The response of germinating sunflower seed to heat tolerance induction

Vigour of pre-emergent sunflower (Helianthus annuus L.) seedlings is reduced when daily peak soil temperatures exceed 44°C resulting in poor emergence. Seedlings of sorghum (Sorghum bicolor L. Moench) are known to acquire thermotolerance to temperatures of 45–50°C as a consequence of a brief pre-exposure of the imbibing seed to 40°C. The aim of this investigation was to determine whether sunflower seedlings can acquire heat tolerance. Seed of three sunflower cultivare was used to compare the response to heat shock of 2 hr at 50°C in untreated and thermotolerance induced incubated seed. Heat tolerance was induced by exposure of the imbibed seed to 40°C for I h, 24 h before the heat shock. The response was assessed by comparing germination percentages and hypocotyl lengths. Germination percentages and hypocotyl lengths of seedlings differed significantly for cultivars. Hypocotyls of seed pre-exposed to 40°C were shorter than untreated seed indicating the inability of sunflower to acquire thermotolerance.