Variation of seed germination response to temperature in tomato landraces: An adaptation strategy to environmental conditions

Abstract Landraces have developed over time, through adaptation to their natural and maternal growing environment and originated by adaptive responses to local habitats. The objective of the present study was to study seed germination response to temperature and to compare heat and cold tolerance of landraces and their relationships with air temperature. We aimed to find if there is a relationship between heat and cold tolerances with mean annual temperatures in which the landraces are growing. The cumulative temperature response index (CTRI) for germination response to temperature was calculated based on the estimated cardinal temperatures for germination rate and percentage. The cardinal temperature for germination percentage of tomato landraces ranged from 7.7 °C to 9.9 °C for the base temperature, 16.6 °C–23.5 °C for the optimum temperature and 35.5 °C–43.6 °C for the ceiling temperature. The cardinal temperature for germination rate in the 5th percentile ranged from 9.9 °C to 12.8 °C for the base temperature, 26.7 °C–30.9 °C for the optimum temperature and 36.0 °C–39.0 °C for the ceiling temperature among the tomato landraces. The highest Heat CTRI (H-CTRI) was obtained in Gorgan, Shiraz and Varamin landraces (5.6) and the highest Cold CTRI (C-CTRI) were calculated in Sanandaj landrace (5.7). We found significant relationships between long-term annual air temperature and CTRIs, showing an adaptation to environmental conditions in which the tomato landraces are grown for a long-term period. Adapted landraces to cold conditions such as Sanandaj had a higher C-CTRI thereby they tolerate low temperatures. Also, adapted landraces to warm conditions such as Gorgan, Shiraz and Varamin had a higher H-CTRI and more tolerant of high temperatures.