First Report of Pear Blossom Blast Caused by Pseudomonas syringae pv. syringae in China

Isolation and identification of specific lytic bacteriophages as a biocontrol agent against Serratia odorifera PBA-IAUF-1 and Kluyvera intermedia PBA-IAUF-6 causing bacterial canker in the grape and Siberian pear

Bacterial canker, a prevalent disease among fruit trees, is a significant concern. The use of phage therapy is presently seen as a dependable biological strategy to control bacterial diseases in fruits. The objective of this research was to use various biochemical and molecular techniques to determine the types of bacteria responsible for causing cankers in various fruits. Additionally, their ability to cause disease in the fruit tissues was assessed, the specific bacteriophages targeting these bacteria were isolated and identified. The bacteria were separated from different parts of the infected fruits like grapes and Siberian pears. The selection of fruit tissues showing signs of canker disease was performed, and the validation of the isolates' pathogenicity was confirmed following Koch's principles. Subsequently, in order to establish a conclusive identification of the bacterial species, molecular identification was conducted through the sequencing of a specific fragment within the 16S rRNA following amplification by PCR by using universal primers, RW01 and DG74. Isolation and titration of phages specific to fruit spoilage bacteria was done by spot and double-layer agar method, and the growth curve of the isolated bacteriophage was drawn. The phages were detected by transmission electron microscopy (TEM). The results of the study proved the presence of canker causing agents, Kluyvera intermedia PBA-IAUF-6 with the code Sh6 in the Siberian pears, and Serratia odorifera PBA-IAUF-1 with the code Rz3 in the grape fruits, which were deposited in GenBank with the accession numbers of KU878579 and KU168605, respectively. Isolation of the specific bacteriophages to the S. odorifera PBA-IAUF-1 and K. intermedia PBA-IAUF-6 bacterial strains were done from the effluent of South Isfahan wastewater treatment plant and Caspian Sea water, respectively. The titer of the specific phage to S. odorifera PBA-IAUF-1 and K. intermedia PBA-IAUF-6 was detected in the samples as 2.2 × 10-5 and 5 × 10-11 PFU/ml, respectively. An electron micrograph of a bacteriophage that targets two different bacterial strains revealed phages with a geometrically shaped head and a flexible tail, which resembled viruses from the Siphoviridae family.

Pseudomonas syringae pv. syringae Associated With Mango Trees, a Particular Pathogen Within the "Hodgepodge" of the Pseudomonas syringae Complex

The Pseudomonas syringae complex comprises different genetic groups that include strains from both agricultural and environmental habitats. This complex group has been used for decades as a "hodgepodge," including many taxonomically related species. More than 60 pathovars of P. syringae have been described based on distinct host ranges and disease symptoms they cause. These pathovars cause disease relying on an array of virulence mechanisms. However, P. syringae pv. syringae (Pss) is the most polyphagous bacterium in the P. syringae complex, based on its wide host range, that primarily affects woody and herbaceous host plants. In early 1990s, bacterial apical necrosis (BAN) of mango trees, a critical disease elicited by Pss in Southern Spain was described for the first time. Pss exhibits important epiphytic traits and virulence factors, which may promote its survival and pathogenicity in mango trees and in other plant hosts. Over more than two decades, Pss strains isolated from mango trees have been comprehensively investigated to elucidate the mechanisms that governs their epiphytic and pathogenic lifestyles. In particular, the vast majority of Pss strains isolated from mango trees produce an antimetabolite toxin, called mangotoxin, whose leading role in virulence has been clearly demonstrated. Moreover, phenotypic, genetic and phylogenetic approaches support that Pss strains producers of BAN symptoms on mango trees all belong to a single phylotype within phylogroup 2, are adapted to the mango host, and produce mangotoxin. Remarkably, a genome sequencing project of the Pss model strain UMAF0158 revealed the presence of other factors that may play major roles in its different lifestyles, such as the presence of two different type III secretion systems, two type VI secretion systems and an operon for cellulose biosynthesis. The role of cellulose in increasing mango leaf colonization and biofilm formation, and impairing virulence of Pss, suggests that cellulose may play a pivotal role with regards to the balance of its different lifestyles. In addition, 62-kb plasmids belonging to the pPT23A-family of plasmids (PFPs) have been strongly associated with Pss strains that inhabit mango trees. Further, complete sequence and comparative genomic analyses revealed major roles of PFPs in detoxification of copper compounds and ultraviolet radiation resistance, both improving the epiphytic lifestyle of Pss on mango surfaces. Hence, in this review we summarize the research that has been conducted on Pss by our research group to elucidate the molecular mechanisms that underpin the epiphytic and pathogenic lifestyle on mango trees. Finally, future directions in this particular plant-pathogen story are discussed.