Drought Stress and Trinexapac-ethyl Modify Phytohormone Content Within Kentucky Bluegrass Leaves

PGR applications aimed to interfere with gibberellic acid (GA) biosynthesis or accumulation is a widespread practice in the production and maintenance of turfgrasses. If suppression of GA combined with drought stress modifies the content of other hormones in turfgrasses, PGR application could affect the susceptibility of grasses to various abiotic stresses and biotic pathogens. This growth chamber study aimed to investigate how drought stress and Primo (Syngenta Corp; Trinexapac-ethyl; TE) application affect the content of abscisic acid (ABA), auxin (in the form of indole acetic acid, IAA), jasmonic acid (JA), and salicylic acid (SA) in one commercially available cultivar 'Kenblue' and one experimental type, A06-46, of Kentucky bluegrass. Drought stress caused an accumulation of all four of these hormones that began around 8 day of drought stress or at a 20-40 % loss of water from leaves. TE application combined with drought stress caused an earlier increase in SA and IAA content and delayed the increase in JA and ABA content compared to drought-stressed plants not treated with PGR. An increase in SA, JA, and IAA was found at severe water deficit conditions (26 % RWC) in TE-treated plants compared to plants not treated with TE. The results indicate that both negative and positive consequences to plant defense strategies could result from the use of PGRs, which could potentially highly impact recommendations of how to best use PGR compounds in turfgrasses and other crop species.