Assessment of cold resistance in tobacco varieties using JIP-test parameters and seedling growth

Cold stress (CS) is a significant natural hazard, and distinguishing between plant cold resistance and sensitivity is critical for cultivar breeding and the development of germplasm resources. This study used 205 tobacco (Nicotiana tabacum L.) varieties from around the world to investigate the changes in the chlorophyll a fluorescence (OJIP) transients, JIP-test parameters, and seedling growth caused by seven days of CS (5°C) treatment. Their cold resistance was assessed using the cold-resistant coefficient, derived from the relative growth rate of shoots, damage scores, and JIP-test parameters. The results showed that total electron carriers per reaction center (S_m) and relative variable fluorescence at the I-step (V_I) were better indicators of cold resistance than maximum quantum yield of photochemistry at t = 0 (F_v/F_m), which was widely used to assess plant cold resistance. Next, the study examined the effects of CS and subsequent recovery on OJIP transients, JIP-test parameters, and seedling growth in two highly resistant (HR) and two highly sensitive (HS) varieties to confirm the reliability of the assessment methods. The results indicated that HR varieties experienced less photoinhibitory damage to photosystem II, exhibited lower growth inhibition during CS, and showed better recovery during the recovery period compared to HS varieties. These findings suggested that the JIP-test parameters could serve as a reliable tool for assessing tobacco cold resistance and aid in selecting varieties with enhanced resilience to CS.