RESPONSE OF NATIVE EASTERN NORTH-AMERICAN TRIFOLIUM SPP TO ROOT-KNOT NEMATODES

The true clovers (Trifolium spp.) are important pasture plants, but mo st of the cultivated species have low resistance to root-knot nematode s (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 L am. & Poir.; T. reflexum L., T. stoloniferum Muhlenberg, and T. virgin icum Small ex Small & Vail.) were evaluated in two greenhouse experime nts, conducted in spring 1992 and 1993, for response to four RKN speci es, 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 ea ch of T. ambiguum M.B. and T. repens L. were evaluated. Responses dete rmined were numbers of galls or egg masses 8-wk after inoculation rate d 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 perenni als, 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 resp onse among RKN. The kura and white clover lines and T. riograndense we re highly susceptible to RKN (ratings > 4.5). The federally endangered species, T. stoloniferum, rated less than 1.0 in response to M. arena ria, M. incognita, and M. javanica. The recently described rare specie s, T. calcaricum, had the most resistant response of any species evalu ated. 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 mol ecular methods of gene transfer.