Eight seeds of okra were planted in each pot. 10 daysafter germination plants were thinned to 5 plants perpot. Plants were irrigated up to full field capacity (FC)dur ing 14 da ys a fter ger mina tion to a chievemaximum germination and equilibrium in plantgrowth, afterward okra plants were subjected to threelevels of drought i.e.,100% FC (control/normalirrigation), 50% FC and 25% FC. Field capacity wasca lcula ted ba sed on sa tur a tion per centa ge a sdescr ibed by Wilcox (1951). Unifor m cultur a lpractices were carried out throughout the researchperiod. After 20 days of drought treatment, plantswere uprooted and phenotypic characters viz. plantheight, fresh weight, and dry weight were measuredas per the standard procedures

Chlorophyll and carotenoids content was measuredby the method explained by Lichtenther (1987).About 0.2 g of grounded leaf sample was extractedwith 80% acetone till the residue becomes colourless.Absorbance of the acetone extract was measured at470, 663 a nd 646 nm with the help ofspectr ophotometer (fr om Ger ma ny, Ca r y-50).Chlorophyll and carotenoids concentration was thenmeasured by following formula.

Soluble protein content in the okra leaf sample wasmeasured by the method described by Lowry et al.(1951)

Method of Bates et al. (1973) was implemented toevaluate the proline content. 5g plant grounded plantsample was mixed in 3% sulfosalicylic acid (aqu) andthe mixture was centrifuged at 10,000 rpm. Thesupernatant was mixed with 2 mL of ninhydrin ) and2 mL of glacial acetic acid, and the solution wasboiled for 1h at 100 °C. The reaction is allowed totake place in ice bath and after the completion of r ea ction 4mL toluene to extr a ct the mixtur ea nd absor ba nce at 520nm wer e r ead by usingspectrophotometer.

MSI was measured as per Premachandra et al.(1991). Fresh leaf material (1.0 g) was cut into smalldiscs, washed with deionized water and placed in glasstest tubes along with blank. 10 mL of deionized waterwas added to each test tube so that leaf discs getsubmerged. The test tubes were kept in a water bathfor 30 min at 45 °C. After cooling, the electricalconductivity of water (C1) was measured using theconductivity meter. Water was again poured back tothe same leaf discs and kept in the water bath at 100°C for 10 min. The final electrical conductivity wasmeasured. Percent conductivity was used to calculatemembr ane sta bility index using the following formul

Where

The experimental data were subjected to analysis ofvariance (ANOVA) using windows software Statistix8.1 with two-factor factorial arrangements. Eachtreatment was replicated three times. The effects ofdrought on okra varieties were determined by theLeast Significant Difference test (LSD) at pd”0.05,where the F test was significant (Steel and Torrie 1960)

Plant height is the major character significantly affected due to drought. In the present study, maximum plant height (17.73cm) was observed in control whereas lowest plant height (7.86cm) was recorded in plants subject to 25% FC. Okra cultivar Sabz Pari exhibits highest height (13.77cm) whereas lowest height (11.66 cm) was recorded in Pusa green (Table 1). The combined effects of drought and variety showed that Sabz Pari exhibited highest plant height among all other cultivars under all droughts. Maximum plant height 18, 15 and 8.33cm was recorded in Sabz Pari at 100%, 50% and 25% drought stress respectively whereas lowest plant height 17.66, 13 and 8 cm was observed in Mehak Pari under 100%, 50% and 25% drought. (Fig. 1).,

Fig. 1
Effect of drought stress on plant height of okra cultivars

Highest plant fresh weight (16.63g) was recorded at control (100%FC) whereas, lowest values (12.42g) were observed in plants subjected to water stress of 25% FC. Analysis of variance showed highly statistical difference (p<0.01) among okra cultivars for fresh weight and applied drought. Okra cultivar Pusa green showed maximum fresh weight (15.25g) whereas minimum fresh weight (13.93g) was obtained by Mehak Pari (Table 1). Results regarding interaction of drought and okra cultivars indicates that all okra cultivars showed reduction in their fresh weight as drought stress is elevated. Highest fresh weight (17.20g) was recorded in okra cultivar Pusa Green and Clemson under control condition (100% FC) whereas 25% FC drought stress significantly reduced the fresh weight and lowest values of fresh weight (11. 26g) were observed in okra cultivar Mehak Pari, meanwhile under same drought level okra cultivars Pusa Green while Clemson retained maximum biomass and showed maximum fresh weight of 14.20g and 13. 3g, respectively (Fig. 2). Results of our experiment correspond with findings of Idrees et al. (2010), Singh and Usha (2003) and Munir et al. (2016) who observed similar reduction in fresh weight of lemon grass, wheat and okra, respectively, when exposed to elevating drought.

