Identification, Bio-characters And Chemical Screening Of Pathogens Causing Black Spot Of "Dongzao" Jujube

A new disease-Dongzao jujube black spot in Hebei and Shandong provinceswas reported. Investigations among 7 cities or counties during 2004²005 showed that Dongzao jujube black spot was very common in the production areas in Hebei and Shandong provinces. It was more serious in Xian county and Huanghua city, Hebei province. The black spot of Dongzao jujube first occurs on the fruit in early July with the typical symptom of black patches emerged on the whole cutis, and the fruits are too bitter to be eaten. 653 isolates were obtained from 219 infected Dongzao jujube samples, then purified and reinoculated. Results showed that the two pathogens isolated had pathogenicity to Dongzao jujube. According to Koch's Postulate and morphological character, two fungal pathogens were identified as Alternaria alternata (Fr.) Keissler and Phoma destructiva Plowr. Both pathogens can cause the disease singly or together. Their occurrence frequencies were 48.8% and 45.6%, respectively.Study on virulence indicated that the pathogenicity of these pathogens was certain. Symptoms after inoculation by two pathogens were coincident with the natural symptoms in field. Re-isolation frequencies of P. destructiva and A. alternata in field were 87.0% and 87.5%, respectively. Re-isolation frequencies in laboratory for two pathogens were 79.5% and 83.6%, respectively.The mycelial growth, conidial germination and sporulation of the two pathogens were tested under different temperature, pH, relative humidity, light, carbon and nitrogen sources. The suitable temperature for mycelial growth of P. destructiva was from 20℃ to 35℃. The optimum temperature was 25℃. The fungus grows slowly at 3℃ and 10℃. The suitable pH for mycelial growth is from 6 to 9, with the optimum pH 7. Peptone is the best carbon source in axenic culture. Sporulation was favorable with KNO₃ and continuous light. The spores can germinate in water drop at the temperature of 10℃³0℃, with the optimum of 25℃. The pH value for spore germination is from 2 to 12, with the optimum of 7. Humidity affected the conidial germination significantly. When in water or the relative humidity nearly reached 100%, the percentage of conidial germination is the highest among all the treatments. The conidial germination rate reduced as moisture capacity decreased. Conidia can hardly germinate at relative humidity 90%.A. alternata can grow well at 20℃³5℃, with the optimum temperature of 25℃. The fungus can not grow at 40℃. The range of the pH for mycelial growth is 2¹2, the optimum being 6⁷. For the conidial germination, the favorable range of the pH value is from 6 to 9. the range of the temperature is 22℃³0℃. Meanwhile, in water the conidial germination rate is the highest. It was also recorded that glucose, maltoseand lactose could promote the mycelial growth. Sucrose and KNO3 could promote the number of sporulation. The treatment of darkness or continuous light or with 12h alternative light did not show significant effect on the mycelial growth, but the treatment of the darkness could promote sporulation.The bio-assessment tests of different fungicides showed that mancozeb, chlorothalonil and thiram were the best for controlling the disease among all the chemicals tested.