Tuesday, July 2, 2013

Bacterial Etiolation and Decline

Paul R. Giordano and Dr. J.M. Vargas, Jr.
Michigan State University

Early characterization of the new disease named bacterial etiolation and decline, and the pathogen that causes it - Acidovorax avenae subsp. avenae (for the sake of my sanity, I will call it Acidovorax from here on) have been well documented .  Much of the controversy surrounding the disease comes from its unpredictable and inconsistent symptomology in nature (on the golf course).  A key constraint in the progress of the research has been the inability to consistently reproduce the etiolation or abnormal elongation symptoms.  Golf courses afflicted with this disease TYPICALLY show symptoms of yellowing and elongation as summer temperatures begin to rise into the 80’s. As temperatures progress into the 90’s and humidity is high, these chlorotic, overgrown areas begin to thin, and eventually die.  Early research on creeping bentgrass with Acidovorax showed severe damage and blight; however, the etiolation symptom was not reliably reproduced.  This posed a problem, particularly among turfgrass pathologists who have tirelessly argued over whether this is a “true” disease or not.

Bacterial etiolation on plots at HTRC.

Trial and error and continued research efforts have (finally) given rise to reliable induction of etiolation symptoms through inoculation of the bacteria into roots of creeping bentgrass plants (data currently submitted for publication). This confirms the association of Acidovorax with etiolation in a controlled environment, however, unless it can be done in a field setting, there will always be questions related to the true cause and nature of the disease.

Bacterial streaming from a turfgrass leaf.
Over the past 4 years, field research on bacterial etiolation at numerous sites around the country has taken place. Initial trials were set up at Quail Hollow in Charlotte, North Carolina, and subsequent research has been conducted on golf courses in Dayton, OH, Toledo, OH and, of course, East Lansing, MI.  The studies on golf courses have provided some interesting results, however, the disease symptoms are often sporadic, and conducting research on in-play, high-end putting greens has many inherent limitations. This is why the Hancock Turfgrass Research Center is an ideal proving ground for disease research: we have complete control of the management practices and freedom to encourage disease in a very deliberate manner. 

Unfortunately, achieving consistent etoliation the past three years have been relatively unsuccessful. Last summer we observed short-lived etiolation during a hot spell in mid-July, but symptoms were inconsistent and not uniform throughout the study.  Since Ph.D. students are (ideally) around for about 4 years...the clock is ticking for some quality field results.  Channeling this desperation, we devised a strategy this past winter to finally get bacterial etiolation on our research plots. This plan incorporated all of the knowledge we have gained from the project thus far, as well as some anecdotal observations we have made over the years…Lo, and behold, it worked!     

Clever thinking by Dr. Vargas suggested we bring in entirely new creeping bentgrass sod to the area. This notion was based on observations at golf courses with Acidovorax problems. Usually the areas that were plugged or sodded with nursery creeping bentgrass showed symptoms within a few days of transplanting.  The new sod was established in mid May of this year, and since then, the management strategy has been aggressive: double mowing, rolling, heavy topdressing, and low fertility, all of which have shown to be common factors on golf courses battling bacterial etiolation.  Symptoms of etiolation appeared last week, after a brief, but much appreciated stint of warm, humid weather (plant pathologists get inexplicably excited during disease weather). Yellow, elongated plants were full of Acidovorax, as determined by microscopic observations of bacterial streaming.  Several treatments are under investigation on plots this summer, which hopefully yield informative results related to symptom suppression or alleviation.
Sodding a new green at the HTRC.
No promises are being made, but this is shaping up to be a banner year for bacterial etiolation at MSU’s Turfgrass Field Day in August.  Stay tuned for more on this emerging disease and the exciting and pioneering research we are doing at Michigan State. 

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