2.1 Laboratory Experiment
A pot experiment were conducted under laboratory condition with temperature 10 to 15 C and 13 to 14 hours light duration, to assess the effect of three drought level Control 100% Field Capacity, Stress 80% Field Capacity, stress 60% Field Capacity. Field soil, sand and peat compost were mixed in equal proportion and filled in 36 pots at the rate of 1835g in each pot. Two conventional wheat genotypes Opata and chirya-1, and two Synthetic genotypes i.e. SD-28 and SD-32 were studied. Nine pots were used for each wheat genotype to test each genotype at three drought levels with three replications. The pots were tapped on the floor enough to bring the soil mixture to a uniform height to get soil bulk density (SBD) and corresponding total soil porosity (TSP)
The height of soil mixture in each pot required to get the desired SBD were calculated by following formula.
VSM (cm3)
Height (cm) = _____________________________
π × (Diameter of pot (cm) 2
2
Where VSM (volume of soil mixture) were calculated by formula
Mass of soil mixture taken in each pot (g)
VSM (cm3) = ______________________________________
Desired SBD (g cm -3)
The pots were irrigated with a uniform volume of tap water to saturate all the pore space of soil mixture and kept aside for drying. The volume of water (VW) required saturating the soil mixture in the pots were calculated by the formula.
VW (cm3) = TSP (cm3 cm-3) × VSM (cm3)
Where TSP were calculated assuming soil particles density (SPD) of 2.65 (g cm3) using the formula
SBD (g cm3)
TSP (cm3 cm-3) = 1- ________________
SPD (g cm3)
Volumetric soil water content (VSWC) were monitored daily from each pot with Domain Reflectometer (TDR) model TRIME –FM ( IMKO Micromodultechnik GmbH, Germany) the seed were sown in pots when VSWC was at FC (assuming FC as 50% of the saturation and taking saturation =TSP). VSWC will be calculated by formula.
TSP (cm3ncm-3 ×50
VSWC at FC (cm3 cm-3) = ______________________
100
Similarly, VSWC at other drought levels was calculate with their respective formulae.
TSP (cm3 cm3) ×40
VSWC at 80% FC (cm3 cm-3) = _____________________
100
TSP (cm3 cm3) ×30
VSWC at 80% FC (cm3 cm-3) = _____________________
100
After germination VSWC were maintained in each pot at FC for three weeks, Monitoring VSWC and fulfilling the irrigation requirements daily. The VW require maintaining each pot at FC was calculated by the formula:
VW (cm3) = (VSWC at FC (cm3 cm-3) – VSWC from TDR (cm3 cm-3)) × VSM (cm3)
After three weeks the irrigation supply was cut off from the pots to which drought treatment were applied and VSWC was monitored daily until the respective drought level will achieved. Afterwards, VW required 3maintaining different drought levels were applied daily to respective pots calculating by their respective formulas.
VW (cm3) = (VSWC at 80% FC (cm3 cm-3) – VSWC from TDR (cm3 cm-3)) × VSM (cm3)
VW (cm3) = (VSWC at 60% FC (cm3 cm-3) – VSWC from TDR (cm3 cm-3)) × VSM (cm3)
The drought stress will be maintained for 30 days and after that samples were collected for physiological and molecular study.