Biological Characteristics of the Pathogenic Fungus Causing Leaf Spot Disease of Watermelon

The leaf spot disease of watermelon is a fungal disease.The biological characteristics of Alternaria cucumerina was studied.The results showed that the mycelium could grow better on PDA medium and medium of watermelon juice,colony diameter was 8.0cm.25℃ was the optimum temperature with colony diameter of 7.1cm.For mycelial growth,the suitable carbon source was glucose,the suitable nitrogen source was sodium nitrate,and the suitable pH was 7,with colony diameter of 7.2 cm,8.7 cm and 8.0cm in the three conditions,respectively.The lethal temperature of mycelium was 52℃,10min.Mycelium could grow in brightness,darkness,and alternating light-dark,best in brightness.For spore germination of pathogen,suitable conditions were 25℃ and pH 7,and the rate of germination was the highest with 2% sodium nitrate,with spore germination rate of 90.2%,95.6% and 96.4%.