Induction of octoploid genotypes and cold tolerance assessment in Neolamarckia cadamba

As an evergreen broad-leaved and multipurpose tree species, Neolamarckia cadamba has various uses, including pharmaceutical applications, woody forage, wood products and papermaking. However, its growth cessation, while exposing chilling injury below 2℃ severely restricts its cultivation range. To address this limitation, we developed an efficient octoploid induction system by treating in-vitro epicotyls with colchicine. The optimal results were achieved using 300 mg/L colchicine treatment for 3 d, with the adventitious bud induction rate of 30 % with 1.96 adventitious buds per explant and the octoploid induction frequency of 33.25 %. Compared with tetraploid counterparts, octoploid N. cadamba exhibited shorter seedling height, thicker stems, smaller and rounder leaves as well as larger guard cells. Moreover, octoploids showed greater adaptation to cold treatment at 2℃ and resumed growth more quickly than tetraploid counterparts after temperature recovery. The physiological and biochemical analysis indicated that octoploid N. cadamba had stronger photosynthesis and more stable membrane structure than tetraploid counterparts under cold stress. Additionally, octoploid N. cadamba had higher activity of antioxidant enzymes (SOD, POD, CAT) and lower H 2 O 2 content to improve cold stress tolerance. In summary, our study succeeded in establishing an efficient method to obtain octoploid N. cadamba, and demonstrated that polyploids have better cold tolerance. These findings will not only help to provide cold-tolerant variety of N. cadamba and promote the cultivation area in the future, but also provide a reference for stress-tolerant breeding through chromosome doubling in other tree species. • Induction of octoploids through in vitro tissue culture in Neolamarckia cadamba. • Chromosome doubling in N. cadamba confers enhanced cold tolerance. • Octoploids demonstrate higher photosynthetic rates. • Accumulate permeation-regulating substances to maintain membrane structure stability. • Increasing antioxidant enzyme activity in response to low temperature.