(3ξ,4ξ,5ξ,6ξ,7ξ,11ξ)-3,6-Dihydroxy-8-oxo-9-eremophilene-12-oic Acid, a New Phytotoxin of Ssp. Isolates Associated with Fruit Spots on Apple ( × Borkh.)

sp. infections on apple ( × Borkh.) lead to impaired fruit quality and yield losses by leaf blotches and fruit spots, caused by host-specific toxins (HSTs) of the apple pathotype like AM-toxins. Fungal isolates were obtained during severe outbreaks on cv. Gala, Golden Delicious, and Cripps Pink/Rosy Glow in South Tyrol and other regions in northern Italy. The isolates were tested for pathogenicity using assays with detached apple leaves. Conidial suspensions of pathogenic isolates were shown to provoke necrotic lesions also in apple seedlings and on fruits. Detached-leaf assay-guided fractionation of the isolates' culture supernatant and a high-resolution liquid chromatography-mass spectrometry (LC-MS) analysis tentatively identified 27 known phytotoxins and a new putative toxin, (3ξ,4ξ,5ξ,6ξ,7ξ,11ξ)-3,6-dihydroxy-8-oxo-9-eremophilene-12-oic acid (). The constitution and the relative configuration of the ring stereocenters of were elucidated by NMR spectroscopy, revealing unique structural features among phytotoxins. Indeed, molecular analysis revealed the lack of the toxin-related genes , , and in all isolates from the region, suggesting that Alternaria apple blotch in the area was associated with another metabolite (.