Comparative Effects of Salicylic Acid and Calcium Carbide on Some Morphological and Physiological Parameters of Sweet Pepper

Abstract

Calcium carbide (CaC2) has occupied an important position among different sources of ethylene (C2H4) for improving growth and yield of vegetables. Calcium carbide dependent C2H4 can cause noteworthy improvements in growth, yield and fruit quality of vegetables but its effect on physiological and morphological parameters of vegetables is completely concentration dependent. Under critical environmental conditions, an abrupt release of C2H4 from CaC2 can impede growth and yield of a crop as it initiates leaf, flower and fruit senescence and finally great loss of yields. However, CaC2 dependent released C2H4 can be more constructive and worthwhile for non-conventional production of vegetables if it is applied along with salicylic acid (SA). Salicylic acid not only impedes C2H4 biosynthesis but also plays a crucial role in plant physiology as a stress hormone. As comparative effects of C2H4 released from CaC2 and SA are not thoroughly investigated particularly for production of vegetables with improved quality, therefore, a series of laboratory, pot and field studies were conducted to scrutinize the effectiveness of CaC2 dependent C2H4 with and without application of SA for seed germination, physiological, morphological, yield and quality parameters of sweet pepper. Experiments were conducted in three sections. Section I, II and III consisted of four laboratory, three wire-house/pot and two field experiments, respectively. From first experiment of section-I, polyethylene and paint were selected as the most effective materials for coating CaC2. In second experiment of section-I, it was observed that CaC2 up to 14 mg plate-1 induced early seed germination with 100% germination rate and better seedling growth parameters but application of CaC2 ˃16 mg plate-1 inhibited seed germination and seedling growth parameters of sweet pepper. Similarly, results of third experiment of section-I revealed that SA concentration ≤0.4 mM can be used to improve germination percentage and seedling vigor of sweet pepper. In last experiment of section-I, it was noted that SA alleviated injurious effects of CaC2 with ˃16 mg plate-1 on seed germination and seedling growth parameters. In section-II, data revealed that 20 mg CaC2 kg-1 soil while 0.3 mM SA can be used for maximization of sweet pepper productivity. In last pot trial, effect of CaC2 with and without SA was investigated on growth, yield and fruit quality of sweet pepper under salinity stress. It was observed that detrimental effects of excessive C2H4 from CaC2 on physiology, photosynthesis, growth and yield of sweet pepper were mitigated by the foliar application of SA under saline conditions. On the basis of preliminary trials of section I and II, two field experiments were conducted on two different locations (section-III). Results of both field experiments showed that application of CaC2 along with foliar application of SA improved photosynthetic activity by 7-77%, plant water use and carboxylation efficiency by 10-211%, antioxidant and enzyme activities by 15-53% and finally fruit yield by 5-34% with a significant increase in fertilizer use efficiency compared to that of plants without SA and CaC2 application (control). Additionally, quality parameters related to chemical composition of sweet pepper fruits were also improved by the application of CaC2 with foliar application of SA. These parameters are very much required for improvement in shelf life. In short, results confirm the synergistic role of SA and CaC2 for improving physiology, growth, yield and quality of sweet pepper. Our results suggest that application of 200 mg plant-1 polyethylene coated CaC2 with foliar application 0.1 or 0.3 mM SA is relatively more economically beneficial and effective than application of 200 mg plant-1 polyethylene coated CaC2 without foliar application of SA. Moreover, results also indicated that SA treated plants were tolerated abrupt release of C2H4 from applied CaC2 to a greater extent.