Physiological and biochemical contrasting responses associated with growth performances in sunflower seedlings after a cold stress

In the climate change context, extreme events have become more frequents. Spring is the sunflower sowing season. Late frosts events or several days of low temperatures often occur causing delays in crop growth and even losses in plant density per hectare. Tolerance to low temperatures is an important trait considering that the sunflower production area is expanding to marginal regions with suboptimal growing conditions. Furthermore, an early sowing practice to maximize the sunflower growing period is commonly implemented in Argentina and in others countries. An interesting approach to identifying tolerant genotypes in breeding programs is exploring biochemical and physiological traits involved in growth recovery after cold exposure in sunflower seedlings. In this research, the physiological and biochemical responses of two contrasting sunflower genotypes were evaluated. Commercial hybrids Pampero (PM) and Sierra (SA) were exposed to cold treatment at 5°C for 96 hours. Growth performance, malondialdehyde content, superoxide dismutase and catalase enzyme activities, chlorophyll content and electrolyte leakage were assessed at 0, 24, 48 and 72 hours after the cold treatment. Different patterns between genotypes were observed. The sensitive genotype PM showed higher oxidative damage, lower membrane stability, reduced catalase and reduced superoxide dismutase activities, in contrast with the tolerant genotype. Moreover, tolerant genotype SA showed a great capacity to recover the chlorophyll content and restart growth while the sensitive genotype showed only a slight increase in chlorophyll content and a clear delay in growth.