Incidence of apothecia of Tapesia yallundae at setaside sites in England and sensitivity of the ascospore offspring to the fungicides benomyl and prochloraz

Abstract

A total of 45 field sites in England were surveyed once for the presence of apothecia of Tapesia yallundae from 1992 to 1994. Apothecia were found at 21 locations and were mainly present on less than 3% of stems. However, apothecia were found on 1532% of stems at four sites. Analysis of the growth characteristics of ascospore isolates from seven sites showed that most produced colonies characteristic of the W‐type of T. yallundae, with only one site yielding the R‐type, Most ascospore isolates were resistant to the fungicide benomyl and effectively all remained sensitive to prochloraz. The results of the study are discussed in relation to the fungicidal control and epidemiology of T. yallundae, and the risk of spread of disease from set‐aside sites.

Development of apothecia of the eyespot pathogen Tapesia on cereal crop stubble residue in England

“…In the first, apothecia were shown to develop on 1–2% of straw stems at nine out of 37 stubble sites in Germany (King, 1991). Similar results were found in a later survey of the UK, with apothecia detected at 20 of 41 set‐aside sites sampled, mainly on less than 3% of stems but on 15–32% of straw stems at some sites (Dyer & Lucas, 1995).…”

“…These apothecia discharged ascospores that gave rise to mycelial colonies bearing conidia corresponding to the W‐type of P. herpotrichoides and the teleomorph was named Tapesia yallundae (Wallwork, 1987; Wallwork & Spooner, 1988). Apothecia of T. yallundae have since been detected in the field in New Zealand, many European countries and in South Africa (Sanderson & King, 1988; Hunter, 1989; Moreau et al ., 1989; Cavelier, 1994; Robbertse et al ., 1994; Sindberg et al ., 1994; Dyer & Lucas, 1995). In all instances, apothecia were found only on straw stubble left after harvest, rather than on living plant hosts.…”

Genetic Control of Resistance to the Sterol 14α-Demethylase Inhibitor Fungicide Prochloraz in the Cereal Eyespot Pathogen Tapesia yallundae

“…Progeny and parents from crosses between strains sensitive to prochloraz and strains resistant to prochloraz were assayed on growth media amended with either 0.05, 0.15, 0.5, 1.0, 2.0 or 5.0 mg of prochloraz per liter, by inoculating plates with three replicate hyphal plugs (13). Values for the percent growth inhibition relative to that observed on unamended control plates were plotted graphically, and IG 50 s were derived from best-fit line equations.…”

Development of apothecia ofTapesia yallundae in contrasting populations selected by fungicides

“…This does not necessarily indicate that sexually compatible isolates [Dyer et al, 1993] were already present in the field population because isolates were applied to some plots in 1984 and their mating types were not determined. Other work suggests that sexual reproduction may occur frequently in fields of standing stubble left after an eyespot-infected wheat crop [Dyer and Lucas, 1995]. This is likely to become increasingly common with the establishment of rotational set-aside [Ansell and Tranter, 1992], a procedure likely, therefore, to increase genetic recombination and opportunities for variation in the pathogen.…”

“…Although a slight decrease in sensitivity to prochloraz has been detected in the R-type fungus in populations that had been exposed to repeated applications of prochloraz in this experiment [Bateman et al, 1995] and in other experiments in France [Migeon, Mathon and Chudzicki, 1993], no isolates with effective resistance to prochloraz was found during screening of the ascospore progeny. However, W-type ascospore isolates with a five-fold range in sensitivity have been found elsewhere [Dyer and Lucas, 1995]. Sexual reproduction between field strains with decreased sensitivity to prochloraz may result gradually in decreased sensitivity in populations of T. yalIundae.…”