Aspectos epidemiológicos da queima das folhas da cenoura ( daucus carota l.) causada por alternaria dauci (Kühn) Groves & Skolko. (parte I): sobrevivência de Alternaria dauoi (Kühn) Groves & Skolko em restos culturais da cenoura (daucus carota l.)sobrevivência de Alternaria dauoi (Kühn) Groves & Skolko em restos culturais da cenoura (daucus carota l.)

Abstract

The spore viability of Alte1•naria dauai {Kuhn} Graves & Skolko in carrot (Daucus carota L.) debris wich w􀀋 re kept at different levels of ternperature and relative hurni dity, whithout light, was studied. The temperature levels te􀀐 ted were 8, 16, 24 and 329C, and the relative humidity levels 3, 18, 51, 73 and 100%. The treatments were different combin􀀚 tions of these levels. Hwnidity was the more important factor in preserving the fungos spore ability to germinate and its infectivity. Under conditions of high relative humidity and temperatures of 24 and 329C, the spores rapidly lost their V! ability. This did not happen when the relative humidity was 􀀥 qual to, or below, 51%. The survival of fungus myceliurn on carrot peti ales was studied in non-treated organic soil, at different hu rnidity levels, at three different depths, during a period of 120 days. Soil humidity was the factor of major significance in the persistence of the mycelium, followed by depths and t! me factores. In petioles kept at depths of 10 and 20 cm in h􀈈 mid soil,the survival was greatly reduced, while survival was markedly higher in those kept at the surface of dry soil. The effect of humidity on the viability of m􀈽 celiurn was studied also under soiless condition. Petioles w􀉌 re maintained in relative hurnidity controlled chamber, at 249 e. In satured atmosphere (100% humidity), the myceliwn viab! lity was lost in less than 20 days. It was concluded that both, the conidial and mycelial form of Alternaria dauai are quite sensitive to high hwniQity levels.