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The present investigation was conducted with an objective to study the impact of high temperature stress on yield and its components for selecting heat tolerant genotypes. Nine genetically diverse homozygous genotypes of wheat, viz., PBW 343, WH 283, WH 542, PBW 435, UP 2565, UP 2425, EIGN1, EIGN8 and Raj 3765, were selected to generate the experimental material which comprised six parental and segregating generations (P1, P2, F1, F2, BC1 and BS1 of BC1). Observations were recorded on 12 morphological traits. Based on generation mean analysis, highly significant differences were found among the generations with respect to all the 12 morphological characters studied in timely and late sown environment. It was observed that the performance was influenced by high temperature under late sown conditions, as evident from the decreasing pattern for all the characters. The duration of linear grain growth was greatly reduced as temperature increased in late sown heat stress condition. Grain growth rate among the parental genotypes was highest in UP 2425 and cross PBW 343 × PBW 435 in both the environments. Based on the mean performance of crosses in normal and late sown conditions, it can be concluded that cross EIGN 1 ×? Raj 3765 was found best for 1000-grain weight, biological yield and grain yield. Grain growth rate among the parental genotypes was highest in UP 2425 and cross PBW 343 × PBW 435 in both the environments. These offered promise for selection of wheat genotypes possessing inherent mechanisms for tolerance to terminal heat stress. [ABSTRACT FROM AUTHOR]

Wheat plant architecture has been continually evolving over the past many years primarily in response to increase in the yield potential. One of the most important factors for improvement in the wheat yield potential was the use of Rht genes in the early 1960s. Use of rye chromatin is a successful approach for introducing yield-enhancing genes into elite genetic backgrounds; for example, the use of the lines with 1BL/1RS translocation contributed to productivity and disease resistance. In addition, the role of plant architectures has been analyzed for manipulation of various traits responsible for light capture, photosynthesis, interactions between them and their suitability under various geographic conditions affecting the availability of sunlight. Recent works suggest that this was not just due to shorter stems, but more efficient investment of dry matter in spikes and grains may also be related to more erect canopies and greater leaf photosynthetic activity improving crop photosynthesis around flowering, to more grain sites per unit spike dry matter, and to more stored carbohydrates in stems at flowering. The combined use of Ppd1 and Ppd2 genes also has noticeable individual effects on flowering, but when only one of these genes is active, it results in an intermediate flowering effect. The influence of these genes in making wheat mature at very early, intermediate and late durations is tremendous. The major yield contributing factors in wheat are harvest index, number of grains per meter, in addition to high nitrogen use efficiency which may be used for improving assimilates (source) capacity, including early vigor, stay-green leaf-angle, and remobilization of stem reserves. For developing genotypes with better capacity for utilizing stored assimilate, particularly under stress environments, emphasis should be given for key traits, e.g., grain growth, grain yield, and its components associated with stem reserve mobilization. [ABSTRACT FROM AUTHOR]