Identification of Alternaria alternata from Melon and Study of Its Carbohydrate Active Enzymes Activity

Morphological identification of three strains of fungi A2015, A2018 and A2019 isolated from muskmelon with black spot disease during storage were carried out. The results showed that all the three strains belonged to Alternaria Nees. At the initial stage of growth, they were white, the hyphae were crisscrossing and flocculent, and the conidia were dark inverted rod-shaped and had transverse and longitudinal septa in later stage. The activity of polygalacturonase （PG）, pectin methylesterase （PME）, cellulase （Cx） and β -Glucosidase （β -Glu） of the isolated three muskmelon Alternaria alternata and the Alternaria gaisen strain 3.18017 purchased from China Genera Microbiological Culture Collection Center （CGMCC） were determined to study the activity characteristics of enzymes with infectivity produced from Alternaria infecting muskmelon. The results showed that during the infection of melons by four Alternaria alternata strains, PG activity reached the highest at the third day, and the enzyme activity of strain A2015 reached 20 924.25 μg·h^-1·g^-1FW; Cx and β -Glu activity reached the highest at the 6th day, up to250.20 μg·h^-1·g^-1FW and 8 619.21 μg·h^-1·g^-1FW respectively; PME activity reached the highest at the 7th day which was 0.24 μg·h^-1·g^-1FW. Which suggested that the order of enzyme production was PG, Cx, β-Glu and PME in Alternaria alternata infection of melon, in this order, the cell wall was gradually degraded and infected, the fungi invaded into the melon body. The results could effectively provide a theoretical basis of the characteristics of the pathogens for the later targeted prevention and treatment of melon black spot disease and defence against the invasion of Alternaria alternata.