S. Sikder
Department of Crop Physiology and Ecology, Hajee Mohammad Danesh Science & Technology University, Dinajpur, Bangladesh
N.K. Paul
Department of Botany, Rajshahi University, Bangladesh
Wheat, Membrane thermostability, CTD, PSR mobilization, Heat tolerance
Crop Botany Laboratory of Hajee Mohammad Danesh Science and Technology University (HSTU), Dinajpur
Variety and Species
Membrane Thermostability (MTS) Test For determination of membrane thermostability the experiment was conducted in a completely randomized design with three replications in the Crop Botany Laboratory of Hajee Mohammad Danesh Science and Technology University (HSTU), Dinajpur during November, 2005. Six wheat cultivars viz., Gourab, Sourav, Kanchan, Shatabdi, Sonora and Kalyansona were evaluated for acquired thermal tolerance in membrane thermostability (MTS) test in control environment. Seedling was grown on moistened, folded germination paper at room temperature. Fifteen seeds were set for germination for each unit. Seedlings were watered daily for proper growth. The seedlings were then acclimatized at high temperature when the first leaf attained about 8-10 cm height (about 8-10 days after germination) by placing in a water bath with their roots immerged in water (about 1 cm). The water bath was maintained at 39oC for 24 hours. Following acclimation, two 3.5 cm long segments were excised from each of 10 healthy seedlings per cultivar to form the experimental unit. Leaf segments were rinsed twice in deionized water, and placed in 22×150 mm test tubes with 10 mL of deionized water. The test tube was covered with an aluminium foil. Severe heat stress was applied by submerging test tubes to a depth equal to the height of water in tubes (about 4 cm) in a water bath at 49oC for 30 minutes. After that, the test tubes were held over night at room temperature. Conductance was measured with an electrical conductivity meter (HI 8033, Hanna Instruments, Italy) after standardizing it with a 0.005N KCl solution. The test tubes were then autoclaved for ten minutes at 120oC and 0.10 MPa and conductance was measured again as an indication of the maximum potential leakage from a given sample. Membrane thermostability (MTS) was expressed in percentage unit as the reciprocal of relative leakage. MTS = (1-T1 / T2) × 100, where, T1 and T2 are the conductivity readings before and after autoclaving, respectively. PSR Mobilization and Canopy Temperature Depression (CTD) - For dermination of pre-anthesis stem reserves (PSR) and CTD (oC) the experiment was conducted at the research farm of Crop Physiology and Ecology Department of HSTU, Dinajpur during 2005-06. Six wheat cultivars (Gourab, Sourav, Kanchan, Shatabdi, Sonora and Kalyansona) were used as study materials. The seeds were sown on November 30 and December 30 of 2005. November 30 sowing was considered as normal growing condition, whereas December 30 sowing was regarded as late growing post-anthesis heat stress condition. The experiment was replicated thrice in a split plot design where two growing conditions (sowing times) were placed in main plots and six wheat cultivar were in sub-plots. Seeds were sown in rows 20 cm apart at the rate of 120 kg ha-1 in a unit plot size of 3m x 2m. A fertilizer dose of 100-60-40-20 kg ha-1 N, P2O5, K2O and S was applied in the form of urea, triple super phosphate (TSP), muriate of potash (MP) and gypsum, respectively. Three irrigations were given at crown root initiation, maximum tillering and grain filling stages. Other inter cultural operation were done properly. The pre-anthesis stem reserves contribution towards the final grain weight was determined. This is based on the net loss in weight of above ground vegetative organs between anthesis and maturity with the difference yield and net assimilation. It was calculated as: Pre-anthesis stem contribution (%) = (Change of stem dry weight (g) from anthers to maturity/Changes of grain dry weight (g) from anthers to maturity) x 100, =[(S2 - S1)/(G2 - G1)]/ x 100, where, S1 = Stem dry weight (g) at anthesis, S2 = Stem dry weight (g) at maturity, G1 = Grain dry weight (g) at anthesis and G2 = Grain dry weight (g) at maturity Therefore, a hand held infra-red thermometer (Model: Crop TRAK Item no. 2955L – Spectrum Technologies, Inc.) was used to measure canopy temperature depression (CTD) i.e. the difference between ambient air temperature and canopy temperature in degree centigrade. The CTD was recorded at 5 days after anthesis during noon period under bright sunlight and less wind. Grain Weight per Plant - Grain weight per plant was determined from ten randomly selected plants in each plot at harvest and the relative performance for grain weight per plant was calculated as Asana and Williams (1965) by the following formula: Relative performance (%) = (Grain weight per plant under stress condition/Grain weight per plant under normal condition) x 100. Heat Susceptibility Index - Heat susceptibility index (S) was calculated for grain yield per plant as following formula: S = (1- Y/Yp) / (1- X/Xp), where, Y = Variable of a cultivar in a stress environment, Yp = Variable of a cultivar in a stress-free environment, X = Mean of Y of all the cultivars, Xp = Mean of Yp of all the cultivars. (S<1.0, stress tolerant and S>1.0, stress susceptible). Statistical Analysis - The data were analyzed by partitioning the total variance with the help of computer by using MSTAT-C programme. The treatment means were compared using Duncan’s Multiple Range Test (DMRT).
Thai Journal of Agricultural Science 2010, 43(4): 251-258
Journal