Fig. 2
Effect of drought stress on fresh weight of okra cultivars

Results regarding plant dry weight indicate that highest plant dry weight (3.70g) was recorded at control (100% FC) whereas lowest dry weight (1.22g) was observed in plants subjected to maximum water stress of 25% FC. Okra cultivar Pusa green showed maximum dry weight (2.74g) whereas minimum dry weight (2.41g) was obtained for Pusa Swani (Table 1). The interaction effect between drought and okra cultivars suggested a prominent reduction in dry weight for all cultivars. At 100% FC (normal irrigation) and maximum dry weight (3.86g) was recorded in Pusa Green while under same condition minimum dry weight (3.5g) were recorded in Pusa Swani. Meanwhile at highest drought stress (25%FC) least dry weight (0.76g) was recorded by Mehak Pari while under same drought Pusa green produced highest dry weight (1.6g) (Fig. 3). Similar results were observed by Idrees et al. (2010),Singh and Usha (2003) and Munir et al. (2016)in lemon grass, wheat and okra respectively.

It was noted that maximum Chlorophyll-a content (10.98 mg/g FW) were recorded in 100% FC whereas minimum Chlorophyll-a content (9.0 mg/g FW) were observed in 25% FC. Okra cultivar Sabz Pari had highest Chlorophyll-a content (14.38 mg/g FW) while lowest values (5.43 mg/g FW) were recorded in Mehak Pari (Table-1). The combined results of drought and okra varieties revealed that there is a gradual reduction in chlorophyll content with increase in drought stress. At 100% FC (normal irrigation), okra cultivars Sabz Pari had maximum chlorophyll (15.23mg/g) while Mehak Pari had lowest chlorophyll content (6.46mg/g) ,. At 25% FC, Sabz Pari

Fig. 3
Effect of drought stress on Dry weight of okra cultivars

Fig. 4
Effect of drought stress on Chlorophyll a content of okra cultivars

maintained highest chlorophyll content (13.76mg/g) while Mehak Pari produced lowest values of chlorophyll (4.56mg/g) (Fig. 4). A reduction in chlorophyll content was also reported in drought stressed cotton (Massacci et al., 2008) and Catharanthus roseus (Jaleel et al., 2009).

Maximum Chlorophyll b content (20.39 mg/g FW) was recorded in 100% FC (normal irrigation) whereas minimum Chlorophyll b content (18.6 mg/g FW) were observed in 25% FC drought. Okra cultivar Sabz Pari had highest Chlorophyll b content (24.41 mg/g FW) while lowest values (13.51 mg/g FW) was recorded in Mehak Pari (Table 1). The combined results of drought and okra varieties revealed that there was a gradual reduction in chlorophyll content with increase in drought stress. At 100% FC (normal irrigation) okra cultivars Sabz Pari showed maximum chlorophyll b (25.7mg/g) while a same irrigation lowest chlorophyll b content (14.56mg/g) were observed in Mehak Pari, on the other hand at highest drought (25% FC) Sabz Pari maintained highest chlorophyll b content (13.76mg/g) while Mehak Pari produced lowest values of chlorophyll b (4.56mg/g) (Fig. 5). The chlorophyll content decreased to a significant level at higher water deficits sunflower plants (Kiani et al., 2008) and Vaccinium myrtillus (Tahkokorpi et al., 2007).

Fig. 5
Effect of drought stress on Chlorophyll-b content of okra cultivars

Effects of drought on total chlorophyll content indicate that maximum Total chlorophyll content (31.37 mg/g FW) was noted under no drought stress (normal irrigation) whereas minimum total chlorophyll (27.71 mg/g FW) was recorded under 25% FC drought (Table 1). Results concerning total chlorophyll content of okra cultivars reveled that Sabz Pari produced highest total chlorophyll content (38.80 mg/g FW) while lowest values (18.94 mg/g FW) were recorded in Mehak Pari (Table 1). The combined results of okra and drought stress revealed that significant reduction was observed with increase in drought stress. Highest total chlorophyll of 40.93, 38.66 and 36.6 mg/g was recorded in Sabz at 100%, 50% and 25% FC conditions, while lowest chlorophyll content 21.03,18.83 and 16.96 mg/g was obtained by Mehak Pari at 100%, 50% and 25% FC (Fig. 6). Ram et al. (2014) and Amin et al. (2009) also observed that under drought conditions, reduction in chlorophyll content was noted in watermelon and okra respectively.

