Poa annua ‘remembers’ being mowed

Poa annua plants pass along an awareness of mowing stress to offspring. Learn more about the discovery, the research that inadvertently brought it to light, and what it means for Poa breeding.


Filed to: Poa annua

Poa annua remembers mowing

Preparations for an experiment on a Poa annua green at Penn State’s Valentine Turfgrass Research Center in University Park, Pa. Photo by Pete Landschoot

There might not be a more polarizing golf course turfgrass than Poa annua, and researchers at Penn State University recently added a bit of lore to the love-it-or-hate-it (and sometimes both) nature of the global grass species commonly called annual bluegrass: It remembers — across generations.

“That should freak people out a little bit,” Penn State doctoral candidate Chris Benson says with a laugh. “Every day, it gets more and more advanced.”

No, Poa hasn’t become sapient, but researchers at Penn State recently found it has the ability to pass along to its progeny whether it has been mowed or not — potentially solving a riddle that had vexed David Huff, Ph.D., professor of turfgrass breeding and genetics, for decades.

Huff joined the Penn State faculty in 1994, “looking for a research project the industry would support,” he says. He considered Kentucky bluegrass fairways and fine fescue roughs, but “no one was interested in those.” Huff thought back to his grad school days at the University of California, Davis, and recalled an idea he’d had about Poa annua putting greens.

“The problem in California ... they’re not necessarily against having Poa annua as a putting surface,” Huff says. “It’s that it’s such a mixture of genotypes with differential growth rates. You end up with a bumpy surface at the end of the day. As a breeder, I thought, ‘That’s easy to solve — just breed a uniform strain.’”

What he was suggesting was, in a way, heresy. At Penn State, the unofficial Home of Creeping Bentgrass, young Huff was proposing to pursue the weed that, many believed, could be the ruin of those bentgrass greens. About the time late Penn State colleague Tom Watschke, Ph.D., was studying herbicides to eradicate Poa, Huff was hoping to popularize it. He garnered the support of his colleagues, guidance from storied superintendent Mark Kuhns, CGCS — GCSAA’s 2009 president and 2020 winner of the association’s Col. John Morley Distinguished Service Award — and funding from the USGA. Eventually, Huff developed nearly a dozen elite dwarf strains that showed commercial potential.

“I had some really beautiful lines,” Huff says. “We were growing them all over the place, and it was looking really good. We had disease resistance; they were heat-tolerant with high shoot density.”

As Huff transitioned to seed increase — the process of turning a small amount of seed into progressively larger amounts — he noticed something. “When we weren’t mowing, just collecting the seed, I looked at the plants, and they weren’t dwarf anymore,” he recalls. “They weren’t the high-quality greens-type we had bred. They were wild-type Poa annua. That was really disappointing at the time.”

Editor’s note: Browse all of GCM’s recent Poa annua coverage.

At first, Huff thought wild Poa from a nearby field was sullying his elite strains. The team used herbicides and grew the Poa in plastic. They fumigated. And fumed. No matter what the team did, Huff’s elite strains would always revert to the wild weed at the heart of their genetic makeup.

Poa annua mowing

A variety of greens-type Poa annua before (left) and after three years of seed production increase. The “after” version has reverted back to a more “wild-type” annual bluegrass. Photo by David Huff

“I mothballed the whole seed-breeding program,” Huff says. “Put it in a closet.”

The project was out of sight, but not out of mind. Huff put a succession of three graduate students, including Benson, on the mystery, and their research pointed to epigenetics — the study of how genes can work differently based on environment or behaviors, without changes to the underlying DNA. Epigenetic changes, unlike genetic changes, can be environmentally reversible.

The team found evidence, which was published recently in the journal Crop Science, that the act of mowing Poa annua increases global DNA methylation — that is, the addition of methyl groups to DNA that can change a DNA segment’s activity without changing its sequence — and this process can pass along the environmental effects of mowing to Poa’s unmowed offspring. That’s the remembering part. When mowing stress was removed during seed increase, the Poa blew off the methyl caps and “forgot” the stress of mowing.

While the research showed a global increase in DNA methylation, Huff & Co. don’t know which specific genes are capped. That would require a resource-heavy genomic sequence. But Huff is confident that now that he and his researchers have solved the mystery of his elite Poa’s proclivity to forget, they can successfully overcome it.

“I thought, ‘Hallelujah. Now I know what to do with Poa annua seed production,’” Huff says. “I unmothballed (the previous projects) and set out a trial in 2019 with 44 entries. We developed a novel seed-harvesting technique that allows us to harvest the seed of greens-type Poa annua without letting it revert to wild-type. It’s basically a redo of the breeding program — and we have some beautiful Poas.”

Andrew Hartsock is GCM’s managing editor.