Abstract/Summary

As the global population continues to rise, new solutions are required to increase productivity of food systems. One such approach is to increase the efficiency of crop photosynthesis by genetic manipulation of rate-limiting enzymes, a method proven to be successful in a range of model and cereal crop species. This thesis aims to apply this to cultivated strawberry (Fragaria x ananassa Duch.) by first exploring species-specific factors limiting photosynthetic efficiency and then generating transgenic lines with enhanced photosynthesis. Variation of photosynthesis across a polytunnel was recorded to better understand photosynthesis in strawberry. It was found that availability of photosynthetically active radiation and stomatal behaviour are key factors in determining photosynthetic carbon assimilation and that this determines patterns in fruit yield seen across the tunnel. Plasmids were constructed containing coding sequences for sedoheptulose-1,7- bisphosphatase (SBPase), a Calvin-Benson-Bassham Cycle enzyme, and adenosine diphosphate glucose pyrophosphorylase (AGPase), a starch synthesis enzyme. Both genes have formerly been implicated in limiting photosynthetic rate, making interesting targets for study. Transgenic plants expressing both genes in concert and AGPase alone were regenerated from transformed callus tissue on hygromycin selection, though this rate of regeneration was significantly delayed by the selectable marker. The photosynthetic efficiency of transgenic plants was then tested via chlorophyll fluorescence imaging. A small, non-significant increase in photosystem II operating efficiency was observed in the double expressing line only, suggesting AGPase does not limit photosynthetic rate in strawberry while SBPase might. However, both transgenic lines had an increase non-photochemical quenching, suggesting a role of starch synthesis in regulation of the photosystem. Overall, these results lay the groundwork for realising increased photosynthetic efficiency in strawberry and other fruiting crops and describe genetic and physiological targets limiting strawberry photosynthetic rate for future study.