Taxonomia polifásica de bactérias diazotróficas do gênero Sphingomonas spp. e efeito da inoculação em plantas de arroz

Abstract

Rice (Oryza sativa L.) is a widely consumed food on the planet, suppling more than 50% of the world's food. Approximately 150 million hectares are used for its cultivation, and of these, 32% grow in upland conditions. Rice is usually grown in N-deficient soils, demanding that the element be supplied to the field by commercially available N fertilizers. Unfortunately, a substantial amount of the N applied as fertilizers is lost through different mechanisms, causing environmental pollution and economical problems. Utilization of biological N2 fixation (BNF) technology may decrease the application of N fertilizers, reducing environmental and economical risks. Among the wide variety of bacteria that are associated with rice plants, Sphingomonas spp. are often found; although the first nitrogen-fixing specie has been reported only recently. Due the large number of Sphingomonas spp. obtained from rice plants grown in the experimental field of Embrapa Agrobiologia, this study aimed to study the genetic diversity and identify these isolates through molecular, physiological and quimiotaxonomic methods, as well as assess the behavior of the population and the efficiency of some isolated in growth-promoting of upland condition rice plants cultivated in a greenhouse. The results showed that only 50% of the isolates presented in vitro nitrogenase activity and the gene related to BNF. All diazotrophic isolates were identified as Sphingomonas spp., showing little genetic diversity among themselves and greater similarity to Sphingomonas azotifigens. The population of diazotrophic bacteria showed great numbers present in the rice roots. There was an increase in grain yield of rice by 48% when inoculated with some strains of Sphingomonas spp. and Herbaspirillum seropedicae (ZAE94) on the treatment without inoculation and without nitrogen.