Agriculture Reference
In-Depth Information
mapping for several traits of importance for rice breeding, along with
current work on GWAS.
1. Genetics of Interspeci
c Hybrid Sterility.
Oryza glaberrima
, the
African cultivated species of rice, is recognized as an interesting source
of agronomically important traits for breeding of Asian cultivated rice,
Oryza sativa
(Bocco et al. 2012; Ndjiondjiop et al. 2012). However, its use
has been constantly hampered by the strong reproductive barrier sepa-
rating the two cultivated rice species (Sano et al. 1979). Sano (1990)
identi
ed the main factor for this sterility barrier to be
S
1
gene. With
L
Institut de recherche pour le développement (IRD, France), we began
research aiming at high-resolution mapping of the
S
1
gene on chromo-
some 6, using four interspeci
'
Oryza glaberrima
populations and looking at allelic frequencies on chromosome 6 for SSR
and retrotransposon-based insertion polymorphism (R-BIP) markers.
This led to the mapping of
S
1
to a 28 kb region, and to the identi
cBC
1
F
1
Oryza sativa
×
cation
of two tightly linked genes acting in epistasis with
S
1
. A genetic model
for gametic elimination in the F
1
hybrid was developed, and inferences
on patterns of sequence divergence between the two species were made
(Garavito et al. 2010; Guyot et al. 2011).
2. Mapping of QTLs with Resistance to RHBV.
Rice
hoja blanca
disease
occurs in cyclic epidemics that cause severe yield losses in rice in LAC.
The causal agent
rice hoja blanca virus
(RHBV) is transmitted by the
planthopper vector
T. oryzicolus
, but cannot be transmitted mechani-
cally, which makes breeding for resistance to RHBV very dif
cult. Con-
trolled infestations of rice with viruliferous vectors help to select lines
possessing various degrees of resistance, but at a high cost. The
'
cultivars Fedearroz 2000 (Fd2000) and Fedearroz 50 (Fd50), both showing
signi
'
Indica
cant resistance to RHBV and
T. oryzicolus
, were crossed with the
highly susceptible
tropical japonica
line WC366, which produced F
2
/F
3
families(218 and 291 families, respectively). The F
2
plants were geno-
typed with evenly dispersed SSRs and the F
3
populations were scored for
resistance to RHBV systemic infection and feeding damage by
T. oryzi-
colus
. A major QTL explaining
50% of the resistance to RHBV was
found at the same location on chromosome 4 in both populations. Two
QTLs were identi
∼
ed for resistance to
T. oryzicolus
on chromosome 5 in
the cross Fd2000
×
WC366. This comparative study using two distinct rice populations has
allowed a better understanding of the genetics and interaction of resist-
ance to RHBV and its vector. We are using this information to introgress
the resistance QTLs into elite germplasm (see Section IV.C).
×
WC366 and on chromosome 7 in the cross Fd50
