Bacillus amyloliquefaciens subsp. plantarum strain D747 to control the kiwifruit bacterial canker disease

The efficacy of the bio-fungicide Amylo-X®, based on Bacillus amyloliquefaciens subsp. plantarum (Bap) strain D747, was evaluated in vivo against Pseudomonas syringae pv. actinidiae (Psa), the causal agent of kiwifruit bacterial canker disease. By in vivo tests, under controlled conditions, Amylo-X®reduced the disease severity caused by Psa in Actinidia chinensis var. deliciosa and in A. chinensis var. chinensis plants providing a protection of about 50 and 70%, respectively. By in vivo trials Bap strain D747 was able to colonize A. chinensis var. chinensis female flowers up to 96 h (ca. 105-7 CFU flower-1) and to persist on A. chinensis var. deliciosa leaves up to 4 weeks (ca. 104-6 CFU cm-2), during 2017 and 2018 in northern and central Italy (Emilia Romagna and Lazio Regions). In particular, on flowers, Bap strain D747 caused a significant reduction in the Psa population as compared to the control samples. In Lazio Region field trials, during 2018, Amylo-X®reduced the disease severity on leaves of A. deliciosa plants with a protection up to 40%. The strain Bap D747 sensitivity to streptomycin sulphate was confirmed by applying the most commonly used concentration in those countries where antibiotics are allowed against phytopathogenic bacteria. Moreover, the strain D747 treated at roots was able to reduce the leaf spot severity provoked by Psa in A. chinensis var. chinensis plants.