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Article|01 Nov 2018|OPEN
Pathways of flower infection and pollen-mediated dispersion of Pseudomonas syringae pv. actinidiae, the causal agent of kiwifruit bacterial canker
Irene Donati1, Antonio Cellini1, Giampaolo Buriani1, Sofia Mauri1, Callum Kay2, Gianni Tacconi3 & Francesco Spinelli1,
1Department of Agricultural and Food Sciences - DISTAL, Alma Mater Studiorum—University of Bologna, viale Fanin 44, 40127 Bologna, Italy
2ZESPRI GLOBAL Supply, 400 Maunganui Road, Mount Maunganui, New Zealand
3Consiglio per la Ricerca e la Sperimentazione in Agricoltura—Genomics Research Centre, via S. Protaso 302, 29017 Fiorenzuola d’Arda, Italy

Horticulture Research 5,
Article number: 56 (2018)
doi: 10.1038/hortres.2018.56
Views: 597

Received: 15 Nov 2017
Revised: 29 May 2018
Accepted: 04 Jun 2018
Published online: 01 Nov 2018

Abstract

Flowers can provide a protected and nutrient-rich environment to the epiphytic microflora, thus representing a sensible entry point for pathogens such as Pseudomonas syringae pv. actinidiae (Psa). This bacterium can colonize both male and female Actinidia flowers, causing flower browning and fall, and systemic invasion of the host plant, eventually leading to its death. However, the process of flower colonization and penetration into the host tissues has not yet been fully elucidated. In addition, the presence of Psa in the pollen from infected flowers, and the role of pollination in the spread of Psa requires confirmation.

The present study employed a Psa strain constitutively expressing the fluorescent GFPuv protein, to visualize in vivo flower colonization. Microscopy observations were performed by means of confocal laser scanning and wide-field fluorescent microscopy, and were coupled with the study of Psa population dynamics by quantitative PCR (q-PCR). The pathogen was shown to colonize stigmata, move along the stylar furrow, and penetrate the receptacles via the style or nectarhodes. Once the receptacle was invaded, the pathogen migrated along the flower pedicel and became systemic. Psa was also able to colonize the anthers epiphytically and endophytically. Infected male flowers produced contaminated pollen, which could transmit Psa to healthy plants. Finally, pollinators (Apis mellifera and Bombus terrestris) were studied in natural conditions, showing that, although they can be contaminated with Psa, the pathogen’s transmission via pollinators is contrasted by its short survival in the hive.