What are the physiological disorders of Rose in greenhouse cultivation?
The shoot, which flowers normally in a greenhouse rose to have sepals, petals, and reproductive parts which are fully expanded. The failure in developing a flower on the apical end of the stem is the most common occurrence and such shoots are termed as blind ones. The sepals and petals will be present, but it attains a considerable length and thickness when it develops at the top of the plant. This may be caused by insufficient light, residues of chemicals, insect, pests, fungal diseases and other factors.
Bullheads or malformed flowers:
The petals at the centre of the bud remain as the ones which are partial and the bud appears flat in structure. These are common on very vigorous shoots, particularly bottom breaks, and there is a possibility that there is a lack of carbohydrates to develop the petals. The cause of bull heading is as yet unknown, however, thrips infestation will also cause malformed flowers.
Off- coloured flowers present a problem with some yellow varieties. In such cases, the petals may be in a green colour or a dirty white instead of a clear yellow. Raising the temperature at night up to several degrees will decrease the number of off-coloured flowers. Occasionally, the pink or red varieties give bluish-coloured flowers. This is very often associated with the use of organic phosphate and various other kinds of insecticides.
The area of the stem just below the flower starts to wilt wilts and does not support the head. Sometimes this happens due to insufficient absorption of water; cutting off the lower 1 to 2 inches of stem and placing the cut stem in water at 37°C will revive the flower.
Blackening of rose petals:
This happens due to low temperature and high anthocyanin content. The GA3 treatment, causes accumulation of anthocyanin in petals of Baccara species of roses. This effect is more occurred at low temperatures (20°C at day and 4°C at night) than at higher temperatures (30°C at day and 20°C at night).
Deficiency of Iron can cause pale foliage. Adjusting the pH level of the soil will solve this problem.