Pathogen identification and causative analysis of ulceration of sporophyte of seaweed Undaria pinnatifida
LI Yun1,ZHANG Saisai1,SUN Yang1,WANG Hongfei2,CHEN Wenbo1*
1.Dalian Modern Agricultural Production Development Service Center, Dalian 116023, China; 2.School of Life Science, Liaoning Normal University, Dalian 116081, China
Abstract: To study the ulceration of seaweed Undariapinnatifida in Longwangtang and Tieshan sea areas in Dalian City, two dominant bacterial strains LH43 and LQ2 were isolated and purified from ulcerated sporophytes of the seaweed by bacterial isolation method and molecular biological method. The artificial infection test confirmed that the isolated strains caused the thallus of the seaweed to ulceration, with the similar diseases in nature, and more pathogenic in LH43 than that in LQ2. The amplification, sequencing and comparison of the 16S rDNA gene sequences revealed that LH43 had 99% homology with Pseudoalteromonasarctica, and LQ2 had 100% homology with Psychrobacteraquimaris. The phylogenetic tree indicated that LH43 and Pseudoalteromonasarctica were clustered into one branch, and that LQ2 and Psychrobacteraquimaris were clustered into one branch. The biochemical test and related comparison revealed that the two strains had the consistent physical and chemical indices with those of Pseudoalteromonasarctica and Psychrobacteraquimaris. The enzyme activity detection showed that 5-10 ℃ was of the optimal growth temperature range for LH43 strain and LQ2 strain, with the maximal enzyme activity of the extracellular products - alginic acid lyase produced by the two strains at 15 ℃. The drug sensitive test showed that LH43 strain was highly sensitive to gentamicin, kanamycin, fleroxacin and streptomycin, while LQ2 strain was highly sensitive to gentamicin, kanamycin, penicillin and azithromycin. Collectively, it has been proved that the decay disease of Undariapinnatifida may be caused by the joint action of alginate lyase produced by Pseudoalteromonasarctica and Psychrobacteraquimaris under unfavorable environment.