Host status of cover crops for root-lesion nematodes (Pratylenchus spp.) associated with apple orchards in South Africa

The host response of 17 cover crop cultivars to infection by single-species populations of Pratylenchus hippeastri, Pratylenchus vulnus and Pratylenchus penetrans, the three most common root-lesion nematode species in apple orchards in South Africa (SA), was evaluated under glasshouse conditions. Reproduction of the three Pratylenchus species was assessed 12 weeks after infection of the cover crop plants based on the reproductive potential (RF) and their (relative) susceptibility compared with the most susceptible control plant included in the experiment. Most of the cover crop cultivars (12 out of 17) were poor hosts of all three Pratylenchus species: brown mustard ‘Caliente 199’, white mustard ‘Braco’, canola/rapeseed ‘Garnet’, tillage radish ‘Groundhog’, barrel medics ‘Jester’, ribwort plantain ‘Captain’, creeping fescue (cultivar unknown), black oats ‘SAIA’, perennial ryegrass ‘Champion blend’, tall fescue ‘Speedway’, triticale ‘Korog’ and french marigold ‘Naughty Marietta’. These 12 cover crop cultivars did not support reproduction of P. hippeastri, P. vulnus and P. penetrans, and have thus the potential to limit the build-up of large, damaging populations of these three root-lesion nematode species. Five out of the 17 cover crop cultivars were identified as good hosts of one or more of the three Pratylenchus species: pink serradella ‘Margarita’ and subterranean clover ‘Aarbei Klawer’ were good hosts of P. penetrans only; rye ‘Duiker Max’ was a good host of both P. hippeastri and P. penetrans; Indian buckwheat (cultivar unknown) and garden nasturtium ‘Jewel Choice mix’ were good hosts of all three Pratylenchus species. These five cover crop cultivars have thus the potential to enable the build-up of large damaging populations of either one, two or three of the root-lesion nematode species and may act as primary sources of infection of apple roots. Their use as cover crops in apple orchards infested with root-lesion nematodes should be avoided.