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Microorganisms are considered a genetic resource with great potential for achieving sustainable development of agricultural areas. The objective of this research was to determine the effect of microorganism application forms on the production of biomass, gas exchange, and nutrient content in upland rice. The experiment was conducted under greenhouse conditions in a completely randomized design in a factorial 7 × 3 + 1, with four replications. The treatments consisted of combining seven microorganisms with three application forms (microbiolized seed; microbiolized seed + soil drenched with a microorganism suspension at 7 and 15 days after sowing (DAS); and microbiolized seed + plant sprayed with a microorganism suspension at 7 and 15 DAS) and a control (water). Treatments with Serratia sp. (BRM32114), Bacillus sp. (BRM32110 and BRM32109), and Trichoderma asperellum pool provided, on average, the highest photosynthetic rate values and dry matter biomass of rice shoots. Plants treated with Burkolderia sp. (BRM32113), Serratia sp. (BRM32114), and Pseudomonas sp. (BRM32111 and BRM32112) led to the greatest nutrient uptake by rice shoots. Serratia sp. (BRM 32114) was the most effective for promoting an increase in the photosynthetic rate, and for the greatest accumulation of nutrients and dry matter at 84 DAS, in rice shoots, which differed from the control treatment. The use of microorganisms can bring numerous benefits of rice, such as improving physiological characteristics, nutrient uptake, biomass production, and grain yield.

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This study was carried out to select Trichoderma isolates from Amazon forest soil samples, identify their potential for sheath blight (Rhizoctonia solani) suppression in rice, and promote plant growth. Four out of the 13 isolates (T.06, T.09, T.12, T.52) which showed in vitro potential were evaluated through assays under greenhouse conditions utilizing four application methods: 1) preventive and curative sprays; 2) seed treatment + curative sprays; 3) seed treatment; 4) substrate treatment. These four isolates also showed reduced R. solani mycelial growth and sclerotial viability (>50%) and were positive for phosphate solubilization and cellulose degradation. They significantly reduced sheath blight severity when applied as seed treatment, substrate incorporation or foliar spray. However, the preventive and curative sprays were the most efficient method, reducing sheath blight severity by 43% and the area under the disease progress curve by 45%. Isolates T.12 and T.52 applied in substrate treatment increased aerial and root dry weight by 61.2 and 32.9%, respectively. These two isolates showed potential as growth stimulants and can be used as novel biological products and bioinoculants in agriculture for increasing grain yield. RESUMO: Foi realizada a seleção de isolados de Trichoderma spp. provenientes de amostras de solo da Floresta Amazônica e identificado o seu potencial para suprimir a queima da bainha (QB) (Rhizoctonia solani) e para promover o crescimento de plantas de arroz. Quatro de 13 isolados (T.06, T.09, T.12, T.52) que mostraram potencial in vitro foram avaliados em experimentos em casa de vegetação, utilizando-se quatro métodos de aplicação: 1) pulverização preventiva e curativa; 2) tratamento de semente + pulverização curativa; 3) tratamento de semente; 4) tratamento do substrato. Esses quatro isolados, in vitro, reduziram o crescimento micelial de Rhizoctonia solani e a viabilidade do escleródio (>50%), sendo positivos para solubilização de fósforo e degradação da celulose. Em casa de vegetação, os quatro isolados reduziram significativamente a severidade da QB quando aplicados via tratamento de semente, incorporados ao substrato e por pulverização foliar. Entretanto, a pulverização preventiva + curativa foi mais eficiente, reduzindo em 43% a severidade da QB e em 45% a área sob curva de progresso da doença. Os T.12 e T.52 aplicados via substrato promoveram o incremento em massa seca da parte aérea e radicular em 61,2 e 32,9%, respectivamente. Esses dois isolados mostraram potencial como promotores do crescimento e poderão ser usados como novo produto biológico e bioinoculantes na agricultura para aumento de produtividade. Rice sheath blight biocontrol and growth promotion by Trichoderma isolates from the Amazon Biocontrole da queima da bainha em arroz e promoção do crescimento por isolados de Trichoderma da Amazônia

_ Phenotypic virulence analysis was made on population of Pyricularia grisea isolates collected from 10 upland cultivars in three distinct rice breeding sites, with the objective of studying the degree of similarity in the phenotypic virulence among the isolates, the composition of races, and their virulence pattern. Sixteen races were identified based on the reaction type on eight standard international differentials, the predominant ones being IB-9 and IB-41. The virulence frequency was high on IAC 47 and IAC 165 among medium and early maturing cultivars, respectively. The frequency of isolates virulent was greater on upland rice cultivars (51.1%) than on irrigated rice cultivars (21.8%). Both virulent and avirulent isolates were present in the population of P. grisea to the known genes in the near isogenic lines. Of 72 test isolates, 94.4% were virulent for genes Pi-3 and Pi-4a. The virulence frequencies were relatively lower in decreasing order on Pi-1, Pi-4b and Pi-2. The coefficient of similarity ranged from 0.28 to 1.0 among the isolates pertaining to different races, while within the race IB-9, it varied from 0.56 to 1.0. Considering the coefficient of similarity of 0.81, 72% of isolates of race IB-9 exhibited similar pattern of virulence.Index terms: pathotype, Oryza sativa, Magnaporthe grisea, physiologic races, pathogenicity. Análise fenotípica da virulência dos isolados de Pyricularia grisea, coletados em cultivares de arroz de terras altasResumo _ Foi conduzido um estudo de virulência fenotípica da população de Pyricularia grisea, coletada de 10 cultivares de arroz de terras altas, em três locais distintos, objetivando determinar o grau de similaridade entre virulência fenotípica de isolados, a composição de raças fisiológicas e seu padrão de virulência nas cultivares de arroz. Identificaram-se 16 raças, com base no tipo de reação nas oito diferenciadoras internacionais, das quais IB-9 e IB-41 foram as predominantes. A freqüência de virulência foi alta nas cultivares IAC 47 e IAC 165 entre as de ciclo médio e precoce, respectivamente. A freqüência dos isolados virulentos nas cultivares de terras altas foi maior (51,1%) do que nas cultivares irrigadas (21,8%). Ambos os isolados virulentos e avirulentos às linhas isogênicas estavam presentes na população de P. grisea testada. Dos 72 isolados estudados, 94,4% foram virulentos aos genes Pi-3 e Pi-4a. A freqüência de virulência foi relativamente baixa, em ordem decrescente, em Pi-1, Pi-4b e Pi-2. O coeficiente de similaridade variou de 0,28 a 1,0 entre as diferentes raças dos isolados. O coeficiente de similaridade entre os isolados pertencentes ao grupo IB-9 variou de 0,56 a 1,0. Considerando o coeficiente de similaridade de 0,81, 72% dos isolados IB-9 apresentaram o mesmo padrão de virulência.Termos para indexação: patótipo, Oryza sativa, Magnaporthe grisea, raça fisiológica, patogenicidade.

