VIEW ARTICLE

Ecology and Epidemiology

Application of Survival Ratio for Monocyclic Process of Hemileia vastatrix in Predicting Coffee Rust Infection Rates. A. C. Kushalappa, Departamento de Fitopatologia, Universidade Federal de Viçosa, Minas Gerais, 36.570, Brazil; M. Akutsu(2), and A. Ludwig(3). (2)Departamento de Fitopatologia, Universidade Federal de Viçosa, Minas Gerais, 36.570, Brazil; (3)Centro de Processamento de Dados, Universidade Federal de Viçosa, Minas Gerais, 36.570, Brazil. Phytopathology 73:96-103. Accepted for publication 14 April 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-96.

Apparent infection rates corrected for leaf formation (?”) were determined based on proportion of leaves (PLR) and leaf area rusted (PRA) on 60 branches marked among 15 plants on 1 ha of cultivar Mundo Novo coffee in Vicosa, Minas Gerais, Brazil, at 14-day intervals from August 1978 to July 1980. Hourly temperature and leaf wetness were recorded and the data were transformed to infection equivalents for environment (INFEE) and to dissemination equivalents for environment (DISEE). The INFEE was determined by laboratory experiments to be the product of infection equivalents for hours of free water and for temperature, which were calculated from the function of hours of free water and of temperature, respectively, for infection, as determined by laboratory experiments. The functions are Y = 1 - 1.996 exp (- 0.1089t) and Y' = sin² (188.1x - 41.6x² - 151.3x³), respectively, in which Y and Y' are the proportions of maximum infection observed (= INFEE), x is the Schrödter's temperature equivalent, and t is hours of free water. DISEE was based on the proportion of rainy and windy days (for 28 days before DP) multiplied by the proportion of leaf density. The monocyclic process equivalents for environment (MPEE) related to the whole monocyclic process was derived from MPEE = DISEE × INFEE. The inoculum was quantified as the proportion of leaf area occupied by visible spores and proportion of spore area index (PSAI). The calculated proportion of spores surviving dissemination and able to cause infection was designated as the proportion of infective spore area index, PISAI = PSAI × DISEE × INFEE. The following regression equations were developed to predict coffee rust infection rates: Y₁ = 2.0804 + 0.1533X₁ + 0.0852X₂ (r² = 0.72), and Y₂ = 1.393 + 0.1149X₁ + 0.0708X₂ (r² = 0.49), in which Y is ?” for 28 days after the date of prediction (Y₁ is based on PLR, Y₂ is based on PRA), X₁ is logit PISAI and X₂ is host available for infection, - logit xy when xy is PLR or PRA on the date of prediction corrected for leaf formation during the 28 days after the date of prediction.