Screening for Brown Rust Resistance in Sugarcane by Whorl Inoculation

Authors: Sood, Sushma; Comstock, Jack; Glynn, Neil

Submitted to: American Society of Sugar Cane Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 5/7/2007
Publication Date: 6/15/2007
Citation: Sood, S.G., Comstock, J.C., Glynn, N.C. 2007. Screening for Brown Rust Resistance in Sugarcane by Whorl Inoculation. American Society of Sugar Cane Technologists. 27:59

Interpretive Summary: Brown rust, caused by Puccinia melanocephala, is an agronomically important disease of sugarcane in Florida. Cultivar resistance is the best means of managing the disease. Unfortunately, natural infection is not always efficient in determining resistant cultivars and a more reliable screening method is a necessity for effective selection of resistant genotypes. P. melanocephala is an obligate pathogen; this makes the artificial inoculation of large numbers of cultivars difficult since a large quantity of rust spores is required along with environmental conditions that favor infection and disease development. A whorl inoculation technique was evaluated and optimum concentration of inocula was determined on ten varieties of known rust reaction. The disease reaction was comparable to historical rust reaction data of the variety by using inocula containing 105 spores ml-1. This technique was used to screen for rust resistant cultivars in the field. A 0.1 ml of spore suspension containing105 spores ml-1 was used to inoculate 43 varieties in Stage III increase and 18 varieties in Stage IV of Canal Point cultivar development program. Inoculations were performed by placing the spore suspension in the leaf whorl of three individual stalks per stool using a pipette. Four replicates per variety were used; inoculated stalks were identified by cutting the tops off the leaves. 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. Plants were rated for their reaction to rust two and four weeks after inoculation. 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 small amount of inocula, less time and labor. Moreover, the reliability of whorl inoculation technique is high.

Technical Abstract: Brown rust, caused by Puccinia melanocephala, is an agronomically important disease of sugarcane in Florida. Cultivar resistance is the best means of managing the disease. Unfortunately, natural infection is not always efficient in determining resistant cultivars and a more reliable screening method is a necessity for effective selection of resistant genotypes. P. melanocephala is an obligate pathogen; this makes the artificial inoculation of large numbers of cultivars difficult since a large quantity of rust spores is required along with environmental conditions that favor infection and disease development. A whorl inoculation technique was evaluated and optimum concentration of inocula was determined on ten varieties of known rust reaction. The disease reaction was comparable to historical rust reaction data of the variety by using inocula containing 105 spores ml-1. This technique was used to screen for rust resistant cultivars in the field. A 0.1 ml of spore suspension containing105 spores ml-1 was used to inoculate 43 varieties in Stage III increase and 18 varieties in Stage IV of Canal Point cultivar development program. Inoculations were performed by placing the spore suspension in the leaf whorl of three individual stalks per stool using a pipette. Four replicates per variety were used; inoculated stalks were identified by cutting the tops off the leaves. 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. Plants were rated for their reaction to rust two and four weeks after inoculation. 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 small amount of inocula, less time and labor. Moreover, the reliability of whorl inoculation technique is high.