Factors affecting adventitious regeneration from in vitro leaf explants of ‘Improved French’ plum, the most important dried plum cultivar in the USA

Abstract

An adventitious shoot regeneration protocol from in vitro leaves of the most important dried plum cultivar in the USA, ‘Improved French’, has been established. Factors affecting regeneration were studied in order to optimise regeneration. The proliferation medium in which the shoots, used as the source of leaf explants, were cultured had a strong influence on subsequent regeneration. Shoot regeneration was observed at a mean frequency of 52% when a Murashige‐based and Skoog‐based shoot culture medium with 3 μM N6‐benzylaminopurine and 0.25 μM indole‐3‐butyric acid (IBA) was employed compared with shoot regeneration frequencies of less than 5% for a Quoirin‐based and Lepoivre‐based shoot culture medium, with 8.9 μM N6‐benzylaminopurine and 0.49 μM IBA. The shoot regeneration medium contained α‐naphthaleneacetic acid at 2.0–6.0 μM and thidiazuron at 4.5–15.0 μM. 2,4 Dichlorophenoxy‐acetic acid at 9.0 μM was included in the medium but only for the first 4 days of culture. Shoot regeneration frequencies were positively related to thidiazuron concentration and significantly greater (P < 0.05) for 9–15 μM thidiazuron than for the media with 4.5 μM thidiazuron. Leaf explants, incubated in a 16‐h‐light/8‐h‐dark photoperiod or in the dark for 1 week followed by exposure to light, showed significantly more organogenic activity (P < 0.01) than was observed for leaves cultured in the dark for 2 or 3 weeks before they were transferred to the light. The utilisation of Bacto agar (0.7%) as the gelling agent increased organogenesis compared with media gelled with TC Agar (0.7%), or an agar–gellan gum blend (Agargel™) (0.45%). The addition of the ethylene inhibitor silver thiosulphate at 60–120 μM also improved organogenesis. When all the studied factors were optimised, a regeneration rate of 65% was achieved. Rooting frequency of regenerated shoots was significantly increased (P < 0.05) by the use of full‐strength Murashige and Skoog salts (40%) or 100 mg L−1 phloroglucinol (53%) to the rooting medium.