Results regarding carotenoids (mg/g FW) of okra plant depicts highly significant statistical difference (p<0.01) among okra cultivars, applied drought and their interaction (Table 1; Fig. 7). It was noted that maximum carotenoids (14.28mg/g FW) were recorded in 100% FC (control) whereas minimum carotenoids values (11.08 mg/g FW) were observed in 25% FC drought stress. Among the okra cultivars studied maximum carotenoids (18.57 mg/g FW) were observed in Sabz Pari while lowest concentration of carotenoids (6.91 mg/g FW) was recorded in Mehak Pari (Table 1). The combined effect of drought stress and okra cultivars for carotenoids suggested that okra cultivar Sabz Pari showed highest carotenoids (20.43, 18.4 and 16.9 mg/g at 100%, 50% and 25% FC drought, respectively), while lowest carotenoids (5.26,7.23 and 5.26 mg/g at 100%, 50% and 25% FC respectively) were observed in Mehak Pari (Fig. 7). Similar findings were previously obtained by Altaf et al. (2015) in okra, Idrees et al. (2010) in lemon grass and by Ram et al. (2014) in water melon.

Fig. 6
Effect of drought stress on total Chlorophyll content of okra cultivars

Fig. 7
Effect of drought stress on Carotenoids of okra cultivars

It was noted that maximum proteins (8.06 mg/g FW) were recorded in 100% FC whereas minimum protein (2.73 mg/g FW) were observed in 25% FC drought. Results regarding okra cultivars suggested non- significant variation for protein content, maximum protein (5.44 mg/g FW) were observed in Pusa green, Clemson, Sabz Pari and in Mehak Pari while lowest concentration of protein (4.66 mg/g FW) was recorded in Pusa Swani. The combined results of drought stress and okra cultivars for protein showed that okra cultivar Pusa green showed highest protein (9.0 mg/ g FW) at control condition, while lowest protein (2.33 mg/g FW) was observed in Pusa Swani at highest drought stress i.e., 25% FC (Fig. 8). Amin et al. (2009) obtained similar results in okra and Kabiri et al. (2014) in Nigella sativa.

Fig. 8
Effect of drought stress on total protein of okra cultivars

Maximum proline content (21.36µg/g) was noted in those okra plants which were exposed to 25% FC drought whereas minimum proline content (18.47µg/g) was recorded in control plants (100% FC). Okra cultivars showed significant variations in respect to proline content, okra cultivar Sabz Pari had highest proline content (27.78µg/g) while lowest proline value (11.57µg/g) was recorded in Mehak Pari (Table 1). The combined results of drought stress and okra cultivars suggested an increase in proline content of all okra cultivar with increase in drought stress and among all okra cultivar Sabz Pari showed highest proline content of 29.5, 27.63 and 26.23µg/g at 25%, 50% and 100% FC drought respectively, while okra cultivar Mehak Pari showed lowest proline content of 13.1,11.4 and10.23µg/g were observed in Mehak Pari at 125%, 50% and 100% FC drought respectively (Fig. 9). Similar observation was recorded by Rokhzadi (2014) in chick pea, Amin et al. (2009) in okra and Idrees et al. (2010) in lemon grass.

Fig. 9
Effect of drought stress on proline content of okra cultivars

Effects of drought on membrane stability index (MSI) indicated that maximum MSI (72.26%) was noted at 25% drought whereas minimum MSI (35.93%) was recorded in control plants. Okra cultivars showed non-significant variations in respect to MSI, okra cultivar Sabz Pari produced highest MSI(56.33%) while lowest MSI values (51.88%) were recorded in Pusa green. The interaction of drought and okra varieties on MSI showed that okra cultivar Mehak Pari produced maximum MSI (73.33%) when grown in 25% FC drought, while least MSI (31.66%) were produced by Pusa green when grown at normal irrigation (Fig. 10). The results of the present study agree with Idress et al. (2010) for lemon grass and Sakhabutdinova et al. (2006) for wheat.

Fig. 10
Effect of drought stress on Membrane Stability index of okra cultivars