On-field assessment of the environmental modulation of malting quality in barley crops

Abstract

Malt extract is the most relevant parameter describing malting quality in barley. The observed differences in malt extract from crops grown in different environments are complex to explain, and their interpretation might represent an opportunity to improve malting quality for barley crops grown under field conditions. Although the effect of some grain attributes on malt extract are overall known (e.g. protein content and grain size) other are less understood and are complex to replicate across experiments, with few evidence of how they are controlled by the environment during grain filling (e.g. hordeins and pasting properties). Four commercial malting barley cultivars were sown on eleven sowing dates across four years to explore a wide range of thermal conditions during grain filling. Contrasting nitrogen availabilities were included to promote variability in the protein content. Grain plumpness, protein content, pasting temperature, and the amount of D- and γ-hordeins showed a significant effect on malt extract. Protein content showed a negative effect on malt extract only when it was above a threshold value of ca. 10 %, although that threshold varied between cultivars. Pasting temperature presented a significant interaction with protein content. D-hordein showed a negative effect on malt extract only when the protein content was below the threshold, explaining some of the contradictory results reported in the literature. Evidence of a negative effect of γ-hordeins on malt extract was found as well. The period between pollination and physiological maturity was arbitrarily divided into thermal-time intervals, and correlation analyses were performed between mean temperature during each period and the grain attributes affecting malt extract. For all the cultivars, only two attributes were found to be modulated by the thermal environment explored by the crop during grain filling: pasting temperature was positively correlated to the mean temperature explored by the crop during the middle of grain filling, whereas grain plumpness was negatively correlated with the mean temperature during the second half of grain filling. Quantitative models reported in the present study in addition to offering an explanation of how malting quality is shaped in the field, constitute a useful tool for agro-climatic zoning for the suitability of high-quality malting barley production.