Journal of Apicultural Science

Characteristics of nectaries and nectar in flowers of two Rhododendron species

Journal of Apicultural Science. Volume 53, Issue 1, Pages 17-27, ISSN (Print) 1643-4439
The morphology of nectaries and nectar secretion in flowers of Rhododendron catawbiense and R. japonicum were compared. The structure of the secretory epidermis was analysed using scanning electron microscopy (SEM). The weight of nectar and percentage of sugar content in nectar as well as the efficiency of different sugars from 10 flowers of the studied taxa were determined.
The nectaries in flowers of Rhododendron catawbiense were larger and they formed more distinctive protuberances at the base of the ovary than in R. japonicum. The surface of the nectaries of both species was striated at places and their upper part was covered with densely growing non-glandular trichomes. The stomata in R. catawbiense were distributed individually and evenly over the whole surface of the nectary, whereas in R. japonicum they occurred in small clusters or formed densely packed stomatal fields. The beginning of nectar secretion was observed already at the opening bud stage. Nectar was secreted by stomata which were at different growth stages throughout the whole secretion period. A positive correlation was found between nectary size and nectar production. The average weight of nectar secreted throughout the lifespan of the flower of R. catawbiense was 16.6 mg, whereas in R. japonicum it was 6.3mg. The sugar content in nectar reached 63% and 37%, respectively. The efficiency of the various sugars from R. catawbiense was 10.4 mg/flower, 4.5 times higher than in R. japonicum (2.4 mg/flower).
nectary, morphology, SEM, nectar secretion, Rhododendron catawbiense, R japonicum
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