ARS | Publication request: Sugarcane brown rust – determining genetic variation in the pathogen and identifying potential novel sources of resistance

Submitted to: American Society of Sugar Cane Technologists
Publication Type: Abstract Only
Publication Acceptance Date: June 19, 2008
Publication Date: June 19, 2008
Citation: Glynn, N.C., Comstock, J.C. 2008. Sugarcane brown rust – determining genetic variation in the pathogen and identifying potential novel sources of resistance. American Society of Sugar Cane Technologists. Sugar Journal 2008 71:9-10

Technical Abstract: A major reason for the withdrawal of sugarcane cultivars from production in is the breakdown of resistance to brown rust caused by Puccinia melanaocephala. Genetic characterization of diversity among races of P. melanocephala would help in breeding for resistance to the pathogen. Breeding for durable resistance could also be improved through the identification and utilization of novel sources of resistance, such sources may be present within Saccharum spontaneum. The objectives of this work were i) to develop SSR markers for the brown rust pathogen P. melanocephala and ii) to characterize the sensitivities of a set of S. spontaneum clones taken from the sugarcane world collection. Several approaches were examined for developing SSR markers to P. melanocephala. SSR markers for the cereal rust fungi P. graminis, P. striiformis and P. triticina were examined but all were ineffective against DNA from P. melanocephala. Secondly, mining the P. graminis genome for SSR’s followed by genus level homology searches by BLAST analysis also proved to be a poor means of identifying sequence candidates for cloning SSRs. Finally DNA of P. melanocephala was used to produce a genomic library enriched for primarily dinucleotide repeats. Several hundred enriched fragments were sequenced and assembled, of these 120 were amenable to primer design. To identify potentially novel sources of brown rust resistance, approximately 200 clones of Saccharum spontaneum were retrieved from the sugarcane world collection and tested for brown rust susceptibility using previously described whorl inoculation methods. Three tillers from each clone were inoculated and experiments were repeated three times, disease severity was recorded according to a five point scale of 0 (resistant) to 4 (highly sensitive). Clones were observed in each rating category. Approaches to utilizing the analysis of variation in P. melanocephala through SSR genotyping and these potentially novel sources of resistance within S. spontaneum are discussed.