Title:
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Genetic and physiological basis of drought tolerance in barley (Hordeum vulgare L.)
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'Vater availability is the main factor limiting agricultural productivity and
may result in considerable yield reduction around the world. Therefore,
identification of genetic variation for drought tolerance and exposure of this
variation to appropriate drought conditions for selection are the main objectives
of research for many crop plants. In this study twenty-five barley (Hordeum
vulgare L.) populations consisting of accessions, landraces and modern varieties
from different parts of the world, mainly arid, semi-arid and Mediterranean
regions, were grown in PEG (6000) solutions in a controlled-temperature growth
room. All measurements on physiological and genedc aspects of drought tolerance
were made after one and two weeks' growth. Results from the screening trial
indicated that increasing PEG concentrations caused significant reductions in root
length, shoot length, fresh and dry weight of root and shoot of all populations.
Root to shoot dry weight ratio increased with decreasing water potential.
Importantly populations responded differently to PEG treatments.
There was considerable variation amongst populations in response to
drought stress. Estimation of broad-sense heritability (1t 2
B) for root and shoot
traits showed that a great proportion of the variation in response to drought was
genetically determined. Results from principle component analysis indicated that
screening could be carried out on the basis of the root to shoot dry weight ratio,
which had higher genotypic· coefficient variability and phenotypic coefficient
variability under drought stress. Populations 'PK 30109', 'PK 30118' were
relatively tolerant whilst cuItivar 'Rihane-03'and landrace 'Shair' were
intermediate and 'Ir. line', with a lower relative root length and root to shoot dry
weight ratio was relatively sensitive.
Accumulation of most solutes in roots and shoots increased due to both
drought and salinity. Proline and glycine-betaine in leaves increased in stress
conditions, whereas the level of polyols in soil culture increased under drought
stress, whilst it decreased in saline conditions. Total amino acids concentration
increased in saline and PEG treatments, but there were no differences between
controls and stressed-plants grown in soil culture. Populations varied in solute
accumulation.
Although both organic and inorganic solutes contributed to osmotic
adjustment, the major contribution was made by inorganic solutes in drought
conditions. Potassium content increased in drought conditions (PEG and soil
culture), but was constant in saline conditions. Drought-stressed plants
accumulated more sodium compared to control conditions. The ~/Na+ ratio
reduced with the decrease in plant growth under drought stress, so that in the soil
experiment landrace 'Shair' showed higher leaf ~lNa+ ratio in drought stress
compared to 'Rihane-03' and 'Ir. line'. Potassium and total water soluble
carbohydrates had higher concentrations than other solutes in drought conditions.
Salinity decreased all aspects of growth, but was more severe in root
characters including length, fresh and dry weight. In contrast drought stress
caused greater reductions in the shoot than the root. Relative water content
decreased due to drought and salt stresses, whilst osmotic adjustments increased
in both stress conditions..Membrane stability index decreased with decrease in
leaf water potential induced by PEG.
Supplied by The British Library - 'The world's knowledge'
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