Effect of citric acid (CA) priming and exogenous application on germination and early seedling growth of okra (Abelmoschus esculentus L.) plants under salinity stress condition

Salinity is a significant barrier to the healthy germination of seeds, the development of seedlings and ultimately the yield of crops. Salinity tolerance can be effectively induced through seed priming and exogenous application of various treatment agents. The vegetable crop okra is a healthy and well-liked one worldwide. Literature shows that salt stress negatively disturbs the growth of okra plants. In the present research, we investigated the effects of citric acid (CA) as priming and exogenous agents to alleviate the salinity-inhibited germination and early growth of okra plants. The seeds were pretreated with CA (1 mM and 2 mM) and soaked in distilled water (control) for 60 min. Germinated seeds were grown in hydroponic solution and subjected to salt stress (50 mM and 100 mM NaCl) with three independent replications and same concentrations of CA (1 mM and 2 mM) were exogenously sprayed. Our results showed that, seed priming with 1 mM CA significantly produced the highest percentage of germination (GP), germination index (GI), germination energy (GE), seed vigor index (SVI), radicle length and weight, hypocotyl length and weight, and number of lateral roots while decreased mean germination time of okra seeds while compared to the control treatment. Additionally, the findings demonstrated that salt stress dramatically reduced root and shoot length, plant height, root and shoot fresh weight and dry weight, and relative water content (RWC). Under salt stress, the addition of 1 mM and 2 mM CA significantly increased the RWC, root and shoot length, root and shoot fresh and dry weight, and plant height. These results provide information that CA priming improves germination parameters and exogenous treatments can improve the salt tolerance, and seedling characteristics of okra. Therefore, our results suggest that 1 mM CA can be utilized as a seed priming and exogenous application agent reducing the impacts of salt stress and promoting early seedling development of okra.