Efeito da coinoculação de rizobactérias Streptomyces no perfil de exsudados de raízes e no crescimento de plantas de milho (Zea mays L.)

Abstract

(Artigo 2 - Co-inoculation with Streptomyces isolates promotes growth of maize plants and affects the profile of metabolites exudated by the roots) Microorganisms, individually or in consortium, present in the rhizosphere, promote plant growth and their interaction with the roots are mediated by root exudates. The present study evaluated the growth of maize plants (Zea mays L.) and the metabolic profile of root exudates by treating seeds with Streptomyces rhizobacteria, isolated or in co-inoculation. Maize seeds were bacterized with isolates CLV89, CLV104 and CLV179, individually or in dual or triple co-inoculation. Non-bacterized seeds and seeds treated with the commercial inoculant Azospirillum brasiliense were used as negative and positive controls, respectively. Vegetative growth was analyzed, and root colonization was confirmed by scanning electron microscopy. Exudates from 21-day-old plants were collected in 100 mL of sterile filtered water during 24 h under continuous light. Amino acids, reducing sugars, proteins and phenolic compounds were quantified through colorimetric reactions. The profile of phenolic compounds was determined by HPLC. The Streptomyces isolates produced indoleacetic acid auxin and its metabolites, siderophores, ammonia and phenazines. CLV104 effectively promoted the growth of maize compared to the other isolates. Triple co-inoculation, which included CLV104, showed similar effect on plant growth to that found with the single inoculation with CLV104, although reduced root growth was observed. Co-inoculation CLV89+CLV104 promoted root and leaf growth. The exudation of amino acids, proteins and sugars of plants treated with the three isolates was significantly higher than that of the single inoculation and the controls. The profile of phenolic compounds exuded by the roots varied according to the treatment, indicating that the interaction between roots and Streptomyces is mediated, at least in part, by exudates, and the rhizodeposition of phenolic compounds varied specifically with the isolate colonizing the roots.