Identification, Characterization, and Distribution of Acidovorax Avenae Subsp. Avenae Associated with Creeping Bentgrass (Agrostis stolonifera L.) Etiolation and Decline.

Bacterial etiolation and decline caused by Acdivorax avenae subsp. avenae, is an emerging disease of creeping bentgrass (Agrostis stolonifera L.) in and around the transition zone growing region of the United States.  It is suspected that the disease has been present for many years, although diagnosis of the first occurrence was not reported until 2010.  Reoccurring symptoms on golf course putting greens include irregular areas of chlorotic, abnormally growing, elongated plants. High temperatures and sustained turfgrass stresses result in the necrosis and thinning of the yellow, etiolated areas.  Solicitation of samples from golf courses in 2010-2011 was undertaken to investigate the prevalence and dissemination of A. avenae subsp. avenae on creeping bentgrass.  At least 21 isolates from 13 states associated with these outbreaks on golf courses were confirmed as A. avenae subsp. avenae by pathogenicity assays and 16S rDNA sequencing at two independent University research laboratories.  Pathogenicity testing of common bacterial isolates from creeping bentgrass samples exhibiting heavy bacterial streaming, confirmed the ubiquitous A. avenae subsp. avenae to be the only bacterium isolated from samples to cause significant disease symptoms and creeping bentgrass decline.   Host range inoculations revealed turfgrass isolates of A. avenae subsp. avenae to be pathogenic on all A. stolonifera cultivars tested, with slight but significant differences in disease severity on particular cultivars.  Other turfgrass hosts tested were found to be only mildly susceptible to A. avenae subsp. avenae infection.  Temperature optima for virulence on A. stolonifera were established in a controlled growth chamber environment confirming disease severity to be highest between 30⁰ C and 35⁰ C.  This study initiates research on Acidovorax avenae subsp. avenae pathogenicity causing a previously uncharacterized disease of creeping bentgrass putting greens in the United States.