Wheat Quality: Late Season Alpha-Amylase

Robert Kratochvil, Extension Agronomist, University of Maryland

I have heard reports that the first wheat harvested on the Delmarva this year is having falling numbers ranging between 160 and 320s.  The falling number measurement is used by the industry to assess the amount of starch (flour) damage that has occurred due to pre-harvest sprouting.  When falling number is below 275s, the quality of the flour milled from the wheat may not be suitable for some of the end-use products made with it.

This low falling number report is perplexing because there have not been the weather conditions (rainy days) that are conducive to pre-harvest sprouting. So, what happened?  Besides a period of rainy weather just prior to harvest causing pre-harvest sprouting that results in an increase in alpha-amylase (the enzyme that cleaves some of the starch into sugar and is released in a wheat kernel when water is imbibed) causing lower falling numbers, there is also a genetic cause that is triggered by temperature shock.  This genetic cause is called late maturity alpha amylase.  It is triggered by a temperature shock (change from lower to higher temperatures or vice versa) in a relatively short period of time (i.e. 2-3 days).  It has its greatest impact if the temperature shock occurs when the wheat is approximately 25-30 days past flowering.  May temperatures were like a roller coaster ride with considerable ups and downs during the month.  The first wheat being harvested (and the wheat that is reported to have the lower falling numbers) was flowering around the last week of April.  A review of May temperatures on the Lower Eastern Shore indicated that temperatures roller coastered from 57 degrees on the 13th of May to 91 degrees on the 17th of May and then back down to 64 degrees on the 24th of May before going back up to 80 degrees on the 27th of May.  I think these temperature fluctuations may have been enough of a shock to trigger this phenomenon of late maturity alpha amylase.  The reason the range for the falling numbers is 160-320s is likely due to varietal differences.

I believe that these lower falling numbers will be limited to mid-Shore and south and possibly the southern part of Maryland west of the Bay because as the wheat production region moves north and west the wheat flowered as much as a week to 10 days later allowing it to avoid the temperature shock extremes during the most critical period.  It would be helpful to get information about the varieties that have had the lower falling numbers (below 275s) as there currently is no information about which are susceptible to onset of late season alpha-amylase.

 

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