Efeito da temperatura e período de permanência em câmara úmida na intensidade das manchas dos cladódios da palma-forrageira (nopalea cochenillifera) e avaliações de cultivar em relação às doenças

Abstract

The sweet cactus is a culture of socioeconomic importance in the semi-arid northeastern, constitute one of the main alternatives to feed the flocks in the season of the drought. In Alagoas the sweet cactus is the second crop more planted, being surpassed only by the sugar-cane. Culture also reaches relevance in the states of Pernambuco, Paraíba and Ceará. Although rustic, sweet cactus can be a host for a series of pathogens, which under certain conditions may compromise the production. Among the diseases that highlights the stain of cladodes, which causes lesions circulars, initially yellowish and subsequently necrotic that commonly cross the whole thickness of the cladode (pad). The disease was reported in several Brazilian states, having been associated to different phytopathogenic fungi. The epidemiological aspects of the disease has not yet been investigated, as well as plant-pathogen interaction will be. In this way the present work had as objective to verify the effect of temperature and moisture chamber permanence in the intensity of the spots of cladodes caused by Colletotrichum gloeosporioidese, Fusarium sp. and assess response to cultivate in relation to the same pathogens. For the experiments that have investigated the effects of the temperature and humidity in the development of the disease were inoculated cladodes variety "Streetwise" with one isolate of Collettrichum gloeosporioides and one of Fusarium sp. To test the effect of temperature, after the inoculations the cladodes were incubated in BOD adjusted for 22, 26, 30 or 34oC. In experiment to determine the effect of moisture the cladodes were kept, after inoculations, in a humid chamber for periods of 12, 24, 36 and 48 hours. In both experiments if determined the diameter of lesions to seven days after inoculation. To test the response of the cultivar in relation to two pathogens, cladodes of "Streetwise", "Texas Nopalera", "Palma Alagoas", “Negro Michoacan” and “Tamazunchale” were inoculated and kept in BOD at 22 0C for seven days, when the diameters of the lesions were determined. Generally milder temperatures and humidity more prolonged periods favored the development of the disease, being 22oC and 48 hours of permanence in the wet chamber conditions that have provided more extensive lesions, whether for C. gloeosporioides, either for Fusarium sp. With regard to the behavior of the cultivar was found that "Texas Nopalera" and "Tamazunchale" developed lesions significantly lower than the other cultivar when inoculated with Fusarium sp. In relation to C. gloeosporioides stood out, "Negro Michoacán" and "Tamazuchale" as the most resistant.

Key words: Nopalea spp., Epidemiology, Sweet cactus disease.