Location: Sugarcane ResearchTitle: Frequency and distribution of the brown rust resistance gene Bru1 and implications for the Louisiana sugarcane breeding programme Author
Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2014
Publication Date: 4/30/2014
Publication URL: http://handle.nal.usda.gov/10113/59503
Citation: Parco, A.A., Mavir, A.C., Hale, A.L., Hoy, J.W., Kimbeng, C.A., Pontif, M.J., Gravois, K.A., Baisakh, N. 2014. Frequency and distribution of the brown rust resistance gene Bru1 and implications for the Louisiana sugarcane breeding programme. Plant Breeding. DOI: 10.1111/pbr.12186. Interpretive Summary: Brown rust is a disease that has caused a great deal of damage to the Louisiana sugarcane industry. Selection for resistance to this disease is difficult because of natural year-to-year variation, and because of the ability of the fungus to adapt to resistant sugarcane varieties. A major gene, Bru1, was previously identified and has been shown to contribute resistance to brown rust in multiple sugarcane industries. When Louisiana varieties and breeding lines were screened very few contained the Bru1 gene for brown rust resistance; however, the gene was present at a much higher frequency in wild relatives used in the breeding program. There appears to be other sources of resistance to brown rust in the Louisiana breeding program that are not based on this gene (e.g. L99-233), and, at times, this gene does not confer resistance in our environment. Results from this study indicate that improvements can be made in resistance to rust both by increasing the frequency of the Bru1 gene in Louisiana varieties, and by identifying and breeding with other sources of resistance to the disease.
Technical Abstract: Brown rust, caused by the fungus Puccinia melanocephala, is an important disease of sugarcane posing an increasing threat to sugarcane industries worldwide. A major gene, Bru1, has been shown to contribute a significant proportion of brown rust resistance in multiple sugarcane industries. The recently developed Bru1-linked molecular diagnostic markers, R12H16 and 9020-F4, have made molecular breeding of brown rust resistant sugarcane cultivars possible. Marker-assisted screening of Louisiana sugarcane germplasm showed that the frequency of Bru1was low (4.3 %) among sugarcane cultivars and elite breeding clones. Only five (CP77-310, Ho 09-827, L 01-299, L 10-146, NCo 310) out of 117 clones tested positive. Likewise, among progeny of crosses involving wild/exotic germplasm, only 14 out of 208 clones (6.7 %) were positive. However, Bru1 was present at a higher frequency (52 out of 181 clones, 28.7 %) in wild/exotic germplasm where variant band profiles were also observed due to allelic sequence variation. Commercial cultivar, L 01-299, which contained Bru1, was resistant to brown rust. However, Bru1-positive cultivar, L 10-146, was susceptible while Bru1-negative cultivars, such as L 99-233, showed resistance to brown rust. The results indicate further utilization of Bru1 would be desirable and that diverse genetic resources are available for Bru1 introgression. Cultivars and wild/exotic clones that lack Bru1, but display brown rust resistance, offer an opportunity to identify alternate sources of resistance, which can be pyramided with Bru1 for effective and durable resistance in sugarcane against the changing pathogen without overreliance on Bru1.