| Bacterial canker of kiwifruit,caused by Pseudomonas syringae pv.actinidiae(Psa),is one of the most damading disease of kiwifruit.It has caused huge economic losses on a global scale and its scope of harm is expanding.In order to clarify the genetic diversity of Psa in China and its gobal transmission pathway,we selecte 21 strains of kiwifruit canker which comes from 7 areas for resequencing.Based on this,18 possible sequences of Psa strains from different countries and regions were used to analyze their possible propagation paths using BEAST.The results are as follows.A total of about 16 Gb of valid sequencing data was obtained by resequencing 21 strains of Psa,which contained a large number of mutations.Principal component analysis and phylogenetic analysis divide 21 strains into three major groups,indicating differences between different groups of Psa.The results of fixed coefficient analysis showed that the FST values of all populations were less than 0.05.The results of nucleotide polymorphism analysis showed that the θπ value of all strains was only 3.74×10-6,and the difference between the groups was not obvious.These results indicate that the genetic difference of Psa among different populations is small,and the genetic diversity is at a low level.Gene flow(Nm)analysis showed that the Nm values of different populations were greater than 4,indicating that there was a large gene exchange between the pathogens of each group.Among them,Shanxi and Sichuan provinces had the greatest genetic communication with other provinces.Tajima’D values for all populations were greater than 0 which indicated that all populations were subject to balancing selection.Calculation of Ka/Ks indicated that most Psa genes are subject to purifying selection,wheres a few genes are under positive selection.The BEAST analysis clearly shows that Psa was introduced to China from Japan,South Korea and Portugal,which constitutes a two-way spread between China and the three countries.Psa spreads from China to Italy,New Zealand and Chile,unidirectionally.Similarly,Psa spreads from Portugal to New Zealand.The results reveal that the spread of Psa is not a single transmission from one region to another,but there is mututal and repeated communication between different regions.At the same time,it is speculated that the bacterial canker is caused by artificial cultivation to change the growth environment of kiwifruit,and it originated in many places in the world during the same period.This study reveals the genetic diversity of Psa in China and its gobal transmission,and provides a large amount of Psa genomic data,which could offer a theoretical basis for reducing the spread of pathogenic and further research on disease prevention. |
