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

Abstract

A reservoir of infection of Tapesia yallundae may exist after harvest in bases of cereal stems due to the presence of apothecia capable of discharging infective ascospores. Apothecia of T. yallundae developed in a seasonal pattern on winter barley inoculated with the pathogen, with maximum numbers of apothecia produced on stubble 5±7 months after harvest. A similar pattern of development was observed on infected winter wheat. However, the peak in numbers of mature apothecia was observed 2 months later than in winter barley. Apothecia capable of discharging ascospores were present for up to 6 months on stubble. Apothecia of T. acuformis were not detected on spring or winter barley, or spring or winter wheat stubble, despite inoculation of growing crops with isolates of compatible mating type.

Differences in MAT gene distribution and expression between Rhynchosporium species on grasses

“…the wild, as has been suggested for the closely related O. acuformis (Dyer et al, 2001). It should be noted that an exclusively asexual life cycle might contribute to the considerable success of Rhynchosporium as a plant pathogen: it allows the production of large numbers of conidia for dispersal in a shorter time than that required for ascospore production; there are lower metabolic costs associated with asexual than sexual sporulation; asexual reproduction can normally occur over a wider range of environmental conditions; and sexual recombination might break up favourable sets of genes (Dyer & O'Gorman, 2012;Lehtonen et al, 2012).…”

“…The data presented suggest that a lack of isolates of compatible mating types in natural populations is unlikely to be the reason, as had been suggested for some other fungal species (Dyer & Paoletti, ; Rhaiem et al ., ). Alternatively, it is possible that field isolates may require very specific environmental conditions to induce sexuality that may occur infrequently in the wild, as has been suggested for the closely related O. acuformis (Dyer et al ., ). It should be noted that an exclusively asexual life cycle might contribute to the considerable success of Rhynchosporium as a plant pathogen: it allows the production of large numbers of conidia for dispersal in a shorter time than that required for ascospore production; there are lower metabolic costs associated with asexual than sexual sporulation; asexual reproduction can normally occur over a wider range of environmental conditions; and sexual recombination might break up favourable sets of genes (Dyer & O'Gorman, ; Lehtonen et al ., ).…”

“…In addition, sequencing of the internal transcribed spacer region (Goodwin, 2002) revealed that R. commune is closely related to the discomycete species Oculimacula yallundae (synonym Tapesia yallundae; causal agent of eyespot disease of wheat) and Pyrenopeziza brassicae (light leaf spot of oilseed rape). Both of these pathogens, and the closely related Oculimacula acuformis (synonym Tapesia acuformis), have a heterothallic mating system, with known sexual cycles leading to the production of apothecia and airborne ascospores on their respective hosts (Dyer et al, 1996(Dyer et al, , 2001Gilles et al, 2001a). Based on the biology of these closely related crop pathogens, it is likely that, if a sexual cycle does exist for R. commune, it will involve the production of relatively small apothecia (<500 lm in diameter) that require rainfall for maturation on senescing host tissue (Dyer et al, 2001;Gilles et al, 2001a;Goodwin, 2002;Welham et al, 2004).…”

Distribution and frequency of mating types in the asexual fungusSeptoria passerinii

“…Stubble or residue was also required for sexual reproduction to occur under field conditions in the wheat leaf pathogens Leptosphaeria nodorum E. Müll. and Pyrenophora teres Drechsler (Dyer et al 2001). The perithecia of M. graminicola were found in wheat stubble collected during autumn and early winter in New Zealand, but perithecia were most numerous on old, diseased leaves sampled in early winter (Sanderson 1972).…”

First report of apothecia of Tapesia yallundae occurring on the wild grass Holcus lanatus (Yorkshire Fog) in New Zealand

“…The pathogen has also been detected on many wild and cultivated grasses even if characteristic eyespot symptoms are not visible (Lucas et al ., 2000). The pathogen exhibits a heterothallic mating system and apothecia of the sexual stage have been detected on straw stubble in many European countries, Australasia, southern Africa and North America (Dyer et al ., 2001). During field studies in New Zealand in 1995, apothecia resembling those of T. yallundae were discovered on decaying stem bases of Holcus lanatus (Yorkshire Fog) at the margin of one wheat field near Carterton, Wairarapa, North Island.…”