Tales Jesus Fernandes

DESCRIÇÃO DA CURVA DE CRESCIMENTO DE FRUTOS DO CAJUEIRO POR MODELOS NÃO LINEARES

O objetivo do trabalho foi avaliar o ajuste dos modelos Gompertz e Logistico, com estrutura de erros independentes e autoregressivos, no desenvolvimento de frutos de caju, com base em medidas de comprimento e largura do fruto, tomados ao longo do tempo. A estimacao dos parâmetros foi feita por meio de rotinas no software R, utilizando-se o metodo dos minimos quadrados e o processo iterativo de Gauss- Newton. Os modelos foram comparados pelos criterios: coeficiente de determinacao ajustado (R2 aj), desvio padrao residual (DPR), criterio de informacao Akaike (AIC) ecriteriobayesiano de Schwarz (BIC). Para os dois modelos, os dados apresentaram autocorrelacao residual positiva, tanto para a variavel comprimento como para a largura do fruto, descrita por processo autoregressivo de primeiraordem. Em geral, por todos criterios de avaliacao da qualidade de ajuste, os dados se ajustaram ao modelo Logistico com uma estrutura autoregressiva da primeira ordem, havendo no entanto superestimacao do tamanhodo fruto nas ultimas idades, tanto no crescimento em comprimento (cm) e largura (cm).

MODELOS NÃO LINEARES NA DESCRIÇÃO DO CRESCIMENTO DE FRUTOS DE CACAU COM VIOLAÇÕES DOS PRESSUPOSTOS

Cacao (Theobroma cacao L.) is an important fruit in the Brazilian economy, which is mainly cultivated in the southern State of Bahia. The optimal stage for harvesting is a major factor for fruit quality and the knowledge on its growth curves can help, especially in identifying the ideal maturation stage for harvesting. Nonlinear regression models have been widely used for description of growth curves. However, several studies in this subject do not consider the residual analysis, the existence of a possible dependence between longitudinal observations, or the sample variance heterogeneity, compromising the modeling quality. The objective of this work was to compare the fit of nonlinear regression models, considering residual analysis and assumption violations, in the description of the cacao (clone Sial-105) fruit growth. The data evaluated were extracted from Brito and Silva (1983), who conducted the experiment in the Cacao Research Center, Ilheus, State of Bahia. The variables fruit length, diameter and volume as a function of fruit age were studied. The use of weighting and incorporation of residual dependencies was efficient, since the modeling became more consistent, improving the model fit. Considering the first-order autoregressive structure, when needed, leads to significant reduction in the residual standard deviation, making the estimates more reliable. The Logistic model was the most efficient for the description of the cacao fruit growth.

Temperature and light intensity interaction on Cercospora coffeicola sporulation and conidia germination

Difficulty in obtaining abundant sporulation in culture of many species of Cercospora may be the limiting factor for studies of biology, systematics, and inoculation of the genus. Therefore, it is necessary to understand the nutritional and environmental requirements that influence mycelial growth, sporulation and germination. As it is difficult to obtain conidia of Cercospora coffeicola in vitro, different temperatures (17, 22, 27, and 32 °C) and light intensities (80, 160, 240, and 320 μmol m-2 s-1) were evaluated to optimize pathogen sporulation and assess favorable conditions for spore germination, aiming for a strategy of disease control. The dark treatment (0 μmol m-2 s-1) was added for sporulation. A significant interaction was found between temperature and light intensity for both variables. The highest sporulation rate of C. coffeicola occurred at a light intensity of 240 μmol m-2 s-1 and air temperature of 22 °C, reaching 5.9x106 con mL-1. Germination was higher at temperature 17 °C and light intensity of 320 μmol m-2 s-1, reaching 52%. Interaction between light intensity and temperature proved to influence the processes of sporulation and germination of C. coffeicola.