Environmental Impact on Cereal Crop Grain Damage from Pre-harvest Sprouting and Late Maturity Alpha-Amylase

Pre-harvest sprouting (PHS) and late maturity alpha-amylase (LMA) result from increased alpha-amylase (AA) activity in wheat, rice, barley, rye, and maize grain prior to harvest leading to undesirable degradation of seed starch. The starch degradation can reduce grain quality and thus crop values by up to 30% and in severe cases make them unfit for human consumption and usable only as animal feed. Specific environmental conditions of temperature and rain occurring at or near seed maturity lead to the onset of PHS or LMA. While environmental effects cannot be controlled in the field, genetic resistance/tolerance is possible. Genetic control of PHS and LMA is complicated by the numerous factors involved in modulating AA which ultimately leads to starch degradation. This includes multiple enzymatic pathways, multiple plant hormones, a complex signaling pathway, several physical factors, and potential protein inhibitors that have been found to mitigate AA. Here we review how AA activity is measured; what environmental, physical, chemical, and genetic factors influence it; and perspective on how PHS and LMA can be best mitigated with changes in climate favoring an increase in their occurrence in cereal crops, which form the bulk of calories consumed worldwide.