Synergistic Inhibition — Strohel and Porter 



119 



Table 1. Sources and sensitivities toward salicylate (SA) of the plant-pathogenic fvnigi employed. Organismal names 

 are presented as genus and species, with abbreviation employed in the text. The sources listed indicate the diseased 

 plant material from which fungi were isolated. Assays were of mycelial growth from mycelial plugs (MG), spore ger- 

 mination (SG) or mycelial growth from spores (MGS) conducted in potato-dextrose agar (PDA) in standard 15 X 100 

 mm Petri dishes or in a liquid glucose-salts medium (GS) in 24-well plates. ICj,,,, and ICg,, values represent the con- 

 centrations of SA found to inhibit MG, SG, or MGS by either 100% or 50%, relative to controls not exposed to SA. 

 Ranges of values indicate the tested SA concentrations between which interpolated IC values logically fall. 



Organisms 



Sources 



Assay 



IC,„„ (mM SA) 



IC,„ (niM SA) 



Botnjtis cinerea (BC) 



Rose (flower) Petal blight 



MG/PDA 



10.0-20.0 



2.0-5.00 



Colletotrichum gratninicola (CG) 



Corn (leaf) Anthracnose 



SG/GS 



0.75-1.0 



0.5-0.75 



Dendrophonia obscurans (DO) 



Strawberry Leaf blight 



MG/PDA 



5.0-10.0 



1.0-2.0 



Diplocarpon rosae (DR) 



Rose (leaf) Black spot 



MG/PDA 



>10.0 



1.0-2.0 



Monilinia fnicticola (MF) 



Peach (fruit) Broum rot 



MGS/GS 



<10.0 



2.0-5.0 



Pestalotia sp. (PESP) 



Grape (leaf) associated with 



MG/GS 



10.0 



2.0-5.0 



Black rot lesions 



SG/GS 



>2 



>2 



Pythium sp. (PYSP) 



Turf Web blight 



MG/PDA 



>20.{) 



5.0-10.0 



evaluated the hypothesis that SA might syn- 

 ergistically enhance the activity of other anti- 

 fungal materials. Although SA has been re- 

 ported to synergistically enhance plant re- 

 sponses to molecules that elicit the expression 

 of disease resistance mechanisms (Shirasu et 

 al. 1997), there appear to be no previously 

 pubhshed reports of synergism of SA with oth- 

 er antifungal materials, other than our own ab- 

 stract (Strobel and Porter 2005) of a poster 

 presented at the 2004 Annual Meeting of the 

 Kentucky Academy of Science. Synergistic in- 

 teractions between conventional fungicides 

 have been reported (Kosman and Cohen 

 1996). 



MATERIALS AND METHODS 



Culture Media and Related Materials 



Deionized or double-distilled water were 

 used throughout these investigations. Potato- 

 dextrose agar (PDA) and potato-dextrose 

 broth (PDB) were purchased from Fisher Sci- 

 entific, 4500 Turnberry Drive, Hanover Park, 

 IL 60103. Sodium salicylate (SA; USP grade) 

 was purchased from Sigma-Aldrich, P.O. Box 

 14508, St. Louis, MO 63178. Glucose was pur- 

 chased from Mallinckrodt Baker, Inc., P.O. 

 Box 800, Paris By-Pass, US 68, Paris, KY 

 40361. Mineral salts were of ACS grade or 

 higher, and were purchased from Fisher or 

 Sigma. One liter of the liquid glucose-salts 

 (GS) medium we employed contained the fol- 

 lowing ingredients: glucose, 10 g; with mac- 

 ronutrients NH4NO3, 700 mg; KH^PO^, 1200 

 mg; MgS04-7H20, 300 mg; CaCl2-2H20, 300 

 mg; and the following micronutrients: 



MnCl24H20, FeCl3-6H.O, ZnS04.H20, and 

 CUSO4, 80 |jLg each. Stocks of each mineral 

 nutrient (macronutrients, 100 X; micronutri- 

 ents, 1000 X) were autoclaved separately, as 

 were glucose solutions. A commercially-for- 

 mulated herbicide was used as our paraquat 

 (PQ) source (Gramoxone Extra, 2.5 lbs of PQ 

 per gallon, Syngenta Corporation, 2200 Con- 

 cord Pike, PO. Box 8353, Wilmington, DE 

 19803). Two commercially available neem 

 (NM) preparations, both listing clarified hy- 

 drophobic extract of neem oil as the active in- 

 gredient (a.i.), were purchased locally. These 

 were Green Light Tomato and Vegetable 

 Spray, Ready-To-Use, containing 0.9% a.i. 

 (NMRTU; Green Light Company, San Anto- 

 nio, TX 75418) and Garden Safe® Fungicide 

 3® Concentrate containing 70% a.i. (NMC; 

 Schultz Company, Bridgeton, MO 63044). 

 Polystyrene Petri plates (100 X 15 mm) and 

 polystyrene 24-well BD Falcon culture plates 

 were purchased from Fisher. Fluorescent 

 lighting tubes were purchased locally. The ger- 

 micidal ultraviolet lamp (model UVG-54) em- 

 ployed for visualization of SA fluorescence was 

 purchased from UVP, Inc., 2066 W. 11th 

 Street, Upland, CA 91786. 



Characteristics, Sources, and Maintenance of 

 Microorganisms 



The names, in-text abbreviations, character- 

 istics, and sources of the microorganisms em- 

 ployed in this research are presented in Table 

 1. We isolated all fungi (except Colletotrichum 

 graminicola, CG) from naturally-infected 

 plant materials collected in the area of Lex- 



