| dc.description.abstract | In terms of tonnage, sorghum is Africa's second most important cereal. The
continent produces about 20 million tonnes of sorghum per annum, about onethird
of the world crop. The crop is widely grown in the semi arid tropics where
local farmers depend on the natural rainfall and the crop is subject to unpredictable
drought stress factors.
The objective of this study was to assess the genetic diversity and the wide range
of sorghum accessions grown in Kenya under drought stress conditions. A total of
139 accessions were characterized and evaluated for drought tolerance and stay
green during the dry seasons of 2007 and 2008 at the University of Nairobi,
Kibwezi farm. All accessions were grown in 2 m entry rows using an alpha lattice
design. Both qualitative and quantitative traits were used to assess the phenotypic
variability. There was significant phenotypic variability in the diverse traits of
sorghum measured. There was a clear indication of the suitability of the
genotypes to specific environments. The early maturing accessions exhibiting an
adaptation to drought escape, originated mainly from dry and marginal Northeastern
and eastern provinces of Kenya. In both seasons, water stress caused
decrease in plant height. Under drought stressed conditions, grain yield was
significantly correlated to days to 50% flowering, and also to the number of
productive tillers. Grain yield, Days to flowering, rates of senescence (15, 30 and
45 DAF) showed high and significant broad-senescence heritabilities under
drought conditions indicating that these traits are highly heritable and can be
selected for under drought stress conditions. Green leaf area or 'stay-green' levels
was higher in the season with less drought stress than in the more stressed one.
Correlations for stay-green measured either at 15, 30 or 45 days after flowering
were highly significant. Accessions with high green leaf area yielded higher than
those with lower green leaf areas in both seasons. Accessions clustered in groups
C and A gave useful higher grain yields, seed mass and also stay green than
those clustered in groups Band D. Principal Component Analysis hi-plots
identified a total of three similar groups. One group was mainly influenced by days
to 50% flowering, the other one was mainly attributed to the green leaf area (stay
green) and the last group was mainly influenced by yield, 100 seed mass, plant
height and lodging. Kenyan sorghum germ-plasm can therefore be categorized as
having been selected for early maturing drought escaping types, drought tolerant
stay-green types and high yielding drought susceptible genetic materials.
Molecular data on diversity demonstrates that the Kenyan sorghum accessions
contain a great deal of genetic diversity as indicated by the the Nei's genetic
diversity. The high genetic diversity value among the sorghum accessions
indicates that the level of genetic diversity was not influenced by selection.
The FST values observed in this study are relatively low, indicating a reduced
degree in allelic fixation. The cluster analysis based on genetic similarity among
the bulked sorghum accessions examined showed a clear demarcation of the
germplasm mainly according to their breeding origin. | en |
