A total of 20 spring wheat genotypes were evaluated under three growing conditions (optimum, late and very late) at the research farm of the Wheat Research Center, Bangladesh to assess the variation in grain yield, protein and starch content under heat stress. All genotypes were significantly affected by high temperature stress in late and very late sowing conditions, resulting in a decrease in days to heading and maturity, ultimately affecting yield, protein and starch content. Considering yield performance, genotype 'E-8' was best under optimum (6245 kg ha -1 ), late (5220 kg ha -1) and very late sowing (4657 kg ha -1 ) conditions while 'E-40' was the worst. With respect to yield reduction, genotype 'E-72' was heat-tolerant (13% yield reduction) while 'Prodip' (49% yield reduction) was heatsusceptible. On the other hand, it was found that the percentage protein increased as heat stress increased. Under heat stress, genotype 'E-65' and 'E-60' had the highest and lowest protein content (15.5% and 12%), respectively. With respect to starch content, 'Prodip' and 'E-37' had the highest while 'E-14' and 'E-72' had the lowest content (64.8% vs. 62.9%), respectively in all sowing conditions.

Eight modern wheat varieties (viz., Sourav, Gourab, Shatabdi, Sufi, Bijoy, Prodip, BARI Gom-25 and BARI Gom-26) were evaluated to find out the suitable variety for optimum and late sown condition, to find out heat tolerant and heat sensitive variety and to find out the optimum sowing time for a specific variety. The experiment was conducted in the research farm of Wheat Research Center (25°38´ N, 88°41´ E and 38.20 m above sea level.), Bangladesh, under eight sowing times (viz., 8 Nov., 15 Nov., 22 Nov., 29 Nov., 6 Dec., 13 Dec., 20 Dec. and 27 Dec.). Results showed that wheat sown in November 22 to December 20 was significantly better compared to November 08, 15 and December 27, from the studied aspects of yield and yield components. Considering overall sowing performance of all genotypes Shatabdi is the best, followed by BARI Gom-26 (2nd), Sourav (3rd), Prodip (4th), Bijoy (5th), Gourab (6th), Sufi (7th) and BARI Gom-25 (least). In extremely heat stress (November 08 and December 27) condition Prodip was found to be heat sensitive genotype (yield reduction 41.18 and 28.92%), followed by BARI Gom-26 (yield reduction 41.15 and 22.73%). Both in too early and very late heat stress conditions, genotypes Sourav and BARI Gom-25 were found to be heat tolerant. In very early (November 08), variety Sourav (yield reduction 20.47%) is recommended, followed by BARI Gom-25 (yield reduction 27.91%) and in very late (December 27), Sufi is the best (yield reduction 8.60%), followed by Bijoy (yield reduction 11.05%).

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A line × tester analysis was conducted in maize involving 12 lines and 3 testers for grain yield and its components to determine the heterosis as well as general combining ability (GCA) and specific combining ability (SCA) effects. Highly significant genotypic differences were observed indicated wide range of variability present among the genotypes. GCA and SCA variance for yield per plant number of kernels per row and 100-kernels weight were observed significant, which indicated importance of additive as type of gene action for these characters. The ratio of SCA and GCA variances were high for the all character studied that revealed the preponderance of non additive type of gene action. Standard heterosis ranged from -28.29 to 28.41%; -12.29 to 24.38%; -1.11 to 24.44%; -14.75 to 6.67%; -17.24 to 11.26% and -10.94 to 20.83% for grain yield per plant, number of grains per row, number of rows per ear, ear length, ear diameter and 100-kernel weight, respectively. The lines IPB 911-16, IPB 911-12, IPB 911-2, IPB 911-18 and IPB 911-47 showed significant positive GCA effect and simultaneously possessed high mean value indicating that the per se performance of the parents could prove as an useful index for combining ability. The crosses exhibited significant SCA effects involved high x high, high x low, low x high, average x low and low x low general combining parents. The cross combinations with significant positive SCA effect having high mean values might be used for obtaining high yielding hybrids. The information on the nature of gene action with respective variety and characters might be used depending on the breeding objectives.DOI: http://dx.doi.org/10.3329/bjpbg.v21i1.17045