Detection, breeding and selection of durable resistance to brown rust in sugarcane

Document Type

Article

Publication Date

11-1-2017

Abstract

Brown rust, caused by Puccinia melanocephala, is an important disease of sugarcane in Louisiana. The adaptability of the pathogen has repeatedly resulted in resistant cultivars becoming susceptible once they are widely grown. The frequency of the brown rust resistance gene Bru1 was low in the breeding and selection populations in Louisiana. Through markers-assisted screening and selection, the frequency of Bru1 is increasing in the breeding populations being developed for gene introgression. Bru1 has provided resistance in diverse germplasm across widespread regions. However, over reliance on one resistance source is inadvisable. Development of a controlled conditions inoculation method allowed evaluation of cultivar reactions to pathogen urediniospore populations collected from major cultivars that had become susceptible. These experiments demonstrated virulence specialization within the pathogen to host genotypes. In addition, quantitative resistance providing a partial but effective level of resistance to all pathogen urediniospore populations under conditions highly favorable for infection was detected in one cultivar, L99-233. Researchers are attempting to identify genes associated with quantitative resistance in this cultivar and develop molecular markers. A small-scale transcriptome analysis of L99-233 through suppressive subtraction hybridization identified genes involved in primary metabolism, signal transduction, nucleic acid binding and protease activities to be differentially expressed in response to fungal infection. Analysis of expression kinetics of a selected set of genes showed transient upregulation of their mRNA accumulation in susceptible cultivars, but their transcripts were also upregulated up to 1 week post-inoculation in the resistant cultivars. The maintenance of high amounts of mRNAs of the genes for a prolonged time period appeared to be the contributing factor for resistance to brown rust. Breeding and selection for Bru1 and other genes for quantitative resistance could provide effective and durable resistance to brown rust in future cultivars.

Publication Source (Journal or Book title)

International Sugar Journal

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