Hybrid Triploid Induced by Megaspore Chromosome Doubling in Jujube (Ziziphus jujuba Mill.) ‘Maya’ and Its Characteristics

Polyploid breeding is an important strategy for tree improvement because polyploid individuals typically show superior traits, such as improved growth, stress resistance, and superior fruit quality. Artificial induction of chromosome doubling of female gametes is an effective approach to obtain triploid progeny. However, no triploid fruit tree cultivars have been developed using this approach. The objective of this study was to explore the utility of chromosome doubling in female gametes of ‘Maya’ jujube to produce triploid individuals. The temporal relationship between flower bud morphology and the megaspore meiotic stage was studied to guide the optimal timing of colchicine treatment. Colchicine solution was applied to bearing shoots of mature ‘Maya’ jujube trees in a field experiment using two treatment methods (improved cotton leaching and injection method) and three concentrations (0.3%, 0.4%, and 0.5%). The water transport rate of ‘Maya’ jujube shoots was studied using dye solution to judge the effectiveness and timing of the colchicine treatment methods. Two triploids were identified among the progenies from the colchicine-treated shoots. The highest efficiency of triploid production was 3.3% when flower buds of diameter 1.76–2.12 mm were treated with 0.3% colchicine solution for 4 h using an improved cotton leaching method. The ground diameter, plant thorn length, leaf width, leaf area, stomatal length, stomatal width, chlorophyll content, and photosynthetic parameters of one triploid individual were significantly higher than those of diploids of identical parentage at 18 months old. Thus, induction of 2n megaspores is an effective approach to generate triploid jujube. These results are expected to promote and accelerate triploid breeding in fruit trees.

COMPARISON OF DIPLOID AND TRIPLOID SUGAR BEETS

In a small replicated field trial, percentage sugar and root weight were negatively correlated in both diploid and triploid individual beets, but the decreases in percentage sugar for every 100-gm. increase in root weight differed significantly, being on the average 0.34% for the diploids and 0.17% for the triploids. As root weight increased beyond 900 gm. the yield of sugar per 100 gm. of root weight increased more rapidly in the triploids than in the diploids. Under the conditions of this test, triploid beets exceeded the diploids in root weight by 12.2%, in yield of sugar per beet by 14.9%, and in dry top weight by 17.8%. The triploids exceeded the diploids in area index of the leaves by 34.4% and in area index of the stomata by 42.6%.