In vitro amphidiploid induction of a distant hybrid Populus simonii × P. euphratica cv. ‘Xiaohuyang-2’ and its effect on plant morphology and anatomy

Highly gametic sterility of a distant hybrid Populus simonii × P. euphratica cv. ‘Xiaohuyang-2’ restricts its utilization in breeding programs of Populus. Amphidiploid induction by somatic chromosome doubling is expected to restore its gametic fertility. In this study, nodal-segment and leaf explants of ‘Xiaohuyang-2’ were used to induce chromosome doubling with colchicine in vitro. Although chromosome doubling of the nodal-segment explants only produced mixoploids, the treatments of leaf explants on adventitious bud regeneration medium successfully produced 4 amphidiploids, which might be attributed to the direct organogenesis of the adventitious buds on the leaf explants. This is the first report of amphidiploid induction in a distant hybrid between Populus section Tacamahaca and sect. Turanga. The highest amphidiploid induction frequency was 16.7 %. Both the explant survival rate and polyploidization frequency were significantly affected by colchicine concentration and exposure time. The amphidiploid plants significantly differed from the diploid and mixoploid plants in morphological and anatomical characteristics. They had larger, thicker, and greener leaves than the diploids and mixoploids. The increase in ploidy level also resulted in changes in stomatal features. The induced amphidiploid plants of the distant hybrid ‘Xiaohuyang-2’ are expected to play important roles in breeding programs of Populus in the future, which can be used as a bridge parent with the ability of unreduced gamete formation to cross with fast-growth germplasms to produce triploids pyramiding desirable traits of fast growth, easy cutting propagation, and salt and drought tolerances.