There is growing interest in using plant-beneficial microorganisms to partially replace chemicals and help reduce the environmental impact of agriculture. Formulated microbial products or inoculants for agriculture contain single strains or a consortium of live microbes, well characterized and biosafe, which can contribute to the growth, health, and development of a plant host. This concept conforms to the definition of probiotics. However, some plant-growth-promoting microorganisms (PGPMs) have been considered a category of biostimulants since some years ago, despite the traditional concept of biostimulants involves substances or materials with no fertilizer value, which in minute amounts promote plant growth. The inclusion of PGPMs together with substances has also involved a significant distortion of the classical concept of biostimulants. Regulations such as the recent EU Fertilizing Products Regulation (EU No. 2019/1009) have incorporated the new definition of biostimulants and included microbials as a subcategory of biostimulants. We discuss that this regulation and the forthcoming European harmonized standards disregard some key features of microbial products, such as the live, true biological nature of their active principles. The factors that determine the complex functional compatibility of plant–microbe associations, and important biosafety issues that concern the intentional release of microbes into the environment, seem to be also ignored. We anticipate that by equating microbials to chemicals, the biological nature of microbial products and their specific requirements will be underestimated, with pernicious consequences for their future development and success.

Cuban rice cultivars INCA LP-5 and INCA LP-7 are widely distributed in Cuba and Caribbean countries. Although there are studies about rhizospheric bacteria associated with these cultivars, there are no reports about their seed-associated bacteria. This study aimed to isolate endophytic bacteria from rice seeds and select those with the greatest plant growth-promoting traits. A total of nineteen bacterial strains from the genera Pantoea, Bacillus, Paenibacillus, and Pseudomonas were isolated from the husk and endosperm of rice seeds. The strains Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were classified as the most promissory to increase rice growth as they demonstrated the presence of multiple plant growth-promoting traits such as the production of auxins, phosphate, and potassium solubilization, the production of siderophores, and the inhibition of the phytopathogen Pyricularia oryzae. The inoculation of strains of Pantoea sp. and Pseudomonas spp. in rice improves the height, root length, fresh weight, and dry weight of the shoot and root after 21 days post-inoculation in hydroponic assays. This study constitutes the first report on Cuban rice cultivars about the presence of endophytes in seeds and their potential to promote seedling growth. Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were selected as the more promising strains for the development of bio-stimulators or bio-inoculants for Cuban rice crops.

Rhizobia have been studied for the symbiosis that they establish with the roots of legumes. However, the colonization and promotion of growth in non-leguminous plants has also been demonstrated. The aim of this work was the biochemical and molecular identification of rhizosphere rhizobia present inthe rhizosphere of two commercial maize cultivars. Cultivableisolates were obtained in yeast-mannitol-agar (YMA) mediumfrom rhizospheric soil and the rhizoplane. The cultural (size,color, mucus, etc.), morphological, and staining (cell shape,response to staining and sporulation) characteristics weredetermined as well as isolate responses to eight biochemicaltests (acid-base production, citrate, oxidase, catalase, H2Sproduction, urease, gelatinase and the oxidative-fermentativeassay) that are valuable for rhizobia identification. The genuswas determined by 16S rDNA gene sequencing. We obtained 81total isolates of which 30.86% showed the cultural, morphological and staining characteristics expected for rhizobia and only 20% of these corresponded to the genus Rhizobium.

Introduction. The rice cultivar INCA LP-7 is one of the eleven principal cultivars in Cuba due to their high yield potential, salinity tolerance, and pathogens resistance. However, there are not reports about the isolation, identification, and characterization of bacteria associated to this cultivar that promote its growth. Objective. To select promising bacteria from the rhizosphere of the INCA LP-7 rice cultivar to promote the crop growth. Materials and methods. The investigation was carried out in 2015 and 2016 at the Instituto Nacional de Ciencias Agropecuarias, Cuba and Instituto de Investigaciones Biologicas Clemente Estable, Uruguay. The 16SrNA gene of bacteria associated with the INCA LP-7 rice cultivar was isolated and identified by sequencing. Characterization was performed as plant growth promoting bacteria and the effect of bacterial inoculation on rice growth was studied. Results. Eleven rizopheric bacteria were isolated from rice plants of the INCA LP-7cultivar. A phylogenetic analysis showed that for the first time in Cuba Pantoea, Acinetobacter, and Mitsuaria genera were reported associated with rice. Rhizobium and Enterobacter genera were also informed as rhizospheric bacteria of INCA LP-7 rice cultivar. Some isolates solubilize inorganic phosphates and potassium, produce siderophores and indolic compound, had exo-celulase and protease activity and formed biofilm. The inoculation of isolates belonging to Pantoea genus produced an increase in height, root length, and biomass of rice plants under greenhouse conditions. Conclusions. Pantoea sp. GG1 and Pantoea sp. GG2 were the most promising strains for the inoculation of the INCA LP-7 rice cultivar. This is the first report in Cuba that focuses on the characterization of the bacterial microbiota part associated to Cuban rice cultivar INCA LP-7 and reports bacteria of the Pantoea genus as crop growth promoters.

Introduction. Chitosan and plant growth promoting rhizobacteria are recognized as agricultural biostimulants for the biological benefits they provide to plants. Objective. To evaluate the combined application of chitosan concentrations and the Azofert-S¨ inoculant on soybean seeds, on the survival of Bradyrhizobium elkanii and the vegetative growth of the plants. Materials and methods. The research was developed in the plant growth room of Plant Physiology and Biochemistry Department of the Instituto Nacional de Ciencias Agricolas, Cuba, in 2016. The effect of chitosan and Azofert-S¨ inoculant applied to soybean seeds was determined on the number of viable bacteria in seeds and the behavior of morphoagronomic and physio-biochemical indicators related to the nodulation and vegetative development of plants. Results. The chitosan concentrations evaluated in the compatibility test did not affect the number of viable cells in the seeds, except for 500 and 1000 mg l-1, which improved the bacteria survival at the beginning of the test and 500 mg l-1 at ten days of seed storage. The latter concentration also benefited root and stem length, leaf area, and nitrate reductase enzymatic activity in leaves. The combined application of Azofert® - chitosan and seed inoculation alone enhanced the concentration of nitrogen and other nutrients in nodules and trifoliolus. The concentration of flavonoids and total phenols increased with the concentration of 10 mg l-1 of chitosan, although it decreased the concentration of total soluble and reductive carbohydrates in leaves. Conclusion. The biostimulants were compatible when applied on seeds at the time of sowing and benefited the nodulation, nutrition, and vegetative development of soybeans plants, depending on the concentration of the polymer.