The Agrobacterium rhizogenes T-DNA oncogene rolD under the control of its own 5' regulatory region was transferred to day-neutral tobacco plants. The main trait induced by rolD in transgenic plants is a striking precocity in flower setting and a strong enhancement of the flowering potential. In rolD plants, early flowering is followed by the very rapid growth of numerous lateral inflorescences. The analysis of several morphological and histological parameters suggests that some characteristic morphological abnormalities observed in rolD plants can be accounted for by their early reproductive phase transition and points to the involvement in the transition of a greater portion of the plant body than is the case for untransformed tobacco. The in vitro morphogenic potential of tissues from rolD plants was also tested. Superficial thin cell layer explants from rolD plants show an earlier and much enhanced flower organogenesis, compared to controls, both on flowering and on hormone-free medium.

Since 2008, Pseudomonas syringae pv. actinidiae virulent strains (Psa-V) have quickly spread across the main areas of kiwifruit (Actinidia deliciosa and A. chinensis) cultivation causing sudden and re-emerging outbreaks of bacterial canker to both species. The disease caused by Psa-V strains is considered worldwide as pandemic. Recently, P. syringae strains (ex Psa-LV, now called PsD) phylogenetically related to Psa-V have been isolated from kiwifruit, but cause only minor damage (i.e. leaf spot) to the host. The different biological significance of these bacterial populations affecting kiwifruit highlights the importance of having a diagnostic method able to detect Psa-V, which is currently solely responsible for the severe damage to the kiwifruit industry. In order to improve the specific molecular detection of Psa-V, a real-time PCR assay has been developed based on EvaGreen chemistry, together with a novel qualitative PCR (PCR-C). Both methods are based on specific primer sets for the hrpW gene of Psa. The real-time PCR and PCR-C were highly specific, detecting down to 50 and 200 fg, respectively, and were applied to a range of organs/tissues of kiwifruit with and without symptoms. These methods are important tools for both sanitary and certification programmes, and will help to avoid the spread of Psa-V and to check possible inoculum sources. In addition to being used as routine tests, they will also enable the study of the biology of Psa-V and the disease that it causes, whilst avoiding the detection of other populations of related P. syringae present in kiwifruit.

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A 1 kb DNA band from strains of Brenneria nigrifluens, as shown by amplification of their genomic DNA by polymerase chain reaction (PCR) using minisatellite primer designed on the minisatellite sequence of the M13 phage, was isolated, cloned and sequenced. Specific oligonucleotides (F1-C3) were selected into this 1 kb DNA sequence and used in a PCR assay to detect and identify strains of B. nigrifluens. Several strains of B. nigrifluens were assessed with F1-C3 primers producing a specific band of approximately 250 bp pairs in length. This target was successfully amplified from purified genomic DNA, from bacterial culture and directly from infected walnut bark tissue. No amplification was obtained when the PCR assay was performed on other plant-pathogenic species from the following genera Brenneria, Erwinia, Agrobacterium, Pseudomonas, Ralstonia, Pectobacterium, Xanthomonas and from walnut-associated bacteria, indicating the specificity of these primers. The PCR assay with the primers described here provides a rapid, specific and sensitive diagnostic method for B. nigrifluens and a useful tool for epidemiological studies.

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