Characteristics of the pollen morphology and viability of Bougainvillea (Nyctaginaceae)

Abstract

Pollen grains of 92 Bougainvillea genotypes were examined using a light microscope (LM) and scanning electron microscope (SEM) to identify taxonomic characteristics and the relationship between pollen morphology and germination capacity. The shapes of fresh pollen grains of Bougainvillea genotypes are spheroidal to prolate-spheroidal or suboblate after infolding. The sexine of Bougainvillea pollen grains consists of columellae and a reticulate cristatum, with or without microechini. The distribution pattern of the tectum microechini is uniform on the pollen grains within each genotype, yet it is variable among the different genotypes. Pollen with a smooth reticulate cristatum was observed in the genotypes of B. peruviana, while pollen with muri covering the cristatum were found in the genotypes of B. glabra and B. spectabilis. The pollen grains of each Bougainvillea germplasm have a wide range of diameters. The mean diameter of the pollen grains of the diploid genotypes ranged from 22.2 to 32.1 μm, while that of the polyploid genotypes ranged from 26.7 to 40.4 μm. The germinated pollen grains were observed in the diploid and tetraploid genotypes, the pollen germination rate of which was commonly less than 20 %. The size of germinated pollen grains was significantly larger than that of the silent ones, which indicated that the nonuniform distribution of grain size is a key reason for the low germination capacity of Bougainvillea pollen.