Overwintering Ability Of Acidovorax Citrulli And Colonization Dymamic Differences Between Subgroups In The Same Host

Watermelon bacterial fruit blotch is bacterial diseases of watermelon and melon and widely distributed around the world, its pathogenic bacteria is Acidovorax Citrulli (Aac). The pathogen can infect watermelon, melon and other cucurbitaceae crops, when plants or seeds are infected with the pathogenic bacteria, it can cause the outbreaking of the host disease and lead to serious economic yield loss. Pathogen characteristics and survival traits are the basis for prevention and treatment of the disease. This paper focused on the subject of Acidovorax Citrulli and studied its overwintering ability; Used the second generation sequencing technology to complete the genome sequencing and assembly of subgroup I strain and subgroup II strain of Acidovorax Citrulli; Researched the colonization dynamic differences of subgroup I strain and subgroup II strain in watermelon and melon plant tissue through quantitative analysis; Identified and validated one newfound strain Bacillus amyloliquefaciens were carried out, and tested the indoor bacteriostatic activity of the strain to Acidovorax Citrulli and its control efficacy differences to two subgroup strains. The research content provided an important scientific theoretical basis and technical support for preventing and controlling watermelon bacterial fruit blotch scientifically and effectively. The main results were as follows:1. Wild strain Acidovorax Citrulli Aac-5 as the researched object, detected the survivability in loess and flower soil that placed in different low temperature conditions and different depth soil among regions. Isolated, retrieved and cultured the soil treated with different conditions, used plate count method to calculate colony numbers, then compared the results to conclude that Acidovorax Citrulli can stay alive at 4℃,-20℃ and -50℃ conditions, and also can live thtough the winter when underground 10 cm,20 cm and on surface in each region; Overall, the amount of survival of Acidovorax Citrulli in flower soil was higher than that in loess; And the amount of wintering survival bacteria in southern region was higher than that in north region, and the pathogenicity of corresponding Acidovorax Citrulli recycled strains was relatively stronger than that in the north region after processed.2. Used the second generation sequencing technology, Illumina Miseq 2000 platform to determinate and assemble the sequence of whole genome of subgroup I strain pslb65 and subgroup II strain pslbtw6, it was finally concluded that Acidovorax Citrulli subgroup I strain pslb65 was a circular chromosome of 4903443 bp, contained 4532 ORF, the rate of gene encoding was 88.61%, the average content of GC was 68.8%, annotation to 54 RNA; Acidovorax Citrulli subgroup II strain pslbtw6 was a circular chromosome of 5080614 bp, contained 4759 ORF, the rate of gene encoding was 88.41%, the average content of GC was 68.7%, annotation to 51 RNA; Subgroup I strain pslb65 of Acidovorax Citrulli had closely-related evolution relationship with group I sequencing strain M6 and so it was divided into a group with M6.3. Under the greenhouse condition, watermelon and melon seeds were inoculated with subgroup I strain pslb3 and subgroup II strain pslbtw43 that marked with GFP, regularly recycled hypocotyl, root, stem, cotyledon and leaf, recycled Acidovorax Citrulli and used plate method to count colony numbers. The results showed that the subgroup I strain pslb3 and subgroup II strain pslbtw43 both can colonize on watermelon and melon organizations, the colonization ability was strongest on the cotyledon, and was weakest on the blades. The colonization ability of subgroup I strain pslb3 in the tissue of melon was stronger than that of subgroup II strain pslbtw43, and the colonization ability of group II strain pslbtw43 in tissue of watermelon was stronger than that of subgroup I strain pslb3.4. One bio-control strain which had antagonism function on Acidovorax Citrulli was separated and screened, it was determined of Bacillus amyloliquefaciens after a process of identification, named JD001. It was verified that the strain had good inhibitory effect to Acidovorax Citrulli. The effect of strain JD001 respectively restrain the two subgroups of Acidovorax Citrulli was simultaneously tested, and compared the control effect of two subgroups of strains on watermelon and melon plants, arrived at the JD001 strain had good indoor bacteriostatic effect on both subgroup I strain pslb3 and subgroup II strain pslbtw43, the control effect of subgroup I strain pslb3 on watermelon plant was higher than that of subgroup II strain pslbtw43, and the control effect of subgroup II strain pslbtw43 on melon plant was higher than that of subgroup I strain pslb3.