Increasing agricultural water use efficiency is a critical strategy for addressing the global water deficit. Supplemental irrigation (SI) has been identified as an effective means of achieving this goal while maintaining crop yields. However, there is a lack of understanding regarding the impact of SI on crop quality, which is an important consideration. This thesis focuses on the effects of SI on starch quality in wheat (Paper 1) and barley (Paper 2). The results demonstrate that SI has significant effects on crop starch quality, which underscores the importance of understanding the impact of different agricultural environmental conditions on starch quality (Paper 3).
Paper 1 mainly indicates that SI has little effect on yield and starch molecular structure in wheat, but significantly decreased the relative crystallinity of starch and increases the relative content of B-type granules. Additionally, the study found that tillage practices can influence the effect of SI on starch, with flat tillage enhancing the effect on granule specific surface area and viscosity. In vitro digestion analysis showed that SI significantly enhanced the resistant starch content of starch, indicating SI treated wheat provides starch provide the trait of slowlydigestion characterization.
In Paper 2, the effects of SI on the yield and starch quality of two barley genotypes, Golden Promise (GP) and amylose-only barley starch (AO), were analyzed. GP is a common barley genotype in Europe and AO is a GMO-mutant which is interesting due to its high resistant starch content. The results showed that SI decreased the photosynthetic capacity, grain yield, and starch content in both the endosperm and leaves of GP, while AO was more tolerant to SI.Starch molecular structure analysis revealed that SI treatment increased the relative content of amylopectin side chains with DP>36 in GP and that of amylose side chains with DP≤24 in AO.The transcriptomic analysis suggested that these changes may have been linked to increased expression of SSIIa in GP and decreased expression of SSI and SSIIa in AO. Furthermore, FTIR analysis revealed that SI treatment led to a reduction in the 1047/1022 cm-1 ratio in both GP and AO, indicating changes in the granular surface of the starch. In addition, the size and crystallinity of starch granules increased with SI treatment, which is opposite to the effect of SI on wheat in Paper 1. The study also showed that SI treatment led to an increase in the content of rapidly digested starch in GP but increased the proportion of slowly digested starch in AO, which contrasts with the effect of SI on the digestion of wheat starch. This finding highlights the different effects of SI on the structure and digestion of starch in wheat and underscoring the importance of considering crop type when assessing the impact of SI on starch
quality.
Above two papers found significant effects of SI on the multi-scale structure of starch in wheat and barley, as well as the digestibility of starch. Botanical sources and genotype were found to be a significant factor affecting the effects of SI on starch and highlight the complexity of agricultural treatments on starch quality and the need to investigate the underlying mechanisms. Therefore, in Paper 3, I reviewed the impact of various environmental conditions on starch biosynthesis, structure, and physicochemical properties. Water stress, heat stress, high nitrogen, salinity, shading stress, and CO2 stress can all affect starch quality in various ways. I proposed the classification of agricultural treatments as a fifth type of starch modification, in addition to chemical, physical, enzymatic, and genetic methods. This study highlights the potential of agricultural modification to create functional starches that meet the demand for clean label foods and ingredients. Further research in this area is important for enhancing the functionality of starch in both food and non-food applications