30 research outputs found
The assessment of infectious-disease for brown rust (Puccinia hordei) of barley
The measurement of infectious disease (sporulating area), as opposed to the more conventional visually estimated total disease (sporulating area and chlorosis), was investigated for brown rust on spring barley. Visual estimates by four assessors of percentage leaf area occupied by uredinia overestimated the actual percentages by, on average, 8.7 times. It was concluded that better estimates of infectious disease came from uredinium densities (uredinium counts and measurements of leaf area). The progress of uredinium density in crops was exponential up to the time when leaves senesced at the end of their development. Three-parameter exponential functions were fitted to epidemics on 26 different leaf layers in five crops grown in three years. It is suggested that the lack of sigmoid progress curves, as would be found with conventional total disease assessment, occurred because chlorosis was excluded from the assessment. Chlorosis, which can affect a large proportion of leaf area, has an upper limit which gives rise to the asymptotic form of conventional disease progress curves. Uredinium densities had skewed distributions and the variances were correlated with the mean values. These characteristics were rectified most effectively by cube-root transformation. An incidence-severity relationship between the percentage of diseased leaves in a sample and the mean cube-root transformed uredinium density was linear up to incidences of about 83%
Relatieve luchtvochtigheid en windsnelheid en het dagelijks ritme in de verspreiding van urediniosporen van Puccinia arachidis
Stress-corrosion cracking in aluminum beverage can ends—issues, observations, and potential solutions
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The effect of potato variety mixtures on epidemics of late blight, in relation to plot size and level of resistance
Potatoes of a number of varieties of contrasting levels of resistance were planted in pure or mixed stands in four experiments over 3 years. Three experiments compared the late blight severity and progress in mixtures with that in pure stands. Disease on susceptible or moderately resistant varieties typical of those in commercial use was similar in mixtures and pure stands. In 2 of 3 years, there were slight reductions on cv. Sante, which is moderately susceptible, in mixture with cv. Cara, which is moderately resistant. Cara was unaffected by this mixture. Mixtures of an immune or near-immune partner with Cara or Sante substantially reduced disease on the latter. The effect of the size of plots of individual varieties or mixtures on blight severity was compared in two experiments. Larger plots had a greater area under the disease progress curve, but the average rate of disease progress was greater in smaller plots; this may be because most disease progress took place later, under more favourable conditions, in the smaller plots. In one experiment, two planting densities were used. Density had no effect on disease and did not interact with mixture effects. The overall conclusion is that, while mixtures of potato varieties may be desirable for other reasons, they do not offer any improvement on the average of the disease resistance of the components