Location: Sugarcane ResearchTitle: Detection, breeding, and selection of durable resistance to brown rust in sugarcane
|HOY, J - LSU Agcenter|
|BAISAKH, N - LSU Agcenter|
|AVELLANEDA, M - LSU Agcenter|
|KIMBENG, C - LSU Agcenter|
Submitted to: International Society of Sugar Cane Technologists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/28/2016
Publication Date: 12/5/2016
Citation: Hoy, J.W., Baisakh, N., Avellaneda, M.C., Kimbeng, C.A., Hale, A.L. 2016. Detection, breeding, and selection of durable resistance to brown rust in sugarcane. Proceedings of the International Society of Sugar Cane Technologists. 26:1034-1039.
Interpretive Summary: Brown rust is a major disease of sugarcane in Louisiana. The fungus is able to adapt to host-plant resistance, causing previously resistant varieties to become susceptible. A DNA marker (Bru1) for resistance to the fungus has been identified; however the frequency in the Louisiana breeding population is low. Over the past several years, targeted crossing using the marker for resistance has led to an increase in the frequency of this DNA marker in the Louisiana breeding program. While the increase of this brown rust resistance gene is an important step toward breeding resistant varieties, over-reliance on one resistance source is not advisable. Development of protocols for inoculation under controlled conditions allowed for the evaluation of cultivar reactions to rust spores collected from other major varieties (different from the one being tested). Experiments demonstrated that spores collected from a particular variety were most virulent to the variety from which they were collected. One cultivar, L99-233, was resistant to rust spores regardless of the source. Researchers are attempting to identify genes associated with the broad-spectrum resistance in this cultivar and to develop molecular markers associated with these genes. A small-scale analysis of gene expression in L99-233 identified genes involved in the response to fungal infection. Analysis showed a select set of genes were expressed more for a short period of time in susceptible cultivars, but high expression remained for a longer period of time in the resistant cultivars. This prolonged expression in the resistant cultivars appeared to be the contributing factor for resistance to brown rust. Breeding and selection for Bru1 and other genes could provide effective and durable resistance to brown rust in future cultivars.
Technical 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.