Azospirillum Brasilense Application in Pre-Sprouted Seedlings (PSS) of Sugarcane

The use of sugarcane pre-sprouted seedlings (PSS) of high quality is a key factor for success of sugarcane production system in Brazil, and the use of plant growth-promoting bacteria (PGPB) can be decisive in obtaining high-quality seedlings. However, it is not known which rate of inoculant containing Azospirillum brasilense should be used. Thus, this study was conducted to evaluate the efficiency of Azospirillum brasilense inoculation and establish the optimal rate of inoculant application on the development of  sugarcane PSS (Saccharum officinarum). Pre-sprouted seedlings from commercial hybrids IACSP95-5000, RB855035, RB855536, and RB867515, produced from individual buds (mini-sets) of 3.0 cm were transplanted at 12 days after sprouting into 290 mL tubes. Treatments were arranged in completely randomized design, in 4 × 5 factorial scheme: four genotypes (IACSP95-5000, RB867515, RB855035 and RB855536) and five rates of commercial inoculant AzoTotal®, containing the strains AbV5 and AbV6 [0 (control); 0.5; 1.0; 2.0 and 4.0 mL per tube], four replicates. The inoculant rates increased the plant height, shoot dry matter, root dry matter, total dry matter, height: diameter ratio, and Dickson quality index of PSS of the genotypes IACSP95-5000, RB855035 and RB867515, as well as an increase in number of leaves and stalk diameter of RB855035 and RB867515. The genotype RB855536 has no response to application of inoculant containing A. brasilense during the production phase of pre- sprouted seedlings. The optimal application rate of inoculant containing A. brasilense for production of high-quality pre-sprouted sugarcane seedlings varies between 2 and 3 mL of inoculant per seedling.   Keywords: Saccharum officinarum. Diazotrophic bacteria. Nitrogen. Inoculation.     Resumo O uso de mudas pre-brotadas (MPB) de cana-de-acucar (Saccharum officinarum) de qualidade e fator chave para sucesso da producao de cana-de-acucar no Brasil e o uso de bacterias promotoras de crescimento de plantas pode ser determinante na obtencao de mudas de qualidade. Entretanto, nao se tem conhecimento da dose ideal de inoculante contendo Azospirillum brasilense. Este estudo foi conduzido com o objetivo de avaliar a eficiencia da inoculacao de Azospirillum brasilense e estabelecer a dose ideal no desenvolvimento de MPB de cana-de-acucar. MPB de quatro variedades de cana-de-acucar, oriundas de minirrebolos de 3,0 cm foram transplantadas aos 12 dias apos a brotacao para tubetes de 290 mL. Os tratamentos foram dispostos em delineamento casualizado, esquema fatorial 4 × 5: quatro variedades (IACSP95-5000, RB867515, RB855035 e RB855536) e cinco doses do inoculante comercial AzoTotal®, contendo as estirpes AbV5 e AbV6 [0 (controle); 0,5; 1,0; 2,0 e 4,0 mL por tubetes], com quatro repeticoes. As doses de inoculantes resultaram no aumento da altura das plantas, materia seca da parte aerea, materia seca das raizes, materia seca total, relacao altura: diâmetro e no indice de qualidade de Dickson das MPB das variedades IACSP95-5000, RB855035 e RB867515, alem de resultar no aumento do numero de folhas e diâmetro do colmo das variedades RB855035 e RB867515. A variedade RB855536 nao responde a aplicacao de inoculante durante a fase de producao de MPB. A dose otima do inoculante para na producao de MPB de qualidade pode variar entre 2 e 3 mL de inoculante por muda.   Palavras-chave: Saccharum officinarum. Bacterias diazotroficas. Nitrogenio. Inoculacao.