Identification And Biological Charicteristics Of Cucurbit Bacterial Fruit Blotch Pathogen

The study has carried on several research to cucurbit bacterial fruit blotch through modern molecular identification and traditional biological methods.Two strains were isolated from the diseased plant which was suspected to be the cucurbit bacterial fruit blotch that occured in Henan province of China.According to their morphology, cultural characteristics, pathogenicity, host range, ELISA and molecular identification,the strains were identified as pathogen Acidovorax avenae subsp.citrulli (acronym:Aac). It was the first demonstration that watermolon and melon bacterial fruit blotch in Henan was caused by Acidovorax avenae subsp.citrulli. The Intergenic Transcribed Spacers (ITS) region between 16S and 23S rDNA genes were amplified by universal PCR primers. The result showed that ITS sequences of the strains in Henan and Hainan were up to 98.67% and 99.55% with the similarity of American strain FC520 respectively.Some factors related to the cucurbit bacterial fruit blotch were investigated in the green house, such as time of seeds immersion in pathogen solution, temperature affecting invasion by pathogen, the quantities of pathogen on seeds surface.The time of seeds immersion in pathogen showed the incidence of disease was highest when seeds soaked in 30min and 1h with disease incidences up to 95%.It proved that the pathogen sticked to the surface of seeds quickily.The tempreture experiment showed that high temperature was favorable to the emergence of this disease and 35℃ was the most suitable for it.The amount of the pathogenes on watermelon seeds surface showed that the concentration between 10~4 CFU/ml ～10~8 CFU/ml could cause disease.the incidence of disease came to the culmination at 10~8CFU/ml, which indicates that pathogen has an extremely strong aggressiveness.Inoculation by spraying different isolates of pathogen suspension on watermelon female flowers and young fruits was conducted in the field. The result showed that all fruits produced from inoculated flowers did not display the symptom.Inoculated young fruits showed symptom after three weeks.The fruits had two kinds of symptoms: restricted lesion and expanding lesion.This pathogen invade the seeds both at flowering stage and fruit-setting stage. Flowering stage was the important period for infection. The seeds from the fruits with restricted lesion had the pathogen. The incidence of disease on seedlings has the remarkable difference with the various strains or the different inoculated position with the same strain. In the assay the...