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

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

Registration of \u27L 99-233\u27 sugarcane

\u27L 99-233\u27 (Reg. No. CV-139, PI 655534) sugarcane (a complex hybrid of Saccharum officinarum L., S. barberi Jeswiet, S. spontaneum L., and S. sinense Roxb. amend. Jeswiet) was released on 25 Apr. 2006 by the Louisiana State University Agricultural Center in cooperation with the USDA-ARS and the American Sugar Cane League Inc. L 99-233 was released because of its high sugar and cane yields along with excellent ratooning ability. Data from 93 outfield trials indicate that L 99-233 produced approximately 18% greater sugar yield than LCP 85-384 when averaged across all crops. The sucrose content of L 99-233 was similar to LCP 85-384. The new cultivar is resistant to brown rust (Puccinia melanocephala H. and P. Sydow) and leaf scald [Xanthomonas albilineans (Ashby) Dowson], moderately susceptible to smut disease (Ustilago scitaminea Sydow & P. Sydow), moderately resistant to mosaic diseases, and susceptible to the sugarcane borer (Diatraea saccharalis F.). The cross for L 99-233 (XL94-8) was made in the fall of 1994. Early stage clonal selection was made from 1996 to 1998, which culminated in permanent clonal assignment in 1999. Replicated yield trials were conducted in south Louisiana from 2000 through 2005. Plant Patent no. 18,826 was issued for L 99-233 on 20 May 2008. © Crop Science Society of America