Researchers crack low phytate soybean puzzle

LINDELL BEACH, B.C. – U.S. researchers have made a breakthrough in their attempts to increase available phosphorus content in soybeans to improve animal nutrition.

Reducing phytate is key to making more phosphorus available to livestock because it is the principle storage form of phosphorus in plant tissue but is indigestible for non-ruminants.

The conventional belief has been that low phytate seeds have poorer germination and emergence, but recent research is suggesting otherwise.

A study published inCrop Sciencefound that one modified soybean variety had better seedling field emergence than the control seeds, which had normal phytate and phosphorus values.

The performance of this soybean line, developed by the U.S. Department of Agriculture, proves that it’s possible to improve seed germination and field emergence of crops of modified phosphorus soybeans.

“Based on our experience with the North Carolina line, soybean breeders working with the low-phytate trait now know that good seed germination and emergence is an attainable objective,” said Katy Martin Rainey, assistant professor of soybean breeding and genetics at Virginia Tech and one of the study’s authors.

“Our study provides breeders with critical insights on how to do this.”

Rainey said the total amount of phosphorus in the seeds is not increased. Instead, its allocation to different forms or molecules is altered, making more phosphorus available.

“The total phosphorus content is the same in the seeds of normal versus low phytate seeds, but low phytate soybean seeds have three times more inorganic phosphorus because there is an inverse relationship between the two,” she said.

“Low phytate soybeans can be labelled modified phosphorus soybeans, or high inorganic phosphorus soybeans. (Another) label for low phytate soybeans is high bio-available phosphorus soybeans. For nonruminant animals, phytate is indigestible whereas inorganic phosphorus is easily digested and absorbed.”

The team studied six varieties with modified phosphorus content and two with normal content. The studies were conducted in 12 environments in six locations over two years in the U.S. Midwest and southeast.

The researchers recorded variations in the levels of total phosphorus, phytate and inorganic phosphorus content throughout the environments and variations in seedling emergence ranging from a mean of 45 to 96 percent. The results were attributed to variables in soil phosphorus content, soil type, soil temperature, moisture conditions, and possibly disease pressures.

The study focused on soybeans, but other crops could also benefit.

“The data are definitely applicable to other crops such as common bean and other grain legumes, barley and wheat if lower seed phytate is, or becomes, an objective for breeding in those species,” said Rainey.

“The seedling emergence data are especially critical to defining the problem in other crops. The phosphorus content data are somewhat specific to soybean, though the information on variation over environments might be useful in other crops.”

She said it can be a matter of debate whether lowering phytate reduces seed germination, field emergence and seedling vigour in species for which low phytate mutations have been identified. Low vigour is still the subject of research.

“We are fairly certain that the problem of low vigour seedlings is often a byproduct of reducing phytate in seeds,” she said.

“So in our study, the seedlings of most varieties had low vigour because they came from low phytate seeds produced by low phytate varieties. A focus of my research is to determine how to improve vigour in low phytate soybean seedlings. I am fairly certain it can be achieved because we have observed a low phytate soybean variety with high seedling emergence. I believe this can be done with crop breeding, by designing the appropriate crosses and by using various tools to select simultaneously for modified phosphorus content and excellent seedling vigour.”

Rainey said researchers still face challenges.

The biggest one is to identity preservation and market development, a problem common to all modified seeds. It is one thing to develop soybean cultivars with more perfect seed composition and agronomic performance, but much harder to segregate the special bean from the mass production of soybean seeds.

It is also expensive to develop a market for the special beans, although it can be done if a trait is valuable enough.

Rainey said high oleic soybean oil is a good example. It can be challenging to change animal feed formulations because the factories that produce the feed are large and factors that affect their bottom line are complex.

It will be at least five years before modified seeds will be commercially available, although soybean breeders have access to the mutations.

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