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Doctoral thesis, 2009

On Phaeosphaeria nodorum in wheat

Edin, Eva

Abstract

The fungus Phaeosphaeria nodorum (anamorph Stagonospora nodorum) causes stagonospora nodorum blotch on wheat. Besides environmental conditions the biology of the pathogen is an important parameter that determines the epidemiology of the disease. The dispersal pattern of the pathogen depends on the mode of reproduction. The studies reported in this thesis show that P. nodorum not only reproduces sexually but also sexually. This conclusion is based on the random distribution of the two mating types and the diverse genetic structure of the population. The sexual ascospores are windborne and able to initiate epidemics in new wheat fields, whereas asexual spores, conidia, give rise to new lesions when spread upwards in the canopy and to adjacent plants through splash water droplets. Isolates of P. nodorum vary in aggressiveness towards wheat in terms of latency period and production of pycnidia. The wheat cultivars commonly grown in Sweden have similar susceptibility to P. nodorum. Use of low inoculum concentrations could be useful in cultivar screening in breeding programs due to the comparability to natural infection. In agricultural practice, fungicides are used as a control of leaf spot pathogens. This thesis includes the first report of isolates of P. nodorum that have lost their sensitivity to the strobilurin substance azoxystrobin. The majority (79% of 227 isolates) of the P. nodorum isolates collected in 2003-2005 had the amino acid substitution g143a in the gene encoding cytochrome b, which is associated with loss of sensitivity to strobilurins in other pathogenic fungi. The substances propiconazole, prothioconazole and cyprodinil were efficient in reducing the fungal growth. Wheat leaves are colonised by other fungal species besides pathogenic fungi. The fungal community on wheat leaves also contains saprotrophic fungi and yeasts. P. nodorum was common in fields sampled in 2003 and 2004 but in 2005 the pathogenic fungi Pyrenophora tritici-repentis and Mycosphaerella graminicola, causing tan spot and septoria tritici blotch respectively, were more common in the sampled fields.

Keywords

triticum aestivum; cereal crops; varieties; leptosphaeria nodorum; stagonospora; fungal diseases; genetic variation; sexual reproduction; disease transmission; leaves; fungicides; sweden

Published in

Acta Universitatis Agriculturae Sueciae
2009, number: 2009:1
ISBN: 9789186195489
Publisher: Dept. of Forest Mycology and Pathology, Swedish University of Agricultural Sciences

Authors' information

Edin, Eva
Swedish University of Agricultural Sciences, Department of Forest Mycology and Pathology

UKÄ Subject classification

Agricultural Science
Microbiology

URI (permanent link to this page)

https://res.slu.se/id/publ/20007