Callus induction and plantlet regeneration inCichorium intybus L.: 1. A cytological study

Explants ofCichorium intybus L. (2 n=18) storage roots were grownin vitro on a modified Heller's medium lacking auxins and cytokinins. Investigation on the nuclear cytology of callus induction and on chromosome number variation inin vitro regenerated shoots and roots demonstrated: a) amitosis phenomenon (nuclear fragmentation) in developing primary callus, confirmed by cytophotometric analysis in calli at different growth stages; b) chromosome-number mosaicism (extensive aneuploid chromosome numbers in addition to the diploid number) in almost all shoot apical meristems of plantlets regenerated from primary callus; c) no chromosome mosaicism in roots regenerated from the same expiants. The present results are discussed in relation to the origin of callus by nuclear fragmentation and cytological chimeras in regenerated organs.