In the present study, onion plants were tested under controlled conditions for the development of a climate model based on the influence of temperature (10, 15, 20 and 25°C) and leaf wetness duration (6, 12, 24 and 48 hours) on the severity of Botrytis leaf blight of onion caused by Botrytis squamosa. The relative lesion density was influenced by temperature and leaf wetness duration (P <0.05). The disease was most severe at 20°C. Data were subjected to nonlinear regression analysis. Beta generalized function was used to adjust severity and temperature data, while a logistic function was chosen to represent the effect of leaf wetness on the severity of Botrytis leaf blight. The response surface obtained by the product of two functions was expressed as ES = 0.008192 * (((x-5)1.01089) * ((30-x)1.19052)) * (0.33859/(1+3.77989 * exp (-0.10923*y))), where ES represents the estimated severity value (0.1); x, the temperature (°C); and y, the leaf wetness (in hours). This climate model should be validated under field conditions to verify its use as a computational system for the forecasting of Botrytis leaf blight in onion.

In the present study, the influence of temperature (15, 20, 25, 30 and 35°C) and leaf wetness period (6, 12, 24 and 48 hours) on the severity of Cercospora leaf spot of beet, caused by Cercospora beticola, was studied under controlled conditions. Lesion density was influenced by temperature and leaf wetness duration (P<0.05). Data were subjected to nonlinear regression analysis. The generalized beta function was used for fitting the disease severity and temperature data, while a logistic function was chosen to represent the effect of leaf wetness on the severity of Cercospora leaf spot. The response surface resultant of the product of the two functions was expressed as ES = 0.0001105 * (((x-8)2.294387) * ((36-x)0.955017)) * (0.39219/(1+25.93072 * exp (-0.16704*y))), where: ES represents the estimated severity value (0.1); x, the temperature (ºC) and y, the leaf wetness duration (hours). This model should be validated under field conditions to assess its use as a computational forecast system for Cercospora leaf spot of beet.

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RESUMO A produção de mudas de cebola na região do Alto Vale do Itajaí, SC ocorre predominantemente através de canteiros, onde as plantas ficam expostas aos fatores bióticos e abióticos que influenciam diretamente na sanidade foliar e no seu rendimento. Diante disso, o objetivo deste trabalho foi avaliar a influência da cobertura dos canteiros com túnel baixo sobre o rendimento e a intensidade de doenças foliares. Os experimentos foram realizados nos anos de 2012 e 2013 no Instituto Federal Catarinense, Campus de Rio do Sul, SC. Os tratamentos foram com e sem o uso de túnel baixo. O delineamento utilizado foi o de blocos casualizados com quatro repetições e dez plantas avaliadas em cada repetição. Os dados foram submetidos à análise de variância pelo teste F e se significativos comparados pelo teste de Tukey 5%. A massa fresca da parte aérea com o uso do túnel foram superiores em relação ao sistema convencional em 127,38% e 125,40% no ano de 2012 e 2013 respectivamente. Em 2012 ocorreu uma diferença de 42,88% na área abaixo da curva de progresso da doença (AACPD) da queima das pontas e no ano de 2013 uma diferença de 87,27% e 85% na AACPD e severidade final respectivamente para o míldio. As mudas produzidas em canteiros com túnel baixo apresentaram superioridade no rendimento e sanidade foliar em relação às obtidas no sistema de produção convencional.