G.L. Bateman

Development of stem-base pathogens on different cultivars of winter wheat determined by quantitative PCR

The progress of development of stem-base pathogens in crops of second winter wheat was plotted in nine experiments in three years. The amount of each pathogen present was determined by quantitative PCR. Where Tapesia yallundae was present in quantifiable amounts, it usually developed earlier than the other eyespot pathogen, T. acuformis. Both species were usually present in greater amounts on cultivars which are more susceptible to eyespot. The sharp eyespot pathogen, Rhizoctonia cerealis, developed more erratically than either of the Tapesia spp. and there were no consistent effects on different cultivars. Fusarium spp., the cause of brown foot rot, were rarely present in quantifiable amounts, but Microdochium nivale was usually present as one or both of the varieties nivale and majus. Late-season (after anthesis) decreases in M. nivale suggest that any brown foot rot symptoms attributable to this fungus would have fully developed earlier. Cultivar differences in amounts of M. nivale were most clear in stems during internode extension and when relatively large amounts of DNA were present. Such differences approximately reflected eyespot susceptibility, cv. Soissons containing most and cv. Lynx containing least DNA. The results emphasise the difficulty in relating diagnoses, by quantitative PCR or other means, at early growth stages when decisions to apply fungicides against stem-base disease are made, to later disease severity.

Comparisons of isolates of the take-all fungus, Gaeumannomyces graminis var. tritici, from different cereal sequences using DNA probes and non-molecular methods.

Abstract A mitochondrial ribosomal DNA probe (pEG34) that distinguishes two main restriction fragment length polymorphism (RFLP) types of isolate of the take-all fungus Gaeumannomyces graminis var. tritici was used to compare isolates from different host species. RFLP analysis confirmed that one type (designated T2), unlike the other type (T1), was associated more with barley than with triticale or wheat. RFLP analysis and other methods were also used to compared isolates of the take-all fungus from wheat seedlings grown in soil from first and second wheat crops, from wheat crops grown in longer sequences, and from oat crops grown as breaks from susceptible cereals. These provided samples from different stages of disease build up and decline in the take-all epidemic. Differences in frequencies of some characteristics were found at conventional significance levels (P ≤ 0.05): in a cereal sequence experiment at Rothamsted, U.K., isolates containing dsRNA were less frequent in T2 isolates than T1 isolates except in second wheats; perithecia were produced more abundantly on roots of wheat seedlings inoculated with T1 isolates than with T2 isolates, regardless of their origin. A weaker association (P ≤ 0.1) was also found: T2 isolates were often more frequent from second wheat crops, before take-all peaked in wheat sequences, than from other wheat crops or oats break crops. Collectively, the findings add only modest support to the controversial hypothesis that changes in the population of the take-all fungus occur during repeated cropping of wheat. The limitations of traditional sampling and assessment methods in such studies are discussed.

Changes in populations of Pseudocercosporella herpotrichoides in successive crops of winter wheat in relation to initial populations and fungicide treatments

Abstract The effects of two applications annually of carbendazim, prochloraz or a mixture of carbendazim and prochloraz on five populations of the eyespot fungus, Pseudocercosporella herpotrichoides , were studied in successive crops of winter wheat. Initially, populations were established by inoculation of plots with mixtures of isolate types which were mainly MBC-sensitive W-type, MBC-resistant W-type, MBC-sensitive R-type or MBC-resistant R-type. Further plots which were not inoculated had, initially, a mainly MBC-sensitive W-type population. Plants were sampled each April and July for 3 years. Carbendazim treatments resulted in an almost entirely MBC-resistant population by July of the first year, regardless of the proportion of MBC-resistant isolates in the initial inoculum. Although treatment with prochloraz greatly decreased populations of the eyespot fungus, its effect on the number of MBC-sensitive isolates was usually not significant. Prochloraz effectively controlled the MBC-resistant fungus and was usually more effective against the W-type than the R-type of the fungus. Treatment with the mixture of carbendazim and prochloraz also greatly decreased populations, but the selective effect of each component fungicide was less marked. Regardless of fungicide treatment, a smaller proportion of R-type isolates was recovered from severe than from slight stem lesions in July, indicating that the times of lesion establishment or rates of development of the R-type and W-type were not the same. Migration of fungal types between plots appeared to have little influence on the outcome of selection.

Coemansia species from the rhizospheres of wheat and barley in the United Kingdom

Coemansia aciculifera, C. scorpioidea and C. thaxteri were found in the rhizosphere of wheat and a fungus resembling C. spiralis was found in the rhizosphere of barley from two fields in eastern England when serially washed root pieces were incubated on low nutrient agar (SNA).

Morphological variation in the Coemansia spiralis complex

The possibility that the Coemansia spiralis complex contains three species is discussed on the basis of six descriptions. The name C. spiralis is retained for the fungus first described with the appropriate generic placement and incorporates C. nantahalensis. The second species, for which preserved material is not available, is named as C. bainieri nom. nov., and C. linderi sp. nov. is the third species.

Mycoparasitism of Coemansia species

The mode of hyphal interaction and parasitism of Coemansia spp., mainly C. aciculifera and C. thaxteri, by Gliocladium roseum, Fusarium flocciferum and Verticillium psalliotae, species that occurred with the Coemansia spp. in wheat rhizospheres, was observed in mixed cultures on low nutrient medium. Two types of interaction occurred. G. roseum and F. flocciferum coiled round, penetrated and grew within the hosts hyphae. V. psalliotae grew parallel to and along the hosts hyphae, coiling only rarely, and sometimes formed thick mycelial layers on the hosts sporangiophores. After infection by each fungus, the hosts hyphae became narrower, collapsed and then disintegrated. The observations suggest parasitism followed by lysis rather than the involvement of antibiotics.

Four rare microfungi from the rhizosphere of wheat in the United Kingdom

Four rare microfungi, Dactylaria appendiculata, Exserohilum novae-zelandiae, Monacrosporium psychrophilum and Pleurocatena acicularis, were found when root pieces taken from wheat crops were incubated on low nutrient agar (SNA).

Fungicidal control of foliar diseases of white lupin (Lupinus albus)

Abstract A range of fungicides was tested against rust (Uromyces lupinicolus) and brown spot (Pleiochaeta setosa) on autumn-sown white lupin (Lupinus albus) in three experiments in harvest years 1995, 1997 and 1998. Rust was severe in all three years but did not develop in an additional experiment in 1996. Brown spot occurred only in 1997 and 1998 when natural inoculum was augmented by an artificial source and weather conditions were favourable for inoculum dispersal and disease development. Tebuconazole was the only fungicide tested that controlled rust consistently, whereas iprodione+thiophanate-methyl, tebuconazole and prochloraz each decreased the severity of brown spot. Yield increases in 1997 and 1998 were thought to be attributable mainly to control of rust. Fungicides were most effective when applied as soon as symptoms were observed. Two applications of an effective fungicide generally controlled disease more than a single application; a third application gave no additional benefit.

Ramulispora cerealis sp. nov. from the stems of cereals in the United Kingdom.

A new species of Ramulispora, R. cerealis sp. nov., isolated from the stem base of a barley plant, is described.