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Doctoral thesis, 2011

Setosphaeria turcica, fungal mating and plant defence

Martin, Tom

Abstract

The heterothallic ascomycete Setosphaeria turcica (anamorph: Exserohlium turcicum) causes turcicum leaf blight on maize and sorghum. A survey was undertaken in Uganda to examine the sorghum – S. turcica interaction in terms of disease severity and incidence, overall fungal population structure, and new resistant resources. Highest disease severities were recorded on caudatum accessions, whereas kafir genotypes were most resistant. Highly resistant sorghum accessions originating from a regional collection were found among the five local sorghum races. The disease was more severe in the most humid farmlands. Upon cross inoculation on maize differential lines, S. turcica isolates corresponding to race 0, 1, 2 and 3 were found, increasing the number of known races in Uganda. The two S. turcica mating type genes MAT1-1 and MAT1-2 were found in 20 of 23 districts sampled and in equal proportions on sorghum and maize indicating that sexual recombination is present in Uganda. Fungal mating types in Pezizomycotina are characterised by genes encoding either an HMG or α1 domain protein, occupying the same locus on corresponding chromosomes. We present sequence comparisons, phylogenetic analyses, and in silico predictions of secondary and tertiary structures, which support our hypothesis that the α1 domain is related to the HMG domain and share a common ancestor. We have also characterized a new conserved motif in α1 proteins of Pezizomycotina. This motif is immediately adjacent to and downstream of the α1 domain. The S. turcica genome contains 123 unique protein sequences not found in related fungi. These are of importance for plant cell wall degradation, ion-binding and transport. Genome comparisons of maize versus Brassica infecting fungi revealed 628 maize specific protein groups including a number of potential effectors. Six NB-LRR encoding St genes residing in three pairs in one locus on chromosome 5 in sorghum were found to mediate resistance to S. turcica. The St gene homologs have all highly conserved sequences, and commonly reside as gene pairs in the grass genomes.

Keywords

setosphaeria turcica; blight; fungal diseases; evolution; genes; zea mays; sorghum; uganda

Published in

Acta Universitatis Agriculturae Sueciae
2011, number: 2011:66
ISBN: 978-91-576-7610-8
Publisher: Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences

Authors' information

Martin, Thomas
Swedish University of Agricultural Sciences, Department of Plant Biology

UKÄ Subject classification

Plant Biotechnology
Botany

URI (permanent link to this page)

https://res.slu.se/id/publ/34917