Pathways of flower infection and pollen-mediated dispersion of Pseudomonas syringae pv. actinidiae, the causal agent of kiwifruit bacterial canker

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.

Osmoprotectants and Antioxidative Enzymes as Screening Tools for Salinity Tolerance in Radish (Raphanus sativus)

The research addresses the identification of a screening methodology for salt stress tolerance in radish cultivars. In the first experiment, two different radish cultivars(long white and round red) were compared in their morphological and physiological responses to different salinity levels. Round red radish showed better morphological and physiological responses to incremental salinity in terms of yield and better adaptation of overall water relations. In the second experiment, the most tolerant genotype from the first experiment was used as a control against other seven round red radish genotypes ranked by their salinity tolerance according to morphological, physiological and biochemical indices. Salt stress did not significantly affect malondialdehyde(MDA) and hydrogen peroxide(H2O2) content, and ascorbate peroxidase(APX) activity in the studied cultivars. Nonetheless, the relatively salt tolerant cultivar SAXA2 showed higher ability to accumulate compatible solutes(e.g.proline and proteins) and maintain osmotic adjustment. In addition, cultivar SAXA2 also showed considerable increase in glutathione reductase(GR) activity. Our results supported that accumulation of proline and higher GR activity are associated with radish salt tolerance, whereas no relationship with salinity was observed in superoxide dismutase(SOD), MDA and H2O2 content.