A thesis submitted for the degree of Master of Philosophy atThe University of Queensland in 2013 School of Agriculture and Food Sciences i ABSTRACTSweetpotato propagation is cultivated through use of sprout (slip) or vine cutting. Production of sprout is increased by best selection of storage root sizes to optimize growth and yield.Cultivars of different storage root sizes produced variable numbers of sprouts, varying in length and thickness and to explore this four storage root sizes in an open field bed were trialed. Beauregard and Northern Star storage roots selected from the large, medium, smallmedium and small storage root category sown in bed and sprouts at three length classes were first measured 47 days after sowing. The next three harvests were measured at 21 days interval while the fifth harvest was at 44 days after the fourth, calculated from the Growing Degree Days (GDD) units. Beauregard produced significantly higher number of sprout at >20 cm but fewer > 35 cm length than Northern Star. The sprout length 20 -35 cm class increased for both varieties after Harvest 1 but Beauregard tended to increase less for this class than Northern Star with progressive harvests. In the fifth harvest 20 -35 cm length class for both varieties had reduced although Northern Star produced more for this class than Beauregard. A significantly higher number of sprouts were produced by large root but not significantly different from the medium root. Sprout categories for < 20 and 20 -35 cm were greater for large and medium roots than smaller roots. The thickness of sprout progressively decreased in numbers as storage roots size decreased. Sprouts longer than 20 cm are considered best propagation material for farmers and to achieve this within the best possible short period is an advantage to farmers.The experiment study on seven sweetpotato varieties for pathogen tested (PT) and nonpathogen tested (NPT) was investigated at 60 days after planting (DAP), 120 DAP and 220 DAP for yield differences. There was no significant difference (P < 0.05) for all varieties for early root growth at 60 (DAP). No significant difference was observed for PT and Non-PT for the marketable yield but a significant increase in non-marketable yield at 120 DAP and 220 DAP for PT and non-PT was presumably due to virus infection.The number of marketable storage root production declined as the crop grew older but the opposite trend occurred for the non-marketable yield which increased three fold in the final harvest compared to the previous harvest. Northern Star produced the highest number and weight of marketable and non-marketable roots compared to the other six varieties.ii LD02 and Beauregard were the second best varieties in terms of marketable roots while L49, Vekeoli and Lola Tonga had the least potential. Northern Star followed by Beauregard and LD02 proved their supremacy by their ability to partition dry matter to bulk storage root.Beauregard was the only variety observed with SPFMV infection in the foliage.High soil temperatures affected the...