ASHS 2024 Conference

In many tropical fruit production areas, including southern Florida, a rise in ocean levels resulting from climate change is anticipated to lead to greater inland intrusion of saltwater, thereby increasing salinity of the soil and/or irrigation water. Thus, knowing the salinity level of the soil or irrigation water that negatively impacts tropical fruit crops, including papaya, is important to alleviate salinity-induced damage to these crops. A study was conducted to evaluate physiological and growth responses of two papaya (Carica papaya L.) cultivars grown commercially in Florida (‘Red Lady’ and ‘Exp15’) to different irrigation salinity levels. Papaya seedlings were transplanted into 11.4-liter pots with Krome very gravelly loam soil; a calcareous soil collected from the papaya production area in south Florida. Each plant was manually irrigated three times per week with 1 liter of deionized water containing different concentrations artificial sea salt (Instant Ocean®) to obtain 4 salinity levels based on electrical conductivity (EC) of the irrigation water i.e., 0 (control), 3, 6, and 9 dS/m. Plants performance under different salinity levels was evaluated by determining net CO2 assimilation (A), stomatal conductance (gs), transpiration (E), the leaf chlorophyll index (LCI), and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) on a weekly basis throughout the study. Normalized difference vegetation Index (NDVI) values derived from multispectral images were also collected weekly. After seven weeks, plants were harvested and leaf relative water content (RWC), leaf water potential, leaf area, and leaf, stem, and root dry weights were determined for all plants. Five weeks after treatments were initiated, for both cultivars, plants in the 6 and 9 dS/m treatments had lower A, E, gs, LCI, and Fv/Fm than plants in the other treatments. At the end of the experiment, plants in the 3, 6, and 9 dS/m treatments had significantly lower A, E, gs, LCI, Fv/Fm, leaf water potential, leaf area, and leaf, stem, and root dry weights than plants in the other treatments. Also at the end of the experiment, ‘Exp15’ plants in the 9 dS/m treatment had lower NDVI values than plants in the other treatments, whereas there was no difference in NDVI among treatments for ‘Red Lady’. There was no significant effect of salinity treatment on RWC. The findings suggest that 'Red Lady' and ‘Exp15’ papaya plants are unable to withstand salinity levels of 3 dS/m or higher in the calcareous agricultural soil of southern Florida.