Rice is an important crop ranking third after maize and wheat in Kenya. Its demand is
growing at 12% per annum, while production has stagnated for quite a number of years.
This situation has lead to consumption outstripping production by about 84%. There is
therefore an urgent need to step up domestic production.
To understand farmers’ preferences, the first survey on rice production was carried out.
To supplement on this survey information, focus group discussions and key informants
were incorporated to further shed more information. The farmers demonstrated their
preferences for varieties that were high yielding, hybrid rice and with high nutrient use
efficiency and these constituted 53.7% of their wishes. Among the crops grown by the
selected farmers, rice was the most important followed by maize, however, the
hectarage of maize was higher followed by rice. The farmers also identified labour costs
as a factor limiting production especially for irrigated rice and thus they preferred upland
rice due to its ease of production. Farmers identified land preparation, inputs, planting,
weeding and harvesting as the most expensive activities. The existing varieties were
viewed as being highly dependent on inputs which they could not afford. The main
fertilizers used were Diammonium Phosphate (DAP), Sulphate of Ammonia (SA),
Calcium Ammonium Nitrate (CAN) and NPK (23:23:0), the amounts used were low even
though the farmers were aware that soil fertility was low.
No studies or attempts had been carried out to determine performance of rice genotypes
and their heritability parameters for adaptation to low soil nitrogen (N) and phosphorous
(P) conditions identified by the farmers as a major constraint in Kenya. Since the existing
genetic base was narrow, accessions were acquired to broaden the variability of the
local cultivars. However, their adaptation to local conditions was important for them to be
useful. Evaluation of 390 accessions showed that genotypes and soil environments were
highly significant for all the ten traits studied. The degree of genetic determination (H(2))
ranged from 8.0% for 1000 grain weight to 27% for top biomass. The phenotypic
coefficient of variation of genotypes ranged from 12% for days to maturity to 149% for
top biomass, while, that of days to maturity ranged from 14% to 160% for top biomass.
The genetic advance (GA) had values ranging from, 0.2 for phosphorous tolerance to
1081 for grain yield, while the genetic advance expressed as percent of the mean was
6% for days to maturity and 88% for top biomass. The mean values for the ten
characters studied had wide variability under the four soil environments with days to
maturity ranging from 188 for genotype ARCCU1Fa1-L4P3-HB under both N and P
application (N+P+) to 177 for genotype CT16333(1)-CA-1-M under none N and P
application (N-P-) condition. The highest yielding genotype was CT16328-CA-18-M
under none N and P application with 5916 kg ha(-1). The germplasm revealed usable
variability under low soil N and P adaptation and thus warrant rice improvement for traits
of interest to farmers.
In order to establish the genetic factors controlling upland rice adaptation to contrasting
soil N and P a study was conducted to determine genotypes with better performance
under the prevailing farmers’ production environments. The GCA and SCA mean
squares were significant and their interactions with environment were highly significant.
The GCA:SCA ratios were mostly less than 1.0 for the majority of the traits under most of
the soil N and P environments, indicating preponderance of nonadditive genetic effects.
The maternal and nonmaternal mean squares were significantly different from zero
(P<0.05) for most of the ten traits under study, indicating influence of cytoplasm effects and cytoplasm by nuclear gene interactions, respectively. The GCA effects for the
parents were significant under different experimental environments but they had both
positive and negative signs indicating different directions of influencing the trait of
interest. The genotypes had both specific and broad adaptation as exhibited by their
diverse rankings under different environments.
The relationship between leaf and grain nitrogen (N) and phosphorous (P) with actual
tolerance to low and high soil N and P conditions indicated significant genotypes,
environments and genotypes by environment interactions. The analysis of genetic
components gave highly significant GCA and SCA mean squares for the days to
heading, anthesis and maturity, phosphorous and nitrogen tolerance, top biomass, plant
height, number of panicles, 1000 seed weight and grain yield under the four soil
experimental environments. The general combining ability (GCA) effects for parents
were significant for both F(2) and F(3) segregants for the above ten traits and under the
experimental conditions. The leaf and seed N and P contents gave significant genotype
mean squares values for the three mega-environments. The GCA and SCA mean
squares were significant for leaf and seed N and P for the three locations. The same
case was observed for GCA effects for the parents, with all the nine parents showing
significant values for leaf N and P for the three locations. The GCA:SCA mean square
ratios were generally larger than 1.0 values for leaf N and grain P for the three locations.
This clearly manifested the predominant role of additive gene action over the dominance
effects and that improvement for tolerance to low soil N and P condition was practical.
The fragrance in rice is an important quality traits and an experiment was conducted to
establish the association of organoleptic test and the variations in SSR marker (RM223)
among the parents. Plant leaves of the parental genotypes were sampled for DNA
analysis using SSR markers RM223 and RM284. The RM223 was polymorphic while,
RM284 gave monomorphic results. Four alleles were detected as follows: 146, 155, 161,
and 163. The GCA:SCA ratio was 1.48 indicating that the fixable additive effects were
greater than the nonadditive effects in inheritance of fragrance. Test for independence
using Chi-square indicated that there was no association between organoleptic and
variations in SSR markers. The performance of the aromatic lines was generally lower
than that of non-aromatic lines for the agronomic traits. There was negative relationship
between fragrant score and other agronomic traits such as grain yield across the three
soil N and P regimes. The NERICA1 was found to be a good donor for aroma based on
sensory testing and can be exploited in a breeding programme.
Analysis on genetic components governing grain yield was investigated using Hayman’s
analysis to generate various components of variation and to elucidate their potential,
utilization, and provide a thorough understanding of their role in grain yield development
and improvement. The additive gene action was significant for all cases of soil N and P
environments and the two mega-environments. They were also far above the dominant
gene effects, indicating the need to use mass selection in the early generations of
segregating populations. The narrow sense heritability (h2(ns))
for upland rice grain yield
was 21.52% and 4.22% under soil P and N conditions, respectively. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/8145 |
| Date | January 2010 |
| Creators | Munji, Kimani John. |
| Contributors | Tongoona, Pangirayi., Derera, John., Danson, Jedidah W. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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