Thermal shock at a high temperature for a short period increases the germination success of the chestnut tree Lecythis pisonis Cambess

•High temperatures for a short period of time increase expression of vigor and seedling emergence.•High temperatures for long periods result in the formation of abnormal seedlings.•High temperatures for a short time increase enzyme activity and decrease MDA.•H2O2 may have acted as a signaling molecule favoring seedling emergence.•Heat shock 30–45 °C promoted high rates of global DNA methylation. Seed germination occurs within temperature ranges suitable for each species. Understanding the optimal germination temperature allows seasonal planning during planting, increases cultivation optimization, and reduces costs in the production of species of economic or sustainable interest. The species L. pisonis presents great difficulty in propagating via seeds, especially in a controlled environment, showing low vigor at inadequate temperatures. Because of this, the objectives of this study are related to the application of heat treatments on the physiology of seeds and the initial growth of L. pisonis seedlings. After sowing, thermal shocks were applied at different temperatures and exposure times for 90 days, with these treatments being divided into experiments 1 and 2. Emergence, emergence speed index and mean seedling time of emergence were evaluated for 90 days were evaluated. Then, seedling growth, chlorophyll fluorescence, chlorophyll a and b index, maximum quantum yield of PS II, oxidative stress enzymes, lipid peroxidation, hydrogen peroxide and DNA methylation in seedlings were evaluated. In experiment 1, L. pisonis seeds exposed to thermal shock of 30–45 °C (20 h/4 h) showed high seedling emergence (88 %), emergence speed index (0.55), and an efficient antioxidant system, with increased activity of the enzymes SOD and CAT. It was also observed in experiment 1 that fixed temperatures of 40, 45, and 50 °C lead to the loss of seed viability and that high temperatures for long periods cause a decrease in vigor, seed deterioration, damage to the photosynthetic system (PS II) and formation of seedlings with the absence of root system. In experiment 2, the 30–45 °C treatment (21 h/3 h) showed greater seedling emergence (84 %) and emergence speed index (0.80) in a shorter time (23 days), with high activity of the SOD enzyme. It was also observed that exposure to high temperatures for long periods (30–45 °C for 19 h/5 h, 18 h/6 h, and 17 h/7 h) caused a decrease in shoot growth and reduced the dry mass of the roots; however, it did not negatively affect the photo