2019 ASHS Annual Conference

Salinity is a rising concern in many lettuce-growing regions, limiting yield and productivity. Lettuce (Lactuca sativa L.) is sensitive to salt stress, which reduces biomass and causes other undesirable effects. Salinity tolerant lettuce varieties are the most economical and effective means to sustainably grow lettuce and maintain high yield and quality of the product. We sought to identify physiological traits important in salt tolerance that allows lettuce adaptation to high salinity while maintaining its productivity. Following-up on information from previous salinity tolerance studies, 5 sensitive and 5 tolerant cultivars and accessions were chosen in the current study for more detailed analysis of their reactions to salinity in growth chamber tests; they included crisphead, butterhead, romaine, and leaf types of cultivated lettuce and its wild relative (L. serriola L.). Physiological parameters were measured four weeks after transplanting two-day old seedlings into 4-inch pots filled with sand and hydrated with Hoagland nutrient solution. To understand the state of the photosynthetic apparatus, chlorophyll fluorescence parameters and leaf area were measured using the PlantScreen system (Photon Systems Instruments). The 10 genotypes showed a broad range of reaction to salinity, exhibiting zero to 64% reduction in leaf area and 16% to 67% reduction in fresh weight compared to control, with PI 253468 at the lower end and ‘Laura’ at the higher end of reduction for both parameters. Salinity treatment increased chlorophyll content 5% to 21% in all cultivated genotypes, while decreasing it 5% to 17% in wild lettuce. Photosynthetic CO₂ assimilation did not change significantly in response to salinity in any genotypes. Salinity significantly increased photoinhibition and photooxidative stresses, however, in the most sensitive accessions. These results suggest that cultivated lettuce may adapt to salinity, in part, via upregulation of chlorophyll synthesis in order to maintain photosynthetic activity. Further study is needed to better understand this phenomenon.