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RAPID CLONAL PROPAGATION OF PATHOGEN-FREE PELARGONIUM PLANTS STARTING FROM SHOOT TIPS AND APICAL MERISTEMS
By this, the risk for epidemic spread of diseases exists, which can eventually be transmitted in a latent state to the cuttings.
The symptoms of this kind of diseases are among others a reduction of the growth of the mother plants which results in a decrease in cutting production, bad rooting of the cuttings and inferior flowering of the daughter plants.
This all has a serious repercussion on the rendability of the culture.
The culture of shoot tips or meristems should allow us to produce non-infected clones.
Since Morel and Martin (1952) brought the experimental proof that the apical meristem of virus infected dahlia varieties was free of pathogens, the culture of shoot tips was used with success for several plants (Murashige, 1974).
Also with Pelargonium, virus-free clones were obtained by the culture of 3 mm and 1–1,5, mm shoot tips (Pillai & Hildebrandt, 1968a, Reuther, 1975). Also internodal regions, pith with the surrounding vascular tissue, petiole and anthers were cultured (Chen & Galston, 1967a and b; Pillai & Hildebrandt, 1968b, 1969; Abo El-Nil & Hildebrandt, 1971, 1973a and b, 1976). Those authors pretend it is possible to obtain a non infected clone by chance through a serie of callus cultures or even by cell culture (Chen & Galston, 1967a).
With 9 cultured varieties of zonale hybrids, Pillai & Hildebrandt (1968, 1969) could only obtain a low percentage of rooted shoots.
Add to this that a substantial number of the plantlets differed from the mother plants.
The absence or the loss of the organogenetic characteristics of a tissue and the frequent observation of epigenetic and genetic variations have been reported for many plants, especially when unorganized callus tissue is involved.
For those reasons Murashige (1974) suggested that in vitro propagation systems should start with shoot tips, since these are most likely to be genetically uniform, and that they should avoid callus stages.
This communication is an abstract of the results obtained in view of the elaboration of a commercial propagation system for Pelargonium starting from shoot tips.
Experiments with meristems were also performed in case the virus diseases could not be eliminated with shoot tips.