3-Epideoxyradicinol and the biosynthesis of deoxyradicinin

A novel phytotoxic compound, in addition to the known phytotoxin deoxyradicinin, has been isolated from Alternaria helianthi and its structure elucidated as 3-epideoxyradicinol. Its epimer is also briefly described. The polyacetate biosynthetic origin of deoxyradicinin has been demonstrated.     

Phytotoxins from Alternaria helianthi: radicinin,and the structures of deoxyradicinol and radianthin

A novel compound, radianthin, with phytotoxic activity was isolated from liquid cultures of Alternaria helianthi and identified as a pyrone related to radicinin. A second metabolite was identified as radicinin itself while deoxyradicinol is described for the first time as a natural product.     

Zinniol induces chlorophyll retention in barley leaves: the selective action of a non host-specific phytotoxin

A biologically active compound was isolated from liquid cultures of Alternaria tagetica and identified as zinniol. The selective action of zinniol, a non host-specific phytotoxin which induces necrosis in a number of unrelated plant species, has been demonstrated: enhanced chlorophyll retention occurs in zinniol-treated leaf tissue of three cereal species.     

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi is described. A comparison of conditions led to the following standard conditions being recommended. The first or second pair of leaves of seedling plants at the V8 growth stage are inoculated using inoculum grown on sunflower leaf extract agar for 5–10 days at an inoculum density of 1–2 spores cm² of leaf tissue. A 48 h dew period should be applied to plants covered by a plastic tent. A dew period temperature of 26/26°C night/day and a post-dew period temperature relative to that experienced under local growing conditions should be applied. Lesions are measured 7 days after inoculation, and mean lesion size per plant is calculated. Mean lesion size of lines being tested is expressed as a proportion of the mean lesion size of a susceptible standard included in each screening experiment.     

Confertdiolide,a novel sesquiterpenoid lactone from Parthenium

Four sesquiterpene lactones were isolated from several populations of Parthenium confertum var. lyratum (Gray) collected in Sierra de Arteaga, southern Coahuila. Three of the compounds, hysterin, tetraneurin E and hymenin were previously isolated from other Parthenium species. The fourth constituent is the new cyclopropanoid sesquiterpene dilactone confertdiolide which represents a new structural type. The photolytic conversion of hymenin into confertdiolide confirmed its structure.     

Activity and hematin content of catalase from greening sunflower cotyledons

The specific activity of catalase purified from the peroxisomes of sunflower cotyledons declines in parallel with the total cotyledonary catalase activity during the transition of peroxisomes from glyoxysomal to leaf peroxisomal function. The hematin content of the purified catalase however, remains constant at 4 hematin groups per catalase molecule. The absorbance coefficients of catalase at 404 and 280 nm were determined to be 372 and 540/mM/cm, respectively.     

Sporidesmium filiferum from Tsukuba,Japan

Sporidesmium filiferum isolated from a leaflet ofPhellodendron amurense lying on the soil surface at Tsukuba, Japan is described together with photomicrographs.     

A Novel Isoindoline,Porritoxin Sulfonic Acid,from Alternaria porri and the Structure-phytotoxicity Correlation of Its Related Compounds

Novel zinniol-related compound 3, named porritoxin sulfonic acid, with an isoindoline skeleton was isolated from the culture liquid of Alternaria porri. The structure was determined to be 2-(2″-sulfoethyl)-4-methoxy-5-methyl-6-(3′-methyl-2′-butenyloxy)-2,3-dihydro-1H-isoindol-1-one. The phytotoxic activities of three isoindolines (1-3) were evaluated in a seedling-growth assay against stone leek and lettuce.     

Kingidiol,a kolavane derivative from Baccharis kingii

The aerial parts of Baccharis kingii afforded quercetin 3,3′-dimethyl ether and a new diterpene closely related to hautriwaic acid. Structure and     

On the structure of a novel ether from Artemisia tridentata

1,6,6-Trimethyl-4-ethenyl-2-oxabicyclo-[3. 1.0]hexane was unambiguously synthesized in seven steps from 4,5-dihydro-2-methylfuran. The product possessed IR, ¹H NMR and MS which differed from those of a compound isolated from Artemisia tridentata. This compound has been assigned the above structure on the basis of spectral evidence: consequently the proposed structure is erroneous.     

11β,13-Dihydrolactucin,a sesquiterpene lactone from Launaea mucronata

The roots of Launaea mucronata afforded, in addition to lactucin, lactucin-8-O-acetate and the corresponding dihydro derivative, 11β,13-dihydrolactucin.     

Neocapillen,a new acetylenic hydrocarbon from Artemisia capillaris

During an investigation of Artemisia capillaris, a new acetylenic hydrocarbon, neocapillen, was isolated as a minor component and its structure determined.     

The infection process, sporulation and survival of Alternaria helianthi on sunflower

Electron microscopy was used to study the infection of sunflower leaves by Alternaria helianthi. Conidia germinated by producing one to many germ tubes which grew across the leaf surface before forming appressoria. The fungus directly penetrated its host through the cuticle and epidermis. Entry into the host through wounds and stomates was also observed. Extracellular sheaths were found to be associated with germ tubes and intercellular hyphae of A. helianthi. Conidiophores developed through collapsed stomates, from leaf veins, trichomes and also from mycelium growing across the host leaf surface. Microcylic conidia were produced directly from parent conidia under certain conditions. Studies using a volumetric spore trap showed that the airborne spore concentration followed a distinct periodicity with peaks occurring between 0900 and 1100 h each day. Laboratory studies showed that safflower, noogoora burr and bathurst burr could serve as alternative hosts for A. helianthi. The pathogen was readily isolated from sunflower crop debris from a diseased crop that had been harvested 1 yr earlier.     

Components of quantitative resistance in sunflower to Alternaria helianthi

Components of quantitative resistance, spore production, incubation period, infection frequency and mean lesion size were measured in 17 sunflower accessions inoculated with conidia of Alternuria helianthi under controlled conditions. The same accessions were also rated for disease reaction in the field in 1994 and 1995 using a generated epidemic and varied in their disease reactions from highly susceptible to highly resistant. Spearman's ranking of accessions was highly correlated (r = 0.9) for both years; however, the ranking of components measured under controlled conditions with field severity was generally poor. Regression analysis of components with field severity ratings of the accessions showed that mean lesion size was highly correlated (r = O.74) and infection frequency was moderately correlated (r = 0.58) with the field severity ratings taken over the two years. Infection frequency was also well correlated (r = 0.75) with mean lesion size. Spore production and incubation period were poorly correlated with the field severity ratings for both years. An index based on infection frequency and mean lesion size gave a better correlation with the 1995 field severity ratings than either component alone, but in 1994 the index was not as well correlated with field severity as mean lesion size alone. It is suggested that mean lesion size, determined from plants 7–9 days after inoculation could be used to select for resistance to A. helianthi in the greenhouse. Infection frequency could also be used as a predictor of resistance, but to a lesser degree.     

Mariolin,a germacranolide from Anacyclus radiatus

A new sesquiterpene lactone, the germacranolide mariolin, was isolated from the aerial part of Anacyclus radiatus along with several known compounds. The structure of mariolin was determined by spectroscopic methods.