Enhancement of microspore embryogenesis induction and plantlet regeneration of sweet pepper (Capsicum annuum L.) using putrescine and ascorbic acid

Leaf-induced callus formation in two cultivars: hot pepper 'CM334' and bell pepper 'Dempsey'

Pepper (Capsicum annuum), one of the most economically important vegetables of the Solanaceae family, is cultivated worldwide. To apply versatile genome-editing tools to a pepper genome for precise molecular breeding, an in vitro regeneration protocol is indispensable and callus formation is an essential step in the regeneration of pepper. Here, we show that calli were successfully induced from young leaves (3-4 cm) of pepper plants, the hot pepper C. annum 'CM334' ('CM334') and bell pepper C. annum 'Dempsey' ('Dempsey'), grown on soil for less than 7 weeks. The excised leaf segments of 'CM334' produced white calli in B5 medium containing 3% sucrose (3S), 2 mg/L 6-benzylaminopurine (2BAP), and 1 mg/L α-naphthalene acetic acid (1NAA). The calli were able to proliferate in B5 3S 2BAP medium supplemented with 2-morpholinoethanesulphonic acid (MES) and 1.5 mg/L NAA (1.5NAA). The excised leaf segments of 'Dempsey' produced light-yellow and friable calli in MS medium supplemented with B5 vitamins (MSB5), 3S and 1 mg/L 2,4-dichlorophenoxyacetic acid (1 2,4D), and the calli were also maintained in the same medium. Our findings establish the conditions for leaf-derived callus formation, which is the basis for regeneration of whole plants for two different pepper cultivars, for obtaining stable protoplasts, and eventually for applying genome-editing tools to improve the quality of peppers.