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Development of genetically homogenised populations of the crown rust pathogen (Puccinia coronata f. sp. lolii ) for disease trait dissection in perennial ryegrass (Lolium perenne L.)

Research paper by P. M. Dracatos, M. P. Dobrowolski, J. Lamb, R. S. Olle, A. R. Gendall, N. O. I. Cogan, K. F. Smith, J. W. Forster

Indexed on: 01 Jan '09Published on: 01 Jan '09Published in: Australasian Plant Pathology



Abstract

Genetic analysis of host resistance to the crown rust pathogen of ryegrasses has traditionally involved the use of composite urediniospore collections, which may contain multiple genotypes and virulence races. Consequently, discrimination between major gene responses to alternative races and quantitative resistance has proved challenging for disease trait-dissection studies.Amethod of propagation on detached leaves has been used to derive genetically homogenised crown rust pathogen lines from bulked spore collections obtained from five distinct Australian locations. Spores from individual pustules were repeatedly reinoculated onto fresh leaves. Amplicon complexity was assessed at the conclusion of each cycle using crown rust pathogen expressed sequence tag (EST)-derived simple sequence repeat (SSR) primer pairs. The mean number of amplification products per isolate declined over successive rounds of reinfection. The number of rounds of sequential infection required for decay to stable levels was dependent on the diversity present within the bulked spore collection. Large-scale propagation of the putative homogenised populations developed in the present study may provide inoculum for infection studies to allow quantitative trait loci mapping of specific gene-for-gene responses. The methodology has significant applications for the pyramiding of resistance genes specific to diverse crown rust pathogen genotypes during cultivar development and for pathotyping of existing elite germplasm. This approach is also applicable to other Puccinia species.