Seeds treatment with proline improves host resistance to Macrophomina phaseolina in soybean seedlings under salinity stress conditions

 Soybean seeds of two tested cultivars were soaked for 2 hr in 1 mM and 5 mM proline (Pr.), then growing seedlings were subjected to salinity stress (40 mM NaCl) and at 12 days after sowing (DAS) and at 19 DAS were inoculated with M. phaseolina. Results showed that proline treatment improves vegetative growth parameters (no. of leaves, no. of branches, stem height, root length (cm)). Also, biomass of seedlings (fresh and dry weight) was increased for both cultivars compared with the control. Data also  indicated that chlorophyll pigment and carotenoids contents were significantly increased in both tested cultivars compared with the control. Additionally, means relative water content (RWC) and total phenolics in leaves. However, data exhibited that Giza 35 accumalate less Na⁺ than that recorded for Giza 111, higher content of K⁺ and total protein  compared with unstressed seedlings.  Results did confirm that proline treatment lead to a significant decrease in Na⁺ content and a significant increase in K⁺ content in both cultivars compared with untreated ones. However, proline treatment resulted in a decrease in disease severity which reached to about 70– and 67– for Giza 111 and Giza 35, at 5mM proline respectively. In conclusion, this study explored the dual effect of exogenous proline treatment to cope the adverse effect of both biotic and abiotic stress in soybean plants.