Studies on the Development of Axillary Buds in Relation to Manipulation of Flowering in Phalaenopsis

• Main Authors: Yu-Zu Lin, 林育如
• Other Authors: Nean Lee
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/53307600212101837274

博士 === 國立臺灣大學 === 園藝學研究所 === 90 === This thesis was conducted to study the effects of plant age, axillary bud development, thermoinduction and light condition on manipulation of flowering in phalaenopsis. Like other flowering plants, phalaenopsis must reach a certain size or chronological age befor it can respond to floral promoters. Based on flowering percentage, the juvenile period may persist 4 months in seedlings of Phal. amabilis grown in 5㎝pot. After phase transition at 5~6-month—old seedlings grown in 8㎝pot, juvenility ended and the plants became competent to perceive cool-temperature inductive stimuli while they were further than 7 months old after transferring from flask. A clear linear relationship was apparent (P<0.001) between flower number and plant age after phase transition. Scale primordia number initiated at quiescently axillary buds and apex diameter were shown to be a stable marker for phase transition. The mature form of axillary large buds in Phal. amabilis had 5 further scale primordia initiated and an apex diameter was about twice as large as the juvenile. Furthermore, regressing leaf span, fresh and dry weight, leaf area, stem diameter, root number and root length on plant age showed linear relationships for Phal. amabilis. The sudden change in the slope was coincident with phase transition. Therefore, these developmental parameters could also be used as alternative phase related markers. In phalaenopsis, axillary buds were the source of flowers, so the development and growth potential of axillary buds along the stem was studied. Every mature axillary bud was mostly composed of the upper large bud and the lower small bud, which produced 6 and 4 scales respectively before entering into dormancy in the axil of each leaf. If a second small bud occurred, it contained less than 3 scales in dormant state. According to their various developmental state, the sprouting and growth potential of the upper large bud was more dominant than the lower small one of each axillary bud. When condition for bud initiation became favorable, the large and small buds located at the same node had the ability to sprout and form inflorescence in Phal. amabilis. In contrast, the small bud of each axillary bud had never sprouted in Phal. Taisuco Bright regardless of removing other sprouting buds. Therefore, the differential sprouting ability of axillary large and small buds varied with cultivars. The axillary bud primordia of Phal. amabilis and Phal. Taisuco Bright appeared to produce corresponding with the macroscopic appearance of subtending leaf and mature while 83 and 100 days respective after substending leaf fully unfolded at the third node counted basipetally. The nodes that were most likely to bear flower stalks were node 3-5 in Phal. amabilis and 3-4 in Phal. Taisuco Bright. The sprouting and flowering ability of the fourth axillary bud was most predominant and greatest than others. In basepital direction, the axillary buds along the stem decreased the sprouting percentage and flowering potential in spite of removing upper dominant buds, demonstrating the existence of basipetal gradient of inhibition intrinstic to the buds or due to short range correlations. The sprouting percentage of seventh and fifth axillary bud in Phal. amabilis and Phal. Taisuco Bright respective was less than 20% and therefore the number of axillary buds with sprouting ability along the stem was 5 and 2 in both cultivars during one flowering season. Root pruning in Phal. amabilis could promote the sprouting of axillary buds. Although the number of blasted bud increased with root pruning in both cultivars, the flower number was not affected by root pruning except rootless treatment, and especially greatest in the treatment of aerial root tip excision. Floral evocation in phalaenopsis is stimulated by a period of vernalization. The percentage of axillary bud sprouting increased in highly significant curve with the duration of vernalization at 25/20℃ in Phal. amabilis, reaching a maximum while 16 days of vernalization. However, due to 16 days of vernalization did not satisfy the requirement of flower induction, the apex of stalks was often reversion to leaf production without flowering. It was showed that the duration of thermoinduction for sprouting axillary bud was shorter than floral determination. Reversion to vegetative growth was never observed until 2-3㎝length of flower stalks, before the initiation of the first flower primordium. Therefore this was considered to be the developmental stage which the apex was committed to flowering regardless of transferring to devernalizing temperature 30/25℃. In Phal. Taisuco Bright, the shortest exposure to cool temperature resulting in axillary bud sprouting and floral determination was 33 days. Apices were never observed to revert to vegetative growth while the elongation of axillary buds activated by cool temperature and this was indicated that the apex of sprouting axillary bud has become floral determination before the flower primordia initiation. As the beginning of thermoinduction, starch content decreased significantly in contrast to sucrose in leaves, and this result demonstrated that starch was used as the carbon and energy source for axillary bud sprouting in both cultivar. The first flower primordium was observed when flower stalk reached 3㎝ in length of Phal. amabilis. Clear curved relationship (P＜0.001) was found between the length of flower stalk and total node number and flower buds including primordia initiated in apex. The total flower bud initiated at various length of flower stalk before transferred to 30/25℃ respectively was compared to subsequent flowering response. It showed that flower initiation and development did not prevent at 30/25℃ despite the reduction of flower number when transfer made in comparison with continuously 25/20℃ treatment. The result implied that the possible effect of 30/25℃ on inflorescence development and flowering response after floral determination was involved in reduction the translocation of sucrose from source leaves to the apex of flower stalk. The vernalization stimulus may be modified by the light condition under forcing. With regard to the daylength response, Phal. amabilis and Phal. Taisuco Bright must be considered a facultative intermediate daylength plant for flowering under 23/18℃. The critical daylength for inflorescence development earlier and more uniform was 12 hr. Longer or shorter than the critical daylength, especially 6 or 8 hr, delayed time to flowering and reduced total flower number, but did not prevent flowering. Clear linear and curved relationship were found between the percentage of flower stalk emergence and daily light integral during forcing in Phal. amabilis and Phal. Taisuco Bright, respectively. The saturating PPF for flower stalk emergence was 1.3 in Phal. amabilis and 3.6 mol.m-2.day-1 in Phal. Taisuco Bright. Total flower number increased curvedly as daily light integral increased from 0.4 to 5-6 and 7-8 mol.m-2.day-1 in Phal. amabilis and Phal. Taisuco Bright, respectively. Therefore the light requirement for flowering was much higher than axillary bud sprouting. Following a light saturation process, the percentage of flower stalk emergence and total flower number related to daily light integral increase remained approximately constant or declines. Light intensity had a positive effect on flower stalk number per plant. Daylength, light intensity and the interaction between them on time to flowering and total flower number were significant. A two light levels reciprocal transfer experiment at flower bud visibility indicated that number of flowers and blasted buds appeared to associate with light intensity after flower bud visibility. Low light intensity after flower bud visibility resulted in a great decrease in flower number and increase in blasted bud. The period from flower bud visibility to flower anthesis was greatest sensitivity to light condition during inflorescence development.