Singh, S.K.Patel, Utkarsh2022-12-202022-12-202022M/PBG/351/2020-21https://krishikosh.egranth.ac.in/handle/1/5810190703A research was performed out at the wheat development section, Dr. RPCAU, Pusa, Samastipur, Bihar during rabi 2021-22, to assess the bread wheat lines for terminal thermal stress under delayed sowing conditions. Variability, genetic progress, correlation, path analysis, molecular characterisation and diversity analysis were all investigated. 25 genotypes were cultivated in non-stressed and stressed conditions. Three replications of the lines were set up in each environment using Randomized Block Design. Analysis of variance in two circumstances showed considerable variations amongst the lines for most of the characters under investigation. The traits like tillers per plant (TPP), grains per spike (GPS), grain yield per plant (YPP) manifested high heritability coupled with high genetic advance as percent of mean. YPP was found to be significantly positively associated, with TPP, GPS, chlorophyll content (CHL) and thousand grain weight (TGW). However, a negative association with canopy temperature (CT) and heat susceptibility index (HSI) was noted under both conditions. YPP was non-significantly negatively correlated with days to 50% flowering (DFF) in stressed scenario. CT revealed negative association with YPP, GPS, and CHL. However, it showed significant positive correlation with HSI. This has signified that raised CT has been in close relation with yield loss under thermal stress scenario. The characters such as, TPP and GPS are of prime importance in the process of selection for yield improvement, as they show positive association with grain yield. GPS and TPP had a very high direct effect on the yield and also all other traits gave indirect contribution to the yield through these traits. 25 lines were distinguished into seven and six clusters in timely and late sown scenarios respectively. In non-stressed scenario between cluster I and IV highest inter cluster distance was reported, followed by cluster V and VII, cluster I and VII. Whereas under thermal stress, cluster VI and V reported highest inter cluster distance, followed by cluster IV and V, cluster III and V. Leaf area devoted highest percentage towards the overall divergence followed by leaves per plant, TPP and TGW under timely sown condition. Highest contribution in the overall divergence was reported by LA followed by TPP and LPP. This suggests that selecting genotypes for these characters might be beneficial for further use in breeding programmes in the corresponding environments. Genotype HTWYT-7, HTWYT-15 and HTWYT-23 can be selected as suitable donor parent for characters like TPP, LA, LPP and YPP under timely sown conditions. HD 2967 can be used in breeding programmes for traits like TPP, GPS, LA, LPP, YPP and least CT and HSI in late sown conditions. A set of 10 microsatellite markers have been utilised for estimating the diversity at the molecular levels in the subjected material. These markers have produced clear, scorable and sharp bands for all of the given lines. Based on molecular diversity the 25 lines were separated into 8 clusters. Highest number genotypes were accommodated in cluster IV and lowest in cluster VII. High similarity coefficient was found between HTWYT-4 and HTWYT-5 followed by HTWYT-6 and HTWYT-7.EnglishThesis