Some aspects of the epidemiology of yellow rust on wheat

McGregor, Alastair John (1977) Some aspects of the epidemiology of yellow rust on wheat. University of Southampton, Doctoral Thesis.

Abstract

Experiments wore conducted on the effects of light intensity and temperature on the growth and sporulation of yellow rust on wheat (Pucclnia striiformis West.) and field experiments were conducted to investigate the effects of meteorological factors on epidemic progress. All experiments used race 104 E 137 and three cultivars of contrasting resistance to this race: Maria Huntsman, Maria Nimrod and Marie Beacon.excess of 887., measured in a Stevenson screen, was highly correlated with observed infection in the field on both mature and seedling leaves.Correlation of epidemic progress with weather data by multiple regression was largely unsuccessful owing to the complex nature of the relationship. A visual comparison revealed that a two-week period of low rainfall, mean daily temperatures in excess of 130 and daily maxima in excess of 200 curtailed yellow rust epidemics, but heavily infected leaves desiccated and large yield losses resulted.A provisional critical period model for yellow rust epidemic development was constructed and compared with epidemic progress on field plots in 1973;it was concluded that it would have predicted the optimum fungicide application i date to prevent an 8% yield loss due to yellow rust.The ranking order of the three cultivars was consistent for all components of rust growth and eparulation where cultivar had a significant effect. It was concluded that in these cultivars field resistance could be predicted from glasshouse seedling experiments, and that measurements of sporulatibn from a point inoculation of a leaf was the most useful method of detecting cultivar resistance. Suggestions have been made as to the conditions most suitable for the detection of possible field cultivar resistance using seedlings.The main effect of light was on spore production per unit area; light intensity did not affect latent period or colonisation rate. The number of pustules per unit area of infected leaf and the daily sporulation rate per 2pustule increased linearly with increasing light over the range 10 to 50 Win- and it was concluded that light intensities loss than the photosynthenin saturation level would be limiting for yellow rust spore production. The main effects of temperature were on mycelial growth rate and longevity of sporulation the optimum temperature for yellow rust growth was about 15. Between 7 and 15 temperature had a linear effect on rust growth, but differences in total spore production per leaf were small owing to the reduced duration of sporulation at the higher temperature. A temperature of 20° reduced all components of rust growth and sporulation on all cultivars, but daily sporulation rate on Nimrod and Huntsman was reduced to a far greater degree than that on Beacon. Spore germination in the field was highly variable and not correlated with any of the weather factors measured. Periods of 5h. of relative humidity.

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