The growth of miniature rose (Rosa chinensis Jacq. 'Minima') shoots cultured on liquid medium was greater relative to those cultured on two-phase (solid + liquid) medium or solid medium alone. Shoot multiplication ratio (number of multiple shoots per explant per subculture) on liquid medium was higher with 17.8-26.6 IxM 6-benzyladenine at compared to that at 0-8.9 txM. Shoots grown on 30 ml or more of liquid medium had a higher multiplication ratio than those grown on 10 or 20 ml. The growth and multiplication ratio increased when the culture period was extended from 3 to 6 weeks, although plantlets began to exhibit some chlorosis by the 6 ~h week. These conditions were maintained over four subcultures for cultivars 'Baby Katie', 'Lavender Jewel', 'Red Sunblaze' and 'Royal Sunblaze', with no significant change in multiplication ratio over time.
Experiments were conducted on 6-month-old chinese ixora (Ixora chinensis Lam.) from February 1999 to April 2000. Floral development was studied with scanning electron microscopy (SEM) to determine the flowering sequences. Morphological characters were used to clarify the stages of flowering processes. The time of organogenesis and flowering arrangement was established through field observations. Floral evocation occurred in early September, floral initiation occurred in the middle of September and floral differentiation began in late September. A distinctly convex apex with bracts around the shoulder indicated the beginning of reproductive development. Subsequently, primary inflorescence axes were observed and differentiated into secondary, tertiary, and quaternary inflorescence axes consecutively in about one and a half months. Once the terminal apex reached the inflorescence bud stage, it would flower without abortion, and this may be assessed as no return. The sepals, petals, stamens, and pistil were well developed thereafter and anthesis was achieved in January through March in the following year. The observation of floral differentiation sequences and investigation of floret arrangement made it certain that chinese ixora had cymose inflorescence (cyme), but not corymb. A quadratic equation was established to predict floret number from the differentiation level (a quantitative description of differentiation stage) of a developed inflorescence.
It has long been established that phytoplasma infection is the cause of the free-branching phenotype in poinsettia. However, relatively limited is known about the ecology of the pathogen in planta. The present study evaluated the infection pattern of poinsettia branch-inducing phytoplasma (PoiBI) and its association with poinsettia phenotype during cutting propagation. The presence of this pathogen in the poinsettia variety 'Luv U Pink' was determined using polymerase chain reaction (PCR) and sequence analysis. The infection density of PoiBI in distinct tissue types of different plant segments were then determined using quantitative PCR coupled with plasmid-based standard curves. Both vegetative stage and flowering stage plants were tested. The results showed that despite being considerably variable among plants, the infection densities of PoiBI tend to be higher in source leaves located in the lower parts of the plant. The densities were consistently lower in tissues located at the top of the plants, regardless of the tissue type. Analysis on the infection densities among samples collected from six stock plants used in commercial production also revealed significantly different levels of PoiBI load. An association between PoiBI infection density in the stock plants and the level of branching in cutting-propagated plants (derived from the stock plants) was also observed; stock plants with low infection densities tend to produce smaller proportions of plants exhibiting higher degrees of branching both before and after pinching. These data suggest that uneven distribution of PoiBI within and among stock plants may lead to the production of cuttings with variable phytoplasma densities, which may in turn affect the phenotypic uniformity of the plants produced. Overall, findings from the present work add to the understanding of PoiBI’s ecology and could provide implications to commercial poinsettia production.
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