Nineteenth century French rose (Rosa sp.) germplasm shows a shift over time from a European to an Asian genetic background.

Hybridization with introduced genetic resources is commonly practiced in ornamental plant breeding to introgress desired traits. The 19th century was a golden age for rose breeding in France. The objective here was to study the evolution of rose genetic diversity over this period, which included the introduction of Asian genotypes into Europe. A large sample of 1228 garden roses encompassing the conserved diversity cultivated during the 18th and 19th centuries was genotyped with 32 microsatellite primer pairs. Its genetic diversity and structure were clarified. Wide diversity structured in 16 genetic groups was observed. Genetic differentiation was detected between ancient European and Asian accessions, and a temporal shift from a European to an Asian genetic background was observed in cultivated European hybrids during the 19th century. Frequent crosses with Asian roses throughout the 19th century and/or selection for Asiatic traits may have induced this shift. In addition, the consistency of the results with respect to a horticultural classification is discussed. Some horticultural groups, defined according to phenotype and/or knowledge of their pedigree, seem to be genetically more consistent than others, highlighting the difficulty of classifying cultivated plants. Therefore, the horticultural classification is probably more appropriate for commercial purposes rather than genetic relatedness, especially to define preservation and breeding strategies.

The 13C/12C isotopic signal of day-respired CO2 in variegated leaves of Pelargonium × hortorum.

In leaves, although it is accepted that CO(2) evolved by dark respiration after illumination is naturally (13) C-enriched compared to organic matter or substrate sucrose, much uncertainty remains on whether day respiration produces (13) C-depleted or (13) C-enriched CO(2). Here, we applied equations described previously for mesocosm CO(2) exchange to investigate the carbon isotope composition of CO(2) respired by autotrophic and heterotrophic tissues of Pelargonium × hortorum leaves, taking advantage of leaf variegation. Day-respired CO(2) was slightly (13) C-depleted compared to organic matter both under 21% O(2) and 2% O(2). Furthermore, most, if not all CO(2) molecules evolved in the light came from carbon atoms that had been fixed previously before the experiments, in both variegated and green leaves. We conclude that the usual definition of day respiratory fractionation, that assumes carbon fixed by current net photosynthesis is the respiratory substrate, is not valid in Pelargonium leaves under our conditions. In variegated leaves, total organic matter was slightly (13) C-depleted in white areas and so were most primary metabolites. This small isotopic difference between white and green areas probably came from the small contribution of photosynthetic CO(2) refixation and the specific nitrogen metabolism in white leaf areas.

Methods for in vitro propagation of Pelargonium x Hortorum and others: from meristems to protoplasts.

Geraniums (Pelargonium spp.) are among the most popular bedding and pot plants (25% of the French domestic market). On one hand, as vegetatively propagated plants, Pelargonium are submitted to pathogen pressure. On the other hand, innovation via interspecific hybridisation faces some difficulties. In this chapter, the two first protocols (from seeds and meristems) explain how in vitro plants free of virus could be obtained. The development of this technique is the long-term preservation of genetic resources via meristem cryopreservation. The third protocol describes propagation of Pelargonium with limited risks of variation. This technique also allows the constitution and the maintenance of a plant-stock from which explants can be taken for other studies. The two last protocols describe plant regenerations from leaf discs and mesophyll protoplasts, used for gene transfer and somatic hybridisation. These protocols were established mainly with Pelargonium x hortorum cultivars, but we propose possible solutions for the other species: P. x peltatum, P. x domesticum, P. capitatum and P. graveolens.

Cryopreservation of Pelargonium apices by droplet-vitrification.

The droplet-vitrification method was adapted to Pelargonium apices by optimizing the duration of the loading solution (LS) as well as the plant vitrification solution 2 (PVS2). The excised apices were dehydrated in two steps (20 min in LS and 15 min in PVS2) and then immersed directly in liquid nitrogen (LN). After thawing and unloading in the recovery solution at room temperature for 15 min, apices were plated onto semi-solid Murashige and Skoog medium. This simple protocol without any pretreatment was successfully applied to eight cultivars with a survival level ranging between 55.6 - 96.2 percent and a regrowth level between 9.1 and 70.6 percent. These results prove the feasibility of the long-term storage of Pelargonium germplasm through cryopreservation.