IDENTIFYING A RANDOMLY AMPLIFIED POLYMORPHIC DNA (RAPD) MARKER LINKEDTO A GENE FOR ROOT-KNOT NEMATODE RESISTANCE IN SWEET-POTATO

The inheritance of resistance to root-knot nematode race 3 [Meloidogyn e incognita (Kofoid & White) Chitwood] in sweetpotato [Ipomoea batatas (L.) Lam.] was studied in 71 progenies of the F-1 single-cross popula tion produced from the cross of resistant parent 'Regal' and susceptib le parent 'Vardaman'. The distribution frequency of the progenies base d on log total nematode number (egg + juvenile counts) was a bimodal d istribution with a ratio of approximate to 4 resistant : 1 susceptible . Based on this phenotypic ratio, the proposed genetic model was duple x polysomic inheritance (RRrrrr = resistant parent and rrrrrr = suscep tible parent). Bulk segregant analysis in conjunction with the RAPD te chnique,vas used to identify a RAPD marker linked to a root-knot-nemat ode-resistance gene. Of 760 random decamer primers screened, 9 showed polymorphic bands between the two bulk DNA samples. Primer OPI5(1500) produced a band in the resistant bulk but not in the susceptible bulk, suggesting a linkage in coupling phase. An estimated recombination fr action of 0.2421 +/- 0.057 between the marker and the root-knot-nemato de-resistance gene indicated linkage.