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Molecular Plant Breeding 2011, Vol.2, No.11, 75
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82
http://mpb.sophiapublisher.com
79
This constraint should be taken into consideration
either when diffusing material to farmers or when bre-
eders are selecting donor lines.
2.3 Varietal resistance and tolerance to blast
According to the Africa rice center annual reports,
nine interspecifics, including NERICA9 and NERICA
18, consistently show resistance to blast at various
hotspots across four countries in West Africa. The re-
sistance of the interspecific lines is believed to be as
stable and durable as that of WAB56
-
50 and WAB56
-
104, which are well known for processing horizontal
resistance to the blast resistance in West Africa (Talbe 1).
3 Drought control
To evaluate the drought tolerance on the interspecific,
conducted in the dry season, eleven NERICA varieties
(N1, N2, N3, N4, N5, N6, N7, N8, N9, N10, and N12)
as well as the two parents of NERICA1
-
7, WAB56
-
104 and CG14, were screened together with 87 other
rice genotypes that included
O. sativa spp. indica
,
O.
sativa spp. japonica
and interspecifics (
O. sativa
×
O. glaberrima
), which were sourced from Africa rice
center, CIAT, and IRRI. The screening protocol used
involving 21 days drought to- lerance at 45 days after
sowing (DAS), which coincides with the vegetative/
reproductive phase of crop developpment.
Method: According to the report, the trial was de-
signed as a split-plot protocol with irrigation regime
as the main plot factor and genotype as the sub-plot
factor. Then two irrigation levels were used: one is full
irrigation up to maturity and imposing 21 days, the
other is drought stress starts 45 days.
Thinning, fertilizer application, weeding and spraying
against pests and diseases were carried out. Soil water
status at the trial site was measured in three 20 cm
layers of soil from the surface to 60 cm depth.
The soil at the trial site is an Alfisol with a sandy
texture (82%~89%) from 0~50 cm depth and hence
has low water-holding capacity. Soil moisture content
in the top 20 cm towards the end of drought stress was
2.61% in the stressed treatments and 4.5% in the fully
irrigated treatment. Thus, the researchers said that,
withholding irrigation for 21 days was sufficient to
induce severe drought stress in the trial since the
effective rooting depth of most rice varieties is the top
20 cm of soil.
Symptoms of drought stress results are showed that
Leaf rolling, severity of leaf rolling, leaf drying
increased with duration of drought; they noted that
drought stress significantly (P<0.05) reduced tiller
number, leaf chlorophyll content (SPAD92), numbers
and weights of fertile panicles and grain yield but
increased leaf temperature and delayed flowering.
The flowering was delayed by 10 days in the stress
treatment compared to the non-stressed treatment.
Consequently, grain yield per plant was significantly
reduced from a mean of 12.42 g in the fully irrigated
treatment to 5.063 g in the stress plot.
In conclusion, the experiment shows that the NE-
RICAs exhibited a wide range of responses to drought
stress. However, six out of eleven NERICAs screened
gave higher than the average yield under drought.
Table 1 Evaluation of resistance to blast in 4 sub-Saharan countries
Objective
Methodology
Results
To identify rice lines with durable
resistance to blast in West Africa
67 entries were evaluated for horizontal
resistance to blast in Burkina-Faso,
Nigeria, Mali and Guinea
1 WAB56
-
104
2 WAB56
-
50
3 NERICA9
4 NERICA18
5 WAB881
-
1
-
10
-
37
-
18
-
25
-
P3
-
HB
6 WAB880
-
1
-
38
-
18
-
8
-
P3
-
HB
7 WAB881
-
10
-
37
-
18
-
15
-
P1
-
HB
8 WAB881
-
10
-
37
-
18
-
24
-
P1
-
HB
9 WAB881
-
10
-
37
-
18
-
14
-
P1
-
HB
10 WAB880
-
1
-
38
-
20
-
23
-
P1
-
HB
11 WAB880
-
1
-
38
-
18
-
20
-
P1
-
HB
Note: The source from www.warda.org