Variable disease resistance to Sclerotinia sclerotiorum in traditional New Zealand/Māori sweet potato cultivars

Abstract

Sweet potato (Ipomea batatas (L.) Lam.) or kumara, is a crop of cultural significance brought to New Zealand by Maori nearly 1000 years ago. Current commercial production in New Zealand is based on three cultivars ‘Beauregard’, ‘Owairaka red’ and Tokatoka Gold’, which are affected by the field and storage diseases Sclerotinia sclerotiorum (pink rot) and Rhizopus stolonifer. Access to export markets in the US and EU is compromised by use of fungicides to control these diseases. Appealing alternatives to chemical control of fungal pathogens are genetic resistance and biological control. A possible source of disease resistance is the traditional cultivars which have been selected for survival and sustainable yield over many centuries rather than high yields in intensive cultivation. Therefore we compared 8 traditional cultivars traditional and three commercial cultivars to determine whether there was any significant difference resistance to S. sclerotiorum. Stem cuttings were inoculated with S. sclerotiorum, incubated in moist chambers at 20°C and the lesion length measured daily. The experiment was repeated twice with the 8 traditional cultivars, then three traditional cultivars were chosen and compared with three commercial cultivars. The cultivars showed a range of susceptibilities to S. sclerotiorum, the most resistant being the commercial cultivar ‘Beauregard’ and the traditional cultivar ‘Taputini’, while the most susceptible was the commercial cultivar ‘Tokatoka Gold’. Given that ‘Taputini’ is at least as resistant as the most resistant commercial cultivar it could potentially be used in breeding more resistant and uniquely New Zealand cultivars, and also offers a good option for organic growers and those growing traditional cultivars wanting to replace susceptible sweet potato crops.