Avaliação de isolados de Bacillus spp. quanto à sua capacidade de promover crescimento em mudas de tangor Murcott

Abstract

Citriculture is currently one of the main agricultural activities in Brazil in the fruit growing segment. However, several factors can influence the crop's productivity indices, such as the quality of the seedlings, and its good formation, vigor and health are essential. Therefore, the choice of a quality rootstock is of great importance, since it has a direct influence on the citrus plant aerial parts. The use of microorganisms with potential to promote plant growth may represent a new perspective in crop management, considering the influence they exert on plant nutrition and health, even generating lower environmental impacts on ecosystems. Therefore, the aim of the present study was to evaluate bacteria as growth-promoting agents for Murcott tangor seedlings grafted onto different citrus rootstocks. A total of 10 Bacillus spp. isolated were evaluated in vitro for: indoleacetic acid (IAA) production, phosphate solubilization and nitrogen fixation. The in vivo tests consisted of assays to evaluate bacterial isolates for growth promotion on two different rootstocks: Swingle citrumelo (Citrus paradisi × Poncirus trifoliata) and Rangpur lime (Citrus limonia), which after 300 days were grafted with Murcott tangor (C. sinensis x C. reticulata). The parameters of interest analyzed were the height of the rootstock at 60, 120, 240 and 300 days after sowing and then, at 480 days after sowing (180 days after grafting), the following were evaluated: the total height of the plant, graft height, root length, number of leaves, root and aerial parts green mass and aerial parts dry mass. The results showed that all bacterial isolates were able to produce AIA, to solubilize phosphate, and to fix nitrogen; under laboratory condition; the Bacillus spp. ACB-07 had a positive effect on the growth of Murcott tangor seedlings grafted on Swingle citrumelo, while the isolate ACB-08 showed potential as a growth promoter in Murcott tangor seedlings grafted on Rangpur lime, it was found that the ability of a bacterial isolate to promote the growth of Murcott tangor seedlings depends, among other factors, on the variety of rootstock used.