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Title: TRINEXAPAC-ETHYL AFFECTS KENTUCKY BLUEGRASS (POA PRATENSIS L.) ROOT CHARACTERISTICS

Author
item BEASLEY, JEFFREY - UNIV OF ILLINOIS
item BRANHAM, BRUCE - UNIV OF ILLINOIS
item Ortiz Ribbing, Loretta

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2005
Publication Date: 8/5/2005
Citation: Beasley, J.S., Branham, B.E., Ortiz Ribbing, L.M. 2005. Trinexapac-ethyl affects kentucky bluegrass (poa pratensis l.) root characteristics. Hortscience. 40(5):1539-1542.

Interpretive Summary: Plant growth regulators (PGRs) are commonly used on highly maintained turfgrasses such as those used in golf courses, athletic fields, and home lawns. The effect of PGRs on turfgrass root characteristics has not been studied. This study evaluated the effect of the gibberellin inhibitor, trinexapac-ethyl (TE), on Kentucky bluegrass (KBG) root and shoot growth for seven weeks. Individual KBG plants were grown in a hydroponic system and harvested weekly. At each harvest, tiller height, numbers, and color ratings were recorded. Estimates of total root length (TRL), root surface area (SA), and average root diameter were measured using the WinRhizo® system. Trinexapac-ethyl reduced plant height for 4 weeks followed by a period of post-inhibition growth. Trinexapac-ethyl increased tiller number and slightly enhanced plant color. Trinexapac-ethyl reduced TRL and SA immediately after application followed by an accelerated growth rate. Trinexapac-ethyl had no effect on root diameter. On a tiller basis, TE initially reduced TRL and SA. Initial reductions in TRL and SA per tiller may reduce tiller competitiveness for water and nutrients within a turfgrass canopy. Based on data for TRL and SA per tiller, shoot and root growth must be considered in total to fully understand TE effects on plant growth. Therefore, estimation of root mass may not provide adequate information to fully understand the effects of exogenous-applied PGRs on overall plant growth. Field research is needed to corroborate results from hydroponic-studies and examine the effect of other PGRs at various rates and application timings on turfgrass root and shoot growth.

Technical Abstract: Trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] effects on turfgrass root characteristics are not known. This study evaluated the effects of a single TE application on Kentucky bluegrass (KBG) root and shoot growth for seven weeks. Individual KBG plants were grown in a hydroponic system and harvested weekly. At each harvest, tiller height, numbers, and color ratings were recorded. Estimates of total root length (TRL), root surface area (SA), and average root diameter were measured using the WinRhizo® system. Trinexapac-ethyl reduced plant height for 4 weeks followed by a period of post-inhibition growth. Trinexapac-ethyl increased tiller number over the course of the study and slightly enhanced plant color. Trinexapac-ethyl reduced TRL and SA 48 and 46% at 1 week after treatment (WAT) followed by an accelerated growth rate 1 to 4 WAT. Trinexapac-ethyl had no effect on root diameter. On a tiller basis, TE initially reduced TRL and SA 30 and 31%, respectively. Total root length and SA per tiller of control plants declined toward TRL and SA per tiller of TE-treated plants over time. Initial reductions in TRL and SA per tiller may reduce tiller competitiveness for water and nutrients. Based on data for TRL and SA per tiller, shoot and root growth must be considered in total to fully understand TE effects on plant growth. Field research is needed to corroborate results from hydroponic-studies and examine the effect of various TE rates and multiple applications on turfgrass root and shoot growth.