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Molecular Plant Breeding 2011, Vol.2, No.11, 75
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The first generation of NERICA varieties 1~11, in-
cluding the WAB450 progeny, was developed from cro-
sses of the existing released variety CG14 (
O. glaberrima
Steud.) and WAB56
-
104 (WAB signifies a variety or
line developed at WARDA BOUAKE), which belongs
to the subspecies japonica of
O. sativa
L., an upland
improved variety. On the other hand, NERICAs 12 to
18 are progeny of two series of crosses, using the
same
O. glaberrima
CG14 parent but two different
O.
sativa
parents (WAB56
-
50 and WAB181
-
18). Mor-
phologically diverse, genetically stable and fully
fertile, these interspecific progeny have developed
either through the refined method of conventional
breeding, or with the use of specifically-developed
anther culture and double-haploidization techniques to
overcome sterility and to hasten the breeding process.
Crosses were made and embryo rescue was used to
remove fertilized embryos and grow them in artificial
media. Anther culture allowed rapid fixation and
helped to retain interspecific lines combining desirable
features of the two rice species.
This achievement was indeed a scientific break-
through. Previous conventional breeding efforts else-
where in the world to develop interspecific hybrids of
rice had failed, yielding only infertile offspring of the
two species being used for crossing.
This breakthrough established the Africa rice center’s
lead role in interspecific hybridization and anther
culture for rice (Jones et al., 1997b). Exploitation of
the
O. glaberrima
gene pool increased the scope for
the development of low management input plant types
(Jones, 1997a; Dingkuhn et al., 1998).
O. glaberrima
originates in Africa and is resistant to a number of
major African insect pests and diseases such as stem
borers and rice blast.
O. glaberrima
is also very com-
petitive with weeds (Audebert et al., 1998; Johnson et
al., 1998), the main constraint to rice production ac-
ross ecologies in sub-saharian Africa.
1.3 NERICA varieties ratoonability potential
According to the study conducted by Sanni et al.
(2007), in the savanna zone in 2006 on the named 18
rainfed upland NERICA indicated a large variation in
the ratoon performance among these varieties, with a
ratoon yield ranging from 39% (NERICA17) to 13%
(NERICA2) of the main crop yield, bringing the total
grain yield per plot and per cropping season up to
about 6 500 kg/ha. NERICA14, NERICA15, NE-
RICA17, NERICA18 exhibited the highest ratoon
yield performance. The mechanism contributing to the
ratoonability of these short duration NERICA varieties
was not investigated in the reported study. Similar
findings on the ratoon yield potential of interspecific
progeny, including the NERICA’s was also reported in
other zone (kouko et al., 2006).
1.4 High-potential irrigated and rainfed lowlands
of NERICA
African lowlands constitute one of the most complex
rice ecologies in the world. The rainfed lowlands,
where rice is grown in bunded fields that are flooded
for at least part of the growing season, are more fertile
than the uplands and have the added advantage of
opportunities for irrigation. Most of the traditional
lowland rice varieties grown in West Africa have a
narrow genetic base, which leads to their vulnerability
to diseases and pest. Yet lowlands account for about
30% of the area under rice cultivation in west and
central Africa.
1.5 Differences in the upland and lowland NERICA
varieties development process
The main difference between the development of
lowland NERICA and that of the upland interspecifics
was in the selection of the Asian rice varieties for the
crosses. The Asian
O. sativa
has two main strains, in-
cluding the japonica (traditional rainfed or upland rice)
and the indica (traditional irrigated or lowland rice). In
the creation of upland NERICA varieties, japonica va-
rieties were used in the crosses, while the indica sub-
species was used for developing the new lowland rice.
As in the process of upland NERICA development,
the initial problem was again hybrid (infertile off-
spring of the crosses). The sterility blockage was over-
come by backcrossing (crossing the hybrid to
O. sativa
to restore fertility).
The schematic explanation for NERICA development
was given by the Africa rice center: “after four
backcrosses (
O. sativa
as recurrent), over 500 high-
fertile fixed lines (85%~100% fertility) were selected