The response of salt-stressed Valencia sweet orange (Citrus sinensis) to salicylic acid and methyl jasmonate treatments

Salinity is an obstacle to citriculture worldwide, and is a concern in arid, semiarid, and coastal regions. In the current study, we irrigated one-year-old ‘Valencia’ trees budded onto Kuharske rootstock with 60 mM sodium chloride (NaCl) solution for ten weeks. Subsequently, these trees were sprayed with 50, 75, and 100 mM SA or MeJA to determine whether these phytohormones could alleviate the detrimental effects of salinity. Control trees were not sprayed, including a positive control with saline irrigation and a negative control without saline irrigation. A reduction in plant growth and chlorophyll content following the NaCl treatment was recorded. Subsequent SA and MeJA treatments promoted tree growth and enhanced chlorophyll content in these trees. Additionally, these treatments enhanced the expression of enzymatic antioxidants: POD, CSD, CAT, PAL, APX1, GSTs, aquaporin proteins, and Na+ co-transporters. SA and MeJA treatments also altered the expression of PR1, PR3, PR4, and PR5, while only MeJA altered the expression of PR2. Abscisic acid (ABA) expression was negatively affected by SA treatments, whereas the MeJA application increased ABA expression relative to the salt treated control. Furthermore, sodium (Na+) and chloride (Cl−) analysis indicated that leaves had higher levels of Na+ and Cl− in response to SA and MeJA treatments when compared with the controls. Our results provide perspectives at the possible function of SA and MeJA in ameliorating salt stress in citrus.