Abstract
The populations of the Andean Cupressaceae Austrocedrus chilensis have been severely affected by a disease caused by the phytopathogenic fungus Phytophthora austrocedri. A study was undertaken to disclose changes in the resin composition of P. austrocedri-infected individuals, including naturally infected and artificially inoculated trees, compared with healthy A. chilensis trees. GC-MS and 1H-NMR studies showed a clear differentiation among healthy and infected resins, with the diterpene isopimara-8(9),15-dien-19-ol as a relevant constituent in resins from infected trees. The effect of resin fractions from P. austrocedri infected trees on the pathogen was assessed by measuring the mycelial growth in agar plates. The most active fractions from resin obtained from infected trees inhibited fungal growth by nearly 50% at 1 mg/dish (35.37 µg/cm2). The main constituent in the active fractions were 18-hydroxymanool and the aldehyde torulosal. Both compounds are oxidation products of manool and can be a chemical response of the tree to the pathogen or be formed from the pathogen as a biotransformation product of manool by microbial oxidation. While the diterpene profiles from A. chilensis tree resins can easily differentiate healthy and P. austrocedri infected individuals, the possible conversion of manool to the antifungal derivatives 4 and 6 by the microorganism remains to be established.
Highlights
The exudation of resins, a mixture of monoterpenes, sesquiterpenes, and diterpene resin acids, is a major part of the constitutive defense mechanisms in conifers
The diterpene composition of the conifer Austrocedrus chilensis was reported by Olate et al (2011) [18] and seasonal variation in resin composition was described [19]
The resin samples were compared by thin layer chromatography (TLC) to disclose similarities and differences among the different variables
Summary
The exudation of resins, a mixture of monoterpenes, sesquiterpenes, and diterpene resin acids, is a major part of the constitutive defense mechanisms in conifers. In the last few decades, the Cupressaceae Austrocedrus chilensis, known as “ciprés de la cordillera”, has suffered a devastating disease known as “mal del ciprés” or, recently, as “Austrocedrus chilensis root disease” [20,21,22] This disease is characterized by chlorosis, withering of the foliage, progressive defoliation and the death of the tree. Resin-pockets are usually developed below bark in the advance of the Phytophthora lesion [22] Whether this resin is a specific response to pathogen infection or a structural unspecific response is still unknown. To elucidate this aspect, the composition of A. chilensis resin and its antifungal activity was investigated.
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