Allelopathic compounds reduce the growth and productivity of upland rice plants, especially in consecutive plantations. The rhizobacteria Pseudomonas fluorescens BRM-32111 and Burkholderia pyrrocinia BRM-32113 have been recorded as growth promoters in rice. This study was developed to understand the effect of the application of rhizobacteria on upland rice plants in consecutive plantations. Experiments were conducted in a completely randomized design with four replications of four treatments: rice seed inoculated with P. fluorescens BRM-32111, rice seed inoculated with B. pyrrocinia BRM-32113 (both sown on soil with rice residue), non-inoculated plants sown on soil with rice residue (control with residue (WR)), and non-inoculated plants on soil with no residue (NR). Roots and seedling growth were adversely affected by allelopathic compounds in control WR plants. Plants inoculated with rhizobacteria P. fluorescens BRM-32111 or B. pyrrocinia BRM-32113 induced an increase of 88% in biomass, 3% in the leaf area, 40% in length, 67% in root biomass, 21% in chlorophyll a, 53% in chlorophyll (a+b), 50% in rate of carbon assimilation (A), 227% in A/rubisco carboxylation efficiency (C i) and 63% in water use efficiency (WUE) compared to control WR plants. These results indicate that rhizobacteria P. fluorescens BRM 32111 and B. pyrrocinia BRM 32113 increase the tolerance of rice plants to stress from allelochemicals. There are possible practical agricultural applications of these results for mitigating the effects of environmental allelochemistry on upland rice.
The virulence pattern of the isolates of Pyricularia grisea from commercial fields of the upland rice (Oryza sativa) cultivars 'Primavera' and 'BRS Bonança' was analyzed. A hundred and seventy monoconidial isolates of the pathogen virulent to 'Primavera' and 139 to 'BRS Bonança' collected from eight fields, during two years (2001-2003) were tested, under greenhouse conditions, on six newly released rice cultivars. Differences in virulence pattern were observed in pathogenic populations of 'Primavera' and 'BRS Bonança'. Isolates with virulence to improved cultivars were common in samples from farmers' fields in the absence of aloinfection. The virulence frequency of P. grisea isolates collected from 'Primavera'' to cultivars 'BRS Vencedora', 'BRS Colosso', 'BRS Liderança', 'BRS Soberana', 'BRS Curinga' and 'BRS Talento', was high in descending order. On the other hand, in the fungus population of 'BRS BRS Bonança' virulence frequency was high in 'BRS Talento', followed by 'BRS Curinga', 'BRS Vencedora', 'BRS Liderança', 'BRS Colosso' and 'BRS Soberana'. While virulence to 'BRS Talento' was rare among isolates from 'Primavera', it was most frequent in isolates of 'BRS Bonança'. The six improved rice cultivars permitted to differentiating agriculturally important virulences in the pathogen population which can be utilized in selecting breeding lines for specific resistance, in rice blast improvement program.
Foi estudada a liberação de conídios de Pyricularia grisea no plantio convencional (PC) e direto (PD) de arroz (Oryza sativa) de terras altas, nas fases de desenvolvimento vegetativo e emissão de panículas nos experimentos de campo realizados em dois anos (1998/2000). As coletas de conídios de P. grisea foram realizadas com as armadilhas volumétricas Rotorod sampler. Objetivando quantificar os conídios viáveis e com potencial para causar infecção em folhas novas foram também utilizadas bandejas com plantas de arroz com 25 dias de idade das cultivares Carajás e Primavera expostas no campo, como armadilhas vivas. Na safra 1998/1999, o número de conídios de P. grisea aumentou linearmente com o tempo, entre o estádio de grão pastoso e maduro. Na safra de 1999/2000, a quantidade de conídios coletada aumentou de maneira exponencial, iniciando ao final do estádio emborrachamento até na fase de grão semi-maduro. O número de conídios coletados com a armadilha volumétrica diminuiu exponencialmente com o aumento da precipitação pluviométrica, assim como, reduziu a severidade da brusone nas plantas da armadilha viva tanto para a cultivar Carajás como para Primavera. A produção e a liberação de conídios foi menor no plantio direto tanto na fase vegetativa como durante o enchimento dos grãos nas panículas.
Foram estudados o progresso da brusone (Pyricularia grisea) e o conteúdo de clorofila nas folhas em experimentos de campo, com arroz (Oryza sativa) de terras altas, nos sistemas de plantio direto (PD) e convencional (PC), durante as safras de 1998/1999 e 1999/2000. As taxas aparente de infecção da brusone nas folhas na primeira safra no PC e no PD formam de b = 0,099 (r = 0,97**) e de b = 0,066(r = 0,90**), respectivamente. Na segunda safra foram de b = 0,054(r = 0,99**) no PC e no PD de b = 0,055(r = 0,99**). Entretanto as taxas de progresso da brusone nas folhas não diferiram estatisticamente nos dois sistemas de plantio. Foi observada uma relação linear, positiva e significativa entre conteúdo de clorofila e a severidade da brusone nas folhas.
Agricultural production plays a strategic role in Amazon, since it has economic and food-growing importance, but also represents a great highlight in the cultural and social scenarios. However, such theme still faces some challenges regarding the development of alternative methods capable of achieving sustainable productions, with quality and quantity, and yet with no harm to the natural resources. The Trichoderma fungus has become significant as a biological agent in agricultural species, presenting considerable answers to the development and protection of vegetables, and has also guaranteed the environmental preservation and food safety. Such issues considered, this study intends to guide small agricultural producers about the usage of Trichoderma fungi, emphasizing the agricultural species cultivation. The university extension program took place in four communities promoting workshops about the usage of the Trichoderma and other alternative biofertilizers. Each community was interviewed in an attempt to identify the main difficulties regarding a sustainable agricultural production. As a result, 75% of the communities still used chemicals in their fertilizing and plague control processes and did not use biological-origin products due to the lack of information on where to obtain them and how to use such items; only 25% had alternatives of biological defensives and merely 5% had any knowledge about the usage of biofertilizers like Trichoderma. Such findings evidence it is necessary to continue the extension program actions, focusing on their improvement and expansion, since they benefit society, economy and the environment of the Amazon region.
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