Bedi, SeemaMandeep Kaur2023-12-112023-12-112023Mandeep Kaur (2023). Impact of heat stress on germination and growth in wheat (Triticum aestivum L.): Physiological and biochemical mechanisms (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.https://krishikosh.egranth.ac.in/handle/1/5810202452The present study was conducted with the objectives to screen a diverse set of wheat genotypes for thermo-tolerance and to investigate morpho-physiological and biochemical basis of thermo-tolerance under early sown conditions in Punjab. 467 wheat genotypes (winter wheat x spring wheat) were screened for high temperature tolerance at three temperatures viz., 25oC, 30oC and 35oC under laboratory conditions. Sixty genotypes showing maximum coleoptile length at 30oC were selected and grown in the field at three dates of sowing viz., early (20th October), timely (14th November) and late (5th December) in the years 2019-20 and 2020-21 respectively. Under early sown conditions (ambient temperature ranging between 25 to 28oC), the selected genotypes showed higher percentage of emergence, early growth vigor, root length (at 25 DAS), plant biomass (at 25 DAS), leaf area (at 90 DAS), chlorophyll content in flag leaf (at 90 DAS), tiller numbers, number of spikelets per spike, spike length, 100 seed weight and grain yield per plot as compared to timely and late sown conditions. From these, ten high yielding and two low yielding genotypes were identified. Biochemical estimations and root architecture studies were performed on these ten high yielding genotypes (heat tolerant) and two low yielding genotypes (heat sensitive) at seedling stage. The heat tolerant genotypes showed higher sugar, protein, proline and α-tocopherol content. Higher activity of antioxidant enzymes was observed in heat tolerant genotypes as compared to heat sensitive genotypes. Also, the tolerant genotypes showed more number of seminal roots, nodal roots, root branches and root length as compared to heat sensitive genotypes.EnglishThesis