Plant growth-promoting bacteria have several abilities to promote plant growth and development. One of these skills is the synthesis of indole-3-acetic acid (IAA), which mainly promotes root and shoot development. The bacteria Bacillus subtilis and Azospirillum brasilense have been widely used in agriculture with this function. However, little is known about whether the joint inoculation of these bacteria can reduce plant development by the excess of IAA produced as a result of the joint inoculation. The objective of the present study was to verify the effect of IAA on the inoculation of B. subtilis and A. brasilense in three tomato genotypes. The Micro-Tom genotype without mutation for IAA synthesis, Entire, has high sensitivity to IAA, and the diageotropic genotype (dgt) has low sensitivity to IAA. The results show that the plant parameter most sensitive to microbial inoculation is the number of roots. No treatment increased the shoot dry mass parameters for the Micro-Tom genotype and dgt, root dry mass for the Micro-Tom genotype, plant height for the Micro-Tom and Entire genotypes, root area and root volume for the genotype dgt. The Azm treatment reduced plant height compared to the control in the dgt, the BS + Azw and BS + Azm treatments in the Micro-Tom genotype and the Azw + Azm treatment in the dgt genotype reduced the plant diameter compared to the control. BS and BS + Azw reduced the number of roots in the Micro-Tom. The results strongly support that the mixture of B. subtilis and A. brasilense can reduce some parameters of plant development; however, this effect is possibly an interference in the mode of action of growth promotion of each isolate and is not related to an excess of IAA produced by the bacteria.

The production of 3-indoleacetic acid (IAA) by plant growth-promoting bacteria (PGPR) stimulates root development and plant growth. In addition, morphological changes such as an increased root ramification and root hair production improves nutrient absorption and biomass accumulation. The objective of this work was to evaluate the effect of IAA-producing strains on rice in an advanced stage of its vegetative cycle. Rice was inoculated with Gluconacetobacter diazotrophicus PAL 5 and its lao- mutant, deficient in auxin production, Azospirillum baldaniorum Sp 245, and Escherichia coli DH10b. Both the mutant and wild-type G. diazotrophicus stimulated root elongation, area, volume, and diameter. However, the lao- mutant strain was the only one capable of increasing the number of roots. In turn, inoculation with A. baldaniorum had no significant effect on plant development. The inoculation with E. coli led to changes in root volume, area, and diameter, and a response that may be related to the stress caused by its presence. We conclude that the inoculation with G. diazotrophicus stimulates the root system’s growth independently of their IAA production ability, suggesting that a metabolite other than IAA is responsible for this effect at advanced stages of the rice’s vegetative cycle.

Nas últimas décadas, o Brasil tem apresentado uma tendência de aumento significativo do uso de agrotóxicos. Nesse cenário, como o país é um grande produtor e exportador de alimentos, esse aumento representa um problema ambiental sem precedentes. A ocorrência de agrotóxicos no solo tornou-se um problema ambiental altamente significativo que tem sido agravado pela sua grande utilização em todo mundo e pela ausência de tecnologias de remediação com um bom custo benefício em larga escala. O destino do agrotóxico no solo pode ser afetado por características físicas, químicas e biológicas e pela forma como essas características interagem com os ecossistemas. O presente trabalho teve como objetivo fazer uma análise através de estudos realizados previamente sobre as propriedades físico-químicas do solo que atuam na dinâmica e retenção das moléculas dos agrotóxicos, afim de colaborar para estudos de monitoramento e avaliação que buscam medidas adequadas para o desenvolvimento sustentável e o alcance da neutralidade da degradação do solo.

Millicomposting, a not so well-known biotechnology, involves the biotransformation of vegetable residues into stable organic matter, promoted by the activity of diplopods, popularly known as millipedes. Considering the importance of the substrate in the production of vegetable seedlings, the aim of the present work was to assess the millicomposting technique and evaluate the efficiency of millicompost in the production of seedlings of the American lettuce cultivar Angelina. The millicompost consisted of Bauhinia sp. (cow’s foot leaves), Paspalum notatum (grass clippings), Musa sp. (banana leaves), and cardboard. Physical, physicochemical, and chemical analyses of the obtained millicompost were performed 180 days into the experiment. The lettuce seedlings were grown in expanded polystyrene trays of 200 cells and the evaluations occurred 30 days after sowing. The evaluated phytotechnical characteristics were fresh and dry shoot mass, fresh and dry root mass, plant height, number of leaves, seedling vigor, and clod stability. The millicompost had a higher total nutrient content and lower volume density than the Biomix® organic substrate. All of the developmental parameters of the lettuce seedlings differed between the millicompost and the Biomix® organic substrate; all of the mean values were higher for the millicompost, except for the number of leaves, which did not differ from the Biomix® organic substrate. The millicomposting process facilitated the reuse of organic waste by converting it into quality organic compost and resulted in the efficient production of excellent quality lettuce seedlings.