Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2009
Publication Date: 12/1/2009
Citation: Sood, S.G., Comstock, J.C., Glynn, N.C. 2009. LEAF WHORL INOCULATION METHOD FOR SCREENING SUGARCANE RUST RESISTANCE. Plant Disease. 93:1335-1340.
Interpretive Summary: Interpretive Summary: Sugarcane rust diseases brown rust, and orange rust are important diseases in Florida. Brown rust can cause substantial losses and has been responsible for the withdrawal of several commercial cultivars. In 2007, orange rust was found in Florida and since then it caused significant yield losses in widely planted commercial cultivar CP 80-1743. Natural infection has been the primary means of assessing rust resistance in sugarcane cultivars. Unfortunately, natural infection is not always efficient in identifying resistant cultivars due to variable environmental conditions and other biotic factors such as races and variations in inoculum pressure. In the past some cultivars in the early stages of the Canal Point breeding program that were rated as rust resistant after natural infection developed moderate to severe brown rust just prior to release or just after release. Therefore, a more reliable screening method is needed to effectively select resistant cultivars in the early stages of the breeding program. An inoculation technique was evaluated and optimized to allow the identification of brown and orange rust resistance in sugarcane cultivars. Inoculations were performed in the field by placing a rust spore suspension in the leaf whorl of sugarcane plants, disease assessments were made four weeks after inoculation. Inoculum was prepared by mixing equal amounts of spores collected from different cultivars and locations to minimize disease escapes due to races and inoculum pressure. The leaf whorl inoculation methods that are described are now being used to determine the rust reactions of thousands of clones in the Canal Point breeding program.
Technical Abstract: Technical Abstract: Sugarcane rust diseases, brown rust caused by Puccinia melanocephala, and orange rust caused by P. kuehnii, are agronomically important diseases in Florida. Cultivar resistance is the best means of controlling these diseases. Natural infection has been the primary means of assessing resistance in sugarcane cultivars against rusts. Unfortunately, natural infection is not always efficient in identifying resistant cultivars due to variable environmental conditions. Therefore, a more reliable screening method is needed to effectively select resistant genotypes. An inoculation technique was evaluated for identification of brown and orange rust resistance in sugarcane cultivars. Inoculations were performed in the field by placing a 0.1 ml urediniospore suspension in the leaf whorl of three individual stalks per plant using a pipette. Symptoms appeared on leaves of all the susceptible cultivars after four weeks, emerging as a band of pustules. Plants were rated for their reaction to rust four weeks after inoculation. The optimum concentrations of inoculum for brown and orange rust were determined. The most severe brown rust and orange rust symptoms were observed using inoculum containing 105 and 104 spores/ml, respectively. Clones in several stages of the Canal Point breeding program were screened for their rust reaction by leaf whorl inoculation. The technique enabled rapid screening of a large number of cultivars in field plantings, using a small amount of inoculum, and limited man hours.