|Destefano, Darren - UNIV OF MARYLAND|
|Grybauskas, Arv - UNIV OF MARYLAND|
|Sherald, James - NATIONAL PARK SERVICE|
|Momen, Bahram - UNIV OF MARYLAND|
|Sullivan, Joe - UNIV OF MARYLAND|
Submitted to: Journal Of Arboriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2007
Publication Date: July 2, 2007
Citation: DeStefano, D.A., Grybauskas, A.P., Sherald, J.L., Momen, B., Huang, Q. and Sullivan, J.H. 2007. Effect of the growth regulator Paclobutrazol on growth of the bacterial pathogen Xylella fastidiosa. Arboriculture to Arboriculture and Urban Forestry. 33:246-252. Interpretive Summary: Xylella fastidiosa is a slow growing, xylem inhabiting, nutritionally fastidious and insect transmitted bacterium. The bacterium is associated with bacterial leaf scorch (BLS) and decline in many economically important landscape trees and shrubs including oak, elm, sycamore, maple and oleander. Application of a growth regulator Paclobutrazol (PBZ) to infected plants has been found to cause symptom remission of BLS. This study was undertaken to find out the effect of PBZ on in vitro growth of two X. fastidiosa isolates. We found no significant effect of PBZ on colony growth of X. fastidiosa at the manufacturer's recommended rate of 20 ug ml -1. However, signicant reductions in bacterial growth were observed at a rate of 200 ug m1 -1, indicating that high levels of PBZ may have a direct effect on the growth of X. fastidiosa. This suggests that PBZ may provide a promising treatment for BLS in shade trees by its direct effect on the bacterium and its growth regulator effect on plants. Our work wil be of value primarily to arborists and other members of the nursery and landscape industry, and to plant pathologists interested in control of X. fastidiosa.
Technical Abstract: Xyella fastidiosa is a fastidious, xylem-limited, insect transmitted, bacterial plant pathogen that has a wide host range and causes bacterial leaf scorch (BLS) in shade trees. BLS is a chronic disorder characterized by late season leaf scorch and dieback and is common in urban and suburban areas of the mid-Atlantic and southeast United States. BLS has been recognized since the 1980's and attempted treatments have included antibiotics and plant growth regulators. Application of Paclobutrazol (PBZ), a diastereomeric triazole with both fungistatic and growth regulation properties has caused symptom remission of BLS. In this study we investigated the effect of PBZ on in vitro growth of two X. fastidiosa isolates. Our results showed no significant effect of PBZ on colony growth of X. fastidiosa at the manufacturer's recommended rate of 20 ug ml -1. However, significant reductions in bacterial growth were observed at a rate of 200 ug ml -1, indicating that high levels of PBZ may have a direct effect on the growth of X. fastidiosa. This direct effect and growth regulator effects of PBZ's suggest that PBZ may provide a promising treatment for BLS in shade trees.