Bacterial Canker on Kiwifruit in Italy: Anatomical Changes in the Wood and in the Primary Infection Sites

Abstract

The bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae is a severe threat to kiwifruit production worldwide. Many aspects of P. syringae pv. actinidiae biology and epidemiology still require in-depth investigation. The infection by and spread of P. syringae pv. actinidiae in xylem and phloem was investigated by carrying out artificial inoculation experiments with histological and dendrochronological analyses of naturally diseased plants in Italy. We found that the bacterium can infect host plants by entering natural openings and lesions. In naturally infected kiwifruit plants, P. syringae pv. actinidiae is present in the lenticels as well as in the dead phloem tissue beneath the lenticels, surrounded by a lesion in the periderm which appears to indicate the importance of lenticels to kiwifruit infection. Biofilm formation was observed outside and inside plants. In cases of advanced stages of P. syringae pv. actinidiae infection, neuroses of the phloem occur, which are followed by cambial dieback and most likely by infection of the xylem. Anatomical changes in wood such as reduced ring width, a drastic reduction in vessel size, and the presence of tyloses were observed within several infected sites. In the field, these changes occur only a year after the first leaf symptoms are observed suggesting a significant time lapse between primary and secondary symptoms. It was possible to study the temporal development of P. syringae pv. actinidiae-induced cambial dieback by applying dendrochronology methods which revealed that cambial dieback occurs only during the growing season.

Bactericidal Compounds Controlling Growth of the Plant Pathogen Pseudomonas syringae pv. actinidiae, Which Forms Biofilms Composed of a Novel Exopolysaccharide

“…Previously, it was reported that P. syringae pv. actinidiae NZ V-13 can form biofilms on the external and internal surfaces of plants, and these are likely involved in different phases of infection (9).…”

“…Biofilm formation protects cells against host defense mechanisms as well as various chemical agents. Previously, it was shown that the biofilm growth mode of P. syringae is involved in plant pathogenicity (9)(10)(11). P. syringae pv.…”

“…Biofilm formation by P. syringae pv. actinidiae is involved in different phases of kiwifruit infection both outside and inside the host plant (9). It is likely that plant-pathogenic bacteria can complete the pathogenic cycle, spreading and surviving on plant surfaces and within tissues through cycles of biofilm formation and dispersion (12).…”

Harvesting of southern Piedmont’s orchards pruning residues: evaluations of biomass production and harvesting losses

“…The processed data show both the kiwi tree, although when affected by bacterial canker (Pseudomonas syringae pv actinidiae) which limits their vigor (Balestra et al, 2009;Renzi et al, 2012), and the apple tree can guarantee a good production of biomass (2.5 -3.0 t DM ha -1 ). Nevertheless the harvest of such potential biofuel is extremely difficult and determines heavy biomass losses (from 11 to 47% of the pruning residues depending on the species, variety and pruning technique).…”

Characterization of Chilean Pseudomonas syringae pv actinidiae strains isolated from infected orchards

“…These surface-associated 98 multicellular communities are often used by bacteria because they give them several advantages 99 over the individual-cell mode, particularly regarding their resistance to stressful environmental 100 conditions or to chemical compounds (Verstraeten et al 2008). It has been shown that PSA is 101 able to form biofilms, sessile bacterial communities embedded within and attached to a surface 102 (Ghods et al 2015;Renzi et al 2012). This association allows the bacterial community to be 103 protected from several stress conditions in both, epiphytic and endophytic colonization phases.…”