Pseudomonas syringae pv. actinidiae survival in point-inoculated kiwifruit vines

Abstract

The survival and spread over time of Pseudomonas syringae pv. actinidiae (Psa) in point-inoculated kiwifruit vines is poorly understood. Forty-eight 2-year-old vines of Actinidia chinensis var. deliciosa ‘Hayward’ and A. chinensis var. chinensis ‘Hort16A’ were inoculated 30 cm above the crown, either during the active growth (autumn) or dormant (winter) period in two successive years. Vines were cultivated for 3—4 years, after which bacterial isolations were made at intervals along the vines from crown to tip. Psa was found up to 220 cm above the inoculation point and in some of the crowns, 30 cm below the inoculation point. The sites where Psa was found within vines were not always contiguous. Fewer vines of ‘Hayward’ developed serious symptoms or died than ‘Hort16A’; however, more surviving vines of ‘Hayward’ were Psa-positive than those of ‘Hort16A’. Psa was able to survive for at least 4 years in apparently healthy kiwifruit vines. This has implications for the movement of asymptomatic budwood to areas without Psa.

Development, Management and Utilization of a Kiwifruit (Actinidia spp.) In Vitro Collection: A New Zealand Perspective

“…Many of the in vitro cultures were initiated from plants growing in the field. However, even apparently healthy-looking plants have been demonstrated to carry the Psa-3 bacterium [ 13 , 14 ]. Additionally, plants carry a microbiome that reflects their cultivation history and they may harbor endogenous pathogens that cannot be detected using standard plant tissue culture media [ 15 ].…”

“…For this, the basal part of the plant is excised and transferred into a Petri plate containing a medium comprising 20 g/L potato dextrose agar (PDA) with 5 g/L peptone for one week to encourage proliferation of endogenous pathogens. Plants that show no contamination are retained, but then, depending on the purpose of the in vitro cultures, they might be subjected to further screening for Psa-3 using polymerase chain reaction (PCR) testing in conjunction with incorporation of 3 g/L peptone into growing medium to confirm the plants are Psa-3-free [ 13 , 16 ].…”