Strip-cankering of beech (Fagus sylvatica): Pathology and distribution of symptomatic trees

The pathology and distribution of European beech trees bearing elongated bark lesions (strip-cankers) were investigated. Two types of canker were recognized: those on small trees (<40 cm diameter at breast height (dbh): 1·4 m above ground level) which bore fruit bodies of the xylariaceous ascomycete Biscogniauxia nummularia (Bull.) O. Kuntze, and those on larger specimens (>40 cm dbh) which were consistently associated with the diatrypaceous ascomycete Eutypa spinosa (Pers.) Tul. & C. Tul. All cankers were strictly annual, having formed during single growing seasons following periods of low water availability. The regional and local distribution of trees bearing lesions also appeared to be correlated with environmental conditions, being most severe where low rainfall or high temperatures had occurred. Population studies of the associated fungi, generally considered as saprotrophs, indicated the presence of unique genotypes within individual cankered trees and provided no evidence for the existence of pathotypes within either species. Within the decay columns which underlay canker surfaces, both B. nummularia and E. spinosa formed longitudinally extensive genets, implying non-mycelial spread in colonization. Suppression of both inter- and intraspecific incompatibility between fungi occurred in regions of canker decay columns with elevated water contents. The possible significance of coexistence between the ascomycetes B. nummularia and ' Hypoxylon purpureum ' ( sensu Sharland & Rayner, 1989 b ) and of the formation of heterokaryons by E. spinosa is discussed.     

The Role of Thiamine as a Factor for the Growth of Brochothrix thermosphacta

Thiamine enhances growth of the meat spoilage organism, Brochothrix thermosphacta. It fulfils some, but not all, of the yeast-extract requirement of this organism. Oxythiamine acts as a growth inhibitor at high concentrations and the inhibition is readily reversed by thiamine. The possible roles of thiamine in the metabolism of Br. thermosphacta are discussed.     

THE MEASUREMENT OF TASTE DISCRIMINATION WITH THE SAME-DIFFERENT TASK: A DETECTION-THEORY ANALYSIS

The biases to which the same-different task is prone can be accounted for by having subjects rate their confidence that two stimuli are the same or different. The rating method of detection theory was therefore used to study the discriminability of two concentrations of a fruit drink. A model in which the decision variable was the difference in sensory strength of the two samples provided a satisfactory fit to the Receiver Operating Characteristics of four of the five subjects. The bias-free index of discriminability, d', was estimated for each subject. A combined operating characteristic, derived from jackknifing the data of the individual subjects, revealed an asymmetry characteristic of the differencing model. The results suggest that the same-different task, which is readily understood by subjects, can provide an unbiased measure of the discriminability of foods or beverages.     

Quantitative Studies on the Generation of Aerosols of Erwinia carotovora var. atroseptica by Simulated Raindrop Impaction on Blackleg-infected Potato Stems

Quantitative studies on the generation of bacterial aerosols by simulated raindrop impaction on potato stems infected with the blackleg organism Erwinia carotovora var. atrosep:ica have shown that, theoretically, airborne transmission might result in re-contamination of blackleg-free potato stocks.