Heat tolerance indicators in Pakistani wheat (Triticum aestivum L.) genotypes

The effect of high temperature stress on six wheat cultivars exposed to 35-40 degrees C for 3 h each day for five consecutive days was examined. High temperature significantly affected total proline, soluble protein content, membrane stability index (MSI), yield, and various yield components, and had a direct effect on growth and other physiological attributes of wheat at anthesis and the milky seed stages. The wheat cultivar AS-2002 achieved better osmotic adjustment by accumulating more leaf proline. Higher MSI was also observed in AS-2002, as well as Inqalab-91. The anthesis growth stage was found to be more sensitive to heat stress than seed development at the milky stage. Overall heat stress reduced yield 75% at anthesis and 40% at the milky stage. AS-2002 performed better on the basis of yield and yield components. Seed weight per spike was highest in AS-2002, and lowest in SH-2002. The cumulative response of AS-2002 was better on the basis of physiological and yield attributes. In addition to yield, plant breeders should also include proline and MSI as selection parameter in the breeding program for development of heat tolerant wheat cultivars. Most of the evaluated wheat cultivars/lines were developed for cultivation in the rainfed areas of Pakistan.