MICROPROPAGATION OF POTATO CV SPUNTA - GROWTH IN RELATION TO EXPLANT SIZE AND POSITION ON SOURCE PLANTLET

Apical explants are routinely discarded in potato (Solanum tuberosum L .) micropropagation, but there are no studies on the physiological bas is for this practice. The present paper evaluates the effect of explan t size, and position on source plant, on growth and physiological stat e of potato plantlets, cv. Spunta, subcultured in vitro. Single node c uttings were excised from the basal and apical portions of plantlets, and the middle portion discarded. Single node cuttings from basal and apical portions were cultured with leaf (leafed) and without leaf (lea fless), in order to obtain small and large explants. Growth in terms o f height, number of nodes and dry matter content in the shoots and phy siological state, (such as N content, and dry weight/N ratio, of plant lets originating from each type of explant) was measured. From the exp erimental evidence, we conclude that, in potato plantlets cultivated i n vitro: a) apical and basal explants have similar physiological chara cteristics; b) differences in growth of apical and basal explants corr espond to differences in growth rate; and c) explant growth rate is di rectly related to leaf growth stage. Therefore, there is no physiologi cal basis for discarding the apical portion of plants cultivated in vi tro for micropropagation purpose.