PLANT PARAMETERS RELATED TO SALINITY AND DROUGHT STRESS By FARGHAMA KHALIL Reg. No: 09-US-AGR-16 PLANT BREEDING & GENETICS. DROUGHT. “The inadequate water availability during the life cycle of a crop that restrict the expression of its full genetic yield potential.”
“Mechanisms causing minimum yield loss in a drought environment relative to maximum yield in optimum environment for the crop”.
A crop can minimize yield loss due to drought by following mechanisms:
Early flowering (left) and late flowering (right) sorghum cultivars under late-season drought stress. The late cultivar will not flower at all due to stress.
Osmotic adjustment: An important mechanism of dehydration avoidance. Osmoregulation is +vely associated with yield under stress, allows growth and results in delayed leaf death by maintaining turgor pressure and other mechanisms.
Reduced transpiration: Water saving mechanism. Species reduce transpiration by closure of their stomata in response to water stress before wilting.
Leaf characteristics: Leaf pubescence generally reduces net radiation resulting in lower leaf temperature. This trait shows +ve association with yield under stress. Net radiation can also be reduced by altering the leaf angle from ‘horizontal’, which receives maximum radiation.
“Dehydration tolerance of a genotype means that significantly lower level of changes induced in it than those in another genotype when both are subjected to same level of stress.”
Various measurements of dehydration tolerance are;
F1, F2 andF3 grown under non-stress conditions. In F3 individual plant progenies are evaluated for yield and selection is done.
Should have following attributes:
Various criteria used in breeding for drought resistance in different crops are;
Sorghum leaf epicuticular wax by the scanning electron microscope; left normal (Bm genotype); right low wax (bm genotype).
Wheat seedlings grown in vermiculite and severely desiccated after which they were irrigated. The seedling on the right received 0.1 µmol of ABA in the irrigation water before the onset of stress. Control seedlings are on the left.
Grain of two wheat cultivars subjected to sever drought stress during grain filling (right). Top: cultivar with superior capacity for stem reserve utilization; bottom: normal cultivar. Note the shriveled grain under stress in the latter.
Saline soils: contain soluble salts mainly chlorides and sulfates of Na, Ca, Mg, and K. Their EC is always more than 4.
Alkaline soils: contain >15% exchangeable Na, common salt is sodium carbonate.
Plants growing in saline conditions face 3 types of stress:
Resistance to Salinity-induced water stress:
(1) Ion exclusion
(2) Salt tolerance by cellular compartmentation/ salt excretion
Leaf necrosis: Caused by accumulation of Na, K and Cl ions, used as selection criteria based on ion exclusion.