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Improved nitrogen use-efficient cultivars could be the most economically beneficial and environmentally friendly approach to reduce pollution associated with excessive N fertilization. The performance and genetic gain in grain yield and nitrogen use efficiency (NUE) of a historical set of 12 bread wheat cultivars released for a heat-stressed environment were investigated at four N levels (0 (N0), 43 (N43), 86 (N86), and 129 (N129) kg/ha) for two seasons. Averaged across seasons, increasing N level from N0 to N43, N86, and N129 resulted in yield increases ranging from 4−45%, 13–69%, and 34–87% at N43, N86, and N129, respectively. These yield increases were associated with increases in biomass (r = 0.86, P<0.01). Regressing grain yield of cultivars released during 1960 to 2006 against the year of release showed no trend at N0 and positive nonsignificant trends at N43;. however, significant positive trends were found at N86 and N129 with genetic gain rates of 12.65 and 15.76 kg ha−1 year−1, respectively. This gain was associated with progresses in harvest index (HI) at N43, N86, and N129 but not at N0. On the other hand, during the period from 1960 to 1990, the genetic gain in grain yield at N86 was 24.5 kg ha−1 year−1. Regressing NUE against the year of release showed significant linear trends at N86 and N129 (R2 = 0.511 and R2 = 0.477, respectively), but not at N43. The results indicate that breeders improved grain yield and NUE over 46 years under the heat-stressed environment of Sudan although the rate of increase in yield has been slowed down in recent years. Further improvement in NUE might require broadening the genetic diversity and simultaneous evaluation at low and high N levels.

Wheat (Triticum aestivum L.) is known to be negatively affected by heat stress, and its production is threatened by global warming, particularly in arid regions. Thus, efforts to better understand the molecular responses of wheat to heat stress are required. In the present study, Fourier transform infrared (FTIR) spectroscopy, coupled with chemometrics, was applied to develop a protocol that monitors chemical changes in common wheat under heat stress. Wheat plants at the three-leaf stage were subjected to heat stress at a 42 °C daily maximum temperature for 3 days, and this led to delayed growth in comparison to that of the control. Measurement of FTIR spectra and their principal component analysis showed partially overlapping features between heat-stressed and control leaves. In contrast, supervised machine learning through linear discriminant analysis (LDA) of the spectra demonstrated clear discrimination of heat-stressed leaves from the controls. Analysis of LDA loading suggested that several wavenumbers in the fingerprinting region (400–1800 cm−1) contributed significantly to their discrimination. Novel spectrum-based biomarkers were developed using these discriminative wavenumbers that enabled the successful diagnosis of heat-stressed leaves. Overall, these observations demonstrate the versatility of FTIR-based chemical fingerprints for use in heat-stress profiling in wheat.

Drought and salinity are the primary factors limiting wheat production worldwide. It has been shown that a rice stress-responsive transcription factor encoded by the rice NAC1 gene (SNAC1) plays an important role in drought stress tolerance. Therefore, we introduced the SNAC1 gene under the control of a maize ubiquitin promoter into an elite Chinese wheat variety Yangmai12. Plants expressing SNAC1 displayed significantly enhanced tolerance to drought and salinity in multiple generations, and contained higher levels of water and chlorophyll in their leaves, as compared to wild type. In addition, the fresh and dry weights of the roots of these plants were also increased, and the plants had increased sensitivities to abscisic acid (ABA), which inhibited root and shoot growth. Furthermore, quantitative real-time polymerase chain reactions revealed that the expressions of genes involved in abiotic stress/ABA signaling, such as wheat 1-phosphatidylinositol-3-phosphate-5-kinase, sucrose phosphate synthase, type 2C protein phosphatases and regulatory components of ABA receptor, were effectively regulated by the alien SNAC1 gene. These results indicated high and functional expression of the rice SNAC1 gene in wheat. And our study provided a promising approach to improve the tolerances of wheat cultivars to drought and salinity through genetic engineering.

SUMMARYIn non-traditional, heat-stressed environments, wheat breeding programmes were mainly concerned with the introduction and adaptation of high-yielding, heat-tolerant cultivars regardless of the end-use quality. For the recently developed quality-oriented markets, new cultivars should combine the above-mentioned traits with good grain quality to improve economic feasibility of wheat production in these environments. This study aimed to examine the suitability of the conventional sodium dodecyl sulfate sedimentation (SDSS) test for predicting bread-making quality and to evaluate the effectiveness of a prolonged-swelling SDSS test in improving the predictability of end-use quality under heat stress conditions. Conventional and prolonged-swelling SDSS volumes were measured from whole meal of 15 bread wheat genotypes grown for two seasons under two sowing conditions at Gezira Research Farm, Wad Medani, Sudan. Results of correlations of SDSS volumes with total and insoluble protein contents, mixograph peak height and mixograph descending slope indicated the suitability of the SDSS test in predicting bread-making quality under heat-stress irrigated conditions. However, the absence of significant correlations with some quality attributes, such as mixograph peak time and mixograph curve width, demonstrated the non-exclusiveness of the SDSS test for predicting all bread-making quality attributes. The prolonged-swelling SDSS tests did not improve identification of differences among genotypes over the conventional test despite similarly predicting some quality attributes and showing relatively small increases in the correlation coefficient magnitudes with others. SDSS after 10 min from settlement (SDSS10) showed strong correlations with all other SDSS volumes at various times and with most of quality attributes. This suggested that SDSS10 could be used for evaluation of bread-making quality in early generations of the breeding programme in the hot irrigated conditions of Sudan and similar environments.

Canopy cooling in dry heat-stressed areas is regarded as one of the most physiologically efficient way to attain high grain yields in wheat. Twelve wheat genotypes were grown with four N levels in a 2-year field trial to investigate their efficiency to utilize addition of nitrogen for canopy cooling and high chlorophyll accumulation under a dry but irrigated hot environment in Sudan. Both canopy temperature depression (CTD) and chlorophyll content (CC) increased significantly with addition of 43 (N43), 86 (N86) and 129 (N129) kg N/ha compared to zero N (N0) treatment. The two-season average increases in CTD were 33, 59 and 67% at N43, N86 and N129, respectively, relative to N0. The average increases in CC were 15, 22 and 23% at N43, N86 and N129, respectively. However, genotypes showed a wide range of responses to addition of N especially for CTD. The combined genotypic ranges in percent increase of CTD and CC were 19 to 63% and 4 to 22% at N43, 38 to 88% and 13 to 36% at N86, and 34 to 113% and 15 to 28% At N129, respectively. Strong association was found between CTD and CC, which in-turn, was highly and significantly associated with biomass and grain yield. On the other hand, CTD showed significant negative association with harvest index. The results indicate that application of N fertilizer was reflected in a cooler canopy under the dry heat stress conditions of this study. However, genotypic variation in utilizing N fertilizer in canopy cooling necessitate that this should be done in accordance with the response and efficiency of each cultivar. Key words: Nitrogen fertilizer, canopy temperature depression, chlorophyll content, heat stress, wheat.