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The association between willow (Salix) and rust (Melampsora) is highly specific. Willows named Salix burjatica, S. dasyclados (S. × dasyclados) and S. × calodendron are important in renewable-energy plantations in the UK and western Europe. There has been much controversy over their origin, species status and nomenclature. It has been suggested that they have originated from hybridization between. S. caprea, S. viminalis and S. cinerea. In the present work, 59 willow clones were investigated through morphological examination and detached leaf inoculation using willow differentials, for their association, in southwest England, with M. capraearum and three pathotypes of Melampsora epitea (Me-A, B and C). M. capraearum was found on all clones of S. caprea and its hybrids with S. aurita; Me-A on all S. viminalis clones; Me-B on wild S. cinerea, S. × calodendron, S. × dasyclados'De Biardii 445' and S. 'Spaethii'; Me-C on all S. burjatica clones and most S. × dasyclados clones. Both M. caprearum and Me-A infected all S. × sericans (S. caprea × viminalis) clones and S. × dasyclados'LA041/03'. We suggest that S. × dasyclados'LA041/03' should be treated as S. × sericans (S. caprea × S. viminalis); S. burjatica, S. dasyclados and S. × dasyclados as synonyms; S. × dasyclados 'De Biardii 445' as S. × calodendron 'De Biardii 445'; and S. 'Spaethii' as S. × calodendron 'Spaethii'. [ABSTRACT FROM AUTHOR]

Eighteen isolates of the rust fungus Melampsora from different locations in England were tested for pathogenicity to a large range of willow clones (Salix spp.) in experiments involving inoculation of leaf discs. Seventeen of the isolates were of leaf-infecting M. epitea var. epitea, 16 of which represented forms which alternated on Larix and one of which alternated on Ribes. The remaining isolate was of uncertain identity. Two experiments were carried out. In the first exp>eriment, 24 willow clones consisting of 20 Salix species and interspecific hybrids were inoculated with eight isolates from clones of S. viminalis. In the other experiment, 77 clones from 57 species or hybrids were inoculated with 10 isolates from several Salix spp. The M. epitea var. epitea isolates from S. viminalis clones were all similarly pathogenic, whilst most of the other isolates expressed distinct host specificity. Eight distinct pathotypes were recognized within M. epitea var. epitea. All except one of these alternated on Larix and could be assigned to three formae speciales which had been reported previously in Europe: four pathotypes to f.sp. larici-epitea typica, two to f.sp. larici-retusae, and one to f.sp. tarici-daphnoides. The Ribes-alternating pathotype of M. epitea var. epitea infected only S. purpurea. Nine differential willow hosts are proposed as reference clones to distinguish between the larch-alternating pathotypes, the Ribes-alternating rust and the ‘stem-infecting’ form. The extent of pathogenic variation encountered amongst sexually reproducing rusts suggests that more pathotypes probably exist and will arise in future in response to selection given by long-term clonal willow plantings. [ABSTRACT FROM AUTHOR]

Epidemics of disease caused by Septoria tritici were studied in detail in 11 crops of winter wheat cv. Longbow over 4 years. Serious damage to the uppermost two leaf layers was caused by splash-borne infection from lower in the crop early in the life of the leaves, followed by one or rarely two cycles of multiplication within a leaf layer. Infection conditions rarely limited damage, even in a dry year; the timing and, to a lesser extent, amount of initial inoculum movement to an upper leaf layer was of greater importance. Timing of initial infection was determined by when rain splash occurred in relation to emergence of a leaf layer. Occurrence of infections soon after a leaf layer started to emerge allowed more time for multiplication of disease within that layer. These infections tended to be more severe because the leaves were closer to inoculum sources within the crop. Slight differences in phenology between locations explain why initially random disease distributions sometimes become aggregated. Early-sown crops are at greater risk because they mature more slowly, allowing more disease multiplication and better transfer between leaf layers. [ABSTRACT FROM AUTHOR]

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 assessments, 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%. [ABSTRACT FROM AUTHOR]

The pattern and extent of primary infection by Septoria tritici were compared over a period of 3 years in winter wheat grown at sites with differing histories and from seed stocks obtained in different countries. in the open under airtight cover and in sterilized soil. Only the airtight cover altered the number of lesions found, substantially reducing it. Lesions were evenly distributed. Lesions were found throughout the autumn and occasionally in the winter and spring on wheat seedlings exposed in trays to the open air for periods of 1 week, then given good conditions for infection to occur. This was true even at a site 0-4 km distant from wheat residues, The results show that the main source of primary infection of winter wheat in these experiments was evenly dispersed and airborne. It probably consisted mainly of ascospores of Mycosphaerella graminicola. [ABSTRACT FROM AUTHOR]

In some crops of winter wheat selected from a range monitored in Western Europe during 1981-83, Septoria nodorum and S. tritici were spatially very uniformly distributed from the beginning of the growing season onwards. A cube root transformation produced a constant variance in lesion numbers per leaf, similar for both pathogens at about 0.5. This permits the sample size needed for a given accuracy to be estimated. Counts of conidia washed from leaves by a standard procedure had a constant coefficient of variation, independent o[ disease level. Large samples would be necessary for accurate counts, particularly if leaves from different layers were examined separately. The pattern of lesion numbers on leaves was best described by a negative binomial distribution: this predicts an incidence-severity curve to which the data conformed closely. Hence incidence estimates can be used to estimate severity, which may be more economical of sampling effort. Correlations between lesion counts on different leaves of the same tiller were negative and highly significant for S. nodorum in 1982, but positive and significant for S. tritici in 1983. The causes of this difference are unknown. [ABSTRACT FROM AUTHOR]

This article cites a study that examined the side-effects of downy mildew fungicides on the incidence of hop powdery mildew in England. In a trial on 10 acres of hops in 1972, three downy mildew fungicides were superimposed on to a routine dinocap schedule and compared for their effects on powdery mildew control. Both mildew diseases built up to fairly high levels between the last spray applications and harvest. Copper oxychloride was significantly superior to zineb in restricting development of powdery mildew in hop cones while propineb appeared to be only slightly inferior to copper.

Recent outbreaks of hop black root-rot in England are described in relation to the disease in New Zealand and to previous records in this country. Rates of growth along detached hop storage roots were compared for several isolates of Phytophthora citricola from hop and other host plants. Isolates from New Zealand hops and recently diseased plants in England could not be distinguished from one another, but the original English isolate, obtained in 1942, appeared to be a distinct strain. A number of commercial cultivars exhibited differential responses to infection by the fungus in both detached root and entire rootstock inoculations. The cultivars Northern Brewer and Progress were amongst the most resistant. [ABSTRACT FROM AUTHOR]