Rapid and Efficient Regeneration of Populus ussuriensis Kom. from Root Explants through Direct De Novo Shoot Organogenesis

Abstract

Populus ussuriensis is an important tree species with high economic and ecologic values. However, traditional sexual propagation is time-consuming and inefficient, challenging afforestation and wood production using P. ussuriensis, and requires a rapid and efficient regeneration system. The present study established a rapid, efficient, and stable shoot regeneration method from root explants in P. ussuriensis using several plant growth regulators. Most shoot buds (15.2 per explant) were induced at high efficiency under WPM medium supplemented with 221.98 µM 6-BA, 147.61 µM IBA, and 4.54 µM TDZ within two weeks. The shoot buds were further multiplicated and elongated under WPM medium supplemented with 221.98 µM 6-BA, 147.61 µM IBA, and 57.74 µM GA3 for four weeks. The average number and efficiency of elongation of multiplication and elongation for induced shoot buds were 75.2 and 78%, respectively. All the shoots were rooted within a week and none of them showed abnormality in rooting. The time spent for the entire regeneration of this direct shoot organogenesis was seven weeks, much shorter than conventional indirect organogenesis with the callus induction phase, and no abnormal growth was observed. This novel regeneration system will not only promote the massive propagation, but also accelerate the genetic engineering studies for trait improvement of P. ussuriensis species.