A series of greenhouse and field studies was conducted over 9 years to
characterize three new sources of resistance in cowpea [Vigna unguicu
lata (L.) Walp.] to the southern root-knot nematode [Meloidogyne incog
nita (Kofoid & White) Chitwood] and to determine if the resistances ar
e conditioned by genes allelic to the Rk root-knot nematode resistance
gene in Mississippi Silver'. Three plant introductions (PI), PI 44198
7, PI 441920, and PI 468104, were evaluated for reaction to M. incogni
ta in four greenhouse tests, and in every test each PI exhibited less
galling, egg mass formation, or egg production than 'Mississippi Silve
r'. F, populations of the crosses between 'Mississippi Silver' and eac
h of the three resistant PIs were also evaluated for root-knot nematod
e resistance in a greenhouse test. None of the F2 populations segregat
ed for resistance, indicating that PI 441917, PI 441920, and PI 468104
each has a gene conditioning resistance that is allelic to the Rk gen
e in 'Mississippi Silver'. Our observations on the superior levels of
resistances exhibited by PI 441917, PI 441920, and PI 468104 suggest t
hat the allele at the Rk locus in these lines may not be the Rk allele
, but one or more alleles that condition a superior, dominant-type res
istance. The availability of additional dominant alleles would broaden
the genetic base for root-knot nematode resistance in cowpea.