David J. Robeson

A chemical dichotomy in phytoalexin induction within the tribe vicieae of the leguminosae

Abstract Using either leaf or cotyledon tissues, the phytoalexin response of over 60 representative members of the genera Lathyrus , Lens , Pisum and Vicia was determined. Twenty-nine Vicia species produced furanoacetylenes, as did the two Lens species examined. By contrast, Pisum and Lathyrus failed to produce any of these phytoalexins, but formed pisatin instead. Thus, pisatin was formed as the major phytoalexin in 29 of 31 Lathyrus species tested, representing 10 sections within the genus. This dichotomy in phytoalexin response is discussed in relation to the taxonomy of the tribe Vicieae.

Identification of two chromone phytoalexins in the sweet pea, Lathyrus odoratus

Abstract A major phytoalexin isolated from the Helminthosporium Carbonum -inoculated leaflets and pods of Lathyrus odoratus has been identified by spectroscopic procedures as 5,7-dihydroxy-3-ethylchromone (lathodoratin). Small amounts of the corresponding 7- O -methyl ether (methyl-lathodoratin) are also formed by this plant. Both compounds similarly occur as phytoalexins in the closely related legume L. hirsutus but are absent from the other Lathyrus species examined. The unusual 3-substitution of the chromone nucleus appears to be essential for fungitoxicity since the synthetic isomer 5,7-dihydroxy-2-ethylchromone is apparently inactive.

αβ-Dehydrocurvularin and Curvularin from Alternaria cinerariae

Abstract Secondary metabolite production by the phytopathogen Alternaria cinerariae has been investigated resulting in the isolation and identification of αβ-dehydrocurvularin and curvularin as products of this fungus. The phytotoxicity of these compounds is demonstrated.

New pterocarpan phytoalexins from Lathyrus nissolia

Abstract In addition to 3-hydroxy-9-methoxypterocarpan (medicarpin), the fungus-inoculated phyllodes of Lathyrus nissolia produce two previously unreported isoflavonoid phytoalexins. These compounds have been identified as 3,9-dihydroxy-10- methoxypterocarpan (nissolin) and 3-hydroxy-9,10-dimethoxypterocarpan (methyl-nissolin).

Furanoacetylene and isoflavonoid phytoalexins in Lens culinaris

Abstract The ability of two Lens species to synthesise the furnaoacetylenes wyerone and wyerone epoxide, as well as the pterocarpan variabilin, has been demonstrated. This links Lens more close to Vicia than to the remaining genera of the tribe Vicieae.

A Cercospora isolate from soybean roots produces cebetin B and cercosporin

Abstract A Cercospora isolate (CE14) was isolated from roots of soybean seedlings germinated in vitro . The roots, which appeared red, contained cercosporin which was isolated and quantified. In vitro cultures of CE14 produced cebetin B, previously known as CBT ( C. beticola toxin).

Studies on the mechanism of polyketide-derived biosynthesis of deoxyradicinin and related metabolites of Alternaria helianthi

The polyketide biosynthetic origin of deoxyradicinin, deoxyradicinol and 3-epideoxyradicinol has been demonstrated by incorporation studies with 13C-labelled precursors and 13C n.m.r. spectroscopy. The 13C n.m.r., 2H n.m.r., and mass spectra of deoxyradicinin isolated from fungal cultures grown in the presence of [2H3]sodium acetate indicated an uncommon condensation of two polyketide chains rather than a single hexaketide unit undergoing cyclization and ring-cleavage.

The Production of Pyrenocines A and B by a Novel Alternaria species

Abstract A previously undescribed species of Alternaria was isolated from the leaves of Helianthus tuberosus bearing necrotic lesions. When this isolate was grown in liquid medium two phytotoxic metabolites were produced. These compounds were identified as pyrenocine A and pyrenocine B. The former metabolite was found to be lethal to both isolated protoplasts and whole leaf tissue of Helianthus.

The phytoalexin response of lathyrus sativus (grass pea)

Lathyrus sativus was investigated for the nature of its phytoalexin response with the result that leaflets, immature pods, and seeds were induced to produce 6a-hydroxy- 3-methoxy-8,9-methylenedioxypterocarpan (pisatin). Evidence is presented for the metabolism of pisatin, by the wound pathogen Botrytis cinerea, to a phenolic congener, 3,6a-hydroxy-8,9-methylenedioxypterocarpan

Pisatin as a Major Phytoalexin in Laihyrus

Abstract The pterocarpan pisatin has been identified as a major phytoalexin in fifteen species of Lathyrus. Thus, the genus is closer in its phytoalexin response to Pisum than to Vicia, which is known to produce furanoacetylenes on fungal in vasion.