Response of native eastern North American Trifolium spp to root-knot nematodes

The true clovers (Trifolium spp.) are important pasture plants, but most of the cultivated species have low resistance to root-knot nematodes (RKN) (Meloidogyne spp.). Plant introductions of seven Trifolium spp. native to eastern North America (T. bejariense Moric., T. calcaricum Collins & Weiboldt; T. carolinianum Michx., T. polymorphum Poir. ex Lam. & Poir.; T. reflexum L., T. stoloniferum Muhlenberg, and T. virginicum Small ex Small & Vail.) were evaluated in two greenhouse experiments, conducted in spring 1992 and 1993, for response to four RKN species, Meloidogyne arenaria (Neal) Chitwood race 1, M. hapla Chitwood, M. incognito (Kofoid and White) Chitwood race 3, and M. javanica (Treub) Chitwood. Additionally, T. riograndense Burkhart and one accession each of T. ambiguum M.B. and T. repens L. were evaluated. Responses determined were numbers of galls or egg masses 8-wk after inoculation rated on a 0 to 5 scale where 0 is no galling or egg masses per plant and 5 is greater than 100. Among the annual species, T. carolinianum and T. bejariense were the most resistant annual species. Among the perennials, T. calcaricum and T. stoloniferum were highly resistant (ratings < 1.0) except that T. stoloniferum had an intermediate response to M. hapla (ratings of 2.5-3.5). Trifolium polymorphum was variable in response among RKN. The kura and white clover lines and T. riograndense were highly susceptible to RKN (ratings > 4.5). The federally endangered species, T. stoloniferum, rated less than 1.0 in response to M. arenaria, M. incognita, and M. javanica. The recently described rare species, T. calcaricum, had the most resistant response of any species evaluated. These native eastern North American clovers may contain valuable genes for RKN resistance, but due to sexual incompatibility with the cultivated clover species, exploitation of such genes will require molecular methods of gene transfer.