"Creeping bentgrass (Agrostis stolonifera) putting greens have been plagued by bacterial etiolation disease caused by Acidovorax avenae subsp. avenae (Aaa). Based on the visual symptoms of the disease we aimed to determine whether disease symptoms could be associated with bacterial manipulation of the phytohormone balance in creeping bentgrass tissues. In vitro and in vivo studies of this pathosystem for phytohormone analysis were performed. Aaa and a non-pathogenic, negative control Pseudomonas aureofaciens (Pa) were cultured at room temperature (20-22 °C) for 14 days. For in vivo studies, Aaa infected and uninfected creeping bentgrass 'Tyee' and 'Penn A-4' were grown in hydroponics under optimal 23/20°C day/night temperatures and heat stress 35/30 °C conditions in growth chambers. Bacterial culture or plant samples were taken for analysis of phytohormones: gibberellic acid isoforms (GA1, GA3, GA4, and GA20), jasmonic acid (JA), salicylic acid (SA), indole-3-acetic acid (IAA), zeatin riboside (ZR), and abscisic acid (ABA). GA1, GA3, GA4 and IAA were detected in some Aaa cultures but not in Pa. 'Penn-A4' was more Aaa sensitive under high temperature than 'Tyee'. 'Tyee' infected with Aaa at high temperatures showed higher JA content in all plant tissues, higher SA in stolons and roots, and less GA3 and GA20 in leaf and stolon tissues than 'Penn-A4' in the same conditions. Based on these results we hypothesized that pre-treating plants with SA or JA could be effective in reducing disease symptoms of Aaa in creeping bentgrass. The treatments included foliar application of 10 æmol/L SA, 20 æmol/L SA, 0.5 mM JA in 0.02% ethanol and 2 mM JA in 0.02% ethanol prior to exposure to heat stress (35°C) and optimal temperature (23 °C). Physiological measurements included turf quality, leaf and root electrolyte leakage, chlorophyll content, photochemical efficiency and root viability. The results demonstrate that SA application may reduce disease symptoms of both cultivars under both temperature treatments. The effect of 20 æmol/L SA was the most significant among treatments, especially under optimal temperature. JA application could also reduce Aaa disease severity especially under optimal temperature; however, the effects of 2 mM JA were more significant in cultivar 'Tyee' than 'Penn-A4'. These results suggest that under controlled conditions SA and JA may induce tolerance of creeping bentgrass to Aaa and reduce disease damage. Differential GA isoform accumulation produced by Aaa could contribute to disease severity and JA and SA accumulation may contribute to disease tolerance."--Pages ii-iii.
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