Rm. Bostock et al., Suppression of Monilinia fructicola cutinase production by peach fruit surface phenolic acids, PHYSL MOL P, 54(1-2), 1999, pp. 37-50
Chlorogenic and caffeic acids are major phenolic acids in the epidermis and
subtending cell layers of peach fruit (Prunus persica). Their concentratio
ns are especially high in peach genotypes with a high level of resistance t
o the brown rot fungus, il Monilinia fructicola, and decline as fruit matur
e with a corresponding increase in disease susceptibility. Chlorogenic acid
and caffeic acid at concentrations up to 5 mM did not inhibit M. fructicol
a spore germination or mycelial growth in culture. In cultures amended with
either of these phenolic acids, cutinase activity was reduced with a sharp
decrease apparent at 0.1 mM. The presence of caffeic acid in cultures duri
ng growth on cutin prevented the appearance of two major cutinase isoforms
as well as additional esterases in the filtrates. Cutinase activity was not
directly inhibited by chlorogenic acid or caffeic acid, nor by oxidized ca
ffeic acid. A series of cinnamic and benzoic acids with various degrees of
hydroxylation and methoxylation of the aromatic ring also suppressed cutina
se levels in culture, indicating the effect was not specific to the natural
ly abundant chlorogenic and caffeic acids. Cinnamic acid, with an unsubstit
uted aromatic ring, was least suppressive, and 2,3-dihydroxybenzoic acid, a
known chelating agent that can facilitate iron transport, was most suppres
sive. We propose that the high concentration of chlorogenic acid present in
immature fruit and in fruit from genotypes with high levels of disease res
istance may contribute to the brown rot resistance of the tissue by interfe
rence with the production of factors involved in degradation of host polyme
rs rather than by direct toxicity to the pathogen. Chlorogenic acid and rel
ated phenolics in combination with other factors such as iron could functio
n to arrest M. fructicola in quiescent infections associated with immature
and ripening fruit. (C) 1999 Academic Press.