Molecular Comparation Of Pseudomonas Syringae PV. Lachrymans Strains From Cucumber And Muskmelon

Cucumber angular leaf spot caused by Pseudomonas syringae pv. lachrymans is distributed worldwidely and inflicts different degrees of damage, which can also induce bacterial spot of melon leaves. Previous studies demonstrated that the pathogens of bacterial angular leaf spot on cucumber and melon were both P. syringae pv. lachrymans, but it was found in our lab that there existed certain differences in the pathogenicity and molecular biology between P. syringae pv. lachrymans strains from cucumber and muskmelon. In this study, the pathogenicities of cucumber strains and muskmelon strains from cucumber and muskmelon plants were determined and compared; and then the molecular biological differences were researched on several house-keeping genes; at last, specific primers were designed to distinguish between the isolates from different hosts. The main research achivements are as follows:16S rRNA genes and16S-23S rDNA genes of P. syringae pv. lachrymans strains from cucumber and muskmelon were sequenced, and phylogenetic trees were constructed based on the results. After that, the pathogenicities of isolates of two groups were determined. Results showed that the homology of two different groups strains reached up to99%identitied and that isolates from different plants caused more serious diseases in their origin hosts respectively, indicating that P. syringae pv. lachrymans strains from cucumber and melon belonged to the same species but differed from each other in their pathogenicities.Five house-keeping genes of P. syringae pv. lachrymans strains from cucumber and melon, namely GAPDH gene、rpoD、rpoB、gyrB and glt A were sequenced, and five phylogenetic trees were constructed. Phylogenetic analysis showed that P. syringae pv. lachrymans strains from cucumber and melon were grouped into two separated branch clusters, indicating that the two isolates were genetically different.Through multiple sequence comparison and analysis of GAPDH genes and ITS genes in P. syringae pv. lachrymans strains from cucumber and melon and other pathovars of P. syringae, we designed two pairs of specific primers:G-F/G-R to cucumber strains and ITS-F/ITS-R to melon strains. The two pairs of primers can both distinguish the two groups strains from all other experimental strains, which further confirmed the probability that the two groups strains belonged to different pathvars.In conclusion, we proposed that P. syringae pv. lachrymans strains from muskmelon as a novel pathovar named as Pseudomonas syringae pv. melonis pathovar nov.