The genetic diversity of C. arabica genotypes collected from the northwestern and
southwestern parts of Ethiopia was evaluated using morphological, biochemical and
molecular (AFLP and SSR) markers. The objectives of the study were to (1) estimate
the level of genetic variation among currently grown C. arabica genotypes, (2)
estimate the level of associations among agro-morphological characters, coffee
quality traits and green bean biochemical compounds, (3) compare the level of genetic
variation between coffee genotypes collected from the northwestern and southwestern
parts of Ethiopia and (4) compare the efficiency of AFLP and SSR markers in
detecting genetic variation in C. arabica.
Results of diversity analysis using nine qualitative and 18 quantitative morphological
characters indicated the presence of substantial variability among evaluated coffee
genotypes. Genotypes were significantly different for all 18 quantitative
morphological characters. Higher Shannon-Weaver diversity indices ranging from
0.401 to 0.989 were recorded for nine qualitative morphological characters. Cluster
analysis using qualitative, quantitative and a combination of qualitative and
quantitative characters classified genotypes into two groups. Qualitative characters
failed to independently distinguish seven of the genotypes. Principal component
analysis grouped 18 quantitative characters into 15 principal components and the first
four explained 82.3% of the entire variability among genotypes. Average green bean
yield per tree and bean length were important for the variation explained in three of
the first four principal components.
Correlation analysis performed among 18 agro-morphological characters indicated
positive associations between average green bean yield per tree and all other
characters. Average green bean yield per tree had statistically significant correlations
with percentage of bearing primary branches per tree, bean weight, canopy and trunk
diameters, tree height, bean length and thickness, internode lengths of orthotropic and
primary branches and fruit and petiole lengths. Broad sense heritability varied from 38% for bean thickness to 94% for bean weight and number of secondary branches
per tree. Average green bean yield per tree, canopy diameter, tree height and bean
weight had higher genetic coefficients of variation and broad sense heritabilities.
These characters were positively and significantly correlated, allowing simultaneous
improvement of these traits.
Genotypes were evaluated for variability in four cup quality traits (acidity, body,
flavour and overall standard) and four green bean physical characters (bean shape,
size, uniformity and weight). Considerable variation was observed among genotypes
both for cup quality as well as green bean physical characters. Of all the genotypes,
AD0691 and AD1691 had both desirable cup quality and green bean physical
characters. Cluster analysis performed using cup quality and green bean physical
characters, classified genotypes into two groups. Genotypes were not clustered
according to collection regions. All cup quality traits were positively and significantly
correlated and correlation coefficients ranged from 0.69 to 0.93. Positive correlations
were observed among desirable cup quality and green bean physical characters
indicating that cup quality and green bean physical characters can be improved
simultaneously.
Genotypes were evaluated for green bean caffeine, chlorogenic acids, sucrose and
trigonelline content variability. Analysis of variance indicated significant differences
among genotypes for all biochemical compounds. Green bean caffeine, chlorogenic
acids, sucrose and trigonelline contents ranged between 0.91-1.32%, 2.34-4.67%,
5.30-8.98% and 1.04-1.71%, respectively on dry matter basis. Cluster analysis
classified coffee genotypes into eight groups and genotypes were not clustered
according to collection regions. Coffee genotypes collected from northwestern
Ethiopia were more diverse in green bean caffeine, chlorogenic acids and sucrose
contents compared to southwestern Ethiopia genotypes. On average, southwestern
Ethiopia coffee genotypes had higher green bean caffeine, chlorogenic acids, sucrose
and trigonelline contents compared to northwestern Ethiopia genotypes. Green bean
caffeine content showed negative and statistically significant associations with all
desirable cup quality attributes and correlation coefficients ranged from -0.305 to -0.
407. Desirable cup quality traits and low green bean caffeine content can be selected
simultaneously. Green bean sucrose content showed positive associations with all desirable cup quality and green bean physical characters. Higher green bean sucrose
content, desirable cup quality as well as green bean physical characters can be
improved together.
The genetic diversity of coffee genotypes was investigated using 10 AFLP primer
combinations. Results revealed differences among AFLP primer combinations in
detecting genetic variation among genotypes. Of the 10 primer combinations EcoRI-ACA/
MseI-CAA, EcoRI-ACC/MseI-CAG, EcoRI-ACT/MseI-CAG and EcoRI-AAC/
MseI-CAA were superior in detecting genetic variation. Almost all primer
combinations were positively correlated in estimating pair-wise genetic similarity
coefficients, indicating the similarity of primer combinations in detecting genetic
variation among genotypes. All genotypes were independently distinguished and pair-wise
genetic similarity coefficients ranged from 0.851 to 0.982 with an average of
0.915. Ten genotypes had 18 specific AFLP markers which could be utilised for
genotype fingerprinting. AD1291 and AD1491 were the most dissimilar while
AD3591 and AD3991 were the most similar genotypes. Genotypes were classified
into two groups using UPGMA method of cluster analysis. Genotypes did not cluster
according to collection regions. Results unveiled the presence of genetic variation
among genotypes collected in each region and the presence of close genetic similarity
among some coffee genotypes collected from different regions. The genetic diversity
among coffee genotypes from southwestern Ethiopia was higher compared to those
from northwestern Ethiopia.
Genetic diversity analysis performed using six SSR primer pairs indicated the
presence of considerable genetic variation among some of the genotypes collected
from northwestern and southwestern Ethiopia. Twenty polymorphic SSR markers
were amplified of which two were specific to genotypes AD1491 and AD2991. Using
20 polymorphic SSR markers, 64.3% of the genotypes were independently
distinguished. Pair-wise genetic distances ranged from 0.286 to 1.000. The lowest
pair-wise genetic similarity coefficient was recorded between AD0591 and AD1491
as well as AD1491 and AD4591. Genotypes from southwestern Ethiopia were more
diverse compared to those from northwestern Ethiopia. Molecular markers differ in the amount of information generated per PCR reaction.
The efficiency of 10 AFLP primer combinations and six SSR primer pairs in detecting
genetic variation was compared using 28 C. arabica genotypes. AFLP primer
combinations amplified 220 and SSR primer pairs 20 polymorphic alleles among
evaluated genotypes. AFLP markers independently distinguished all evaluated coffee
genotypes whereas SSR markers distinguished 64.3% of the genotypes. Moreover, 18
genotype specific AFLP markers compared to two SSR genotype specific markers
were identified. The assay efficiency index of AFLP markers (22) was far superior to
that of SSR markers (3.3). AFLP markers surpassed SSR markers in detecting genetic
variation among evaluated arabica coffee genotypes. Results of this study indicated
the presence of good congruence between the two genetic markers in estimating pair-wise
genetic similarity coefficients among genotypes.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07042006-082803 |
| Date | 04 July 2006 |
| Creators | Bekele, Yigsaw Dessalen |
| Contributors | Prof G Osthoff, Prof MT Labuschagne, Dr L Herselman |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07042006-082803/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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