2. Drought stress
It is a period of shortage of rainfall or non-availability of the rainfall to the
crop plants.
More than 20% yield loss is through drought
Drought at seedling stage stops cell division and cause cessation of growth
Drought reduces the length and weight of shoot
Drought reduces the photosynthesis( Affects PS-1 and create reactive electron
species and degrade chloroplast)
Drought at critical stages(Tasselling and Silking) cause severe yield loss
3. Maize: Irrigation profile
Maize needs well distributed rainfall
The rainfall should be 500- 750mm
Tasseling and silking stages(70th and 85th ) are critical
Critical stage needs copious irrigation
7. Ways to improve yield
Growing very high yielding varieties under stress conditions may give
moderate yields
Followed by eliminating negative traits
Improving drought tolerant varieties- recurrent selection
8. Improvement of drought tolerance
Finding drought- tolerant traits and its mechanisms
These genes are multigenic and low frequency genes
The frequency is increased by recurrent selection
9. Mechanism of drought tolerance
May not flower and recover on watering
May close the stomata and reduce transpiration
Increased depth of roots
Short anthesis and silking interval
Degree of leaf rolling
Abscisic acid production
Amino acids like aspargine, proline production, glycine betaine production
10. Breeding programs
Conventional selection
Marker aided Recurrent selection- Asr-1 gene
Quantitative trait loci- checking gene presence in stress and non-stress
conditions
Transgenic programs
Using secondary traits in breeding programmes
