Phytohormone Production of Pathogenic Bacteria (Acidovorax avenae subsp. avenae) in Culture and in Creeping Bentgrass Tissues.

Bacterial etiolation (Acidovorax avenae subsp. avenae; Aaa) causes significant decline of creeping bentgrass putting greens. The bacterium causes necrotic leaf areas and etiolation of plant stems. The physiological mechanisms behind the etiolation and other symptoms are still unknown. Preliminary tests have raised the suspicion that heat stress and plant growth regulators may contribute to disease progression. Therefore, we hypothesize that heat stress and hormone profile changes caused by bacteria activities could contribute to etiolation symptoms.  Here we have performed phytohormone analysis by High Performance Liquid Chromatography of bacterial cultures in vitro and analysis of plant tissues infected with the pathogen. Four isolates of Aaa (MSU1, MSU4, MSU13 and URI1) were analyzed in the nutrient broth studies. Creeping bentgrass cultivars more resistant (’Tyee’) and less resistant (’Penn A-4’!/) were cultivated in hydroponics under 23°C and 35°C in two growth chambers. The results indicate that gibberellic acid (GA3) was the most prevalent hormones produced by the bacteria in liquid culture extracts. In the hydroponic plant study, poor turfgrass performance and root health were exhibited by ‘Penn-A4’ infected with Aaa under heat stress conditions compared to under optimal temperatures. For the hormone profile, heat-stressed plants inoculated with Aaa showed more GA3,GA1, GA4 salicylic acid and abscisic acid, but less IAA content. The results also show uneven distribution of phytohormone in separated parts of plant tissue. More SA was detected in plant roots and more GA was detected in plant leaves and stems than other parts of plants after inoculation. These results could lead to a better understanding of phytohormone profiles in response to heat stress and bacterial infection. We will evaluate the bacteria in Vivo to detect the genes express phytohormone.