K. Meksem et al., 'Forrest' resistance to the soybean cyst nematode is bigenic: saturation mapping of the Rhg1 and Rhg4 loci, THEOR A GEN, 103(5), 2001, pp. 710-717
Field resistance to cyst nematode (SCN) race 3 (Heterodera glycines I.) in
soybean [Glycine max (L.) Merr.] cv 'Forrest' is conditioned by two QTLs: t
he underlying genes are presumed to include Rhg1 on linkage group G and Rhg
4 on linkage group A2. A population of recombinant inbred lines (RILs) and
two populations of near-isogenic lines (NILs) derived from a cross of Forre
st x Essex were used to map the loci affecting resistance to SCN. Bulked se
gregant analysis, with 512 AFLP primer combinations and microsatellite mark
ers, produced a high-density genetic map for the intervals carrying Rhg1 an
d Rhg4. The two QTLs involved in resistance to SCN were strongly associated
with the AFLP marker E(ATG)M(CGA)87 (P = 0.0001, R-2 = 24.5%) on linkage g
roup G, and the AFLP marker E(CCG)M(AAC)405 (P = 0.0001, R-2 = 26.2%) on li
nkage group A2. Two-way analysis of variance showed epistasic interaction (
P = 0.0001, R-2 = 16%) between the two loci controlling SCN resistance in E
ssex x Forrest recombinant inbred lines. Considering the two loci as qualit
ative genes and the resistance as female index FI <5%, jointly the two loci
explained over 98% of the resistance. The locations of the two QTLs were c
onfirmed in the NILs populations. Therefore SCN resistance in Forrest x Ess
ex is bigenic. High-efficiency marker-assisted selection can be performed u
sing the markers to develop cultivars with stable resistance to SCN.