Mal-das-folhas da seringueira: dinâmica de inóculo do patógeno, progresso e danos, em três condições topográficas

• Autor(a) principal: Honorato Júnior, Jaime
• Data de Publicação: 2010
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4382
• topic: Hevea brasiliensis; Microcyclus ulei.; Conídios; Ascósporos; Fenologia; Desfolhamento; Hevea brasiliensis; Microcyclus ulei.; Conidia; Ascospores; Phenology; Defoliation; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

Brazil currently accounts for only 1.15% of the world production of natural rubber. A limiting factor on the rubber production in Brazil is the South American Leaf Blight (SALB), caused by Microcyclus ulei. Considering the lack on the knowledge on SALB, between June 2005 and December 2008 we studied the: i. dynamics of ascospores and conidia of the pathogen, ii. host phenology and disease progress and iii. effects of height, disease severity, and leaf density on the production and growth of rubber trees. The experiments were undertaken in commercial rubber plantations of Igrapiúna - Bahia, in three topographical conditions (strata): top, hillside, and lowland. In each stratum, 25 boxes, each with 1x1x0.5 m, were distributed to collect leaves (five repetitions, each with five boxes). At every week, disease severity, stroma occurrenceand frequency on fallen leaflets, leaf density, phenology and prevalence of leaflets in stages B, C and D, in 60 trees of each stratum were evaluated. Starting July 2008, one volumetric Burkard spore trap was installed in each stratum to trap ascospores and conidia. In each stratum, temperature (average, maximum and minimum), relative humidity (average, maximum and minimum), hours of leaf wetness, hours with relative humidity equal or more than 90%, and hours with temperatures between 22 and 26 º C. were registered. By using path analysis, we studied the effects of weather variation on spore concentration and disease severity, as well as the effects of height, disease severity, and leaf density on both production and growth of rubber trees. Ascospores and conidia were trapped throughout all the experimental period (18 months). Air concentration of ascospores and conidia tended to be higher at night time and daytime, respectively. The numbers of ascospores and conidia collected between 9:00 and 15:00 h, in days with peaks, were positively correlated. Weather variables affected most the number of conidia in the air in the lowland. Higher leaf density and lower disease severity were most common on the top. More number of hours with leaf wetness and minimum relative humidity were registered in the lowland, affecting most disease severity. Altitude affected directly and positively, and severity directly and negatively, both rubber production and growth in all strata. Leaf density indirectly affected both rubber production and growth. There was an average reduction of 47.7% in the production of rubber in the lowland, with average severity of 15.0% and reduction in average leaf density of 50.1%. There is evidence to suggest changes in the life cycle of the pathogen: under favorable weather conditions throughout the year, there is production of ascospores and conidia throughout the year. It was found that the effects of environmental variables on disease are more evident in lowlands and that SALB causes a reduction in the production and growth of rubber, especially in the lowlands. Under these conditions disease management, such as the planting of clones with horizontal resistance, is to be increased.