Epidemiologia da mancha-bacteriana (Xanthomonas axonopodis pv. vignicola) do feijão-caupi

• Autor(a) principal: Lima, Hyanameyka Evangelista de
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1035
• topic: Xanthomonas axonopodis pv. vignicola; Feijão; Epidemiologia; Relação hospedeiro-parasito; Xanthomonas axonopodis pv. vignicola; Bean; Epidemiology; Host-parasite relationship; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

Bacterial blight of cowpea (Vigna unguiculata) caused by Xanthomonas axonopodis pv. vignicola (Xav) have been occurred in Brazil, however, there is no available epidemiological information about this pathosystem. The objective of this study was to know some epidemiological aspects related to bacterial blight of cowpea through studies on greenhouse and field. To evaluate the severity of cowpea bacterial blight, two diagrammatic scales were prepared, one for cultivars with oval leaflets and another one to lanceolate leaflets, using the cultivars BRS Bragança and BRS Mazagão, respectively. The use of diagrammatic scales resulted in higher accuracy and precision of the estimatives performed, and the variance of the absolute errors in the assessment of disease presented values within acceptable limits. Greenhouse and field experiments were installed to evaluate the disease severity in BRS Bragança plants according to the inoculums concentrations of Xav. The severity and defoliation increased with increments of inoculum concentration. Xav was detected in seeds from plants grown in field using CCM medium independent of inoculum concentration. The bacteria incubation period decreased with the elevated leaf wetness period. We calculated the corrected severity of disease based on a combined measurement of severity and defoliation. The severity, the area under the disease progress curve and disease progress rate increased as the leaf wetness period elevated. Soybean (Glycine max) cv. BRS Tracajá, common bean (Phaseolus vulgaris) cv. Pérola and weed species (Euphorbia heterophylla) showed no disease symptoms when inoculated with Xav (107 CFU.mL-1) by spraying. However, common bean plants showed hypersensitivity reactions (HR). All plants presented HR when Xav was infiltrated with a syringe in their tissues, and total tissue necrosis was observed in plants of E. heterophylla at less than 24 hours after inoculation. Other test was also conducted in greenhouse to assess the disease severity at different stages of development of cowpea plants (primary leaves - PL, 2 or 3 trifoliate leaves TL, with open flowers OF, and with pod development - PD) on the time of infection, as well as its influence on defoliation, on components of production and on transmission of bacteria to the seeds. The disease caused defoliation in all cowpea plants, regardless of phenologic stage of the culture and there were significant differences in relative area under the disease progress curve (RAUDPC) among development stages, helping to reduce production of some components, especially of the mass of dry grains (MDG). It was possible to detect Xav in seeds of cowpea plants infected at any development stage and was detected higher amount of CFU.g-1 seed in seeds samples from plants inoculated by Xav on PD stage and TL stage. Subsequently, two field experiments were conducted in two consecutive seasons, for assessing the disease severity, the components of cowpea production and the transmissibility of the bacteria to the seeds. The cultivars used were BRS Bragança and BRS Vita-7, which were inoculated by Xav when de plants were in TL stage and OF stage. The disease severity was higher in BRS Bragança than BRS Vita-7, and there were reductions in some components of production, mainly in MDG. There were differences (p ≤ 0,05) by t test in RAUDPC between TL stage and OF stage in plants BRS Bragança inoculated by Xav. It was possible to detect Xav in seeds of cowpea of two cowpea cultivars, regardless of development stage in which they were inoculated, being detected higher amount of CFU g-1 seed in seeds samples from plants of cultivar BRS Bragança on TL stage inoculated by Xav.