Articles
Scanning electron microscopy: a useful tool for screening Actinidia pollenizers
Article number
1431_62
Pages
481 – 486
Language
English
Abstract
For Actinidia, interspecific hybridization and polyploidy have the potential to introduce novel characteristics and increase desirable qualities.
However, for wide crosses, the selection of suitable male pollenizers is important.
Scanning Electron Microscope (SEM) screening of pollen grains obtained from male pollenizers is a useful approach to assess somatic-ploidy levels.
For this investigation we used SEM to obtain high-resolution images of Actinidia pollen grains extracted from dried and frozen anthers derived from different species and interspecific hybrids.
This included available male A. chinensis var. chinensis accessions from the USDA’s Davis, California collection.
For horizontally-positioned pollen grains we used ImageJ software to measure their cross-sectional area and perimeter.
Mean values were then plotted in Excel to reveal discrete clusters that correspond to different somatic-ploidy levels.
We were able to distinguish between diploid, tetraploid and hexaploid and aneuploid pollenizers with high accuracy.
SEM images were also used to evaluate various male interspecific hybrids for sterility based upon pollen-grain morphology.
Collapsed and shriveled grains were indicative of infertility in the F1. Excess exine ornamentation characterized by thick, lumpy textures in the F1 may suggest at least partial genetic imbalance in otherwise normally-shaped pollen grains when compared with the much smoother exine textures observed in respective parent species.
Where non-even sex ratios are present in the F1, the SEM can be used to effectively screen large seedling populations of Actinidia pollenizers.
Because dried and frozen, Actinidia pollen remains viable and suitable for crosses for -10 years; vials of SEM-vetted pollen samples can be placed in long-term storage for subsequent plant breeding.
This enables successful cross combinations to be replicated even if the original male pollenizer is no longer available.
However, for wide crosses, the selection of suitable male pollenizers is important.
Scanning Electron Microscope (SEM) screening of pollen grains obtained from male pollenizers is a useful approach to assess somatic-ploidy levels.
For this investigation we used SEM to obtain high-resolution images of Actinidia pollen grains extracted from dried and frozen anthers derived from different species and interspecific hybrids.
This included available male A. chinensis var. chinensis accessions from the USDA’s Davis, California collection.
For horizontally-positioned pollen grains we used ImageJ software to measure their cross-sectional area and perimeter.
Mean values were then plotted in Excel to reveal discrete clusters that correspond to different somatic-ploidy levels.
We were able to distinguish between diploid, tetraploid and hexaploid and aneuploid pollenizers with high accuracy.
SEM images were also used to evaluate various male interspecific hybrids for sterility based upon pollen-grain morphology.
Collapsed and shriveled grains were indicative of infertility in the F1. Excess exine ornamentation characterized by thick, lumpy textures in the F1 may suggest at least partial genetic imbalance in otherwise normally-shaped pollen grains when compared with the much smoother exine textures observed in respective parent species.
Where non-even sex ratios are present in the F1, the SEM can be used to effectively screen large seedling populations of Actinidia pollenizers.
Because dried and frozen, Actinidia pollen remains viable and suitable for crosses for -10 years; vials of SEM-vetted pollen samples can be placed in long-term storage for subsequent plant breeding.
This enables successful cross combinations to be replicated even if the original male pollenizer is no longer available.
Publication
Authors
B. Guthrie, J. Thole, J. Smith
Keywords
polyploids, Actinidia breeding, pollen morphology, pollen viability
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