Morfologia e viabilidade de grãos de pólen de Toona ciliata M. Roemer (Meliaceae) em diferentes estádios florais e tempos de armazenamento

Abstract

Toona ciliata is a promising tree species due to its excellent technological properties for use in the timber industry. In addition, this specie has adapted well to the various Brazilian soil and climate conditions, shows resistance to the cedar and mahogany borer (Hypsiphyla grandella), and satisfactory responses to silvicultural and management practices. However, T. ciliata genetic improvement programs have not yet reached a satisfactory level for its use in large-scale reforestation projects. This work aimed to deepen our knowledge about morphology and viability of stored T. ciliata pollen grains in order to solve problems arising from the asynchrony in the flowering phenology of chosen parents, thus enabling controlled pollination programs. After establishing the basics of floral biology and breeding system, anthers of flowers were collected in three developmental stages: flower buds, at pre-anthesis and at anthesis. The anthers were desiccated and stored at -16°C for up to 360 days. After this period the pollen grains were extracted and analyzed for their morphology and viability. The number of pollen grains per anther was higher in flower buds and pre-anthesis. The diameter of pollen grains gradually increased from flower buds to in anthesis. In flower buds the exine was thinner when compared to the other two stages. The percentage of viable pollen grains was high (above 88%) in all three flower development stages, even at 360 days of storage. We concluded that storage period of T. ciliata pollen grains can exceed 360 days and that flower buds can be used for controlled pollinations in breeding programs.