Effect of Explant Origin on Growth and Differentiation of Calli from Tagetes species

Tertiary leaf callus from 13-week-old Tagetes minuta showed 5 to 6-fold higher fresh weight increment than callus from 3 to 7-week-old plants. No such differences were observed in the primary and secondary calli. Similarly, tertiary leaf callus of T. patula showed morphological differentiation that varied with the mineral nutrition to which intact plants had been exposed and that did not appear in the primary and secondary calli. No such effects were observed in T. minuta). These «origin» effects are discussed in relation to «memory» effects and to their applica-tion to plant biotechnical procedures.