Risk of Late-Maturity Alpha-Amylase

Northwest Minnesota saw two unusually cool mornings last week, with minimum temperatures dipping well below 50°F  on Wednesday and Thursday morning (Figure 1). This is a cause of concern for the earliest-seeded spring wheat. Warmer temperatures during grain fill will result in higher Hagberg Falling Number (HFN) values.  Conversely, cooler temperatures will yield, on average, lower HFN. A short period of very low nighttime temperatures (< 50°F) very late in the grain fill period, however, is enough to yield a disproportionate increase of α-amylase in the seed. This phenomenon is referred to as late-maturity α-amylase (LMA). 

Figure 1 - Daily minimum temperature recorded by NDAWN weather stations
across eastern North Dakota and northwestern Minnesota on June 16th, 2025.

LMA is a recessively inherited trait. In standard height wheat varieties, the expression of the trait is constitutive, allowing breeders to effectively select against the trait. In semidwarf wheat varieties, the expression of the trait, however, is highly variable and dependent on a cool temperature shock during the second half of the grainfill period. Identifying which semi-dwarf varieties are at risk for LMA has, to date, been cumbersome because the cool temperature shock does not happen every year.  

A spring wheat variety that has inherently lower HFN and encounters lower temperature during grain fill and/or the conditions that trigger LMA can have an HFN test below 300 seconds even in the absence of sprouting and the associated degradation of the starch and the functional milling and baking qualities. When elevators use the HFN test to determine sprout damage and the test yields a score less than the lower limit of 300 seconds,  it is impossible to tell whether the low test value is a result of sprout damage, the presence of late-maturity α-amylase, or the inherent characteristics of the variety.

You can help the spring wheat breeders in the region to get a better handle on this problem by submitting your HFN test results for individual fields in this Google Form.