A wet fall across the Prairies provided the ideal conditions for pre-harvest sprouting in cereal crops. As a result, falling numbers tests have come to the fore as a quality assessment tool for buyers, with some grain companies performing a falling test on all wheat samples before purchasing.
While, for the most part, harvest conditions were the most difficult in Alberta and Saskatchewan, many regions of Manitoba also saw significant sprouting issues, says Rejean Picard, Manitoba Agriculture farm production adviser. It didn’t help that many farmers were growing the variety Brandon, which has been the most popular CWRS variety across the province lately. “Brandon has many features that producers have done very well with over the past few years, but unfortunately, the wet harvest did not favour this variety this year,” says Picard, who has talked to many producers who have had low falling numbers.
What is the falling numbers test?
The falling numbers test estimates the amount of sprout damage in wheat, barley or rye. It measures the amount of alpha-amylase, an enzyme important in germination which is present in the grain. Alpha-amylase converts starch in the grain kernel into energy for the growth stage of the plant, so the more alpha-amylase that is present the greater the potential for sprouting.
“Falling number” is the time, in seconds, it takes for a plunger to fall through a heated slurry of ground grain. The plunger falls more quickly when more alpha-amylase is present. The faster it falls the lower the number — so a lower falling number means there is more sprout damage.
Many producers this year are seeing lower falling numbers than usual in their wheat and cereals. If they are aiming for milling-quality wheat, they may have issues marketing their grain.
In flour, alpha-amylase breaks down starch into sugars that feeds the yeast, allowing fermentation to occur and making baked products rise and increase in volume. Ensuring there is the right amount of this enzyme present starts with the falling number test.
Millers are looking for consistency above all else. Different companies may have different tolerances for falling number, but generally most wheat shipments must achieve a falling number of 300 seconds or higher. Most Canadian milling wheat usually can achieve 350 to 500 seconds.
The Canadian Grain Commission’s (CGC) Harvest Sample Program (HSP) includes a falling number test for wheat at no cost. A CGC spokesperson said in an email that there has been an increase in HSP participation since falling number results were added in 2018, and that producers are more interested in falling number results this year because of the wet harvest. By mid-December 2019, the CGC had analyzed 5,120 samples for the CWRS wheat class, and 1,204 samples for the CWAD class. Of the CWRS samples, 69 per cent had falling numbers higher than 200 seconds and 56 per cent of the CWAD samples had falling numbers higher than 300 seconds.
“Because of the harvest conditions we had this fall, the falling number is not a grading factor, but it is definitely a marketing factor,” says Picard. “A farmer was telling me the other day that a No. 2 wheat, if it has a falling number below 260, the buyer would not accept it because they would consider it feed wheat. Even though the CGC might grade it as a No. 2 based on the amount of sprouted grain in it, if the falling number is too low when the company tests for it they might reject or heavily discount it.”
More buyers testing falling numbers
Wheat breeder, Santosh Kumar of Agriculture and Agri-Food Canada’s Brandon Research and Development Centre says that the industry is definitely more inclined to perform falling number tests this year than it was five or six years ago.
“There was a major market class reorganization where a number of varieties were moved from the premium-quality wheat class into the Canada Northern Hard Red spring class,” says Kumar. “Part of the reason for that was gluten strength and part of it was how the grain behaves just prior to harvesting, or what stage it is at when it’s harvested, stored and shipped. If there is damage to the grain by either sprouting or poor protein concentration, it starts to reflect on the bread-making quality.”
Grain marketers and seed growers began to look for ways to detect these issues in grain and started using the falling number test, which can be done at the elevator or grain facility.
Breeders improving sprouting resistance
Plant breeders and scientists also use the falling numbers test to evaluate pre-harvest sprouting resistance qualities in new wheat varie-ties, something that has been a major focus of breeding programs in recent years.
For the past five years, Kumar has been working to develop premium- quality hybrid spring wheat varie-ties for the eastern and northern Prairies. Pre-harvest sprouting is a major issue in these regions, so Kumar and his colleagues are taking a multi-pronged approach, encompassing plant physiology research, genomics and genetics to improve sprouting resistance as well as resistance to diseases like fusarium and rust.
“Within AAFC there are multiple centres that are working on not just the research aspect of it, but also the plant breeding,” says Kumar. “We are trying to identify new sources of resistance to pre-harvest sprouting resistance and put them into new varieties that we are developing. We are doing a lot of field work and applied work to bring that trait into the elite germplasm and finally into better varieties.”
In the past, many wheat varieties available had only Poor to Fair ratings for pre-harvest sprouting resistance, but Kumar’s program has made a lot of progress. There are a number of new varieties and breeding lines with sprouting resistance rating to Good.
Recent Canadian Western Red Spring Wheat (CWRS) varieties that have sprouting tolerance include AAC Jatharia (distributed by SeCan) which is rated Good, and AAC Cameron VB (distributed by Canterra), which is rated Fair.
AAC Warman (SeCan) will be available in 2020 and is rated as Fair for sprouting. In 2021-22 growers can look for AAC Magnet (FB Genetics), rated Good for sprouting, and AAC LeRoy (Alliance Seeds) which is also rated Good. AAC Redstar is a new, early-maturing CWRS developed for the Parkland region that also has a Good sprouting resistance rating and should be available to farmers in the next three to four years.
Major funders for the spring wheat program are AAFC, the Canadian National Research Consortium, Western Grains Research Foundation and some minor funds are also coming from a number of provincial governments.
What causes pre-harvest sprouting?
Pre-harvest sprouting occurs when germination begins while the grain is still on the plant. It largely occurs during warm, moist pre-harvest conditions. According to information from Washington State University, rain at temperatures of around 26 C is less likely to cause sprouting than rain when temperatures are around 15 C. Low falling numbers are also more likely when there have been multiple rainy days in a row, as germination is more likely to begin the longer wheat stays wet, even in varieties with good sprouting resistance.
Pre-harvest sprouting is not the only possible cause for a low falling number — a low number can also be a result of late-maturity alpha-amylase (LMA). In this case, heat or cold shock during late grain maturation produces alpha-amylase, although the grain may look visibly sound.
It’s not always easy to visually detect early signs of sprouted grain. For a visible sprout to emerge from the kernel it can take constant rainfall for a number of days, but it is possible to detect a small root protruding from the germ end after as little as 24 hours. As the grain dries, the root can shrink back into the kernel leaving a small crack or crater at the germ end or the germ may break off entirely.
Storing sprouted grain
Some research suggests that storing mildly sprouted grain (with falling number around 220 to 300 seconds) at warm temperatures (23 to 35 C) for a few months can increase its falling number as the alpha-amylase degrades over time But the falling number of badly sprouted grain will not improve with storage as it’s likely there is too much alpha-amylase present or starch damage has occurred.
“For sure, get the grain on aeration right away to try and cool it down,” says Picard. “I know this fall, some producers had it on aeration, and after awhile decided they were better off to dry it to make sure it would be good for long-term storage, so it’s important to get it down to the right moisture content or they can risk having other issues such as mould.”