Occurrence of two races of Puccinia kuehnii causing orange rust of sugarcane in Florida

Authors: SANJEL, S - University Of Florida; HINCAPIE, M - University Of Florida; WANG, Y - University Of Florida; Todd, James; CHAULAGAIN, B - University Of Florida; Sood, Sushma; Comstock, Jack; RAID, R - University Of Florida; ROTT, P - University Of Montpellier

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2021
Publication Date: 5/31/2021
Citation: Sanjel, S., Hincapie, M., Wang, Y., Todd, J.R., Chaulagain, B., Sood, S.G., Comstock, J.C., Raid, R.N., Rott, P. 2021. Occurrence of two races of Puccinia kuehnii causing orange rust of sugarcane in Florida. Plant Pathology. 00:1-10. https://doi.org/10.1111/ppa.13405.
DOI: https://doi.org/10.1111/ppa.13405

Interpretive Summary: Orange rust is an important pathogen of sugarcane that reduces yield in suceptable cultivars. After the introduction of orange rust to the US several resistant cultivars later became suceptable orange rust and this was attributed to changes in the pathogen and the formation of new races. To measure how infecteous these potential races were isolates from the original suceptable and newer suceptable were collected and utilized to innoculate leaves of two different sugarcane cultivars. The isolates from the recent suceptable cultivar were more infecteous than the other isolates indicating a genetic difference. Genetic markers did not indicate large genetic changes between the isolates. The results indicate that growing resistant cultivars will reduce the amount of virulant isolates and their resulting yield loss.

Technical Abstract: Orange rust of sugarcane caused by Puccinia kuehnii was first reported in Florida in 2007. Since then, several sugarcane cultivars that were resistant during the initial epidemics became susceptible within a few years. These shifts in resistance were attributed to the evolution of the pathogen and appearance of new races. To study the variation in virulence of P. kuehnii, healthy leaf pieces of orange rust susceptible sugarcane cultivars were brush inoculated with isolates of P. kuehnii collected from orange rust susceptible cultivars in the field. After inoculation, leaf pieces were placed in an incubator and disease severity based on the number of rust uredinia was determined two weeks post inoculation. Isolates of P. kuehnii collected from sugarcane cultivar CP 89-2143, which only became susceptible to orange rust in 2011-2012, were more virulent than the isolates collected from cultivars that were susceptible since 2007. These data support occurrence of pathogenic specialization within P. kuehnii and existence of at least two races of this pathogen in Florida. Analysis of amplified fragment-length polymorphism among isolates of P. kuehnii from cultivars CP 89-2143 and CL 85-1040 differing in resistance to orange rust revealed genetic variation among rust uredinia. However, this variation was not associated with a specific sugarcane cultivar, suggesting that pathogenic variation was not linked to major genetic changes within the genome of P. kuehnii.