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ThesisItem Open Access Evaluation of seed vigour parameters for heat tolerance in bread wheat(CCSHAU, 2014) Arun Kumar; Dahiya, O.S.Wheat (Triticum aestivum L.) is a widely adapted crop. It is grown from temperate, irrigated to dry and high-rain-fall areas and from warm, humid to dry, cold environments. The genetic purity, physical purity, viability, vigour and uniform seed size are the most important parameters to determine the quality of seed. High seed germination and vigour are pre- requisites for the success of stand establishment of crop plants. Generally stress (moisture/heat) has deleterious effect on germination and vigour of crop.The present investigation was carried out at the department of Seed Science and Technology, CCS Haryana Agricultural University, Hisar. The material comprised of six each heat tolerant and susceptible varieties which were sown on two date i.e. normal (19th, 20th November) and late sown (19th, 20th December). The observations were recorded at grain filling stage (heading to maturity). Heat tolerant varieties had performed better at different stages of seed development in comparison to susceptible. Heat tolerant varieties were found significantly higher for seed weight, seed moisture content, germination, seedling length, vigour index-I & II, seedling dry weight and than susceptible varieties under normal and late sowing condition in both the year. Heat tolerant varieties were recorded significantly lower for days to heading, physiological and harvestable maturity. It means heat tolerant varieties mature earlier than susceptible. Commonly varieties had performed better for all characters studied in normal than late sowing at all stages of seed development. Heat tolerant varieties recorded higher for membrane Thermostability and lower for chlorophyll fluorescence. This might be effect of heat stress during seed development. Both vigour index-I and II were significantly and negatively correlated with maximum, minimum and difference of temperature but positively with sunshine hour and relative humidity in both the years of data recording. It means that as optimum temperature for cultivation of wheat is increasing then vigour of the seed will be decreases. For normal as well as late sown heat tolerant varieties having more DHA, peroxidase, catalase and superoxide dismutase activity at all stages than heat susceptible. All stress enzyme activity was higher in late than normal sowing which was in concurrence with high temperature during seed development. Number of grains per spike (average of five plants), number of grains per spike and grain yield per plant was higher for normal sown than late sown in both the year. Varieties have performed better in second year than in first year. Heat tolerant has performed better than susceptible for almost all agronomic traits. Based on both the tests it can infer that there was better relative storability of the variety for normal than late sowing over the years at all stages of storage.