Response of maize and tomato to the inoculation with diazotrophic bacteria isolated from leaf surface

Author(s)

Andre Alves de Souza

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2017-08-30

Examining board members

Marcio Rodrigues Lambais; Alice de Sousa Cassetari; Rafael Otto; Marisa de Cassia Piccolo

• Advisor: Marcio Rodrigues Lambais

Abstract

The development of alternative technologies to increasing availability and use efficiency of mineral resources for plants is an important step for sustainable agricultural production. In this context, the supply of nitrogen by biological means, using diazotrophic microorganisms, of which the most studied are rhizobia symbiotically associated with legumes, is an important alternative. However, the efficiency of rhizobium-legume symbioses has not yet been achieved in other plant families, mainly due to limitations associated with the optimization of plant-bacterial combinations. In grasses, endophytic diazotrophs have been used as inoculant, with controversial results. However, it is possible that epiphytic diazotrophic microorganisms may have adaptive advantages over endophytes, due to the lower specificity in their associations with plants, and be more efficient in non-leguminous plants. The objective of the present work was to evaluate the effect of an inoculant produced with diazotrophic bacteria isolated from the phyllosphere on the growth of maize and tomato. Assays were carried out under greenhouse conditions using three isolates of diazotrophic bacteria encapsulated in alginate beads under different levels of nitrogen fertilization. The efficiency of the isolates in fixing nitrogen was evaluated determining nitrogenase activities. The populations of diazotrophic bacteria in the rhizosphere were determined by the most probable number (MPN) technique at the end of the experiment. In addition, parameters such as shoot and root biomass were analyzed. The data were submitted to the analysis of variance, and means were compared by the Duncan test (p<0.05), using the statistical program R. Maize plants at 60 days after inoculation with the J8L isolate presented root dry weight and nitrogenase activity in the rhizosphere 26 and 50% higher than the uninoculated control, respectively. Tomato plants, 30 days after inoculation with the E5L isolate, presented shoot and root dry weight 39 and 31% higher than the uninoculated control, respectively. Part of the effects observed in maize and tomato can be explained by the nitrogen fixation activity and auxin production. Nitrogenase activity in the maize rhizosphere, 60 days after inoculation was higher in the soil without N supply. The population of diazothrophic bacteria in the rhizosphere of inoculated and non-inoculated maize and tomato plants were not significantly different, showing a probable influence of the native diazotrophic community on the total diazotrophic population. In general, isolates J8L and E5L promoted growth of maize and tomato, showing potential for use as biofertilizers. (AU)

• FAPESP's process: 16/17042-6 - Response of the corn and of the tomato to inoculation with bacterias diazotrophic epiphytic
• Grantee: André Alves de Souza
• Support Opportunities: Scholarships in Brazil - Master