south Brazil and their growth promotion effect on white clover (Trifolium repens) and rice (Oryza sativa) plants

“…The symbiotic rhizobia isolated from leguminous plants can promote plant growth not only through their biological N fixation ability (in leguminous plants) but also via their inherent PGP capacities: siderophores and indolic compound production and nutrient solubilization (Vargas et al 2009;Souza et al 2012;Ashraf et al 2013). This study indicated that the PGP ability most common among all isolates was indolic compounds production.…”

“…Rhizobia species are considered legume endosymbionts as they can promote plant growth through biological nitrogen fixation, the production of hormones and enzymes, and the solubilization of soil nutrients (Schloter et al 1997;Vargas et al 2009). Strains belonging to several species of the rhizobia genera have previously been isolated from the root nodules of leguminous plants (Zhang et al 1991;Wang et al 2010).…”

Caracterização e influência de rizóbios isolados de alfafa na germinação e desenvolvimento inicial de plântulas de arroz

“…No entanto, nas últimas décadas, outros micro-organismos têm atraído a atenção dos pesquisadores, com vista a uma potencial utilização na agricultura (VARGAS et al, 2009). As bactérias presentes na rizosfera são capazes de contribuir para o aumento da produtividade de algumas lavouras devido à colonização das raízes e estímulo ao crescimento das plantas.…”

“…Diversos micro-organismos vêm sendo relatados como promotores de crescimento em plantas, que incluem os gêneros Azoarcus, Azospirillum, Azotobacter, Arthrobacter, Bacillus, Clostridium, Enterobacter, Gluconacetobacter, Pseudomonas e Serratia, os quais são exclusivamente microorganismos não simbióticos (VARGAS et al, 2009). Além desses micro-organismos, estudos comprovaram a ação benéfica de rizóbios na atividade de promoção de crescimento vegetal em diversas espécies de plantas, a exemplo de milho, sorgo, milheto, canola, alface, mostarda, arroz, cevada (MATIRU & DAKORA, 2004;PERRINE-WALKER et al, 2007).…”

“…O ácido indol-acético, fitohormônio pertencente ao grupo das auxinas, atua na elongação das células vegetais, na formação das raízes laterais e pêlos radiculares, bem como na germinação das sementes (BISWAS et al, 2000). Nas fases iniciais do desenvolvimento das plantas, a inoculação de rizóbios produtores de AIA pode aumentar a velocidade da germinação das sementes inoculadas, como observado em arroz e alface (SCHLINDWEIN et al, 2008;VARGAS et al, 2009;PALANIAPPAN et al, 2010).…”