Bactérias endofíticas Pseudomonas de Piper tuberculatum promovem o crescimento e desenvolvimento em plantas de Piper nigrum.

Abstract

Black pepper (Piper nigrum L.), belonging to the family Piperaceae, is the most important and widespread spice in the world. This crop is native to southern India and is nowadays extensively grown in tropical regions. Brazil is one of the most important pepper producers, with the State of Pará being the main national producer, responsible for approximately 66% of this production. However, the Brazilian production of black pepper has declined dramatically, 47.28% from 2006 to 2014. This fact is mainly related to disease caused by the fungus Fusarium solani f. sp. Piperis, as well as abiotic factors. This pathogen causes fusariosis, which has caused serious losses in the production of black pepper in the Amazon region. While black pepper cultivars are susceptible to fusariosis, some Piperaceae occurring in the Amazon region have shown resistance to infection by the pathogen. Among these, in the species Piper tuberculatum Jacq., known as monkey pepper, endophytic bacteria of the genus Pseudomonas capable of inhibiting the growth of F. solani f. sp. piperis under in vitro conditions, such as the Pt12 and Pt13 isolates, which inhibited fungal growth by 38.96% and 55.31%, respectively. The main objective of this study was to study the interaction of black pepper with endophytic bacteria Pseudomonas sp., Isolated Pt13 and Pseudomonas putida, isolated Pt12, to verify if these endophytes can act on the plant through physiological changes and optimizing the absorption of nutrients from the soil, contributing to the promotion of plant growth and development. Thus, we tried to evaluate the plants inoculated with the isolate Pt12 and Pt13 in morphological and biomass terms. In the assays to evaluate the morphophysiological and growth parameters the plants were inoculated only with the Pt13 isolate, where a positive and significant influence was observed in the physiological parameters of the inoculated plants, such as gas exchange and total chlorophyll. Growth and dry biomass in this experiment were also influenced by the interaction, where root dry mass increase, leaf area expansion and specific leaf area in inoculated plants were observed in comparison with control plants. Black pepper plants were submitted to three inoculation levels: plants inoculated with Pt12, plants inoculated with Pt13 and uninoculated plants, associating these groups with different sources of phosphorus (Arad, single superphosphate and triple superphosphate and a control without phosphorus addition), composing a factorial 3x4x5 (3 levels of inoculation x 4 treatments with phosphorus x 5 replicates). An interaction between plant inoculation levels and phosphorus treatments was observed by the mixed linear effect model. The results showed significant differences among all the inoculation levels of the plants for all studied variables (height, stem diameter, number of leaves, leaf area, specific leaf area, dry mass of shoot, root and total), with the exception of of the root shoot ratio (RRPA). Regarding the treatments with phosphorus, only the diameter of the stem did not differ. Our results showed that endophytic bacteria positively modulated the growth and biome accumulation of the plants under study, and possibly facilitated the absorption and solubilization of phosphorus sources, especially the natural phosphate Arad. In view of the results, we can conclude that endophytes Pt12 and Pt13 are strong candidates to be plant growth promoting bacteria (PGPB) and phosphate solubilizing bacteria (PSB), improving the physiological processes and favoring the growth and development of the plant, facilitating the absorption of nutrients, and can thus be used as biofertilizer in soils poor in phosphorus, as well as potential biocontrol agents.