First report of Puccinia kuehnii causing orange rust of sugarcane in Texas, USA

Authors: Grisham, Michael; Warnke, Kathryn; Maggio, Jeri; DAVIDSON, W - Florida Sugar Cane League; HAUDENSHIELD, J - Former ARS Employee; Hartman, Glen; HERNANDEZ, EDDIE - Rio Farms, Inc; SCOTT, JR., A - Rio Farms, Inc; COMSTOCK, J - Retired ARS Employee; MCCORD, P - Former ARS Employee

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2020
Publication Date: 5/5/2020
Citation: Grisham, M.P., Warnke, K.Z., Maggio, J.R., Davidson, W., Haudenshield, J.S., Hartman, G.L., Hernandez, E., Scott, Jr., A.W., Comstock, J.C., Mccord, P.H. 2020. First report of Puccinia kuehnii causing orange rust of sugarcane in Texas, USA. Plant Disease. https://doi.org/10.1094/PDIS-10-19-2117-PDN.
DOI: https://doi.org/10.1094/PDIS-10-19-2117-PDN

Interpretive Summary: Orange rust of sugarcane caused by Puccinia kuehnii was observed for the first time in the Rio Grande Valley of Texas in 2017. The identity of P. kuehnii was verified by PCR assays conducted independently in two laboratories. The disease was observed in variety trials at three sites in Hidalgo, Cameron, and Willacy Counties on 12 experimental clones and one commercial variety, CP 89-2143. In 2017, approximately 45% of the sugarcane production area in Texas was planted with cultivar CP 89-2143. Although orange rust was observed on CP 89-2143 in the variety trials, no orange rust was reported in commercial plantings of this cultivar. Incidence and severity of orange rust were greater in variety trials located in the eastern portion of the sugarcane production area of the Rio Grande Valley.

Technical Abstract: In April 2017, uredinial lesions typical of orange rust caused by P. kuehnii E.J. Butler were observed on an experimental sugarcane clone HoCP 14-801 (a complex hybrid of Saccharum L. spp.) in a cultivar trial in Hidalgo County, Texas. Additional observations were made in cultivar trials at three other sites in Hidalgo, Cameron, and Willacy Counties during the next five months of 2017. Orange rust symptoms were observed on 12 experimental clones and one commercial check cultivar, CP 89-2143, at one or more of the three trial locations. Lesion and urediniospores morphology features were consistent with those described for P. kuehnii. Telia and teliospores were not observed. Leaf samples containing rust lesions were collected from cultivar CP 89-2143 and experimental clones, HoCP 14-801, HoCP 14-874, and CP 11-2013. Identification of the species causing the orange rust lesions was verified by PCR assays conducted independently in two laboratories. Primers PkPmF and PkPmR were used that amplify fragments of 606 bp from P. kuehnii and 585 bp from P. melanocephala, the causal agent of brown rust of sugarcane. Only a 606 bp fragment was amplified from each sample. Sequences of the fragments were identical to each other, and a BLAST search of GenBank revealed 100% identity to previously reported isolates of P. kuehnii. This is the first report of orange rust in Rio Grande Valley sugarcane production area of Texas. In 2017, approximately 45% of the sugarcane production area in Texas was planted with cultivar CP 89-2143. Although CP 89-2143 was infected with P. kuehnii in check plots of cultivar trials, no orange rust was observed in commercial plantings of this cultivar. Incidence and severity of orange rust were greater in cultivar trials located in the eastern portion of the sugarcane production area of the Rio Grande Valley.