Observation on the pollen morphology of male geotypes in wild Actinidia eriantha population

Abstract:【Objective】The shape and the exine sculpture could be used for examining plant evolution and genetic relationship. The objective of the study was to explore genetic diversity, relationship among naturally exiting male population of Actinidia eriantha Benth.【Methods】Fresh pollen grains were collected from mature staments before anthesis. The specimens came from A. eriantha Benth. male geotypes growing in the Magu Mountain region in Nancheng county, Fuzhou city, Jiangxi province, southeast of China. Morphological characteristics of the materials were typical and representative. Pollens were directly placed on conducting resin without any treatment, coated with gold using a Cressington 108 sputter coater and observed with a Quanta 250 scanning electron microscope(SEM). 15-20 pollen grains were measured for each male geotype. The equatorial and polar faces were studied at 5 000× magnification. The exine sculptures were studied at 15 000× magnification. Five characters were measured: P(polar diameter), E(equatorial diameter), D(colpus length), W(colpus width), and P/E ratio. Data Processing System was used to analyze the data.【Results】The shapes of pollen grain of wild A. eriantha male geotypes were prolate or perprolate, the polar view were trifid circular. The pollen polar axis lengths ranged from 22.42 to 27.73 μm, the coefficient of variation was 4.75%. The equatorial axis length ranged from 12.73 to 14.31 μm, the coefficient of variation was 3.12%. All pollen grains were tricolporate including three ectocolpi and three endopori. Ectocolpi was long but narrow at two ends and arranged in a regular lontiudinal pattern. One or two colpi were observed from equatorial view. Three colpi were found from polar view. Colpus widths ranged from 7.29-9.52 μm, the coefficient of variation was 6.78%. There were significant differences between individual geotypes. According to the NPC(Number, Position, Character) classification system classification, the pollens belonged to N3P4C5 mode. The P/E ratios ranged from 1.65 to 2.06, the coefficient of variation was 4.73%. Three types of pollen surface ornamentation were observed:(1) brain-like, the exine sculpture of pollen grain consisted of curved short lines of brain striate and contour line was clearly wavy. This type pollen grain samples were accounted for 65.22%.(2) Irregularly rugulate, the exine sculpture of pollen grain consisted of irregular strip lobes, contour line was finely wavy. This type was accounted 30.43%.(3) Warty, the exine sculpture of pollen grain was made up of irregular fine block bumps. This type was only accounted 4.35%. By using UPGMA cluster analysis, 23 geotypes could be classified into two groups at similarity distance 3.41 level. One geotype was fallen into the first group, the other 22 geotypes were fallen into the second group. At similarity distance 2.55 level,23 geotypes could be classified into three groups. The No. 1 geotype was fallen into the first group, No. 3, No. 4 and No. 6 were fallen into the third group, the other 20 geotypes could be fallen into the second group. The pollen grain size of the first group was the smallest,the pollen of the third group was the largest. Classification was mainly determined by the differences of pollen grain's shapes. The pollen characteristics implyed that many genotypes were from the same origin.【Conclusion】In this paper, we described the detailed morphological characthers of pollen grains of the 23 A. eriantha male geotypes. There were abundant variations between the size and the exine sculpture of the A. eriantha male geotypes, but the coefficient of variation of some index was very small. Therefore, both the genetic conservatism and the diversity of wild A. eriantha male geotypes exit. Furthermore, the differences of the pollen morphology may be caused by genotype difference.According to the size of pollen, 23 wild male geotypes can be divided into three categories. On the other hand, the A. eriantha was more advanced plant by the size of the pollen grains and the surface ornamentation. The evolution trend of the exine pollen was from irregularly rugulate to brain-like and warty. The difference of exine ornamentation and pollen morphology could provide a basis for the survey of genetic diversity relationship and evolution among A. eriantha male geotypes.