Pollen biology and reproductive ecology of selected paleotropical Dendrobiums and its commercial hybrids

Understanding the reproductive biology is of great importance in the development of novel hybrids in ornamental plants. Pollen fitness-related traits are crucial for the pollination success in any plant species including dendrobiums. The aim of the study was to determine and compare the fitness traits of ten commercial Dendrobium hybrids and two indigenous Dendrobium species, D. crumenatum and D. anosmum found in Sri Lanka. We measured pollen viability, pollen germinability, and fruit production after controlled pollination. The effect of storage temperature on D. crumenatum pollen viability was evaluated to establish a suitable pollen storage method to improve future breeding programmes, as the flowering of dendrobiums is seasonal. The reproductive ecology of selected dendrobiums was studied by the observations of visits of natural pollinators and by assessing floral morphology to predict their potential pollinators. Six commercial hybrids had non-viable pollen while D. crumenatum showed the highest pollen germinability under both in vivo and in vitro conditions. Ninety percent of the commercial hybrids failed in vitro pollen germination whereas under in vivo conditions 50% were successful. Self-incompatibility in D. crumenatum was observed in both hand-pollination and under natural pollination. Pollen of D. crumenatum can be stored for two weeks at 9°C maintaining viability and germinability. Selected dendrobiums have shown adaptations to melittophily, suggesting the pollination by bees. Findings indicated a reduction of male fitness in most of the commercial Dendrobium hybrids and a higher fruit set is seen in selfing than cross-pollination. The present study provides information for developing conservation strategies and future hybridization programmes in paleotropical dendrobiums.