Phenotypic and Isozyme Diversity in Tetraploid Wheats (Triticum Turgidum L.) From Bale and Wello Regions of Ethiopia
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Date
2001-06
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Addis Ababa University
Abstract
Phenotypic and isozyme diversity of 32 landrace populations of tetraploid wheats originating
from two regions (Bale and Wello) of Ethiopia was analysed in this study. A total of 2559
individual plants (45-110 plants pel' population) representing each landrace were considered
for the phenotypic diversity investigation. Investigations were also made on the species
richness (biological diversity) of the popUlations whereby individuals in each landrace were
classified into their own taxonomic classes and analysis of the species diversity was made for
each population, altitudinal class and region of collection. Seven heritable qualitative traits
(seed colDl; glume color, awn color, glume hairiness, beak awn, spike density, and awn
length) were studied. The frequencies of each phenotypic class were used to compute the
ShannoncWeaver index (H') to estimate and analyse the diversity at different levels. For
isozyme analysis, three enzyme systems, Esterase (EST), Aspartate amino trans ph erase
(AAT), alld Leucine amino peptidase (LAP) were used to study the genetic variatioll in 14
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landrace populations selected based on the clustering of the populations from the phenotypic
frequencies. Each population was represented by twenty individuals.
The analysis of species diversity indicated that seven species of wheats from two ploidy levels,
tetraploid and hexaploicl, are planted in mixtures at vG/ying proportions, Triticum turgidum
ssp. durum was the most dominant species accountillg for about 67.32 % of the total
population. A maximum of four species was recorded per each population. Analysis of
phenotypic frequencies and diversity indices were done for tetraploids lumped together and
for durum alolle. Considering tetraploid species, seed color alld beak awn contributed the
highest diversity index (H' = 0.92 for both). Awn color contributed the lowest diversity index
(H' = 0.59). When durum treated alone, glume color followed by beak awn and seed color
contributed the highest diversity index (H' = 0.90, 0.84, alld 0.84, respectively), whereas
glume hairiness had the 10IVest diversity index (H' = 0.48).
Traits sllch as awn color, awn length, glume color and seed color showed statistically
significant differences (p < 0.05) between regions while significant differences (p < 0.05)
were observed for awn length, beak awn, glume hairiness and seed color across gradients of altitudillal classes in tetraploid wheats. Sigllificallt differences were also observed betweell
altitudes and regions for traits in dU1'II1ll treated alone. Variations were, however, largely due
to the differences in the level of the different characters within populations. On regional
basis, higher lIIean diversity index was observed for Wello than Bale. Awn color was
monolllOlphic and jixed for color types in collections originating fi'om Bale whereas a variety
of fi'equencies were observed in Wello. Considering tetraploids, the overall diversity index
was cOlllputed to be H' = 0.81 ± 0.08. The overall region value of H' for durum wheat is 0.63
± 0.08 indicating a decline in the alllount of diversity in durulII wheat as compared with the
index for tetraploid wheats.
The isozyme assay resulted into a total of 5 isozyme loci; 2 of the distinct polymO/phic
regions of enzyme activity (banding paUe/'ll) detected for EST, 2 for AAT, and one fO/; LAP.
The isozyme data also indicated presence of allelic polymO/p/zism was detected at all loci.
The mean number of alleles per locus ranged fi'om 1.4 to 2.2. Considerillg the genetic
variability at the 5 loci, the percentage polymO/phic loci varied fi'om 40% to 80%. A pairwise
comparisoll of populations over jive isozyme loci indicates that the ullbiased genetic
identity rangedfi'om 0.904 to 1.00. Whereas the gelletic distallce rallgedfi'om 0.00 to 0.053,
indicatillg that there is small amount of variatioll amollg populatiOlls. Populations were
grouped/clustered illto six clusters. The landraces ji'om Bale and Wello grouped differently
similar to that of clustering that was based on phenotypic frequencies.
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Biology