Flower development of tuberous-rooted Dahlia ‘Park Princess’ and ‘Miramar’ was studied during 2 forcing seasons using scanning electron and light microscopy techniques. Each cultivar had a flat, rectangular (0.2 × 0.1 mm) vegetative meristem which domed and increased in diameter as the last leaf primordia developed. Subsequently, 8 outer involucrate bract primordia were formed and the meristem bacame round with a diameter of approximately 0.35 mm. The first visible sign of floral initiation was the formation of inner involucrate bract primordia. The floret primordium developed after the subtending bract primordium. The first unpinched plants of ‘Park Princess’ were reproductive 20 days after planting and 100% were reproductive after 30 days. ‘Miramar’ was reproductive 10 days later with a corresponding delay in anthesis. Unpinched ‘Park Princess’ and ‘Miramar’ were reproductive when the 4th and 6th leaf pairs had separated, respectively. When pinched, over 80% of the lateral branches of ‘Park Princess’ and ‘Miramar’ were reproductive after 12 days.
For the first 35 days following planting, the dry weights of the tuberous roots (TR) of Dahlia ‘Park Princess’ and ‘Miramar’ decreased, but simultaneously the dry weights of the fibrous roots (FR) and shoots increased. During the 2nd half of the forcing period shoot and TR dry weights increased rapidly. New TR developed from adventitious roots which formed at the basal nodes of the stem. Ancymidol (0.75 mg/plant) reduced shoot dry weight as well as total height but did not alter TR or FR growth. Plant quality measured by shoot dry weight was reduced when the distal half of each TR was removed before planting. It was not reduced where half of the TR were left intact or when only 1 cm was removed from each TR. The number of days to flower was inversely correlated with plant height measured at 14 and 28 days after planting but not with clump fresh weight.
Tulip bulbs (Tulipa spp.) were placed under ventilated low pressure storage (LPS) conditions for 14 days in either August or September. Compared to 760 mm Hg stored bulbs, LPS suppressed leaf growth and floral development. These effects were highly visible after storage in air at either 76 or 150 mm Hg and in the month of August. When tulip bulbs were forced, LPS treatments applied in August delayed flowering of most cultivars and flower size was occasionally reduced; in September treatments, LPS ventilation with additional O2 and CO2 accelerated flowering of 2 cultivars, but flower size was reduced. When stored under 76 mm Hg in air in August, most cultivars of hyacinth (Hyacinthus spp.) were subsequently delayed in flowering, but daffodils (Narcissus spp.) were not. Except for one cultivar of each species, LPS did not affect the percent of plants flowering, plant height or flower size. Penicillium growth on the bulb tunics was enhanced by humidifying the air under LPS conditions. It is concluded that LPS provides no advantages over the ventilated, temperature controlled units presently employed.
Pinching of forced tuberous-rooted Dahlia ‘Park Princess’ and ‘Miramar’ was evaluated as a method for increasing flower production and plant quality. Pinched plants produced more flowers, flowered later, had smaller flowers, and were taller than unpinched controls. On an individual plant basis, pinching at node 4 generally gave the best results, while pinching at node 2 resulted in the greatest delay and fewest flowers. The more distal the pinch, the greater the number of laterals formed on both cultivars and the higher the percent of laterals flowering on ‘Park Princess’. On a population basis, pinching only those plants with a single strong shoot at node 3 or 4 resulted in the best compromise between increased flower production and the deleterious delayed flowering and increased plant height.
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