Comparison of Physiological Indices in Response to Cold Stress in Wild Tomato (Solanum habrochaites) for Screening of Cold Tolerant Lines

Many plants grown at low temperature exhibit different adaptation strategies involving physiological, ecological and morphological processes. Solanum lycopersicum L. is affected by cold stress at all stages of growth; however, wild tomato species such as S. habrochaites  rapidly  improve after exposure to the cold stress through various changes in physiological processes. In this study, the short-term stress method was used for rapid screening and cold tolerance selection of tomato lines instead of long-term stress at 4 °C.

This study was carried out as a factorial experiment based on completely randomized design with three replications at Ferdowsi University of Mashhad Iran in 2018. Experimental factors included two levels of cold stress (0 and 2 °C) and three tomato lines (LA1777, LA3969 and LA4024). In the study, electrolyte leakage, MDA, anthocyanin, phenol, 1,1-diphenyl-2-picrylhydrazyl DPPH, total soluble carbohydrate content, the maximum efficiency of photosystem II and the activity of the three antioxidant enzymes CAT, POD, and APX were measured.

According to the results of this experiment, LA1777 line showed the lowest leaf wilting after  exposure to low temperatures. There was a significant difference between these lines in terms of electrolyte leakage. Under cold stress conditions, lowest electrolyte leakage and malondialdehyde (MDA) were obtained from wild line LA1777 that compared to sensitive line LA4024. LA1777 and electrolyte leakage at LA4024 at 0 and 2˚C were 14 and 11% higher than LA1777, respectively. Inhibition of DPPH radical activity of tolerant line LA1777 were higher than sensitive line LA4024 at 0 and 2 °C (43 and 45% respectively). Anthocyanin content of LA1777 and LA3969 lines were 49% higher than LA4024 at 0 °C. Under cold stress, the activity of the three antioxidant enzymes CAT, POD, and APX significantly increased in wild line LA1777, indicating better hydrogen peroxide scavenging system. After cold stress, LA1777 and LA3969 had the highest maximum efficiency of photosystem II, respectively, in light-adapted conditions (F'v / F'm), which may be due to higher cell membrane stability. The results showed that instead of long-term cold stress at 4˚C, the short-term stress method can be used for rapid screening of tomato lines for cold tolerance selection. Assessment of physiological parameters such as chlorophyll fluorescence, electrolyte leakage, MDA level, DPPH radical scavenging, catalase, peroxidase and ascorbate peroxidase enzymes showed that these indices can be used to detect cold stress and to quantify the stress in tomato lines.

Based on our data, we conclude that this short-term stress method is a useful method for rapid assessment of tomato chilling tolerance. The physiological parameters used in this study showed adequate difference between tomato lines.