genotypic variation, drough tolerance, drought alleviation, drought mitigation, brassica, potassium application studies, brassica napus l (printol, bullet, rnb-96040, vangard, no. 29-52, ccs-1, asf-7, sponser, bln-877, bln-971, sps-5, shiralee, jewel, ks-75, crusher, norseman, star, 19-h, bard-i, cyclon, manrove, msf-7, 8966-2, a..p., g.a., 6008, 8948-2, deffender, con-i, con-ii, con-iii, dunkled, oscar, rainbow and wester)
brassica compestris l, drought avoidance mechanism, ostomotic adjustment, osmotic potential.
Brassica is a traditional crop in the rain fed areas of Pothwar region. The prevailing drought in the rain fed areas of Pothwar region. The prevailing drought in the rain fed areas affects the overall productivity of the system. Brassica cultivar evaluation experiments for drought tolerance were conducted at three locations and in the glasshouse. Potassium application studies for drought mitigation were also conducted in the field as well as in the glasshouse.
A group of 35 oilseed rape cultivars belonging to Brassica napus L (Printol, Bullet, RNB-96040, Vangard, No. 29-52, CCS-1, ASF-7, Sponser, BLN-877, BLN-971, SPS-5, Shiralee, Jewel, KS-75, Crusher, Norseman, Star, 19-H, BARD-I, Cyclon, Manrove, MSF-7, 8966-2, A..P., G.A., 6008, 8948-2, Deffender, CON-I, CON-II, CON-III, Dunkled, Oscar, Rainbow and Wester) were evaluated for drought tolerance, using alpha design, under three environments in Pothwar region. The check cultivar; BARD-I belonged to Brassica compestris L. Among the agronomic, physiological and quality parameters, number of pods plant, 1000-seed weight, harvest index, leaf relative water content, relative growth rate ant net assimilation rate showed significant relationship with final seed yield. The compensation for different parameters took place that was finally exhibited in the seed yield. Two parameters namely number of days to flowering and number days to maturity were negatively correlated with the seed yield exhibiting the drought avoidance mechanism. The drought avoidance mechanism was not uniformly operative in all the cultivars therefore these parameters were identified as the best indicator of drought avoidance. Based on the performance, the cultivars were identified as relatively drought tolerant, relatively drought tolerant, relatively drought susceptible and intermediate. The cultivars under study were clearly differentiated into groups at Attock location therefore it was concluded that Attock conditions were the best for drought screening experiments.
Ten cultivars based on their performance in field trials; four from relatively drought tolerant (19-H, KS-76, 8948-2, and Wester), three from relatively drought susceptible (CON-II, CON-III and Crusher ) and three from intermediate group (RBN-96040, Rainbow and Printol) were also evaluated for their drought tolerance up to seedling stage to identify reliable parameter to be used as criteria for drought tolerance. Plants subjected to drought treatments showed significant variation in shoot fresh and dry biomass and shoot and root lengths that was due to variation in tissue water content. It was concluded that screening of oilseed rape cultivars for drought tolerance up to the seedling stage is not reliable as none of the characteristics, determined in the experiment was found specific to all the cultivars within each of the groups under study.
The drought mitigation experiments through potassium application were conducted to study the response of two representative cultivars belonging to each of drought tolerant ( 19-H ) and drought susceptible group ( CON-II )
Under glasshouse and field conditions. Potassium application increased the number of pods, plant height, relative water content, relative growth rate, net assimilation rate, leaf area index and decreased osmotic potential and resulted in better final seed yield. The potassium fertilized oilseed rape plants improved their efficiency of compensation for the loss due to drought through increased number of pods per plant and 1000-seed weight. Potassium application increased seed oil content under both the conditions and seed crude protein only under field conditions.
Relatively drought sensitive cultivar CON-II responded well to potassium application and enhanced its ability to tolerate drought. The differential response to two different environments was due to variation in patterns of water deficit. Potassium application induced osmotic adjustment by lowering osmotic potential under water stress conditions but it disappeared under favourable soil moisture conditions. The feasible and economical drought management practice through potassium application should replace the previous potassium recommendation for sustainable crop productivity.