Massarilactones D and H, phytotoxins produced by Kalmusia variispora, associated with grapevine trunk diseases (GTDs) in Iran

A strain of Kalmusia variispora associated with grapevine trunk diseases (GTDs) was identified in Iran and induced disease symptoms on the host in greenhouse conditions. The grapevine pathogens are able to produce a plethora of toxic metabolites belonging to different classes of naturally occurring compounds. Two homogeneous compounds were isolated from the organic extract of K. variispora culture filtrates. They were identified by physic (specific optical rotation), and spectroscopic (essentially 1D 1H and 13C NMR and HR ESIMS) methods as the fungal polyketides massarilactones D and H (1 and 2). The unassigned absolute configuration of massarilactone D was unambiguously determined by X-ray diffractometric analysis. Massarilactones D and H showed phytotoxic activity on Vitis vinifera L. at two concentrations used and depending from the days of inoculation. Phytotoxicity is also increased when the 3,4,7-O,O',O"-triacetyl derivative of massarilactone D (3) was assayed on the host plant. This is the first report on the investigation of phytotoxic metabolites produced by K. variispora isolated from infected grapevine in Iran and they seem to be involved in the development of disease symptoms.