Effect of KNO3-Priming on Agronomic, Physicochemical and Fibre Attributes of Cotton (Gossypium hirsutum L.) Under Saline Conditions

Abstract

Salinity stress presents a challenging dilemma for plant growth and development. It disrupts cotton (Gossypium hirsutum L.) yield through an immediate osmotic and a slower ionic phase, ultimately diminishing its fibre quality. Seed priming, a low-cost seed pre-treatment, mitigates these effects by triggering prior metabolic processes and subsequent gene expression. This pioneering work aimed to improve agronomic, physicochemical parameters and fibre characteristics in cotton genotypes (GH-Baghdadi and GH-Mubarak) by potassium nitrate (KNO₃) mediated osmopriming (1.25% and 1.5% conc.) for 15, 20 and 25 h, along with an un-primed control under saline field conditions. The randomised complete block design experiment in triplicate was conducted in 2019 and 2020 at the soil with electrical conductivity (extract) (EC_e) 9.44 dS m⁻¹ to investigate optimal priming media and priming duration. The results showed that salinity impaired physicochemical and agronomic parameters in the control experiment. However, seed priming with 1.5% KNO₃ for 20 h significantly improved the yield and yield contributing components in both genotypes. Maximum values for chlorophyll (Chl) a and b were recorded at 1.50 and 0.90 mg g⁻¹ fresh weight (FW), respectively, under this treatment. Similarly, the chlorophyll-a fluorescence parameters (Chl-a FPs), such as the maximum quantum yield of photosystem II (Fv/F_m ) (0.83), effective quantum yield of PSII (Φ_PSII) (0.76) and photochemical quenching coefficient (qP) (0.85), indicated improved light harvesting, electron transport and photosynthetic capacity. Furthermore, the net photosynthetic rate (P_n) increased to 19.65 mmol CO₂ m⁻² s⁻¹, while stomatal conductance (g_s) reached 28.39 mmol CO₂ m⁻² s⁻¹ at the same treatment. A strongly positive correlation was found between chl-a FPs and net photosynthetic yield. Enzymatic activities, including catalase (CAT) at 2.17 unit mg⁻¹, superoxide dismutase (SOD) at 1.05 unit mg⁻¹ and peroxidase (POD) at 1.50 unit mg⁻¹ were significantly enhanced, along with leaf potassium (K) (14.3 mg g⁻¹ dry weight [DW]) and calcium (Ca) (6.7 mg g⁻¹ DW), particularly in GH-Mubarak. Seed-cotton yield (SCY) increased to 5274 kg h⁻¹ and fibre strength (FS) improved to 31.3 thousand pounds per square inch (tppsi), while ginning out-turn (GOT) reached a maximum of 45% at 1.5% KNO₃ for 20 h in both genotypes. The micronaire value (4 μg in.⁻²) significantly decreased, indicating improved fibre fineness. Correlation analysis revealed a strong positive correlation between physicochemical and agronomic traits, particularly gas exchange characteristics, chlorophyll content and Chl-a FPs, which are strongly associated with SCY and fibre characteristics. In conclusion, priming cotton seeds with 1.5% KNO₃ for 20 h is a promising strategy for mitigating salinity stress and enhancing physicochemical attributes and agronomic traits, ultimately leading to improved cotton yield and fibre quality.