In vitro induction of autotetraploids from diploid yellow passion fruit mediated by colchicine and oryzalin

In vitro chromosome doubling from hypocotyl segments of yellow passion fruit (Passiflora edulis Sims.) was carried out in the presence of either colchicine (0, 25, 250 and 1,250 mu M) or oryzalin (0, 5, 15 and 30 mu M). Murashige and Skoog (in Physiol Plant 15:473-497, 1962)(MS)-based regeneration medium containing 250 or 1,250 mu M colchicine markedly affected explant development leading to browning and death of the hypocotyl segments. Oryzalin has similar effect to colchicine in inducing polyploidy. In vitro regenerated autotetraploid plants induced by 25 mu M colchicine or 15 mu M oryzalin were further acclimatized and cultivated in hydroponics system in greenhouse. Autotetraploids plants were more vigorous than the control diploids. The chromosome number of diploid plants was 2n = 2x = 18, whereas that found on autotetraploid plants were 2n = 4x = 36. The stomata sizes of the autotetraploids were significantly larger than those on the diploid counterparts, while the frequency of stomata was significantly reduced. Similarly, the chloroplast number of guard cells of autotetraploid plants increased significantly. Two albino plants (4%) were generated in medium with 25 mu M colchicine, indicating phytotoxic effects. These plants are being grown to full maturity in order to test their potential to use in a breeding program.