Optimizing salinity threshold for screening salt tolerance in sponge gourd (Luffa cylindrica L.) genotypes at seedling stage

Abstract

Screening of larger genotypes for salinity tolerance at the seedling stage offers an economical and time-saving approach to alleviate salt stress. The present study was planned to find out the optimum threshold concentration of NaCl for screening salt tolerance in 228 sponge gourd genotypes. The threshold concentration was achieved using the salt injury index (SII) by analysing the effects of NaCl-induced salinity on eight key morpho-physiological traits. The genotypes of sponge gourd were exposed to six NaCl salt concentrations, 25, 50, 75, 100, 125 and 150 mM/L, along with a control treatment. Germination percentage (GP), shoot length (SHL), root length (RL), seedling length (SL), seedling fresh weight (FW), seedling dry weight (DW), and vigour indices I and II (VI-I and VI-II) were recorded up to the 14th day. Salt injury index (SII) was calculated based on morph-physiological traits, revealing that a single concentration of NaCl was not reliable for 50% reduction. Therefore, multiple regression analysis of the salt injury index (SII) conducted and the values were 139 mM/L for GP, 96 mM/L for RL, 90 mM/L for SHL, 92 mM/L for SL, 97 for FW, 133 mM/L for DW and 118 and 133 mM/L for VI-I and VI-II, respectively were able to cause 50% reduction (mean 105.68 mM/L), hence NaCl concentration of 125 mM/L was identified as optimal concentration of NaCl to evaluate salt tolerance, offering standardized in-vitro screening protocol in sponge gourd genotypes for salt tolerance breeding program.