ABSTRACT
The
patterns of gene effects on agronomic and some quality traits of eight
genotypes of rice (Oryza sativa L.) and their progenies were
studied using Diallel analysis method 1 involving parents, F1
hybrids and their reciprocals. The eight genotypes studied were selected for
their agronomic performance and protein content from thirty genotypes evaluated
in a randomized complete block design and replicated three times at the
Teaching and Research Farm of the Federal University of Technology, Owerri,
Nigeria during the planting seasons of 2005 and 2006. The results of the
Diallel analysis conducted during the 2007 planting season indicated larger
magnitude of additive components of variance in attributes like number of
tillers per plant, number of days to anthesis, panicle length , number of
secondary branches per panicle, 1000-seed weight, grain width and grain
length/grain width ratio. Non-additive variance was more important for plant
height at flowering, number of seeds per secondary branch of panicle, grain
length and percentage protein content. The nature and magnitude of general
combining ability(GCA) and specific combining ability(SCA) effects, as well as
the direction of heterosis assessed by the SCA effects, seemed to differ for
different traits and various cross combinations. No parental line consistently
had negative SCA effects for all the traits. Additive gene effects with high
GCA values could be exploited in WITA 4 and Max for higher tillering ability,
NERICA 1, Fofifa 16 and WAB 96-1-1 for earliness; WITA 4 and NERICA 1 for
production of hybrids for greater number of secondary branches per panicle; CT
7127-49 and EMPASC 105 for development of hybrids with greater number of
spikelets per panicle; NERICA 1, CT7127-49 and EMPASC 105 for producing hybrids
with more fertile grains; CT7127-49 and NERICAI for developing progenies with
more seeds per secondary branch of panicle; IR57689-73 and Fofifa 16 for
1000-seed weight and CT 7127-49 and WITA 4 for developing long and fine grains.
WITA 4 and EMPASC 105 were observed to be semi-dwarfs and offer themselves as
candidate genotypes for reduction of plant height to reduce stem lodging and
increase yield. The phenotypic generation means of the parental lines (P1
and P2), F1 and reciprocal cross and the BC1
and BC2, evaluated during the 2009 planting season for the study on
genetic effects of the characters on the breeding lines generated, indicated
that the F1 generation means were higher than their mid-parent
values especially for percentage protein content. The F1 and F2
generation means were not significantly different in the majority of the cases
except for lowland x upland and upland x lowland hybrids for percentage fertile
spikelets and numbers of spikelets per panicle. Varied genetic effects were
observed on the characters for generation mean analysis on six parameter model.
Additive and dominance as well as epistatic gene effects were involved in the
inheritance of most characters. Digenic interactions were significant for most
of the traits. Presence of significant dominance effect combined with duplicate
epitasis restricted the scope for simple selection for most of the characters.
Reciprocal and maternal effects were also implicated for most of the traits.