The goal of the present study was to characterize anatomical and biochemical changes in rice plant roots in response to seed treatment with rhizobacteria (Burkholderia pyrrocinia (R-46) + Pseudomonas fluorescens (R-55)) and Trichoderma asperellum (Ta: mixture of strains T-06, T-09, T-12, and T-52). The experimental design was completely randomized, with six treatments (R-46, R-55, R-46 + R-55, Ta+ R-46 + R-55, Ta, and control) and ten replicates. Treatments Ta and R-46 + R-55 increased the root length and diameter as well as the cortex expansion and induced a 2% expansion of the aerenchymal space. Treatments Ta and R-46 increased the vascular cylinder diameter. The number of protoxylem poles and metaxylem vessel elements was increased by R-46 and R-55. The total phenol content increased with treatments Ta, R-46 + R-55, R-46, and R-55, and all the treatments increased the flavonoid content. The lignin content increased with the Ta and R-55 treatments. All the root architecture modifications resulting from the interaction between seedlings and bioagents (rhizobacteria and Trichoderma spp.) observed in the present study favored the root plasticity of rice seedlings.

Rice blast, caused by Pyricularia oryzae, is the most important disease in rice worldwide. This study investigated the effects of silicon (Si) on the photosynthetic gas exchange parameters (net CO2 assimilation rate [A], stomatal conductance to water vapor [gs], internal-to-ambient CO2 concentration ratio [Ci/Ca], and transpiration rate [E]); chlorophyll fluorescence a (Chla) parameters (maximum photochemical efficiency of photosystem II [Fv/Fm], photochemical [qP] and nonphotochemical [NPQ] quenching coefficients, and electron transport rate [ETR]); concentrations of pigments, malondialdehyde (MDA), and hydrogen peroxide (H2O2); and activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and lypoxigenase (LOX) in rice leaves. Rice plants were grown in a nutrient solution containing 0 or 2 mM Si (-Si or +Si, respectively) with and without P. oryzae inoculation. Blast severity decreased with higher foliar Si concentration. The values of A, gs and E were generally higher for the +Si plants in comparison with the -Si plants upon P. oryzae infection. The Fv/Fm, qp, NPQ, and ETR were greater for the +Si plants relative to the -Si plants at 108 and 132 h after inoculation (hai). The values for qp and ETR were significantly higher for the -Si plants in comparison with the +Si plants at 36 hai, and the NPQ was significantly higher for the -Si plants in comparison with the +Si plants at 0 and 36 hai. The concentrations of Chla, Chlb, Chla+b, and carotenoids were significantly greater in the +Si plants relative to the -Si plants. For the -Si plants, the MDA and H2O2 concentrations were significantly higher than those in the +Si plants. The LOX activity was significantly higher in the +Si plants than in the -Si plants. The SOD and GR activities were significantly higher for the -Si plants than in the +Si plants. The CAT and APX activities were significantly higher in the +Si plants than in the -Si plants. The supply of Si contributed to a decrease in blast severity, improved the gas exchange performance, and caused less dysfunction at the photochemical level.

Crop damage by rice sheath blight, Rhizoctonia solani, can decrease rice yield by up to 45 %. The classical control method of rice sheath blight in the Amazon region is the application of fungicides. Therefore, we tested here the efficiency of a biocontrol agent, Trichoderma asperellum, and fungicides. Two experiments of rice cultivation were carried out with seven treatments: four isolates of T. asperellum, a mixture of the four isolates, the fungicide pencycuron, and the control. The first experiment involved a randomized block design, and seed and foliar spray on all plots. The second experiment involved a split-plot design with foliar spray in main plots and the 1-2 foliar sprays in subplots. Results show that all treatments reduced sheath blight progression rate. In the randomized block experiment T. asperellum reduced disease severity by 19 %, increased grain weight by 34 %, and increased yield by 41 %. In the split-plot design experiment, the mixture of the four T. asperellum isolates grain reduced disease severity by 26 %, increased grain weight by 18.5 %, and increased yield by 26 %. Our results show for the first time that a mixed isolates of T. asperellum was efficient in reducing disease severity and increasing yield and grain weight.