Mr Clarke used molecular genetic techniques to determine the origins of the sweet potato (kumara) and the bottle gourd in Oceania. Both are thought to have been introduced into Oceania by Polynesian voyagers who collected them from South America about 1,000 years ago (the word kumara is used by indigenous South Americans). Using new and improved DNA techniques, Mr Clarke analysed several hundred varieties of sweet potato and about 40 varieties of bottle gourd. The results are consistent with a pre-European introduction of these crops into Polynesia from South America, and have revealed something about their dispersal patterns within Polynesia, including New Zealand.

Mr Clarke used molecular genetic techniques to determine the origins of the sweet potato (kumara) and the bottle gourd in Oceania. Both are thought to have been introduced into Oceania by Polynesian voyagers who collected them from South America about 1,000 years ago (the word kumara is used by indigenous South Americans). Using new and improved DNA techniques, Mr Clarke analysed several hundred varieties of sweet potato and about 40 varieties of bottle gourd. The results are consistent with a pre-European introduction of these crops into Polynesia from South America, and have revealed something about their dispersal patterns within Polynesia, including New Zealand.

Mr Clarke used molecular genetic techniques to determine the origins of the sweet potato (kumara) and the bottle gourd in Oceania. Both are thought to have been introduced into Oceania by Polynesian voyagers who collected them from South America about 1,000 years ago (the word kumara is used by indigenous South Americans). Using new and improved DNA techniques, Mr Clarke analysed several hundred varieties of sweet potato and about 40 varieties of bottle gourd. The results are consistent with a pre-European introduction of these crops into Polynesia from South America, and have revealed something about their dispersal patterns within Polynesia, including New Zealand.

Sweetpotato (Ipomoea batatas (L.) Lam.) is a root crop well established throughout the world's tropical and sub-tropical regions. Despite sweepotato's importance, it has been under-researched relative to many other major crops. The main objective of this thesis is to contribute to a fuller understanding of the genetic and physiological factors underlying the production of sweetpotato storage roots for human consumption. The sweetpotato genome is diverse and subject to high levels of natural somatic mutation. Applying the AFLP (amplified fragment length polymorphism) technique allowed a direct comparison of inter and intra-cultivar DNA (deoxyribonucleic acid) base sequence variation. Analysis of the variation indicated that although sweetpotatoes are clonally propagated, clones show a lack of genetic fidelity to their source. Further, the level of genetic variation within the cultivar 'Owairaka Red' indicated the continuing emergence of distinct new strains. Plant field establishment represents the interaction of both propagation and growth phases of storage root production. A range of establishment techniques were investigated in a field trial under commercial conditions. Sprouts cut from seed roots and held for six days rather than immediate planting improved establishment as measured by growth, at little expense. Plug raised plants also improved establishment, while potentially reducing the degree of intra-cultivar genetic variation. Plant carbohydrate partitioning in three cultivars, 'Beauregard', 'Beniazuma' and 'Owairaka Red' was examined by field trial over the period of storage root growth. While cultivars differed in the proportions of dry matter partitioned to leaf, stem and root organs, the cultivar specific ratios of leaf to stem dry weight were relatively stable over time. Total storage root dry weight increased with time for all cultivars, but the distribution of storage root grades by size was cultivar specific. Within the storage roots % dry weight increased over time in all cultivars, but total sugar concentration only increased for 'Beauregard' and 'Beniazuma'. Finally, a storage root disorder called 'brown centre' curtails the temperate growing season so was investigated using low temperature storage and a field trial with various nutrition regimes. The disorder was found to be associated with susceptible germplasm, high soil nitrogen and harvest time.