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CONTENTS

1. Summary.

2. Introduction.

3. The features of Maize pollen and pollination.

4. Evidence of maize pollen dispersal from monitoring surveys.

5. Estimates of pollen transport by the wind in the vicinity of the crop and rates of cross pollination.

6. Potential long range dispersal.

7. The transfer of maize pollen by Bees and other insects.

8. Discussion and conclusions.

9. References.

10. Appendices.

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1. SUMMARY

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The report reviews evidence from published sources and also from communications from named authorities about maize pollen dispersal. Background material is given on the characteristics of maize pollen including morphology and duration of viability, together with quantities produced and the salient features of pollination.

This information is used with data from empirical studies, dispersion theory models and particle deposition theory to give estimates of deposition rates and concentrations of pollen remaining airborne downwind from a source. However it is not possible to provide accurate assessments for practical use as most empirical work has been done within a narrow range of weather conditions and many studies suffer from the constraints of monitoring only close to the source and of errors in sampling. For example, evidence from previous work can be used as a basis for generalised estimates of percentages of pollen concentrations remaining airborne downwind in low to moderate wind speeds compared with concentrations at 1m from the source. These are approximately 2% at 60m, 1.1% at 200m and between 0.75 % and 0.5 % at 500m. The implications of these figures for potential cross pollination are considered but it is emphasised. that they should be used as rough guidelines only. In addition it should be noted that dispersal gradients would be altered by factors such as climatic conditions and local topography.

Transport on the airflow over longer distances is likely to occur under a range of weather situations including uplift and horizontal movement in convection cells, and uplift and transport in frontal storms. As the maize pollen grains remain viable for about 24 hours in normal weather conditions pollination could occur at sites remote from the source ( e.g. 180 km).

Dispersal away from the vicinity of the crop also takes place by carriage on bees. Evidence is cited that maize pollen is collected by bees in notable amounts. In this way the pollen is transported several miles from the crop plot in suitable weather conditions.

In any assessment of pollen flow from maize plots consideration should be given to the limitations of evidence from empirical studies and from results based on theoretical models. Acknowledgement must be given to the potential movement of maize pollen by bees and the possibilities of long range transport under certain weather conditions.

Dr Jean Emberlin
Beverley Adams-Groom BSc and Julie Tidmarsh BSc
National Pollen Research Unit
University College
Worcester WR2 6 AJ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

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