Abstract
An experiment was conducted to screen different wheat genotypes for heat tolerance at the metabolite level. The experiment was laid out in randomized complete block design (RCBD) with split plot arrangement having four blocks. Main-plot treatments consisted of H-0(control) and Hi [(Heat imposition from complete emergence of spike to grain filling initiation (Feekes Scale = 10.50-11.00)]. Subplot treatments consisted of 11 wheat cultivars ('Punjab-2011', 'AARI-2011', 'Galaxy-2013', 'Millat-2011', 'Aas-2011', 'Fareed-2006', 'Chakwal-50', 'Mairaj-2008', 'Pakistan-2013', 'NIBGE-NIAB-1' and 'Kohistan-97'). 'Aas-2011', 'Chakwal-50' and 'Mairaj-2008' manifested increment in total phenolic content, glycine betaine and proline under heat stress compared with the control plots while all other genotypes showed a decline in secondary metabolite activity. Significantly, the lowest malondialdehyde (MDA) concentration was recorded in 'AAS-2011' (0.91 mu mol g(-1)) and 'Chakwal-50' (0.96 mu mol g(-1)) while the highest was recorded in 'Pakistan-2013' (1.24 mu mol g(-1)). Minimum decrease in grain yield under heat stress was observed in 'Aas-2011' (29%) followed by 'Chakwal-50' and 'Mairaj-2008' (32%) whereas the maximum was observed in 'AARI-2011' (48%). 'Aas-2011', 'Mairaj-2008' and 'Chakwal-50' manifested heat tolerance; 'Pakistan-2013', 'NIBGE-NIAB-1' and 'Kohistan-97' showed heat susceptibility while all the remaining cultivars demonstrated medium heat tolerance on the basis of metabolite, membrane stability and yield components.