Assessing resistance levels of potato cultivars in South Africa against Alternaria alternata

Brown leaf spot caused by Alternaria alternata (Fries) Keissler is one of the most devastating fungal diseases of potato. Management of this disease relies mostly on fungicide applications. However, fungicides are becoming less effective due to the development of fungal resistance to specific chemicals. Additionally, there is limited information on resistance in potato cultivars in South Africa against brown leaf spot. This study aims to evaluate ten commercial potato cultivars for brown leaf spot resistance using detached leaf, tuber and whole plant screening techniques under controlled conditions. The experiment was conducted in 2016 and repeated in 2017. The whole plant assay showed that Labadia, Almera, Sifra, Mondeo, Up-To-Date and Lanorma are resistant to brown spot. Resistance levels in Labadia, Almera, Sifra and Up-To-Date were consistent in the 2016 and 2017 experiments. The detached leaf assay showed Almera, Sifra, Up-To-Date and Mondeo as moderately resistant, while Innovator, Mondial and Markies were moderately susceptible. However, in the tuber assay all cultivars were highly susceptible. Cultivar resistance varied based on the screening technique used, although results suggest that the detached leaf and whole plant assays could be used in potato disease screening programs.