Yield loss caused by Phakopsora pachyrhizi on soybean based in physiological components

• Ano de defesa: 2009
• Autor(a) principal: Schmidt, Jéssica
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa; BR; Etiologia; Epidemiologia; Controle; Doutorado em Fitopatologia; UFV
• Palavras-chave em Português: Ferrugem; Soja; Doenças; Pragas; Phakopsora pachyrhizi; Rust; Soybean; Disease; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA
• Link de acesso: http://locus.ufv.br/handle/123456789/1025

Asian Soybean Rust (ASR), caused by Phakopsora pachyrhizi, has been the most important disease of the soybean in the world, over the last few years, causing significant yield loss. The relationship between ASR and soybean yield was studied in field experiments. Four experiments were conducted in Viçosa, MG in an area belonging to the Plant Pathology department, during the crop seasons 2005, 2006, 2007 and 2008. The cultivars used were Monarca, Conquista, and Vencedora. Soybean was infected under natural conditions and different disease levels were obtained in the first experiment using 25, 50, 75 and 100% of the commercial recommended dose of fungicide and in the other experiments by using none, one, two or three sprays of the fungicide tebuconazole according to plant growth stages – R1, R3 and R5. To quantify the disease effect, two methods were used, one based on disease – severity (x) and Area Under Disease Progress Curve (AUDPC) – and the other based on host physiological components - Healthy Leaf Area Index (HLAI), Healthy leaf Area Duration (HAD), Healthy leaf Area Absorption (HAA), Radiation interception by the healthy tissue (HRI) and Radiation Use Efficiency (RUE). All the above mentioned variables were investigated for their relationship with yield. HAA was considered the best variable for use for the establishment of a management system, due to its consistent behavior among growing seasons, cultivars and growth stages. The virtual model proposed by Bastiaans (1991) was used to determine the P. pachyrhizi effect on the photosynthetic rate of infected leaves. Photosynthetic rate and disease severity were assessed on the eighth leaf of each plant in each plot every other week in three experiments during the 2005, 2007 and 2008 growing seasons. Soybean photosynthetic rate was reduced mainly in the lesions and thus there was a small effect of ASR on the remaining green area of the leaf. The greatest effects on photosynthesis apparently were the loss of chlorophyll content and decreased stomatal conductance.