Agropyrenol and agropyrenal, phytotoxins from Ascochyta agropyrina var. nana, potential herbicides for Elytrigia repens control

Elytrigia repens L. Desv. ex Nevski (commonly known as quack grass), is a perennial weed widespread through the cold temperate regions all over the world. It is managed only by chemical herbicides1,2 because it easily spreads by seed and rhizomes and produces allelopathic metabolites suppressing the growth of other plants. In surveys carried out with the aim to find pathogens of this species, which could have potential as biological agents for its control, a fungus was isolated from naturally diseased leaves of this species and identified as Ascochyta agropyrina (Fairman) Trotter var. nana Punith. Due to the interest of the authors in studying species belonging to the genus Ascochyta as sources of biologically active metabolites, a previous study led to the isolation of a main phytotoxin from the solid culture of this fungus and to its identification as papyracillic acid.3 On liquid medium A. agropyrina produces different toxins the main one of which, named agropyrenol, was characterized as a new disubstituted benzaldehyde on the basis of its chemical and spectroscopic properties. Other two new minor metabolites were isolated from the same culture and named agropyrenal and agropyrenone, respectively. They were characterized as a trisubstituted naphthalene carbaldehyde and a pentasubstituted 3H-benzofuranone, respectively. When assayed on leaves of some weedy plants, i.e. Mercurialis annua, Chenopodium album and Setaria viridis, agropyrenol proved to be phytotoxic, causing the appearance of necrotic lesions, agropyrenal was less active, while agropyrenone was inactive. None of compounds showed antibiotic, fungicidal or zootoxic activity. In this communication the production, isolation, and chemical and biological characterization of the metabolites produced by A. agropyrina var. nana in liquid culture will be illustrated and their potential as safe herbicides will be discussed.