Today’s turfgrass pathologist has extensive training in molecular biology, genetics, genomics and more. However, back in the day, plant pathologists had to rely on the microscope to intensively study the physical characteristics of fungi. Most turf
diseases are caused by fungi, and the fungal pathogen that causes summer patch was once the topic of fierce debate.
In the 1950s and 1960s, this “patch” disease was called fusarium blight because many Fusarium sp. commonly inhabit soils. The other name was SOB (summer obliteration of bluegrasses). From the late 1960s, there’s a famous photo of President
Lyndon Johnson speaking on the White House lawn. No one can recall the speech, but the distinct “frog-eye” pattern of necrotic Kentucky bluegrass meant one thing: summer patch. Kentucky bluegrass lawns and annual bluegrass putting greens
are susceptible to this severe root disease, but no one knew what pathogen caused these circular dead patches of turf that appeared in the summer.
Hence, the great “turfgrass pathology debates” of the 1970s and 1980s began! There were lively and colorful discussions: Was summer patch caused by Fusarium, nematodes, a bacteria, soil-related factors or maybe even a new fungus?
Richard Smiley, Ph.D., a professor at Cornell University at the time, investigated the fusarium blight problem occurring on Long Island, N.Y., during the early 1980s. He determined the disease was not caused by a Fusarium, but a darkly pigmented ectotrophic
root-infecting fungus he named Phialophora. Even though the fungus name was misidentified, Smiley still gets credit for being the first to extract and isolate the correct pathogen from infected turfgrass roots.
What do all good turfgrass pathologists do when faced with a challenging research problem? They put a graduate student on it! Noel Jackson, Ph.D., (1931-2018) at the University of Rhode Island brought in Peter Landschoot for a doctorate program. In those
days, graduate students were “seen and not heard.” Jackson would drive by the laboratory on a Sunday evening to make sure the light was on, and the future Dr. Landschoot was inside meticulously examining tiny and fine turfgrass roots.
One such evening, Landschoot was about to throw away some pots of dead grass he had inoculated with isolates that looked similar to Smiley’s Phialophora fungus. He took one last look at the roots and noticed they were covered with structures
called perithecia — the “perfect stage” of the fungus useful for positive identification of certain types of fungi.
After close examination, Landschoot first considered the causal agent of summer patch to be a Gaeumannomyces. That fungus is also a root colonizer and causes plant disease on its own and is often associated with summer patch. An isolated and dried perithecia
were sent to John Walker, Ph.D., (1930-2022), a classically trained fungal taxonomist located in New South Wales, Australia. Walker was the curator of the Plant Pathology Herbarium, which contained over 70,000 specimens at the time. Walker said the
organism looked more like a Magnaporthe than a Gaeumannomyces.
Next, Landschoot confirmed Walker’s hypothesis by reproducing the perfect stage of the fungus in the laboratory, because finding the perfect stage in nature is rare. Back then, describing vegetative mycelium only got you so far. To confirm the correct
identity of a fungus, you need to see the spores inside the perithecia. He produced the perfect stage by crossing different strains of the fungus in petri dishes and describing the spores. Sure enough, it was a new species he named Magnaporthe poae.
Although Magnaporthe poae recently has been changed to Magnaporthiopsis poae, it remains an ascomycete fungus responsible for summer patch diseases of turfgrasses. The search for the summer patch pathogen was not as famous as the race to discover DNA
and the double helix, but, if Hollywood made a movie about it, here is the cast:
Landschoot — Tom Hanks; Joe Vargas, Ph.D. — Jack Nicholson; Jackson — Sean Connery; Houston Couch, Ph.D. — Laurence Olivier; Smiley — Dustin Hoffman; Walker — Clint Eastwood; John Cisar, Ph.D. — Carroll O’Connor;
Frank Rossi, Ph.D. — Jack Black.
Thank you, Dr. Landschoot, for your contributions to turfgrass pathology and turfgrass science. Best wishes in retirement from the Pennsylvania State University.
Source: Landschoot, P.J., and N. Jackson. 1989. Magnaporthe poae sp. nov., a hyphopodiate fungus with a Phialophora anamorph from grass roots in the United States. Mycological Research 93(1):59-62.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 23-year member of GCSAA.