2009 Annual Report
1a.Objectives (from AD-416)
1. Screen sugarcane clones in the breeding pipeline and germplasm for resistance to ratoon stunt, leaf scald, mosaic, smut, eye spot and yellow leaf using proven techniques.
2. Improve assessment of brown rust resistance. a. Characterize pathogenic variation of brown rust in Florida. b. Evaluate seedlings screening methodology to identify rust resistant families. c. Determine the rust reaction of clones using improved natural infection and artificial inoculation methodologies.
3. Develop and associate molecular markers with disease resistance genes for use in marker-assisted selection.
1b.Approach (from AD-416)
1. Sugarcane clones in the cultivar development program will be screened for their disease reaction to the major diseases (ratoon stunt, leaf scald, mosaic, smut and eye spot) using established artificial inoculation tests. 2. a. Pathogenic variation to rust will be determined by inoculating cultivars that have known reactions with rust collected in locations in Florida to determine differences in reaction patterns. b. Sugarcane seedlings inoculation procedures will be evaluated using various rust spore concentrations and rating the reaction of individuals. c. The rust reaction of clones will be evaluated based on natural infection by produced by rust infected susceptible plants grown adjacent to them and also by artificially inoculating the plants either by whorl or spray inoculations. 3. Previously selected polymorphic SSR’s, developed RGA primers and AFLPs will be used to identify markers by bulk segregation analysis that are associated to brown rust, yellow leaf and ratoon stunt resistance using characterized populations of sugarcane.
The detection of sugarcane orange rust in Florida in 2007 (first confirmed report in western hemisphere) impacted the pathology research. To determine the extent of its distribution sugarcane rust samples were obtained from Central American countries; sugarcane orange rust was confirmed in these new countries: Mexico, El Salvador and Panama. Orange rust susceptibility ratings are being collected on CP cultivars present in Guatemala, Costa Rica and Nicaragua where the disease is present (reported in 2008).
Evaluated artificial inoculation of sugarcane seedlings in the field to determine sugarcane orange rust family reactions: With the introduction of orange rust to Florida resistance must be developed by emphasizing families that have a higher proportion of orange rust resistance progeny and avoid families that have primarily susceptible progeny. Rust symptoms developed adequately for disease assessment of individual plants using the whorl inoculation of field plantings. The methodology is being used to evaluate families (crosses) in the seedling population.
Identification of disease resistant cultivars: Disease susceptible cultivars must be identified to prevent yield losses in the sugarcane industry. Sugarcane clones in the variety development program were screened for their disease reaction and susceptible clones were discarded. Resistant cultivars will allow Florida to continue to produce approximately 20% of the sugar consumed in the United States.
Comstock, J.C. 2008. Sugarcane yield loss due to ratoon stunt. J. Amer. Soc. of Sugar Cane Technol. 28:22-31.
Chavarria, E., Subiros, F., Vega, J., Ralda, G., Glynn, N.C., Comstock, J.C., Castlebury, L.A. 2009. First report of Orange Rust of Sugarcane Caused by Puccinia kuehnii in Costa Rica and Nicaragua. Plant Dis. 93:425.