RESEARCH ARTICLE Morphological Changes in Sugarcane Crop Induced by the Plant Growth-Promoting Bacterium Azospirillum brasilense Ronaldo da Silva Viana 1 • Bruno Rafael de Almeida Moreira 1 • Lucas Aparecido Manzani Lisboa 1 • Ro ˆmulo Sandu Junior 1 • Thiago Assis Rodrigues Nogueira 2 • Paulo Alexandre Monteiro de Figueiredo 1 • Marcelo Carvalho Minhoto Teixeira Filho 2 • Sergio Bispo Ramos 1 Received: 11 April 2019 / Accepted: 27 September 2019 Ó Society for Sugar Research & Promotion 2019 Abstract N fertilizers make the total cost of production of biofuels, sugar and bioelectricity expensive in the sugar- energy industry. Microbes could replace N fertilizers in the nutritional management of sugarcane crop by capturing N 2 from the atmosphere. We accordingly conducted this sci- entific study to investigate the response of sugarcane crop to Azospirillum brasilense. We tested the strain Az-V5 at the doses of 0, 50, 100, 200 and 400 mL ha -1 , by spraying it into the planting furrow, 7, 14 and 21 days after crop planting into 20-l pots filled with sieved Rhodic Hapludox, with a loamy texture. In order to examine biologically modulated morphological changes in the host plant material, namely sugarcane variety ‘RB86-7515,’ we harvested and then assessed 90-day-old plants for plant height, stalk diameter, number of tillers, number of leaves, leaf area, tiller length, dry matter of shoots and root dry matter. Sugarcane plants treated with the bioagent 14 and 21 days after crop planting had lower mean values of plant height, number of leaves, leaf area, dry matter of shoots and root dry matter. Therefore, applying A. brasilense into the planting furrow, instead of spraying it on sugarcane leaves, could protect it for a longer period from biotic and abiotic factors influencing cell via- bility, root colonization and ultimately symbiosis. The conclusion is, therefore, application of A. brasilense into planting furrow is the best environmentally friendly and low- cost strategy to promote growth and development in sugar- cane plants at the beginning of their life cycle. Keywords Diazotrophic bacteria Á N 2 biological fixation Á Plant–bacteria–atmosphere relationship Á Saccharum sp. Introduction Sugarcane (Saccharum sp.) belongs to the Poaceae family. It is one of the world’s favorite energy crops for good reasons—wider adaptability to harsh climates, efficient land use, greater cost-effectiveness, multiple economic ends and so on. Brazil is the world’s largest producer of sugarcane, followed by India and the People’s Republic of China. In this continental-scale tropical country, sugarcane fields extend for roughly 10 million hectares as recorded from Major Crops Bulletin issued regularly by the Ministry of Agriculture, Livestock and Supply (MAPA). The state of Sa ˜o Paulo is the main ethanol production area, holding over 50 % of the domestic production of ethanol (Leal et al. 2013; Bordonal et al. 2018). Soil fertility is among the main biotic and abiotic factors influencing the productivity and technological quality of sugarcane. Nitrogen (N) is the most relevant nutrient for the plant growth and development. It is elementary to metabolic pathways, such as the synthesis of structuring proteins, nucleic acids, phenols, terpenoids, alkaloids, vitamins C and E, flavonoids and other non-enzymatic secondary metabolites. In addition, N is part of ROS- scavenging enzymes playing pivotal roles in the host self- defense system, chlorophylls, carotenoids and endogenous hormones, such as auxins, gibberellins, cytokinins and ethylene, among other biocompounds governing physio- logical and biochemical processes (Costa et al. 2014; Milanez et al. 2015; Nunes et al. 2015; Silva Girio et al. 2015). & Ronaldo da Silva Viana ronaldo.viana@unesp.br; ronaldodsv@hotmail.com 1 College of Agricultural and Technological Science, Sa ˜o Paulo State University (UNESP), Dracena, Sa ˜o Paulo, Brazil 2 Faculty of Engineering of Ilha Solteira, Sa ˜o Paulo State University (UNESP), Ilha Solteira, Sa ˜o Paulo, Brazil 123 Sugar Tech https://doi.org/10.1007/s12355-019-00773-2