Colin Dennis

Antifungal phenanthrenes in yam tubers

Abstract An extract from the peel of yams ( Dioscorea rotundata ) showed anti-fungal activity towards both Cladosporium cladoporioides and a variety of ya

Antifungal activity of post-infectional metabolites from potato tubers

Abstract The antifungal activity of rishitin, phytuberin, anhydro-β-rotunol and solavetivone, metabolites produced in potato tubers in response to microbial infection, was tested against 10 potato pathogens and 3 non-potato pathogens. All of these compounds, except phytuberin, showed antifungal activity against the majority of the fungi when tested at 100 μg/ml, but the presence of organic nutrients in the test system decreased their activity in some cases. Pre-existing germ tubes of certain fungi were often more sensitive to the compounds than normal germ tubes. Phytuberin was only active against P. infestans, causing lysis of the zoospores similar to that caused by the other metabolites. None of the compounds were effective in inhibiting P. infestans and some non-potato pathogens when applied to leaf discs or used as protectant sprays.

The Microviral Flora of Broiler-house Litter and Dust

Summary: A survey of litter samples from broiler houses at widespread licalities in the U.K. revealed a significant difference between the fungal floras before and after the houses had been used for a single crop of birds. Paecilomyces varioti, Trichoderma spp. Aureobasidium pullulans and Hyalodndron lignicola predominated in the fresh litter, but were replaced by present in the final litter samples were also found in the initial and final dust samples, indicating that the dust is a potential source of inoculum. These results are discussed in relation to the formation in broiler-house litter of 2,3,4,6-tetrachloroanisole (a compound associated with a musty taint in chickens), and to the potential formation of mycotoxins.

The effect of post-infectional potato tuber metabolites and surfactants on zoospores of oomycetes

Abstract The effects of post-infectional potato tuber metabolites (rishitin, phytuberin, anhydro-β-rotunol, solavetivone) and surfactants (Deciquam, Manoxol, Triton X-100) on zoospores of Phytophthora spp., Pythium middletonii and Saprolegnia spp. were studied. Treatment of motile zoospores of the Phytophthora spp. with all compounds resulted in loss of motility, disruption of the cytoplasm and bursting of the plasmalemma, whereas with the other fungi, although loss of motility and some granulation of the cytoplasm occurred, no lysis was observed. The viability of treated zoospores of P. middletonii and the Saprolegnia spp. varied according to the treatment. The difference in sensitivity of zoospores of the various species is considered to be due to the time of development of the zoospore wall in relation to loss of motility.

Distribution of Mucor piriformis, Rhizopus sexualis and R. stolonifer in relation to their spoilage of strawberries.

The Zygomycete species were isolated occasionally from flowers and immature fruits, but increased markedly on ripe fruits late in the season. In contrast, Botrytis cinerea was present at consistently high levels on strawberry flowers and fruits from the onset of flowering to the end of the harvesting season. This difference in distribution is due to the susceptibility of strawberry flowers and fruits at all stages of development to infection by Botrytis, whereas the Zygomycetes are only able to infect ripe and damaged white fruits. All species showed a greater potential to infect from a food base compared to a spore inoculum, and damaged fruits were invariably more susceptible to infection than undamaged fruits. The incidence of Mucor piriformis on flowers and fruits increased noticeably when rainsplash occurred, indicating the presence of this species in the soil and debris. Low relative humidities (70–80%) favoured formation of sporangiospores by Rhizopus sexualis and R. stolonifer growing on ripe strawberries, but at relative humidities above 90% R. sexualis formed large numbers of zygospores. M. piriformis produced sporangia at relative humidities from 70 to 100%.

Effect of temperature on viability of sporangiospores of Rhizopus and Mucor species

The effect of storage temperature on viability of sporangiospores of Mucor and Rhizopus species has been studied. Sporangiospores of Rhizopus sexualis and R. stolonifer are very susceptible to chilling temperatures, but the rate of loss of viability is dependent on temperature, storage medium and initiation of germination. ‘Dormant’ spores of strains of R. sexualis are more susceptible than those of R. stolonifer. Sporangiospores of Mucor piriformis do not lose viability under any of the treatments during storage at temperatures as low as −1 °C for 3 weeks.

Distribution of potassium, calcium and magnesium in strawberry fruits in relation to breakdown of the sulphited fruit

Abstract Methods are described for the determination of the free and bound Ca ++ , Mg ++ and K + in flesh and of these cations in achenes of strawberry fruits. A substantial amount of minerals was present in the achenes and the variation in mineral analyses of whole strawberries most probably reflects differences in the relative proportion of achenes to flesh. A negative correlation (r = −0·8) was found between bound Ca ++ and the survival of fungal polygalacturonase in liquor of sulphited fruit. The possible role of calcium in reducing enzymic softening of sulphited strawberries is discussed.