(d). cutting off at least one of the next-generation PLBs from the second cut surface of the lower portion when growing to a preferred height (2-8 mm, for example);
(e). repeating the steps (b) through (d) one or more times if necessary;
(f). cultivating the next-generation PLBs obtained from the step (d) or (e) in a regenerating medium so as to differentiate the next-generation PLBs into plantlets; and
(g). processing a chromosome ploidy analysis to identify the ploidy level of the plantlets.