Abstract:
Ethiopia is frequently affected by drought. As a result, drought is the major factor that affects
sorghum production in Ethiopia. Knowledge of drought tolerance related traits and their
mechanisms are the key component in selecting genotypes that withstand the effects of
drought. The objectives of this study were to assess genetic variability among sorghum
germplasm for root and shoot traits, to map chromosomal regions (QTL) associated with
root and shoot traits related to drought adaptation and to identify SSR markers associated
with drought adaptation traits.The experiment was carried out at Jimma University, College
of Agriculture and Veterinary Medicine under greenhouse condition. One hundred thirty-six
sorghum genotypes were characterized for twelve traits using a high throughput root
phenotyping platform in a randomized complete block design with three replications. Among
these genotypes, 108 of them were used for studying population structure and trait-marker
association analysis using 39 SSR markers. The analysis of variance indicated that highly
significant difference (P<0.01) were observed among the genotypes for all thestudied traits.
The coefficients of correlation among different drought related traits showed that there was a
significant positive and negative association among different drought related traits. The first
three principal components (PCs) with eigenvalues greater than one accounted for 56.4% of
the total genotype variation, the remaining 43.60% accounted for the last nine principal
components.Moderate genotypic variation was exhibited for leaf area, shoot fresh weight,
shoot dry weight, root to shoot ratio and root angle.All 136 genotype were grouped into four
clusters whereby adifferent member within a cluster being assumed to be more closely
related in terms of the trait under consideration with each other than that member in different
clusters is. While highest phenotypic variation was exhibited for leaf area, shoot fresh
weight, shoot dry weight, root dry weight and root to shoot ratio. Broad sense heritability
ranged from 19.35% for root length to 71.08% for shoot fresh weight at seedling stage and
high heritability was recorded for shoot fresh weight (71.08%), leaf area (70.22%) and root
angle (66.22%). High heritability combined with high genetic advance was observed for
shoot fresh weight, root angle, and leaf area. The 108 genotypes were grouped into three
distinct subgroups. The plots of LD (r2
) for pairs of loci, versus the genetic distance in cM,
showed a clear trend on linkage disequilibrium decay in the studied genotypes and based on
trend line it is around 15-20 cM. A total of 25 significant marker-trait associations/QTLs (P
≤ 0.05) were detected with 14 SSR markers and these markers were localized with previously
identified QTL. As a future line of work, genotypes that showed desirable phenotypes such as
narrow root angle need to be evaluated under field condition to verify their performance and
thereby they can be used in the breeding programs. As this study is the first in Ethiopia, the
identified QTLs need to be validated through repeated phenotypic measurement in
independent or related populations. The SSR markers found to be associated with traits need
to be validated before their use in marker-assisted selection.
