Submitted to: International Society of Sugar Cane Technologists Plant Pathology and Molecular Biology Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2008
Publication Date: 6/23/2008
Citation: Comstock, J.C. 2008. Sugarcane Rust Inoculations. International Society of Sugar Cane Technologists Plant Pathology and Molecular Biology Workshop. Interpretive Summary: An artificial inoculation technique for field evaluation of sugarcane brown and orange rusts is described that gives a disease reaction evaluation of sugarcane clones. This technique works effectively for brown rust and ensures that the plants are challenged with the pathogen and is an improvement over relying on natural infection.
Technical Abstract: Sugarcane rusts, brown (caused by Puccinia melanocephala) and orange (caused by P. kuehnii), are agronomically important diseases in Florida. Cultivar resistance is the best means of managing these diseases. Unfortunately, natural infection of brown rust is not always efficient in determining resistant cultivars and a more reliable screening method is a necessity for effective selection of resistant genotypes. Since sugarcane rusts are obligate pathogens, the collection of sufficient rust spores for inoculating leaves can be difficult. A whorl inoculation technique was evaluated because it would minimize inocula usage and potentially allow field inoculations. Inocula concentrations of 100 to 100,000 spores ml-1 of brown rust were tested on ten varieties of known reaction by placing 0.1 ml inocula into the leaf whorl and the brown rust reaction was determined at 2 and 4 weeks after inoculation according to previously described rust rating methods. The 100,000 spores ml-1 gave the comparable results to historical rust reaction data. The field was planted in late November 2006 and inoculated in March 2007 during the morning hours. Field temperature ranged from 61-82 °F, relative humidity was between 47-91% and wind speed was 1-20 mph. Symptoms appeared on leaves (of susceptible cultivars) as a band of pustules. Resistant cultivars showed either flecks or no symptoms while susceptible cultivars had sporulating pustules. The whorl inoculation technique enabled rapid screening of a large number of cultivars in field plantings, requiring a small amount of inoculum, less time and labor. Inoculations using orange rust will also be presented. The reliability of whorl inoculation technique is high.