| 英文摘要
| Dombeya wallichii (Lindl.) K. Schum. is a woody ornamental species in the Malvaceae family. The attractive flower pattern and fragrance make it a popular choice for container gardending or landscape layout. However, its natural flowering period is limited to winter. In this thesis, methods for cutting propagation was evaluated, and environmental factors, e.g. temperature and photoperiod as well as cultural factors, e.g. container size, pruning, and GA3 spray were investigated to document the mentioned variables on plant growth and flowering of Dombeya in order to increase its commercial potential.
In the first part of this thesis, cutting propagation of Dombeya was evaluated. In the fist trial, defoliated softwoods, semi-hardwoods and hardwoods were trimmed to a length of 15 cm and were inserted into propagation medium in early November. All the cuttings survived after 28 days but none rooted. In the second trial, leafy terminal softwoods and defoliated semi-hardwoods and hardwoods were trimmed to a length of 15 cm for cutting. All survived after 28 days but only leafy softwoods successfully rooted. In the third trial, leafy terminal softwoods were trimmed to 5, 10, 15 or 20 cm for cutting. All culltings rooted after 28 days and 56 days. Low rooting rate and root number were recorded in the 5 cm cuttings . Rooting types of Dombeya wallichii included rooting from barks and callus.
In the second part of this thesis, temperature and photoperiod effect on Dombeya flowering were investigated. Single stemmed Dombeya plants were heading to a height of 20 cm with two fully expanded leaves and grown in phytotrons, under natural daylength conditions in May, with day/night temperatures of 15/13℃, 20/15℃, 25/20℃, 30/25℃ or 35/30℃. Plants at 30/25℃ after 84 days were most vigorous, with the longest shoots and the greatest number of leaves per shoot than plants subjected to other temperatures. Plants at 35/30℃ after 119 days had the smallest leaves and diameter of new shoots. The maximum fluorescence (Fm) and maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) of the mature leaf on plants at 15/13°C were the lowest, and the photochemical quenching (qP), non-photochemical quenching coefficient (qN) and non-photochemical quenching (NPQ) of the leaf on plants at 35/30°C declined. Also, leaf net photosynthesis rate (Pn) of plants grown at 35/30°C was significantly lower than other temperature treatments. Flower buds were observed on plants after 112 days at 15/13℃ or 20/15℃, with 7.9 and 9.1 leaves below the first inflorescence, respectively, and on plants after 119 days at 25/20℃, with 12 leaves below the first inflorecence. No flower buds were observed on plants at 30/25℃ or 35/30℃ for 182 days. The results indicated that 15/13℃ is beneficial for flower formation of Dombeya, and 25/20℃ is likely the upper limit temperature for flower formation.
In the second temperature trail, half of the plants originally grown at 30/25℃ and 35/30℃ for 18 weeks beforetransferred to 15/13 °C in early September produced flower buds after 35 days, while those remained at high temperatures did not produce any flower buds, suggesting that high temperature pretreatment did not affect flower formation of Dombeya at low temperatures.
In the third temperature trail, Dombeya with 2.1±0.1 cm flower buds were transferred to phytotrons in early December. Results showed that within the range of 15/13°C to 25/20 °C, warm temperatures were beneficial to flower development and plants grown at 25/20 °C flowered earlier and the number of inflorescences was the highest. However, 30/25°C was not suitable for flower development, as 38.6% buds aborted after treatment for 50 days. Base temperatures of 2.1±0.1 cm flower buds developing to calyx visibility and flower were 1.54°C and 1.82°C, respectively. And the thermal time of 2.1±0.1 cm flower buds reaching to calyx visibility stage and flower stage were about 396-487℃d and 556-645℃d, respectively.
In the photoperiod trial, rooted softwood cuttings with six expanded leaves were placed at 24/14°C in mid- August and illuminated with a photosynthetic photon flux (PPF) of 300 μmol·m-2·s-1 for 8 h daily. After 7, 14, 21, 28, and 35 days, plants were transferred to long day environment and lighted with a PPF of 150 μmol·m-2·s-1 provided with a mixed LED white light panel with red : blue=8:1 for 16 h daily . Results showed that the increase in the number of short-day cycles decreased the number of newly-grown leaves below the flowers and the length of newly-grown internodes , while increased the number of flower buds and the initial flower bud diameter. The result indicated that Dombeya is a facultative short-day plant.
The third part of this thesis reported the effects of container size and pruning severity on growth and flowering in Dombeya. Saplings were trimmed to 30, 60, 90, or 120 cm tall, leaving only the trunk and planted in 47, 32, or 18 L containers in early November. Plants grown in 47 L containers after 150 days were the highest, and the plant height decreased with the decrease of the pruning height. More plant height increment were observed in plants grown in large containers or pruned to 30 cm high after 210 days, and the plant height increment reduced as container size decreased or pruning height increased. After 255 days of treatments, container size had no effect on number of shoots, but number of shoots increased as the pruning height increased from 30 to 120 cm. Shoot length increased with increasing container size or decreaing prun height. Similar reaction was also observed on number of leaves per shoot. More plants grown in large containers produced flower buds after 60 days, while prun height had no effect on it. After 120 days of treatment, the proportion of plants with flower buds were higher in which grown in large containers, and lower in those grown in small containers. Flowering rate of plants grown in small containers was significantly lower after 183 days.
The final part of this thesis investigated the effect of gibberellin on flowering of Dombeya. In early October, 2500 mg·L-1 and 5000 mg·L-1 of GA3 solution were sprayed on the leaves of Dombeya shoots without flower buds. Flower buds were visible 7 days earlier on shoots with GA3 treatment than the un-sprayed control but days to calyx visibility and days to flowering were not affected by GA3. Flower buds were visible after GA3 treatment for 14 days, and the control group without GA3 treatment had visible flower buds 1 week later. There was no significant difference in number of flower buds, inflorescence diameter and peduncle length between treatments.
In the natural flowering period, the third axillary flower bud (diameter 4.4±0.1 cm, peduncle length 12.1±0.3 cm) from the top of Dombeya was sprayed with 250 and 500 mg·L-1 GA3 solution in January. Results showed that GA3 treatment allowed the flower buds to reach the calyx visibility stage about 3-4 days earlier, but had no effect on the days to flowering. |
