Abstract
The inheritance of resistance to root-knot nematode race 3 [Meloidogyne incognita (Kofoid & White) Chitwood] in sweetpotato [Ipomoea batatas (L.) Lam.] was studied in 71 progenies of the F1 single-cross population produced from the cross of resistant parent `Regal' and susceptible parent `Vardaman'. The distribution frequency of the progenies based on log total nematode number (egg + juvenile counts) was a bimodal distribution with a ratio of ≈4 resistant : 1 susceptible. Based on this phenotypic ratio, the proposed genetic model was duplex polysomic inheritance (RRrrrr = resistant parent and rrrrrr = susceptible parent). Bulk segregant analysis in conjunction with the RAPD technique was used to identify a RAPD marker linked to a root-knot-nematode-resistance gene. Of 760 random decamer primers screened, 9 showed polymorphic bands between the two bulk DNA samples. Primer OPI51500 produced a band in the resistant bulk but not in the susceptible bulk, suggesting a linkage in coupling phase. An estimated recombination fraction of 0.2421 ± 0.057 between the marker and the root-knot-nematode-resistance gene indicated linkage.
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