Abstract :
Canoia, lettuce, green bean, dwarf pea, tobacco, tomato, poplar, corn,
wheat, and cucumber leaves were extracted by boiling with 95% ethanol.
The ethano! was removed from the ethanol-water extraet, and the
water-soluble fraction was centrifuged and fihered to remove compounds
with a molecular weight > 1 000 D. The undersides ofthe first
true leaf of a cucumber plant (leaf 1) and the leaf above (leaf 2) were
sprayed with each plant extraet (induction), and 7 days later leaf 3 was
inoculated with a conidial suspension of Coiietotrichvm lagenarium
(challenge). Extracts from all plants tested induced systemic resistance
in leaf 3 to C, lagenarium. Commercially available compounds were
screened to determine structural similarities among the compounds
which can induce systemic resistance. All compounds which induced
resistance in leaf 3 caused some damage to leaves 1 and 2. but not all
compounds which damaged leaves I and 2 induced resistance in leaf 3.
Galacturonic acid, gluctironic acid, salicyhc acid, m-hydroxybenzoic
acid, p-hydroxybenzoic acid, y-resorcylic acid, protocatechuic acid, gallic
acid, hemimelletic acid, trimelletic acid, trimesic acid, phloroglucinol,
and glycine induced systemic resistance, whereas catechol, resorcinol,
hydroquinone, pyrogallol, hydroxyhydroquinone, benzoic acid,
phthalic acid, i-resorcylic acid, ^-resorcylic acid, gentisic acid, 2.3-
dihydroxybenzoic acid, benzaldehyde, 2,3-dihydroxybenzaldehyde, ^-
resorcaldehyde, protocatechuic aldehyde, benzyl alcohol, salicyl alcohol,
myo-inositol, phytic acid, pinitol, and quebrachitol did not. Structural
similarities were not evident among either compounds which
induced systemic resistance or those thai did not