TABLE OF CONTENTS
Title Page
List of Publications
Table of Contents
List of Tables
Abstract
INTRODUCTION
LITERATURE REVIEW
Agronomy of Rice
Rice Quality Criteria
Nutritional Composition of
Rice
Varietal Influence on
Nutrient Composition of Rice
Biological Evaluation of Rice
Protein
Genetic Analysis of Quality
Traits in Rice
Crossing Method
MATERIALS AND METHODS
Sources of Planting Materials
Experiment I(Field Evaluation
of 30 Genotypes Rice of select Parental Materials)
Experiment II (Laboratory
Analysis for the Determination of the Proximate,
Mineral and Grain Physical
Characteristics of the 28 Genotypes of Rice)
Statistical analysis
Experiment III (Production of
Hybrid seeds through Diallel Crossing Method)
Experiment IV (Field Evaluation
of F1 Hybrids and Production of Backcrosses)
Experiment V (Field
Evaluation of Parents, F2’s and Backcrosses)
Statistical analysis
Diallel Cross Analysis
Analysis of the Gene effects
on the characters
RESULTS
Evaluation of 30 Genotypes to
select Suitable Parents
Agronomic Characteristics
Laboratory Analysis
(Proximate and Mineral Component Determination)
Classification of the
Genotypes using Amylose and Grain Physical characters
Variability Parameters
Estimates of Phenotypic and
Genotypic Variance
Combined Analysis of variance
Coefficient of variation
Heritability
Genetic Advance
Correlation Studies
Diallel Analysis
Evaluation of the F1 and F2
generations for Heterosis in Percentage Protein Content
Phenotypic Generation Mean
Performance
Estimates of Gene effects on
Agronomic and Physicochemical Characteristics of the Genotypes
DISCUSSION
SUMMARY AND CONCLUSION
REFERENCE
APPENDICES
INTRODUCTION
Rice (Oryza sativa L.) is a staple food for
billions of people in the world. Kennedy et al. (2002) reported that it
is the predominant staple food for at least 33 developing countries of
the world, providing 27%, 20% and 3% of their dietary energy, protein and fat
supply respectively. Muller (1984) had earlier reported that one-third of the
world’s population depended on rice for over half of their caloric and protein
requirements then. This may have informed why rice production, in much of the
world, increasingly focuses on optimizing grain yield, reducing production
costs and minimizing pollution risks to the environment. In the period of 1961
to 1981, the average world rice harvest increased from
2.23
t ha-1
to 2.86t ha-1, representing a mean
increase of 23%. The usefulness of rice is indeed universal, because man
benefits not only from the starchy grains but it could also be utilized in the
production of starch, alcoholic beverages and soft drinks. Rice consumption in
West Africa has been reported to be increasing (Watanabe, 1998), thereby,
compensating for the reduction of the consumption of other cereals. Global
consumption of rice continues to outpace its production. This is so because of
unabated population growth. The World Bank Population Project (1995) reported
that the global demand of rice then was at 524 million tonnes and projected
that it would increase to over 700 million tones. In Nigeria, rice production
in 2005 and 2006 farming seasons forecasts was 2.7 million metric tonnes (MT)
from 2.3 million metric tonnes in 2004-2005 seasons (Oryza Market Report,
2005). The current awareness of the Nigerian government for the adoption of new
rice varieties to help boost rice production is highly commendable.
Rice breeding efforts over the past three decades have been
concentrated on the development of high-yielding rice varieties to meet the
food need of humanity. Hybrid rice offers the potentials to boost rice yield
potentials. Virmani and Peng (1999) reported that it has a yield advantage
of 15-20% over conventional high-yielding varieties. Choice of outstanding
parents with favourable alleles will no doubt offer opportunity for greater
success for higher yields. Improvements in rice quality are very crucial in
meeting the demands of consumers for healthy, high quality food (Kennedy et
al., 2002). Koutroubas et al. (2004) identified appearance, milling
quality, cooking and processing as well as nutritional quality as the
most important rice grain qualities common to all users. The nutritional
quality of rice is mainly determined by the protein content of the grain.
Tagwireyi and Greiner (1994) reported that 70% of the total protein for human
nutrition in African regions comes from cereals. Studies have shown that
protein content of rice is a quantitative trait (Singh et al., 1977).
Breeding efforts for increased protein content in rice had been largely
unsuccessfully owing to low heritability of protein content and complexity
associated with the inheritance of triploid endosperm tissues, and its protein
content has been reported to be negatively correlated with grain yield and some
cooking and eating
criteria (Juliano, 1990).
Brown (1969)
identified concentration of useful genes in the same genotypes as the main
objective for self-fertilization of crops. Griffing (1956b), however, had
earlier reported that genotypes vary in their ability to transmit desirable
characteristics to their off-springs. It is on this premise, therefore, that
plant breeders try to combine the desirable qualities of different varieties.
The Diallel-cross method introduced by Griffing (1956a,b) and later modified by
Pooni et al. (1984) and Wright (1985) is used in rice principally to
determine the general and specific combining ability of the quantitative
properties (Chan et al., 1990; Hoang and Tan, 1991).
Rice consumption in West Africa has been on the
increase compensating for reduction in consumption of other cereals like
millet, sorghum, maize etc. and thus has.....
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