SCREENING FOR SALT TOLERANCE IN SELECTED AFRICAN NIGHTSHADE LAND RACES

Abstract

African nightshades (Solanum spp) are an important cuisine in Sub-Saharan Africa. Its consumption is increasing due to its nutritional and health benefits, leading to increased demand for this nutritious vegetable across markets in rural and urban areas. This has led to increased production under irrigated cultivation in many regions, including coastal Kenya. In coastal areas, increased salinization of groundwater has led to reduced productivity of vegetables. To mitigate against this challenge there is need to identify and adopt high yielding and stress tolerant varieties. This study was conducted to screen selected lines of African nightshade land races for salt tolerance using morphological and physiological traits. To evaluate the morphological traits, 20 different lines of African nightshade land races were evaluated under different levels of salt stress using a randomized complete block design (RCBD) with factorial arrangement of treatments. Fourteen (14)-day old seedlings were first treated with half strength Hoagland’s solution to acclimatize with the condition for 7 days before being exposed to 3 levels of Sodium chloride (NaCl) concentrations (0, 60 and 120 mM) for 6 weeks. To evaluate physiological traits, nine (9) lines were selected from the 20 lines with high, moderate and low tolerant traits and subjected to the three treatments for 6 weeks. The data on plant height, dry weight, number of leaves, leaf area, chlorophyll, K+/Na+ ratio, and proline was subjected to (ANOVA). Differences among NaCl salt levels within each species were compared using Duncan’s Multiple-Range Test at P=0.05. For morphological traits, results obtained showed a significant interaction (p<0.05) between salt stress and line in influencing the number of leaves, leaf area and the dry weight. Growth parameters were significantly reduced by salt stress. The reductions of the plant height, the number of leaves and the dry weight as a result of salt stress at 60 mM NaCl were 46.7, 36.8 and 54.3% respectively. At 120 mM NaCl, the reductions were 57.8, 58.3 and 76.7%. For the physiological traits, there was a significant interaction (p<0.05) between salt stress and line in influencing the leaf proline and K+/Na+ ratio. At 60 and 120 mM NaCl, proline content progressively increased with an increase in salt stress in all the lines. Proline levels increased by 65.6 and 131.3% at 60 and 120 mM NaCl respectively. The reductions in relative chlorophyll and K+/Na+ ratio at 60 mM NaCl were 31 and 47.1% respectively. At 120 mM NaCl the reductions were 31.5 and 64.6%. At 60 mM NaCl all the lines were tolerant to salt stress, however at 120 mM NaCl all the lines were moderate tolerant to salt stress except TH06 which was susceptible. ACC20, ACC5 and Oleverosi were identified as potentially able to grow under moderate to high salt stress. Experiments were conducted under protected conditions and on hydroponic set up. Further studies using soil as media that may alter plant responses are needed to verify the findings in this work.