Masterman, Andrew John
(1991)
The epidemiology and forecasting of barley yellow dwarf virus in autumn-sown cereals.
PhD thesis, University of Glasgow.
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Abstract
BYDV is sporadic and potentially damaging to autumn-sown cereals in Britain. Currently, the risk of the disease is assessed during the autumn via Infectivity Indexing (II). However, II has a number of limitations. Three mild winters in the late 1980s allowed anholocyclic overwintering of aphids in autumn-sown cereals. In the following springs, widespread and sometimes severe BYDV problems were reported from many parts of Britain. This benefited this research, and also highlighted the importance of weather to aphids and BYDV epidemiology. BYDV occurs as two types: R. padi- and S. avenae-transmitted BYDV. Monitoring of winter barley revealed that these two types not only differ in their propensity to cause yield loss, but also that they have different preconditions. These pre-conditions are weather-related, suggesting that BYDV risk to autumn-sown cereals may be forecast by considering weather patterns in the preceding year. However, the crop sampling also suggests that risk assessments should include aphid monitoring, both in the summer and the autumn: this is necessary if regional differences in BYDV risk are to be identified. Results of BYDV transmission tests with field-collected aphids were largely consistent with laboratory observations: characteristic vector-specificity and vector-efficiency were encountered, and transcapsidation and transmission interference appeared to be common. There were significant differences in BYDV transmission, for both R. padi and S. avenae between host plants, and between years. Analysis of 12.2 m suction trap catches of cereal aphids drew attention to the sensitivity of aphid populations to weather. Both the temperature of the preceding winter and the current spring affect the size of spring aphid catches. With respect to the size of the autumn migration of Rhopalosiphum padi, the temperature of the preceding winter, and the weather of the preceding summer are important, as is the size of the previous autumn's migration. Sampling of a number of habitats for cereal aphids, identified the importance of cereal fields during the summer, both pre- and post-harvest, to S. avenae populations, and ryegrass pasture to R. padi populations. Comparisons of the aphid/BYDV data in winter barley of a region in one season with the comparative data of the following season, suggested local movement of S. avenae. In the three years of study, II failed to assess the BYDV risk to autumn-sown cereals correctly. Apart from mild winters, the failure was due to the importance of aphid morph to R. padi-transmitted BYDV. The proportion of the R. padi migration which is comprised of exules is crucial to the extent of colonisation of autumn-sown cereals by alatae.
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