Effects on growth and comparison of root tissue colonization patterns of Eucalyptus viminalis by pathogenic and nonpathogenic strains of Fusarium oxysporum

Soilborne pathogens, especially Fusarium oxysporum , are responsible for damping-off and root necrosis in Eucalyptus nurseries. New technologies are increasingly considering strategies for plant disease control other than chemical fungicides. Among these, natural fungal antagonists, which are colonizers of the root cortex, are potential biocontrol agents. An in vitro system was used: (1) to test the pathogenic effects of F. oxysporum strain Foeu1 which was recovered from a forest nursery soil; (2) to explore the potential of the nonpathogenic F. oxysporum strain Fo47, which is known for its efficiency in biological control, to suppress damping-off of Eucalyptus seedlings; (3) to compare the patterns of root colonization and host response to invasion by the two Fusarium strains inoculated separately in a time-course study. Root inoculation of E. viminalis with F. oxysporum strain Foeu1 caused damping-off in young seedlings in vitro , whilst disease symptoms were not visible in plants inoculated with F. oxysporum strain Fo47 or when both strains (Foeu1 + Fo47) were inoculated simultaneously. Each strain showed similarities in patterns of root tissue colonization, and in the processes of root penetration and initial colonization. Differential effects on root tissue were observed with fungal development within the cortex: ingress of strain Foeu1 was accompanied by severe host-cell alterations whilst no tissue damage occurred with development of strain Fo47.     

The effect of cane management techniques on raspberry yellow rust (Phragmidium rubi-idaei)

The effects of various cane removal treatments on the epidemiology of Phragmidium rubi-idaei were studied in four experiments in infected raspberry plantations in Wales and Scotland. In 1981, removal of 15 cm high young canes either by cutting or by spraying dinoseb-in-oil reduced infection of a second flush of canes (replacement canes) compared to that of the first flush of canes on untreated plots of cv. Mailing Delight in Wales and of cv. Glen Clova in Scotland. In 1982, removal of 20 cm high young canes reduced infection of cv. Mailing Delight in Wales but in Scotland only removal of 60 cm high canes by cutting reduced infection of replacement canes. Removal of all fruiting canes and old cane stubs reduced rust infection of young canes, but removal of successive flushes of replacement canes did not reduce infection of lateral shoots on the fruiting canes. Dinoseb-in-oil applied to the bases of fruiting canes before emergence of young canes had no effect on infection of young canes in Wales or Scotland. The production of basidiospores was inhibited in vitro by dinoseb-in-oil at concentrations over 1.0 μg a.i./ml.     

An Analysis of Spore Discharge in Sordaria

Sordaria fimicola can develop mature perithecia from which sporesare discharged when grown in darkness or in light. Under conditionsof alternating dark and light (12 hrs.: 12 hrs.) each day, sporedischarge is periodic with a low rate during the dark period,succeeded by a gradual rise to a relatively high rate in thelight period followed by a decline before the onset of the nextdark period. There is no trace of an endogenous rhythm. Transferfrom darkness to light always leads to an increase in the rateof discharge, and from light to dark to a decrease. The heightof the peak of discharge rate attained in light following adark period seems to be related to the length of the precedingdark period. Experiments with light of different colours but of roughly thesame energy value show that it is the blue rays that are mainlyeffective. From cultures of filter-paper yeast-extract mediuman orange pigment can be extracted with a maximum absorption,in the visible spectrum, at 470 mµ. It is possible thatthis is important in connexion with the sensitivity of the fungusto blue light.     

A new species of Centaurea (Asteraceae) from Sicily

A new species of Centaurea, Centaurea sicana , endemic to Sicily, is described. This new taxon is close to Centaurea parlatoris and Centaurea giardinae (Sect. Dissectae), the former occurring at Palermo and in the Madonie Mountains, while the latter occurs on the Etna volcano. The new species has so far been found only on the Sicani Mountains, a limestone mountain range in western Sicily, while the related species occur in the surrounding mountains. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 785–788.