Differential effect of whole-ear shading after heading on the physiology, biochemistry and yield index of stay-green and non-stay-green wheat genotypes

Two winter wheat cultivars (the functional stay-green CN12 and non-stay-green CN19) were used to investigate the effects of ear-shading on grain yield and to elucidate the differential mechanisms of different cultivars. The photosynthetic parameters, chlorophyll fluorescence, antioxidant enzyme activities, and chlorophyll contents were measured 0, 15 and 30 days after heading (DAH) under both shaded and non-shaded conditions. The final grain-yield index was also measured. Shading had a smaller effect on the net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), maximal photochemical efficiency of PSII (Fv/Fm) and coefficient of non-photochemical fluorescence quenching (qN) but a greater effect on both superoxide dismutase (SOD) and catalase (CAT) activities in CN12 than it did in CN19. Shading slightly altered the timeframe of leaf senescence in CN12 and may have accelerated leaf senescence in CN19. Moreover, shading had only a small effect on the weight of grains per spike (WGS) in CN12 compared with CN19, mainly resulting from the number of grains per spike (NGS) rather than the 1000-grain weight (SGW). In conclusion, the flag leaves of functional stay-green wheat could serve as potential "buffers" and/or "compensators" for ear photosynthesis, which is actively regulated by the antioxidant enzyme system and prevents yield loss. Thus, a functional stay-green genotype could be more tolerant to environmental stress than a non-stay-green genotype

Associations of NAM-A1 alleles with the onset of senescence and nitrogen use efficiency under Western Australian conditions

© 2018, Springer Nature B.V. Wheat grain yield and protein content are significantly influenced by the onset of senescence and the duration of the grain filling phase. The onset of senescence also affects Nitrogen use efficiency (NUE) through interacting pathways involving N accumulation and translocation of N into the grains. The objective of this study was to relate variation in NUE and its components with two groups of the NAM-A1 gene alleles; (i) early onset of senescence in cultivars carrying the NAM-A1a allele, (ii) delayed onset of senescence in cultivars carrying the Non-NAM-A1a allele (b, c, d) in wheat cultivars grown under Western Australia conditions. A field trial was carried out over two seasons examining 19 cultivars under different N rates and time of N application. The Normalized Difference Vegetation Index was utilized to determine the onset of senescence after anthesis. The early onset of senescence results in high grain yield, harvest index, and NUE due to improvements in the N utilization ability. Accelerating the onset of senescence results in a short grain filling period leading to grain maturity before the onset of unfavourable summer conditions. The function of alleles of NAM-A1 gene in controlling senescence hence the NUE is highly regulated by environmental conditions. This study concluded that the function of NAM-A1a allele induces the onset of senescence with a positive effect on the NUE and its components under Western Australian conditions