Efficacy of seed priming for inducing stress tolerance in chilli (Capsicum annum L.) under water stress condition

Abstract

A study entitled “Efficacy of seed priming for inducing stress tolerance in chilli (Capsicum annum L.) under water stress condition” was undertaken with the objective to evaluate the various seed priming treatments for water stress tolerance in chilli at the seedling stage and selected best treatments were evaluated for physiological and yield traits under pot culture study. Seeds of the chilli variety ‘Vellayani Athulya’ were primed with 2.5% potassium nitrate (KNO)3, 3%silicon dioxide (SiO2), 2.5mM salicylic acid (SA) and distilled water for 12 hours and subjected to three different stress levels i.e., control, mild stress (5% - PEG 6000) and moderate stress (10% - PEG 6000) during seedling stage. Seed priming experiment was carried out in a factorial completely randomized design (CRD) with the first factor being priming using different solutions and the second factor being the stress levels which were replicated thrice. The results of the first experiment noted that chilli seedlings responded distinctively to the different treatments. 2.5% KNO3 under moderate stress recorded significantly higher proline content (0.24 µM) and enhanced seedling vigour index-I (SVI 1) compared to 3% SiO2 and untreated treatments. The hydrogen peroxide (H2O2) concentration were significantly higher in mild stress with unprimed seeds (0.93 µM), wherein lower content was recorded in 3%SiO2 primed seeds (0.38 µM). Further, reduced malonaldehyde (MDA) content and increased seedling vigor index-II (SVI 2) performance were noted in both 2.5% KNO3 and 3% SiO2 treatments. Seeds failed to germinate under 2.5mM salicylic acid. From the first experiment, 2.5% KNO3 and 3% SiO2 were selected for further study as both were on par with each other. Then the seeds primed with both treatments were sown in portrays. Seedlings were transplanted to pots 30 days after sowing (DAS) and irrigation and other cultural practices were followed according to KAU POP. Water stress was induced by withholding irrigation for four days where relative water content (RWC) of leaves reaches 70% during flower initiation stage. During this period, physiological parameters were taken from both the stress and control plants. The results of second experiment revealed that seeds primed with 3% SiO2 recorded early flowering whereas, seeds primed with 2.5% KNO3 recorded the first fruiting stage. Under water stress conditions, seeds primed with 2.5% KNO3 recorded significantly high values for relative water content (RWC) (67%), cell membrane stability Index (CMSI) (40.33%), total chlorophyll content (TCC) (1.807mg/g), catalase activity (CAT) (510 nmoles of H2O2 used min/g weight of sample), superoxide dismutase (SOD) (492.6 Units/mg of protein), total soluble sugars (TSS) (1.573mg/ml) and total soluble protein (TSP) (1.073mg/ml) where 3% SiO2 primed seeds recorded significantly higher values for total proline content (2.977µmoles of proline/g of tissue). For control conditions, 2.5%KNO3 primed seeds recorded significantly high values for relative water content (RWC) (94%), total chlorophyll content (TCC) (4.577mg/g), catalase activity (CAT) (200 units/min/g weight of sample), peroxidase activity (POD) (0.135 units/min/mg of protein), superoxide dismutase(SOD)(400 units /mg of protein) total soluble sugars (TSS) (3.347 mg/ml), total soluble protein (TSP) (2.012 mg/ml) and 3% SiO2 primed seeds recorded significantly higher cell membrane stability index (CMSI) ( 91.66%), total proline content (1.307 µmoles of proline/ g of tissue). Under stress condition, capsaicin content was recorded high in seeds primed with 2.5% KNO3(0.022%) and ascorbic acid was recorded highest in seeds primed with 3% SiO2(393.567mg) Whereas, in control both capsaicin content (0.129%) and ascorbic acid content (483.083mg) were recorded higher in seeds primed with 2.5% KNO3. Under stress condition, the yield components like plant height(57cm), number of fruits/plant (16 no), fruit yield (44.293g), dry matter (31.6g) and root volume(42cm3 ) were recorded as significantly higher in seeds primed with 2.5% KNO3. Further, the number of seeds/fruit (41 no) and seed yield (3.067g) were recorded as significantly higher in seeds primed with 3% SiO2 and the number of flowers/plant (22 no) were found highest in unprimed seeds whereas, in control condition, 2.5% KNO3 primed seeds recorded significantly higher plant height(58.66cm), fruit yield (86.723g), root volume (69 cm3) and dry matter (46.22g) and 3%SiO2 primed seeds recorded significantly higher number of flowers/plant (33) and seed yield (4.117g). Both 2.5% KNO3 and 3% SiO2 are on par with each other for number of fruits/plant (27), while SiO2 and unprimed seeds are on par to each other for no. of seeds/fruit (74.667). Among the seed priming treatments, 2.5% KNO3 was found to be an effective treatment under water stress conditions as it shows enhanced antioxidants levels, with high water absorption capacity, increased chlorophyll content, soluble sugar and protein content along with the high capsaicin and ascorbic acid content with increased plant height, number of fruits, fruit yield, root volume and dry matter where 3%SiO2 primed seeds recorded high proline, peroxidase activity, ascorbic acid content, no of seeds/plant and seeds yield/plant under water stress conditions. For seed production, 3% SiO2 priming method can be suggested for chilli. Therefore, seed priming with 2.5% KNO3 and 3% SiO2 can be suggested for water stress tolerance in chilli.