|dc.description.abstract||Rice production in Sub-Sahara Africa is hampered by drought stress, low farmer adoption of improved varieties, un-adapted germplasm, problems of crossability between species and
problems of efficient emasculation. This study was initiated to: (1) determine farmer
preferences for rice varieties and production practices, (2) identify drought tolerant parental
lines for use in interspecific crosses, (3) determine crossability between different rice
species, (4) identify drought tolerant interspecific segregants from crosses, and (5) study the
efficacy of ethrel and gibberrilic acid (GA3) as chemical hybridising agents.
Participatory rural appraisal (PRA) was conducted in Sikasso region in the month of
September 2005 to determine farmer preferences for varieties and production constraints. A
total of 125 rice farmers from 10 villages participated. This study found that farmer
preferences for rice traits did not coincide with the breeders' objectives and trait preferences
varied across ecologies. In upland and lowland rice ecologies, the most preferred
characteristic was short duration. In the lowland tall plants was most preferred and short
duration trait ranked second. Long duration ranked as the second most preferred trait after
yield in the irrigated rice ecology. The estimated grain yield reduction was 60% due to
drought stress from all ecologies.
Sixteen genotypes including seven Oryza glaberrima Steud, six interspecific (0.
saliva x 0. glaberrima) inbred genotypes and two improved 0. saliva L. subsp Gaponica)
genotypes, with OS 6, as drought tolerant check were screened for drought tolerance at the
vegetative stage during the dry seasons of 2004 and 2005 at Samanko research station, in
Mali. Most of the genotypes could be regarded as exhibiting drought tolerance and
avoidance mechanisms for most of the morpho-physiological characters under study. High
selection index was observed for WAB 450-I-B-P-103-HB in the two season experiments.
Drought stress tolerance (little leaf drying) was significantly correlated with leaf rolling, leaf
area index, and plant height. Fast drought recovery was significantly correlated with drought
tolerance, tiller number and leaf area index. Effects of genotypes, environment and their
interactions were significant for tiller number, root dry weight and relative leaf water
content. The most stable genotype was RAM 3 for tiller number and relative leaf water
content. Thirteen genotypes were selected on the basis of these traits for rice hybridisation.
A factorial arrangement involving three levels of gametocide concentrations and five
application stages of the female rice parent was undertaken for each gametocide ethrel and
GA3 for two seasons. Per cent empty spikelets and male sterility increased with
concentration of ethrel. Male sterility induction of 41.5% and 42.8% at 2000 ppm was
achieved in 2004 and 2005, respectively, while at 4000 ppm male sterility induction was
40.5 % and 46.1% in 2004 and 2005, respectively. The best application stage of ethrel that
induced highest male sterility was at P4 (panicle primordium differentiation + spikelet
primordium differentiation) of 46.6% in 2004 and 49.2% at PI (panicle primordium
differentiation) in 2005. There was no measurement on GA3 for sterility due to lodging.
Total male sterility was not achieved therefore, these gametocides could not be
recommended for use as hybridising agents.
Crossability was studied in four groups: group A (0. glaberrima x 0. saliva), group
B (0. glaberrima x Interspecific), group C (Interspecific x 0. saliva) and group D
(Interspecifics x Interspecific). High percent seed set was obtained in group D of 19.08%
and group A had 9.29%, in group B the seed set was 11.26% and group Chad 6.62 %. The
three best combiners as female parents based on percentage seed set were CG 14 (0.glaberrima), WAB 450-IBP-I05-HB and WAB450-I-B-P-I03-HB (interspecifics), and for
male parents were NERICA 3, NERICA 2 (interspecifics) and WAB 375-B-9-H3-2 (0.
Genetic components of variance and heritability estimates were studied in F3 and F4
generation progenies from North Carolina II design mating scheme. General combining
ability (GCA), manly due to female and specific combining ability (SCA) were significant
for tiller number, plant height and specific leaf dry weight indicating that additive and non-additive
genetic effects controlled these traits. Heritability estimates for drought tolerance
and leaf rolling were highly significant for all the populations examined, ranging from 0.32
to 0.72 and 0.22 to 0.56, respectively. Drought tolerance expressed as little leaf drying was
significantly associated with less leaf rolling, larger leaf area index, and taller plants. Some
genotypes and progenies such as WBK 39-B-B-B, WBK 30-B-B and WAB 450-I-B-P-I03-HB
were identified as being drought tolerant with the ability to recover quickly from
There was a strong desire for tall plants and short duration rice in upland and
lowland ecologies, while high yield was preferred in irrigated ecology. Therefore, the best
breeding strategy would be ecosystem breeding targeting each of the ecologies. Screening
for secondary traits that have been identified to be significantly associated with rice grain
yield could be used for direct selection for grain yield under drought stressed conditions.
Progenies identified, as drought tolerant would be considered for use as source germplasm
in breeding that target Sikasso region and any other similar ecologies. This study therefore
suggested that participatory research approaches that involve all stakeholders in rice
production would be valuable in identifying and generating drought tolerant and adoptable
rice cultivars in the tropics of Africa with considerable impact on food security.||en