Is foliar spray of proline sufficient for mitigation of salt stress in Brassica juncea cultivars?

The effects of foliar application of proline (20 mM) on growth, physio-biochemical, and yield parameters were assessed in two Brassica juncea (L.) Czern & Coss cultivars, namely, Varuna and RH-30, at different levels (2.8, 4.2, or 5.6 dsm(-1)) of NaCl in soil. At 29 days after sowing (DAS), plants were sprayed with either 20 mM proline or water in the presence or absence of NaCl stress. The NaCl negatively affected parameters related to growth, photosynthesis, and yield in both varieties but more in RH-30 than in Varuna. Exogenous application of proline counteracted the effects of salt stress in Varuna only, by increasing the antioxidative capacity of the plants. Moreover, proline was not effective in alleviating the detrimental effects of higher salt concentrations on the studied parameters. Proline application to unstressed plants increased growth, photosynthesis, and yield parameters in both varieties; however, the effects were more prominent in Varuna than in RH-30.