Abstract
Pseudomonas syringae pv. actinidiae is an important pathogen of kiwifruit (Actinidia deliciosa), and bacterial canker of this host is managed by monitoring and chemical control strategies. The efficacy of the bio-pesticides Amylo-X® (based on Bacillus amyloliquefaciens subsp. plantarum strain D747) and Serenade Max® (strain QST713 of B. subtilis) was evaluated by in vitro and in vivo experiments. Both antagonists inhibited different biovars of the pathogen in in vitro assays; QST713 was more efficient than D747. The two Bacillus strains also colonized A. deliciosa flowers (c. 105-7 cfu per flower) up to 96 h after inoculation. D747 persisted on leaves (c. 104-6 cfu cm-2) up to 4 weeks after inoculation, during 2 years in Emilia Romagna and Latium regions of Italy. On flowers, the antagonists reduced pathogen populations, compared to untreated (control) flowers. On A. deliciosa and A. chinensis plants under controlled conditions, Amylo-X® reduced severity of bacterial canker, providing ca. 50% relative protection on A. deliciosa and 70% on A. chinensis. Serenade Max® was less effective, giving 0% relative protection on A. deliciosa and 40% on A. chinensis. In a field trial, on A. deliciosa plants, Amylo-X® reduced the severity of bacterial canker on leaves, providing ca. 40% relative protection. The sensitivity of both antagonistic strains to streptomycin sulphate was confirmed by testing the most used concentration where antibiotics are approved for management of bacterial pathogens.
Highlights
In the last decade, bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), led to extensive economic losses for kiwifruit producers
Pseudomonas syringae pv. actinidiae is an important pathogen of kiwifruit (Actinidia deliciosa), and bacterial canker of this host is managed by monitoring and chemical control strategies
Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), led to extensive economic losses for kiwifruit producers. The pandemic of this bacterial pathogen started in 2008, mainly in the Actinidia spp., and the pathogen was especially aggressive on A. chinensis cultivars (Abelleira et al, 2011; Mazzaglia et al, 2012; EPPO, 2016)
Summary
Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), led to extensive economic losses for kiwifruit producers. Antibiotics are allowed on most of the continents to control bacterial plant pathogens, but not in Europe, where copper compounds are mostly employed (Balestra and Bovo, 2003; Balestra, 2007; Lee et al, 2005; Vanneste et al, 2011a) Both compounds have different negative properties, including phytotoxicity, pathogen resistance, fruit residues, and accumulation of metal ions in soils (Goto et al, 2004; Marcelletti et al, 2011; Cameron and Sarojini, 2013).Integrated management of kiwifruit bacterial canker is required using multiple strategies for the effective control of the disease. Under controlled conditions and in field trials, the two BCAs were assessed for their capacity to survive on and colonize kiwifruit plants (leaves and flowers), for their efficacy to inhibit Psa epiphytic populations on flowers, and for their effectiveness in reducing the severity of bacterial canker
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