Geraniums are one of the most important balcony plants, not only in Europe but also worldwide. The wholesale value of these plants reaches over $115 million in the USA and a similar value in the EU (Currey et al. 2013). Certain hybrids are also grown for the production of essential oils and absolutes (Blerot et al. 2016).
So, geraniums are counted among herbaceous plants and are associated with some difficulties in plant production. In propagation, rooting success is highly dependent on the postharvest conditions to which the cuttings are exposed after harvest and also on the cultivar chosen (Currey et al. 2013).
Geraniums have been very well known as plant species whose cuttings have short posthavest life (life span after senscence) and are very sensitive to high postharvest temperatures. Unfavorable conditions result in rooting loss and in unmarketability plants due to lower-leaf colouring and abscision. Abscised leaves lead producers very often to protect the rooting plants against Botrytis cinerea using different fungicides or removing the levaes manually. Therefore the production costs increased and the process is environmental problematic (Currey et al. 2013).
It is very well known that cultivar choice can effect the rooting results in cuttings. There are numerous citations which support that different genotypes of different species can root very different in woody plants. Spethmann (1986) has already reported about great differences in rooting success at different oak genotypes. Similar differences in rooting response regarding different cultivars or genotypes have been reported also in numerous of other species, firs, chestnut, olive, haselnut, etc. Miller et al. (1982) have reported already long time ago, that different genotypes of american fir showed very different rooting response. Several reports indicated that cuttings of pure species, like Castanea sativa genotypes root much more difficult as hybrids (for example C. crenata × C. sativa) did (Vielba et al. 2020). Osterc (2007) stressed that also some hybrid cultivars ‘Maraval’ und ‘Marsol’ showed great differences, whereby ‘Maraval’ cuttings overcome ‘Marsol’ cuttings in rooting success. In haselnut cuttings of italian cultivar ‘Nocchione’ rooted much better than cuttings of cultivar ‘Tonde Gentile Romana’ (Cristofori et al. 2010).
Genetic characteristics of species and cultivars which regulate their ability to be popagated should be keep in mind also regarding olives (Fabbri et al. 2004). Wiesman and Lavee (1995) arranged different olive cultivars from different origins into three different groups based on their ability to form roots. There are some cultivars like italian cultivars ‘Leccino’, ‘Leuco carpa’ or african cultivars ‘Temcen’, ‘Dolce de Marocco’ whose cuttings root very well but cuttings of some other cultivars like italian cultivars ‘Ascolana’, ‘Gosso de Sardenia’ or slovene cultivar ‘Istrska belica’ are difficult-to-root.
This, so called genetic effect is in herbaceous plants, opposite as in woody plants, much more rarely mentioned as an important effect which modify rooting result. The reason is probably, in generally the material which is much more willing for root formation. The producers solve normaly this problem with taking more material for propagation when a cultivar is a little more complicate to root.
The real reason causing the genetic effect regarding rooting success is still not clear. Many attempts, especially in woody plants have been made to find the detailed resons for often great differences in rooting response in different genotypes. Long time ago, probably shortly after the discovery of the central auxin effect on rooting, genetically caused differences tried to be explained with IAA accumulation, in term easier-to-root genotypes stronger accumulated IAA than more difficult-to-root did. After that it was postulated very quickly, that only IAA accumulation could not be the only reason which explains the rooting response of different species or cultivars. Epstein et al. (1993) could explain the effect of the exogenously applied auxin on different rooting response. More difficult-to-root sweet cherry cultivar absorbed exogenously applied IBA at a slower rate that easier-to-root cultivar did. Ford et al (2001) made a step forward due to connect the rooting response with polar auxine transport (PAT). Differences of rooting response between easier-to-root Fosythia × intermedia and more difficult-to-root Syringa vulgaris had been ascribed to differences in PAT ability in cuttings of both speceis. Forsythia cuttings showed greater ability for polar transport over the whole year. Osterc et al. (2007) tried to explain differences in rooting responce between two chestnut genotypes ‘Marsol’ and ‘Maraval’ with differences in different phenolic substances which have been accumulated in the propagation material. The ‘Maraval’ cuttings with a better rooting response stronger accumulated different quercetins (rutin, quercetin-3-D-galactoside) compared with ‘Marsol’ cuttings.
Geraniums are described in the praxis as species with a strong cultivar dependant rooting and the species choice is very important for this species. This problem plays also an important role during the process of cultivar selection and breeding. It would be of great importance therefore if the real reason for often strong differences in rooting response of different genotypes could be solved.