Flower Bud Atrophy in Baccara Roses. V. The Effect of Different Growth Substances on Flowering

The effect of various growth regulators on the atrophy of terminal flower buds was tested on Baccara roses. Treatments with gibberellic acid (GA) and 2-chloroethyl trimethyl ammonium chloride (CCC) reduced the atrophy of the flowers. The application of 2-chloroethyl phosphonic acid (CEPA) to the buds enhanced abortion, and the effect was more marked on the lower than on the upper shoot. The stage most sensitive to CEPA was when the shoots were 8–35 cm long. Treatment with abscisic acid (ABA) had no effect of the degree of “blindness”, nor did kinetin applied to the apex affect flowering. Spraying with benzyl adenine increased both the rate of sprouting of the lateral buds and the extent of “blindness” of the sprouting shoots, but did not reduce the number of flowers per branch.     

The Effect of Canopy Wetting on Plant Water Status, CO2 Fixation, Ion Content and Growth Rate of 'Baccara' Roses

The effect of canopy wetting of rose (Rosa hybrida) plants on transpiration rate, stomatal resistance, plant water potential, ion concentration in leaves, and several growth parameters was investigated. Plants were grown in a greenhouse and their canopies were exposed to wetting cycles during the daytime. Canopy wetting decreased transpiration rate and increased diffusive resistance to water vapor transfer. Plant water potential was only slightly increased by wetting, mainly in the spring. Canopy wetting did not prevent the decrease in CO₂ fixation, which took place before midday when plant water potential dropped below – 10 bars during a rise in radiation intensity. The concentrations of Cl^? and Ca²⁺ decreased in wetted leaves, while the concentration of Na⁺ was increased and other cations were hardly affected. Canopy wetting inhibited growth rate of rose shoots and flower formation, and increased the average flower weight.     

Flower Bud Atrophy in Baccara Roses

Changes in gibberellin content and of the production of ethylene in the two upper shoots of roses were measured as affected by decreasing temperature and light intensity, factors which encourage flower atrophy. Decreases in temperature or light intensity to the whole plant reduce the endogenous content of gibberellin in the leaves of the two shoots. The decrease is more rapid and occurs earlier in leaves of the second shoot from the top, where “blindness” is more common. There was also a drop in the gibberellin content, when individual shoots were shaded, although the decrease was more moderate. A lowered light intensity reduced the production of endogenous ethylene by the two shoots, but in the second shoot this production increased after a number of days, before atrophy of the flower bud took place. It is suggested that gibberellin participates in the endogenous control of rose flower development, and the possibility is discussed that it acts by directing the translocation of metabolites to the flower bud.     

Phyllody Malformation in Flowers of Rosaxhybrida cv. Motrea: Effects of Rootstocks, Flower Position, Growth Regulators and Season

Phyllody, a common malformation of Rosaxhybrida cv. Motrea,is characterized by the formation of vegetative structures inplace of stamens and carpels. The incidence of phyllody in thiscultivar is dependent on the type of the root system. The highestproportion of malformed flowers was found in ungrafted plants,this decreased in plants grafted on R. indica major and waslowest on R. canina inermis. Flowers formed on shoots, whichwere located closer to the roots, were more prone to phyllodythan those grown on the upper part of the plants. The incidenceof phyllody was lower in winter than in summer, while shadingof the plants reduced the proportion of malformed flowers regardlessof their root system and the season. Application of gibberellicacid (GA₃) or benzylaminopurine (BAP) greatly promoted the incidenceof phyllody, while paclobutrazol (PBZ) reduced it. The activityof endogenous cytokinins in the xylem exudates from ungraftedplants was higher than in exudates from those grafted on R.indica major, and the lowest activity was found in exudatesfrom plants grafted on R. canina inermis. The involvement ofplant hormones in the development of floral organs in rose flowersis discussed. Key words: Cytokinins, flower malformation, gibberellic acid, homeosis, phyllody, roses     

Environmental Factors involved in the Regulation of Sprouting of Basal Buds in Rose Plants

The plant top is the main factor inhibiting the formation ofjuvenile-like shoots from the basal part of the rose plant.In plants with the whole top removed a cooling period of oneweek at 4 °C had a promotional effect on the outgrowth ofbasal buds. Six days of darkness partially inhibited sproutingof these buds and 9 d suppressed sprouting completely. On theother hand. 3 d in light following plant top removal were sufficientto cause sprouting. Buds on the upper parts of lateral shoots were not affectedby the dark treatment. Key words: Basal buds, Rejuvenation, Roses     

Studies with Liatris spicata Willd. 1. Effect of Temperature on Sprouting, Flowering and Gibberellin Content

Dormancy was induced during storage of Liatris spicata cormsgrown in Israeli summer conditions, but plants left in soilcontinued vegetative growth. Corms of winter-grown plants sproutedfreely. Treatment with GA₃ restored both sprouting and floweringin summer-grown corms, but in winter corms GA₂ was effectiveonly after corms were stored at low temperature. All the plantsflowered after 4 weeks at 2 °C and GA³ treatment. The content of gibberellins in the main bud of freshly excavatedcorms decreased during the first 18 d of storage but increasedto the initial level after 4 months of cold storage. The numberof flowering stems increased to 2.5 per corm when corms werecold-stored up to 75 d, but decreased with a longer storage. Liatris spicata, dormancy, flowering, gibberellin, sprouting     

Involvement of Hormonal Balance in the Control of the 'Bullhead' Malformation in Baccara Rose Flowers

Gibberellin activity is much lower and cytokinin activity ishigher in the flowers of roses grown at a relatively low temperatureand in ‘pbullhead’ malformed flowers which appearin such conditions, compared to ‘normal’ flowersgrown at higher temperatures. Injection of gibberellin intothe receptacle of flowers grown at low temperature preventsthe symptoms of malformation. Injection with cytokinin of thoseflowers had no effect, but addition of BA¹ to GA injection abolishesthe malformation-preventing effect of the gibberellin. Cytokinintreatment of plants grown at higher temperatures causes proliferationof the nectary and promotes appearance of adventitious floretswhich are characteristic symptoms of malformed flowers. The level of auxin is higher in higher temperatures, but therewas no effect on the development of flowers at the various temperaturesby applying auxin. The involvement of hormonal balance in theabnormal development of rose flowers is discussed.     

Studies with Liatris spicata Willd. 2. Effects of Photoperiod on Stem Extension, Flowering and Gibberellin Content

Flower formation in Liatris spicata Willd. was not affectedby photoperiodic treatments, but long days (16 h) had a pronouncedeffect on elongation of the flowering stem. An illuminance of2 Ix was sufficient to produce near maximal elongation. Long days caused a decrease in endogenous gibberellins in thetips of rapidly elongating stems and decreased the number offlowering stems per corm. Liatris spicata, elongation, flowering, gibberellin, light, photoperiod