Potato (Solanum tuberosum L.) production is significantly impacted by drought stress. In light of increasing food demand, it is imperative to identify potato cultivars with enhanced tolerance to drought stress. This study aims to evaluate the stress tolerance level of five potato cultivars, Kufri Jyoti (KJ), Kufri Chandramukhi (KCM), Kufri Chipsona1 (KCS1), Kufri Pukhraj (KPR), and Atlantic (ATL), by in vitro screening using D-mannitol (0, 100, 200, 300, 400, 500 mM) as a drought stress-inducing agent. The increasing D-mannitol concentrations had a detrimental impact on the plant growth of all the cultivars. Based on the dry weight of the cultures under stress conditions in reference to the control (non-stress), the stress tolerance index (STI) was calculated. The impact of D-mannitol on STI was maximum in cultivar ‘KPR’ and minimum in cultivar ‘KJ’. The cultivar ‘KJ’ recorded the highest STI of 0.22, followed by 0.12 for ‘KCS1’ and 0.05 for the cultivar ‘KPR’ on MS1 medium (MS medium containing 10 µM AgNO3) supplemented with 500 mM D-mannitol. Further, the physiological parameters were examined in the microshoots of the higher drought-tolerant cultivar ‘KJ’, moderately drought-tolerant cultivar ‘KCS1’, and the drought-sensitive cultivar ‘KPR’ at multiple time points of the treatment period (0, 4, 8, 12, 16, 20 days). A significant reduction in relative water content, osmotic potential, and chlorophyll and carotenoid contents was observed during the treatment period on MS1 medium containing 300 mM and 500 mM D-mannitol. This reduction was higher in cultivar ‘KPR’ than ‘KCS1’, and the least reduction was recorded in cultivar ‘KJ’ compared to their respective controls. The observed adjustment of the osmotic potential in cultivar ‘KJ’ could be one of the important reasons for its drought stress tolerance.
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