Metabolites produced by Gnomoniopsis castanea associated with necrosis of chestnut galls
© Vinale 2014
Received: 7 April 2014
Accepted: 12 July 2014
Published: 15 August 2014
In this manuscript, we report the isolation and characterization of two secondary metabolites produced by a Gnomoniopsis castanea strain isolated in the Campania region (Italy) from chestnut galls infested with Dryocosmus kuriphilus. The compounds, purified from the fungal culture filtrate by using preparative HPLC-DAD, showed the same spectroscopic data of abscisic acid and 1′,4′-diol of abscisic acid. Phytotoxic activity of the isolated metabolites on chestnut leaves has been also observed.
Many cultivated varieties of chestnut (Castanea spp.) are subjected to severe infestations caused by the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), which can disrupt the fruiting process and reduce a tree's yield by up to 70%. In addition to pest infestation, necrotic symptoms on leaves and galls are often observed due to the development of a gall colonizer identified as the fungus Gnomoniopsis sp. . The new species Gnomoniopsis castanea has been recently described, based on the association with Castanea sativa, the morphology and the phylogenetic analysis of the internal transcribed spacer (ITS) regions of ribosomal DNA and the EF1-a locus. The fungus has been associated with nut rot and caused disease symptoms when artificially inoculated on fruits or flowers .
Many fungi exert their effects on plant synthesizing secondary metabolites that alone reproduce some or even all of the symptoms of the disease caused by the producer organism. Moreover, some fungi interfere with the physiology of the plants by producing hormones, such as gibberellin, gibberellic acid, or indole-3-acetic acid .
Here, we report the isolation and characterization of the major secondary metabolites produced in liquid culture by a Gnomoniopsis strain isolated in the Campania region (Italy) from chestnut galls infested with D. kuriphilus. Sequence analysis of the ITS rDNA region indicated 99% similarity with GenBank sequences of G. castanea confirming the identity of this species characterized as the main causal agent of rot of the ripe nuts, both before and after picking .
Hormones or hormone-like molecules typically have an optimum activity in terms of plant growth regulation between 10−5 and 10−6 M while having a toxic effect at higher concentrations .
ABA has been considered a negative regulator of disease resistance. This effect is due to the interference of ABA with biotic stress signalling that is regulated by salicylic acid, jasmonic acid, and ethylene, and to an additional effect on shared components of stress signalling . The production of ABA by fungi may interfere with the normal physiology of the plant and could explain why phytopathogens secrete this metabolite to plants exogenously.
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