Glyphosate Control of Orange and Brown Rusts in Glyphosate-Sensitive Sugarcane Cultivars

Authors: Del Blanco, Isabel; Glaz, Barry; Kanaan, Moaiad; Sood, Sushma; Comstock, Jack

Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 12/20/2008
Publication Date: 2/1/2009
Citation: Del Blanco, I.A., Glaz, B.S., Kanaan, M.A., Sood, S.G., Comstock, J.C. 2009. Glyphosate Control of Orange and Brown Rusts in Glyphosate-Sensitive Sugarcane Cultivars. American Society of Agronomy Abstracts.

Interpretive Summary: Interpretive Summary: Sugarcane is the major agronomic crop in Florida, and Florida provides about 25% of the sugar produced domestically in the U.S., more than any other state. Fungal diseases called rust cause devastating yield losses in Florida and in other sugarcane growing regions in the world. Reduction of yield and sugar production from brown rust in susceptible cultivars has been reported to be between 10 to 40%. The major source of resistance to brown rust of sugarcane in Florida has been the use of resistant cultivars but resistant cultivars soon become susceptible because the pathogen mutates to new virulent races. In 2007, a new rust pathogen that produces Orange rust was discovered in Florida and it is expected that this new arrival will make yet more difficult to develop sugarcane cultivars with durable resistance. As sugarcane rust infections continue to become more critical, scientists are now working to identify cost-effective fungicides until more durable genetic resistance can be developed. Others have reported that glyphoshate effectively controlled rust in transgenic glyphosate-resistant wheat, but glyphosate-resistant sugarcane is not currently available. The objective of this research was to determine if glyphosate could control brown and orange rusts in sugarcane at a low dose that would not damage the crop. In laboratory studies in which rust was cultured in tubes and petri dishes, rust germination was effectively controlled by low doses of glyphosate. In field experiments with low dosages of glyphosate there was no visible damage to sugarcane plants, existing rust infections were reduced and there were no new infections. More research is needed but results show potential for using this widely know herbicide as an effective fungicide to control rusts in sugarcane.

Technical Abstract: Technical Abstract: Brown and orange rust diseases cause substantial yield reductions on sugarcane (Saccharum spp.) in Florida and other regions where sugarcane is grown. Brown rust caused by Puccinia melanocephala Syd. & P. Syd has been present in Florida since 1978 and orange rust caused by Puccinia kuehnii E.J. Butler was first identified in Florida in 2007. Florida growers have relied on genetic resistance to control brown rust, but this has been problematic because the fungus often overcomes resistance by forming new races. It is expected that orange rust will further add to the difficulty of achieving durable resistance genetically. Others reported that glyphosate [N-(phosphonomethyl) glycine] effectively controlled stripe rust in wheat (Triticum aestivum L.) that was genetically modified for glyphosate resistance. Our objective was to determine if low doses of glyphosate applied to glyphosate sensitive sugarcane cultivars would control the rusts without damaging sugarcane. In-vitro experiments showed significant control of germination and tube elongation in spores of both rusts. In field tests, a dose of 2.34 x 103 µmole per L applied to young sugarcane plants about 100 cm tall, reduced disease and did not visually harm sugarcane. Low rates of glyphosate applied to glyphosate sensitive sugarcane has promise as a chemical control of sugarcane brown and orange rusts. However, more research is needed to determine duration of control, if there is some systemic effect beyond the observed contact mode of action, and if there are effects on sugarcane yield.