G. Pressoir et al., Genetic basis and mapping of the resistance to rice yellow mottle virus. II. Evidence of a complementary epistasis between two QTLs, THEOR A GEN, 97(7), 1998, pp. 1155-1161
The genetic basis of resistance to rice yellow mottle virus (RYMV) was stud
ied in a doubled-haploid (DH) population derived from a cross between the v
ery susceptible indica variety 'IR64' and the resistant upland japonica var
iety Azucena. As a quantitative trait locus (QTL) involved in virus content
estimated with an ELISA test has been previously identified on chromosome
12, we performed a wide search for interactions between this QTL and the re
st of the genome, and between this QTL and morphological traits segregating
in the population. Multiple regression with all identified genetic factors
was used to validate the interactions. Significant epistasis accounting fo
r a major part of the total genetic variation was observed. A complementary
epistasis between the QTL located on chromosome 12 and a QTL located on ch
romosome 7 could be the major genetic factor controlling the virus content.
Resistance was also affected by a morphology-dependent mechanism since til
lering was interfering with the resistance mechanism conditioned by the epi
stasis between the two QTLs. Marker-assisted backcross breeding was develop
ed to introgress the QTLs of chromosome 7 and chromosome 12 in the suscepti
ble 'IR64' genetic background. First results confirmed that if both QTLs do
not segregate in a backcross-derived F-2 population, then the QTL of chrom
osome 12 cannot explain differences in virus content. A near-isogenic line
(NIL) approach is currently being developed to confirm the proposed genetic
model of resistance to RYMV.