Factors affecting shoot initiation from tuber discs of potato (Solanum tuberosum) [tissue culture, adventitious shoot formation, cytokinin, N6-benzylamino-purine, (BAP)]

Discs of cortical and perimedullary tissue from tubers of potato (Solanum tuberosum L. cv. Superior) formed adventitious shoots when cultured on a medium containing Murashige and Skoog's salts, myo-inositol, 100 mg/l; folic acid, 0.5 mg/l; D-biotin, 0.5 mg/l; gibberellic acid (GA(,3)), 0.5 mg/l; thiamine HCl, 0.1 mg/l; glycine, 2.0 mg/l; pyridoxine HCl, 0.5 mg/l; nicotinic acid, 0.5 mg/l; sucrose, 2.5 g/1; casein hydrolysate, 1 g/1; Bacto agar, 9.0 g/1; and a cytokinin [N('6)-benzylaminopurine (BAP), N('6)-gamma, gamma-dimethylallylaminopurine (2iP) or N('6)-furfurylaminopurine (kinetin)]. Discs of pith tissue either failed to survive or produced callus but did not undergo morphogenesis. Cytokinin was essential for explant survival, while BAP at 3.0 mg/l was most efficacious in promoting shoot initiation. Auxin was not essential for shoot initiation or development; however, a low concentration (0.03 mg/l) of a-napthaleneacetic acid (NAA) stimulated both explant survival and the number of shoots produced per disc. Indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) did not stimulate shoot initiation. GA(,3) was essential for both shoot initiation and subsequent shoot development. The highest incidence of morphogenesis (over 100 shoots in 12 weeks) occurred from tuber discs cultured at 18 deg C constant and under a photon flux density of 60 micro-E m-('-2)s('-1). No difference in regenerative ability was found in explants taken from source tubers stored for 0 to 20 weeks at 4 deg C. A histological examination indicated that shoots developed from small clusters of meristematic cells which were iniated from within small protuberances on the surface of the tuber disc 3 weeks after transfer