Exploring The Symptomology and Disease Development Of Bacterial Etiolation and Decline Caused By Acidovorax Avenae Subsp. Avenae.

The emerging disease known as bacterial etiolation on creeping bentgrass (Agrostis stolonifera L.) caused by Acidovorax avenae subsp. avenae is a major concern on golf courses around the United States. Little is known about the epidemiology of the pathogen on turfgrass, and initial studies have only characterized partial aspects of the disease. Field, lab, and growth chamber experiments were conducted in order to better understand disease symptomology and pathogenicity as it relates to temperature. Growth chamber studies using six day/night temperature regimens and inoculations with a pathogenic isolate of A. avenae subsp. avenae (MSU4) were conducted to determine the influence of temperature on disease development and severity on creeping bentgrass (cv. ‘Penn G-2)’. The experiments indicate disease to be most severe at temperatures above 25° C, with stand necrosis being significantly greater, and chlorophyll index significantly lower in inoculated pots compared to the controls after five days and nine days respectively. A separate set of experiments were carried out aimed at inducing etiolation symptoms on creeping bentgrass (cv. ‘Penn G-2’) through an alternative method of inoculation. Root dip assays with suspensions of the MSU4 isolate of A. avenae subsp. avenae showed significant symptoms of stem elongation, chlorosis, and heavy bacterial streaming compared to the maize A. avenae subsp. avenae isolate (AAA 99-2) and a sterile water control. Field inoculations onto established plots of creeping bentgrass (cv. ‘Independence’) with a virulent isolate of A. avenae subsp. avenae resulted in widespread etiolation symptoms during extended periods of high heat and humidity in July, 2012 and June, 2013. Symptom suppression was not achieved with various agricultural antibiotics and other chemical applications; however plots treated with the growth regulator trinexepec-ethyl and ammonium sulfate fertilizer (24.4 kg N ha-1 mo-1) either alone, or in tandem, had the highest observed etiolation ratings of any treatment. Together, these results provide valuable introductory principles on the etiology of an enigmatic disease on an important species of amenity turfgrass.