Influence of Stigmatic Morphology on Flower Colonization by Erwinia amylovora and Pantoea agglomerans

Abstract

The morphology of apple and pear stigma was investigated with confocal laser scanning microscopy and scanning electron microscopy. The floral colonization process by Erwinia amylovora was studied with gfplabelled bacteria and confocal laser scanning microscopy to allow the in vivo observation of the pathogen colonization on intact, viable plant tissues without any kind of staining of the specimens. The interaction on the stigma between Erwinia amylovora and Pantoea agglomerans, both labelled with genes encoding for fluorescent proteins (DsRed-GFP), was also investigated. A stylar groove, covered by papillae and dwelling from the stigma along the style, was visualized. In laboratory conditions, this groove was shown to be an important way for E. amylovora migration towards the nectarthodes. Due to its anatomical structure the groove can sustain bacterial multiplication and thus may play an important role on the interactions between the pathogen and the bacterial antagonist P. agglomerans.Abbreviations: Confocal laser scanning microscopy -CLSM; scanning electron microscopy -SEM

Floral traits affecting fire blight infection and management

“…Originating from the stigma, a groove is running along the style to the nectar cup, apparent in apple and pear, as well as hawthorn and firethorn flowers. In some apple and pear cultivars, similarly to the stigmatic surface, the epidermis of the groove is constituted by stigmatic papillae (Spinelli et al 2005a). The stylar groove epidermis is separated from the transmitting tissue by several layers of parenchymatous and vascular tissue (Cresti et al 1980;Spinelli et al 2005a).…”

“…In some apple and pear cultivars, similarly to the stigmatic surface, the epidermis of the groove is constituted by stigmatic papillae (Spinelli et al 2005a). The stylar groove epidermis is separated from the transmitting tissue by several layers of parenchymatous and vascular tissue (Cresti et al 1980;Spinelli et al 2005a). Both pathogenic (E. amylovora) and antagonistic bacteria (P. agglomerans) exploit the stylar groove during their movement from the stigmatic surface to the nectarthodes.…”

“…Both pathogenic (E. amylovora) and antagonistic bacteria (P. agglomerans) exploit the stylar groove during their movement from the stigmatic surface to the nectarthodes. Similarly to the stigmatic surface, bacterial cells are mainly localized among the numerous papillae in the stylar groove (Spinelli et al 2005a). Higher bacterial populations were detected on the stigma than on the style.…”

“…The rapid growth of bacteria was observed on both sites until they reached the estimated carrying capacity of pistil. For the first 24 h after inoculation, bacteria remained confined to the pistil (Spinelli et al 2005a). Rosen (1936) supposed that bacteria penetrate the stigmatic tissues mostly through intercellular spaces or between two adjoining cells by dissolution of the walls.…”

“…Similarly, Pierstorff (1931), Hildebrand (1937b), Rundle and Beer (1987) suggested that E. amylovora penetrates through the stigma and migrates inside the style towards other plant tissues. However, Mihalik et al (2004) and Spinelli et al (2005a) demonstrated that bacteria never penetrated the living cells of either the stigma or the style, even 96 h after inoculation. Trees (2012) 26:47-66 51…”