Sweetpotato is one of the world's most important food crops, particularly in developing countries. The storage roots have high carbohydrate and vitamin A contents and possess strong antioxidant potential, previously attributed to their hydroxycinnamic acid content. We report on several new purple sweetpotatoes developed for their high anthocyanin content. Although the antioxidant activity of purple sweetpotato extracts was greater than that of sweetpotato lacking anthocyanins, anthocyanins alone could not account for all the activity. Extract components were separated by 2D paper chromatography, and their relative contributions to antioxidant activity were determined. The antioxidant activity of the extracts from sweetpotato was shown to be due to both anthocyanins and hydroxycinnamic acids, additively. Neither the anthocyanin content nor the antioxidant activity of sweetpotato flesh was affected by common cooking methods. These findings may be important in the light of the health-protective properties attributed to both antioxidants and anthocyanins.
The fungus Ceratocystis fimbriata causes a disease of the sweetpotato (Ipomoea batatas) plant commonly known as black rot This study evaluated sweetpotato cultivar susceptibility to C fimbriata infection During crop production infection of sweetpotato storage roots may take place by transmission from contaminated transplants but generally the pathogen is introduced directly through openings in the periderm These openings may take the form of damaged secondary lateral roots lenticels or wounds In a laboratorybased bioassay storage roots were punctured then pointinoculated with the pathogen Following incubation under warm humid conditions the dimensions of black rot lesions were compared The predominant New Zealand cultivar Owairaka Red was demonstrably less susceptible to C fimbriata than the Japanese cultivar Beniazuma but significantly more susceptible than Beauregard from the United States of America (P
The sweetpotato (Ipomoea batatas (L.) Lam) crop, once established, requires little field management apart from weed control. Currently, weeds are minimised by a combination of hand-weeding, inter-row cultivation and the application of paraquat (100 g ai/ha) over the crop. In this study, alternative herbicide treatments were examined in a field trial. Hand-weeding produced the highest marketable yield (26.7 t/ha), significantly more than all other treatments apart from acetochlor (2.4 kg ai/ha), which produced 21.8 t/ha (P< 0.001). Weed numbers were significantly reduced to 3.5% (acetochlor) and 16.2% (paraquat) of the unweeded plots (P< 0.001). There was a strong negative relationship between early weed count and final total root yield (R 2 = 84.0%).
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