THE EFFECT OF GROWTH-REGULATORS, SOURCE OF EXPLANTS AND IRRADIANCE ON IN-VITRO REGENERATION OF ATEMOYA

Multiple shoot formation was induced on different media from excised hypocotyl and the nodal cuttings from 5 year old trees of atemoya (Annona cherimola Mill x A. squamosa L.) cv. African Pride. The highest number of shoots were obtained from the distal part (section near the root) of the hypocotyl cultured at a photosynthetic photon flux (PPF) of 36 mu mol m(-2) s(-1) on Murashige and Skoog basal medium (MS) supplemented with 2% sucrose, 2 mg L(-1) 6-benzylaminopurine (BAP), 0.5 mg L(-1) 6-furfurylaminopurine (kinetin), 0.1 mg L(-1) biotin, 0.1 mg L(-1) calcium pantothenate and solidified with 0.8% agar. The number of shoots of mature nodal cuttings cultured on modified MS medium, supplemented with 1 g L(-1) ammonium nitrate and the above mentioned growth regulators and addenda, was higher than MS basal or Woody Plant Medium. Increasing the kinetin level increased the number of shoots and fresh weight. Increasing the BAP level above 2 mg L(-1) decreased the number of buds, length of shoots and fresh weight. The shoots were incubated in liquid MS medium containing 50 mg L(-1) indole-3-butyric acid (IBA) in the dark and after 3 days were transferred to MS basal medium in the light, supplemented with 0.25% activated charcoal and solidified with 0.8% agar. Forty per cent of the shoots rooted. The rooted plantlets were successfully transferred to soil and planted in the glasshouse and 70 per cent of them showed rapid growth. Root induction was improved by pretreatment of shoots in liquid MS containing IBA. The effects of adding cytokinins, biotin and calcium pantothenate to the hypocotyl sections at different PPF and the effect of ammonium nitrate on multiple shoot production by nodal segments of in vivo grown plants are reported.