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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.

Rice biofertilization with Rhizobium increases the growth and yield of the crop. However, evidence for this has not been observed in Cuban rice cultivars. This research aimed to typify two Rhizobium isolates, considering the use of different carbon sources, their tolerance to stress conditions, and the ability to promote the growth and development of rice. Two Rhizobium sp. isolates (Rpr11 and 5P1) were used and their facility to grow on different carbon sources, pH, and salinity levels was determined. The effect of the inoculation of these bacteria on the growth and yield of rice was evaluated under controlled, greenhouse, and field conditions. Both isolates grew on mannitol, glycerol, maltose, and fructose at the highest concentrations of NaCl (1.0, 1.5 and 2.0%). The isolate 5P1 grew at all evaluated pH levels, especially at pH 5.0 and pH 8.0. The inoculation of both isolates increased the plant biomass and the potassium content. The plants inoculated with 5P1 had the highest contents of nitrogen, total chlorophyll, carbohydrates and proteins, and grain yield. This study is the first in Cuba that shows the beneficial effect of Rhizobium inoculation on the physiology and yield of rice.

A set of four experiments with increasing levels of the three main plant nutrients and liming were established in two lateritic soils at two locations in the coffee-growing area of Puerto Rico. Two coffee cultivars were used in the experiments. The results obtained can be summarized as follows: 1. Nitrogen levels significantly affected coffee yields of the Puerto Rico cultivar in a Catalina clay at Maricao grown under shade. 2. Phosphorus and potassium did not significantly affect the yields of these coffee cultivars at the two locations. 3. Liming did not significantly affect the yields.