Gillian M. Arnold

The temporal relationship between host cell death, phytoalexin accumulation and fungal inhibition during hypersensitive reactions of Phaseolus vulgaris to Colletotrichum lindemuthianum

Resistance of bean hypocotyls to a compatible strain at Colletotrichum lindemuthianum , race γ, was induced by incubating inoculated hypocotyls at 16°G for 72 h, which allowed the formation of short infection hyphae, and then transferring them to 25°G. Incubation at 25°G led to premature death of the infected cell and inhibition of the fungus therein. This response, being similar to the hypersensitive reaction shown by beans to incompatible races of this fungus, was termed “temperature dependent hypersensitivity”. The amount of fungal growth which occurred during resistance to race γ was much greater than that during normal hypersensitivity and this enabled measurements to be made of the lengths of intracellular hyphae throughout the resistance process i.e. from the time of transfer to 25°G until cessation of fungal growth. Comparative measurements of fungal growth, of the onset and development of host necrosis and of the amounts of phytoalexin within the infected tissue indicated that death of infected cells occurred several hours before phytoalexins formed and that inhibition of hyphal growth occurred shortly after the phytoalexins began to accumulate. These findings are consistent with the view that accumulated phytoalexins are responsible for restricting growth of intracellular hyphae during resistance of beans to C. lindemuthianum .

The effects of paclobutrazol and daminozide on the growth and yield of cider apple trees

SummaryThe effects of soil applications (1, 2 or 4 kg a.i. ha-1 to give 0.25, 0.5 or 1.0 g a.i. per tree) or foliar sprays (1000 or 2000 mg l-1 to give 2 or 4 g a.i. per tree) of paclobutrazol (PP 333) were compared with those of foliar daminozide (Alar) sprays (2000 mg l-1 to give 4 g a.i. per tree) on bush cider apple cv Michelin for two years. Extension shoot growth was significantly reduced in the year of application (Year 1) by foliar paclobutrazol and daminozide sprays, and in the following year by the foliar and high-rate soil-applied paclobutrazol but not by daminozide. Foliar applications of paclobutrazol reduced leaf size and darkened leaf colour, delayed flowering and enhanced fruit set. Yields were not affected by any treatment.

Leaf demography in willow short-rotation coppice.

Abstract The production, survivorship and death of cohorts of leaves within the canopies of three clones ( Salix burjatica “Korso”, S. viminalis “Mullatin” and S. x dasyclados ) of willow grown as short-rotation coppice were studied in a field experiment. The initial rate of increase in leaf number was fastest for “Mullatin”, which also had the steepest rate of decline in net leaf number. Inter-clonal variability was not reduced by plotting changes in leaf number against thermal time, accumulated above 0°C. Mean number of leaves was highest for “Mullatin” and least for “Korso”. Leaf production occurred in flushes and there were no significant clonal differences in the relative rate of leaf birth: differences in relative rate of leaf death ( r d ) became apparent after day number 230 (1 Jan = 1); thereafter “Korso” had higher values of r d than the other clones. The time course of r d was summarised by a logistic curve and there was no evidence that the initial asymptote nor the maximal rate of change of r d differed between clones. Leaves of “Korso” had minimum and maximum longevities of about 25 days (or about 250°Cd in thermal time) and 65 days (about 1000°Cd), respectively; minimum leaf longevities for the other two clones were similar to that for “Korso” but their leaves lived for up to 100 days (about 1400°Cd). Changes in the age-structure of the leaf populations with time were little influenced by differences in leaf demography between clones. A positive and significant correlation was found between the rate of production of leaves and temperature up to about 14°C. Thereafter, the correlation was either absent or negative. Results are interpreted in terms of the consequences of differences in canopy demography for coppice biomass production.

Indirect interactions between rust (Melampsora epitea) and leaf beetle (Phratora vulgatissima) damage onsalix

Willows (Salix spp.) are beneficial as a potential source of renewable energy, riparian barriers and riverbank control, yet are considered invasive weeds when they clog watercourses and lead to erosion and flooding. Interactions between willow rustMelampsora epitea (Thüm.) (Uredinales: Melampsoraceae) and leaf beetlePhratora spp. (Coleoptera: Chrysomelidae) feeding damage have an impact on effective pest management and biological control. The present study investigated the effects of(a) prior mechanical leaf damage on rust development, and(b) rust infection on beetle feeding under laboratory conditions for different time intervals and levels of damage. Willow rust infection significantly reduced the amount of leaf area consumed by beetles. The result was similar when a compatible or an incompatible rust pathotype was sprayed ontoSalix viminalis (L.) ‘Mullatin’ plants. There were no overall significant effects of mechanical damage on rust development, although the lowest level of rust infection was found with the incremental damage treatment. There were, however, differences of significance for leaf position and damage status, with damaged leaves at all positions having fewer pustules and a smaller pustule area than the corresponding undamaged leaves. There was no detectable effect of possible volatile emissions from crushed willow leaves on rust infection and development, although the volatile compoundcis-3-hexenyl acetate significantly reduced pustule diameter and overall pustule area. The results are discussed in terms of the implications for pest management and biological control.

The effect of picking date on blossoming and fruit set in the following year for the apple cv. Bramley's Seedling.

SummaryBramley’s Seedling apple trees were picked on four different dates in 1978 (23 August, 16 September, 4 and 26 October). Fruit weight almost doubled between the first and the last pickings. Blossom cluster counts in the following year indicated a significant effect of picking date on flower production, with a strong trend for more flower clusters after early picking. There was a highly significant decrease in final fruit set in 1979 relative to first to last picking dates in 1978. The possible effect of early picking and subsequent warm weather on assimilate reserves, and the role of such reserves in stimulating flowering and fruiting are discussed.

The influence of presentation factors on the sensory assessment of beverages

Abstract Presentation order and preceding samples are known to influence the perception of sensory attributes. In conventional tasting procedures these effects are normally allowed for by the use of suitable experimental designs for assessment order and by averaging responses over assessors. However, it is also important to know how these effects influence perception. Experiments to evaluate and differentiate these order effects when assessing ciders indicated order effects to be most pronounced between first and subsequent samples, with strong characteristics building up during a session. The effect of a preceding sample appeared greater than later order effects and tended to amplify opposite characteristics.

The effect of paclobutrazol on the growth of cider apple trees, cv Michelin, when applied to orchard alleyway swards to suppress grass growth

SummaryPaclobutrazol was applied, with or without mefluidide, to the grassed alleyways between the bare soil tree lines in a bush cider orchard cv Michelin. The chemical not only suppressed grass growth but, in the year following application, produced typical paclobutrazol effects on the trees in adjacent rows including a reduction in growth.