DORMANCY BREAKING IN LILY BULBLETS REGENERATED IN VITRO: EFFECTS ON GROWTH AFTER PLANTING

Abstract

We studied the effect of dormancy-breaking on growth and carbohydrate metabolism in bulblets of Lilium speciosum regenerated in vitro. Dormancy was broken with a cold treatment or a gibberellin treatment. Almost all bulblets sprouted after a cold treatment of six weeks at 5°C. Sprouting and growth were reduced when a shorter cold treatment was given. A soak in a GA-solution also gave high sprouting percentages (with the optimal concentration of 3 mg.l-1 GA4+7) 80% of the bulblets sprouted). However, growth after a GA-treatment was poor and leaves were smaller than in cold-treated bulblets. A combination of a partial cold treatment and a GA-treatment had no effect on growth. We studied carbohydrate metabolism in cold-treated and GA-treated bulblets. During the cold treatment starch and glucomannans were broken down; soluble sugar content increased. During GA-treatment no changes in these carbohydrates occurred. In the first four weeks after planting, about 70% of the starch was broken down in the outer scales of GA-treated bulblets after that, starch breakdown stopped. Thus, poor leaf growth in GA-treated bulblets might be due to incomplete or too late breakdown of carbohydrates in the outer scales. Although new scales were initiated in GA-treated bulblets, these scales did not grow; indicating that leaves of GA-treated bulblets did not produce assimilates efficiently. An increase of soluble sugars in the outer scales of GA-treated bulblets after planting, might indicate a low sink strength in the leaves.