Application of Survival Ratio for Monocyclic Process ofHemileia vastatrixin Predicting Coffee Rust Infection Rates

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Abstract
Apparent infection rates corrected for leaf formation (.rho.") were determined based on proportion of leaves (PLR) and leaf area rusted (PRA) on 60 branches marked among 15 plants on 1 ha of ''Mundo Novo'' coffee [Coffea arabica] in Vicosa, Minas Gerais, Brazil, at 14-day intervals from Aug. 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 Schroedter''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 [the date of prediction]) 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 .times. 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 .times. DISEE .times. 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 .rho." for 28 days after DP [date of prediction] (Y1 is based on PRL, Y2 is based on PRA), X1 is logit PISAI and X2 is host available for infection, -logit xy when xy is PRL or PRA on DP corrected for leaf formation during the 28 days after DP.

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