Physiological effect of seed priming and foliar application of growth regulators in cowpea (Vigna unguiculata L.)

Abstract

An investigation entitled “Physiological effect of seed priming and foliar application of growth regulators in cowpea (Vigna unguiculata L.)” was carried out in two experiments during the period 2020-2021. The objective of the study was elucidation of influence of seed priming and foliar application of growth regulators on morpho-physiological changes, yield and quality in cowpea (Vigna unguiculata L.). Experiment-1 on seed germination and early seedling growth was conducted at College of Agriculture, Padannakkad. It was carried out in complete randomized design with eight treatments and three replications. Treatments included seeds primed with growth regulators viz., thiourea @ 500 ppm (T2); salicylic acid @ 50 ppm (T3); salicylic acid @ 100 ppm (T4); salicylic acid @ 150 ppm (T5); brassinolide @ 0.1 ppm (T6); brassinolide @ 0.3 ppm (T7); brassinolide @ 0.5 ppm (T8) and control (T1) without growth regulators. Minimum number of days taken for 50 per cent seed germination in T4, T6 and T7. 100 per cent seed sprouting and seed germination were recorded in T4 and T7. Maximum seedling survival was recorded in T4 and T7 which was on par with T5 and T6. Whole seedling dry weight and seedling vigour index were significantly enhanced in T7 followed by T4. Based on statistical analysis T4 and T7 were considered as best treatment for further field studies. Experiment-2 was conducted as field study at Instructional Farm II, Karuvacheri, College of Agriculture, Padannakkad. The best seed priming results obtained from Experiment -1 were further studied under field condition in Experiment- 2. It included 14 treatments viz., Standard POP recommendation without thiourea (KAU, 2016) (T1); standard POP with thiourea foliar spray @ 500 ppm (T2); T₁ + salicylic acid foliar spray @ 50 ppm (T3); seed priming with 100 ppm salicylic acid + salicylic acid foliar spray @ 50 ppm (T₄); T₁ + salicylic acid foliar spray @ 100 ppm (T₅); seed priming with 100 ppm salicylic acid + salicylic acid foliar spray @ 100 ppm (T₆); T₁ + salicylic acid foliar spray @ 150 ppm (T₇); seed priming with 100 ppm salicylic acid + salicylic acid foliar spray @ 150 ppm (T₈); T₁ + brassinolide foliar spray @ 0.1 ppm (T9); seed priming with 0.3 ppm brassinolide + brassinolide foliar spray @ 0.1 ppm (T₁₀); T₁ + brassinolide foliar spray @ 0.3 ppm (T₁₁); seed priming with 0.3 ppm brassinolide + brassinolide foliar spray @ 0.3 ppm (T₁₂); T₁ + brassinolide foliar spray @ 0.5 ppm (T₁₃) and seed priming with 0.3 ppm brassinolide + brassinolide foliar spray @ 0.5 ppm (T₁₄). The foliar sprays were given at 20 and 40 DAS. Regarding morphological observations, T6 and T14 significantly superior in plant height, leaf area per plant and number of compound leaves per plant at 25, 45 and 60 DAS. Minimum number of days taken for 50 per cent flowering in T₁₄ which was on par with T6. Minimum number of days for first harvest were recorded in T6 and T₁₄. Duration of crop and greater number of productive flower setting were significantly superior in T14 and T6 which was on par with T12. Efficient translocation of assimilates increased pod length and pod diameter in T6 which was on par with T14. Leaf area index and SPAD chlorophyll meter readings were maximum in T6 and T14 at 25, 45 and 60 DAS. The increase in net photosynthetic area and assimilate translocation, enhanced the total dry matter production, relative growth rate and crop growth rate in T14 followed by T6 during vegetative stage and reproductive stage as well. Maximum relative leaf water content was observed in T6 which was on par with T5, T8, T12 and T14 at 25 DAS and T5, T8, T12, T13 and T14 at 60 DAS. The ratio of variable fluorescence to maximum fluorescence (Fv/Fm) was recorded maximum in T14 which was on par with T6 and T12 at 25 DAS. The maximum effective quantum yield of PS II (Y (II)) were recorded maximum in T6 and T14 which were on par with T10 and T12 at 25 DAS. At 45 DAS, T14 was on par with T6, T8, T10 and T12. At 60 DAS, T14 was on par with T4, T6, T8, T9, T10, T11, T12 and T13. Electron transport rate (ETR) were observed maximum in T6 and T14 which were on par with T8, T10 and T12 at 25 DAS. At 45 DAS, T14 was on par with T6, T8, T10 and T12. At 60 DAS, T14 was on par with T2, T4, T6, T8, T10, T11, T12, and T13. A perusal of biochemical data showed that T6 and T14 had maximum leaf chlorophyll content at 25 DAS. At 45 DAS, T6 had the highest chlorophyll content which was on par with T8, T12 and T14. At 60 DAS, maximum chlorophyll content was recorded in T6 which was on par with T14. Maximum proline content was recorded in T1 at 25, 45 and 60 DAS. Regarding yield parameters average number of pods per plant and average number of seeds per plant were recorded maximum in T6 and T14, Seed yield was found to be increased by 43 per cent in T6 when salicylic acid @ 100 ppm seed priming and foliar application were given and 42.11 per cent increase in seed yield was noticed in T14 when seed priming was given with brassinolide @ 0.3 ppm and foliar spray at 0.5 ppm. Among only foliar spray of growth regulators without considering seed priming, brassinolide @ 0.5 ppm (33.74 per cent) and salicylic acid @ 100 ppm (33.29 per cent) were recorded maximum increase in seed yield. Foliar spray of thiourea was increased the yield by 26.32 per cent over control. Maximum net returns were obtained from treatment of seed priming and foliar spray with salicylic acid 100 ppm (T6) followed by T8 and T5. Even though, the gross returns were maximum from brassinolide treated plants, the net return was less due to higher cost of brassinolide. The highest BC ratio was from salicylic acid treated plants T6 (2.86) followed by T8 (2.73) and T4 (2.67). Among foliar sprayed treatments T5 recorded maximum BC ratio (2.66) and thiourea treatment recorded BC ratio 2.52. Results of the study revealed that seed priming and foliar spray of salicylic acid 100 ppm was significantly superior to all other treatments with respect to yield and net return. It can be concluded that among the treatments seed priming and foliar application of salicylic acid 100 ppm and seed priming with brassinolide @ 0.3 ppm and 0.5 ppm foliar spray showed the best results. Among foliar spray without seed priming salicylic acid 100 ppm and brassinolide 0.5 ppm superior in all parameters. Maximum economic returns were recorded from salicylic acid treated plants, even though highest seed yield and gross returns observed from brassinolide treatment because of high cost of chemical, net returns were minimised. Therefore, seed priming and foliar application of salicylic acid (100 ppm) significantly enhanced seed yield and net returns in cowpea