An insight into pollen morphology and evaluation of pollen viability, germination and mineral composition of some coconut (Cocos nucifera L.) genotypes

Abstract

• Pollen morphology of eight coconut accessions differed in origin, stature, breeding behaviour and tolerance to abiotic stresses were characterised with scanning electron microscope. • Variations in pollen size, shape and exine ornamentation pattern was observed between the coconut genotypes. • Pollen physiological features such as pollen viability, germination and pollen tube length and pollen nutrient composition were evaluated for the eight coconut genotypes. • The results obtained revealed differences in pollen morphological features which can potentially be used for cultivar identification and the information on pollen viability, germination and pollen mineral contents amongst genotypes can support conservation and crop improvement studies of the genotypes. The micro-morphological characteristic of the pollen grain is one of the most important diagnostic traits use for identification and characterization of plants even to the accession levels. In this study, pollen grains characterization of eight different coconut ( Cocos nucifera L.) accessions were carried out. Morphometric observations and structure analysis of the pollen grains were performed using light and scanning electron microscopy. The variation in length and width observed ranged from 55.06 -71.25 µm and 24.38 -36.27 µm amongst the accessions. The pollen grains exhibited an ellipsoidal to elliptical shape with the exine ornamentation ranging from granulate to reticulate. Pollen viability, germination and pollen tube length were significantly different amongst the tested accessions. While pollen viability varied from 92.35 to 96.5%, germination rate and pollen tube length (after 2 h) ranged from 16.05 - 31.59% and 234.95 μm to 414.96 μm respectively. Pollen mineral composition from different accessions also varied significantly with Malayan Orange Dwarf (MOD) recording higher phosphorus (0.93%), calcium (0.64%) and magnesium (0.38%) content while highest potassium (1.01%), sodium (0.71%), iron (149.35 ppm) zinc (119.59 ppm) and boron (45.05 ppm) content was noticed in San Ramon Tall (SNRT). This investigation highlights the fact that these pollen morphological features could be potentially used for differentiating the selected accessions thereby supporting their conservation and crop improvement studies.