Abstract:
Basal stem rot caused by
Sclerotinia sclerotiorum
(Lib.) de Bary is one of the most
important diseases of sunflower. Quantitative trait
loci (QTL) implicated in partial
resistance to two isolates of
S. sclerotiorum
(SSU107 and SSKH41) were investigated using
F
9
recombinant inbred lines (RILs) from the cross bet
ween sunflower parental lines
PAC2 and RHA266. Experiments were conducted in comp
letely randomized design with
3-6 replications under controlled conditions. The r
eaction of genotypes to basal stem rot
disease was evaluated by measuring the percentage o
f necrosis area three days after
inoculation. Combined analysis of experiments showe
d significant interactions between
sunflower genotypes and
S. sclerotiorum
isolates suggesting that partial resistance to
S.
sclerotiorum
should be isolate-specific in sunflower. QTLs were
mapped using an updated
high-density SSR and SNP linkage map. The map consi
sted of 210 SSRs and 11 gene-
derived markers placed in 17 linkage groups (LGs).
The total map length was 1,653.1 cM
with a mean density of 1 marker per 7.44 cM. A tota
l of 14 QTLs were detected for
partial resistance to two isolates. The phenotypic
variance explained by QTLs (R
2
) ranged
from 0.10 to 9.85. The sign of additive gene effect
s showed that favorable alleles for
partial resistance to isolates came from both paren
ts. Six QTLs were common between
two isolates on LGs 1, 8 and 17, whereas the others
were specific for each isolate. Co-
localized QTLs on LG 1 were linked to the glutathio
ne S-transferase gene (GST). The co-
localized QTLs for partial resistance to basal stem
rot isolates could be good candidates
for marker assisted selection (MAS).
Keyword:
Basal stem rot,
Helianthus annuus
L., isolate specificity, partial resistance, QTL
mapping.
