Study of pollen morphology and salinity effect on the pollen grains of four olive (Olea europaea) cultivars

Abstract

Pollen and seed germination tests can be used as effective test in screeing salt-tolerant crop and pollen grain morphology characteristics can be used to determine interspecific and intraspecific relationships among olive species. So, This study was conducted to investigate the effect of different salinity concentrations on pollen germination, tube growth and further evaluation of pollen grain morphological characteristics using Scanning Electron Microscopy (SEM) of four olive (Dezful, Mission, Koroneiki and Tarom2) cultivars. Results showed that polar axis (P), equatorial axis (E), and the distance between furrow edges and ridges width were significantly different between four olive cultivars. The value of polar axis ranged from 18.77 μm in ‘Koroneiki’ up to 20.03 μm in ‘Dezful’, while the mean values of equatorial axis ranged from 12.76 μm for ‘Tarom2’ up to 13.68 μm for ‘Dezful’. The lowest distance between furrow edges (12.13 μm) and width of ridges (8.63 μm) were obtained in ‘Mission’ cultivar. It indicated that ‘Dezful’ and ‘Mission’ olive cultivars produced pollen grains with low mesh density in unit area and incomplete closure. While, ‘Tarom2’ and ‘Koroneiki’ produced pollen grains with high mesh density and complete closure. The results also elucidated that the amount of pollen germination decreased as concentration of salinity increased on the medium. The reduction of pllen germination rate occurred at the 83.71%, 96.68%, 86.83% and 87.38% with additional of 25 mM NaCl in the media of ‘Tarom2’, ‘Dezful’, ‘Mission’ and ‘Koroneiki’ cultivars, respectively. The maximum pollen tube length (171.99 μm) was observed in ‘Tarom2’ cultivar cultured in a salinity-free medium; while pollen tube length was the lowest (3.5 μm) in ‘Dezful’ cultivar cultured in a medium containing 25 mM of NaCl. Findings also revealed information in which was able to categorize cultivars into tolerant (‘Tarom2’), semi-tolerant (‘Mission’ and ‘Koroneiki’) and sensitive (‘Dezful’) based on tolerating critical salinity (lethal salinity) condition at the pollen germination stage. According to the results of this experiment, it can be concluded that investigate the effect of salinity stresses on gametophytic phase could be applied for the screening tolerant olive cultivars to salt stresses.