The KNOTTED-like (KNOX) genes encode homeodomain transcription factors and regulate several processes of plant organ development. The peach (Prunus persica L. Batsch) genome was found to contain 10 KNOX members (KNOPE genes); six of them were experimentally located on the Prunus reference map and the class 1 KNOPE1 was found to link to a quantitative trait locus (QTL) for the internode length in the peach×Ferganensis population. All the KNOPE genes were differentially transcribed in the internodes of growing shoots; the KNOPE1 mRNA abundance decreased progressively from primary (elongation) to secondary growth (radial expansion). During primary growth, the KNOPE1 mRNA was localized in the cortex and in the procambium/metaphloem zones, whereas it was undetected in incipient phloem and xylem fibres. KNOPE1 overexpression in the Arabidopsis bp4 loss-of-function background (35S:KNOPE1/bp genotype) restored the rachis length, suggesting, together with the QTL association, a role for KNOPE1 in peach shoot elongation. Several lignin biosynthesis genes were up-regulated in the bp4 internodes but repressed in the 35S:KNOPE1/bp lines similarly to the wild type. Moreover, the lignin deposition pattern of the 35S:KNOPE1/bp and the wild-type internodes were the same. The KNOPE1 protein was found to recognize in vitro one of the typical KNOX DNA-binding sites that recurred in peach and Arabidopsis lignin genes. KNOPE1 expression was inversely correlated with that of lignin genes and lignin deposition along the peach shoot stems and was down-regulated in lignifying vascular tissues. These data strongly support that KNOPE1 prevents cell lignification by repressing lignin genes during peach stem primary growth.

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Adventitious rooting might be induced in recalcitrant woody genotypes by infection with Agrobacterium rhizogenes, and, in some cases, might also require exogenous auxin. The objective of the present study was to determine how agrobacteria trigger root formation in the stem of a recalcitrant woody microcutting, which cytological events result from the combined presence of infection and exogenous auxin, and which types of roots are induced by infection. Microcuttings of a recalcitrant walnut (Fuglans regia), infected or not with A. rhizogenes strain 1855, were cultured with either indolebutyric acid (IBA), IAA, or without exogenous hormones, to induce rhizogenesis. They were cytohistologically and ultrastructurally investigated at various times in culture. Southern blot and PCR analyses were performed to verify the frequency of transgenic, chimeric and bacterium-containing roots. The infection was sufficient per se to stimulate rhizogenesis. Rooting on the infected cuttings was enhanced by exogenous IBA, which accelerated and increased root meristemoid formation, in comparison with without hormone treatment. Meristemoids were organized both directly by the cambial cells and indirectly by the callus, and showed a pluricellular origin. Inter and intracellular bacteria were observed in the stem throughout the culture period (30 d). They were preferentially present in the vessels, and mainly in those showing polyphenol deposition. In the infected IAA-treated cultures, a high level of secondary xylem formation occurred instead of rhizogenesis. Nontransformed roots were preferentially produced by the infected cuttings treated with the auxins. Bacterium-containing and chimeric roots were produced by infected cuttings independently of the treatment. Thus, in a recalcitrant walnut, nontransformed root meristemoids are stimulated by combining infection and exogenous indolebutyric acid. Furthermore, the persistence of bacteria in the stem during the culture and the pluricellular origin of the meristemoids explain the presence of the bacterium-containing and chimeric roots

A new reliable protocol for the induction of adventitious shoot formation and plant regeneration from apple callus has been developed. High regeneration frequency was obtained with this method in four different genotypes (Jork9, M26, Gala and McIntosh) and callus maintained regeneration ability for several months. The procedure consists of inducing vegetative shoot apices, excised from in vitro shoots, for 20 days in darkness on an MS medium without glycine, supplied with 17.8 μM BA, 2.7 μM NAA and 250 mg l−1 cefotaxime. The explants are then transferred to a fresh auxin-free medium and given light. Histological studies revealed that all the regenerated shoots originated from callus. Regenerated shoots were multiplied, rooted and successfully established in soil

Since 2012, a new pathogenic syndrome has frequently been observed in many areas of kiwifruit cultivation in Italy. The main symptoms include an initial withering of the leaves followed by a total and sudden collapse of plants, mainly occurring during summer. The withered leaves fall and the main and secondary feeder roots appear rotten, sometimes showing a reddish‐brown discoloration. The disease, that affects both the green and yellow‐fleshed cultivars, has been called kiwifruit vine decline and is locally known as moria. The syndrome has been found consistently associated with soil waterlogging, which frequently occurs either after the traditional agronomical practice of irrigating orchards through surface irrigation or after very heavy rainfall. So far, the role played by bacteria in this syndrome has not been investigated. In the present study, Clostridium spp. were isolated from both rotten roots and soils obtained from Italian kiwifruit orchards affected by the syndrome, indicating for the first time that anaerobic bacteria are able to cause damage to woody crops. C. bifermentans and C. subterminale incited symptoms in kiwifruit in both in vivo and in vitro pathogenicity tests. Soil waterlogging seems to potentially favour colonization of kiwifruit roots by anaerobic bacteria, probably because saturation of the soil can facilitate proliferation and persistence of these bacteria during long periods of the vegetative growth of the crop. The occurrence of anaerobic bacteria does not exclude the possibility that other microorganisms can play additional/synergic role(s) in causing the kiwifruit vine decline.