Strategies for controlling explant browning during in vitro culture of herbaceous peony (Paeonia lactiflora) cv. Sara Bernhardt

Explant browning is a serious problem with in vitro cultures of peony. All the five types of explants of herbaceous peony (Paeonia lactiflora) cv. Sara Bernhardt used in the present study exuded phenolic compounds when cut and resulted in media cum explant browning. Maximum explant browning was observed with leaf/ovary segments followed by stem and petiole while minimum with underground buds in ½ MS medium. Incubation of explants for 48 hours at 4°C was found best for minimizing the browning of all types of explants while incubation under 16/8 light cycle at 24 ± 1°C resulted in most browned cultures. Polyvinyl pyrrolidone (5.0 g l⁻¹) proved most effective in alleviating explant browning while antioxidants (citric acid & ascorbic acid) failed to suppress the problem.

Pretreatment of the stock plants by growing them under low light intensity reduced leaf segments explant browning to 4.80% compared to 76.64% recorded with unforced field grown stock plants. Explant harvesting stage significantly influenced leaf segment explant browning which was maximum with explants collected at pink or green leaf stage but was practically absent when unfolded inner green leaves of terminal bud were used as explants.