2012 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 impacted the cultivar development program. Since the detection of orange rust there has been an intensified screening program to identify and develop resistance to orange rust. Annually, over 1600 clones are evaluated annually for their disease reactions. Now resistant cultivars are being released for this disease. Additionally, the Sugarcane Field Station in conjunction with the USDA-ARS Systematic Mycology and Microbiology Laboratory helped confirm the orange rust pathogen, Puccinia kuehnii in Guatemala, Costa Rica, Nicaragua, El Salvador, Jamaica, Panama, Belize, Cameroon, Ivory Coast, Ecuador and Dominican Republic. This project is related to the new project number 6625-22000-010-00D, “Management of Diseases of Saccharum Hybrids through Development and Evaluation of Resistant Germplasm”.
Selection of brown rust resistant clones. Screening was conducted by rating plants with artificially and natural infected in multiple stages of the development program. Clones in Stage II were also tested for the major brown rust resistance gene, Bru1. Approximately 30 % contain the gene. Because the brown rust incidence was higher this year and sufficient for evaluation all of the 14,434 clones in the Stage I were evaluated for their brown rust reaction. Eliminating the susceptible clones will improve subsequent control of brown rust when cultivars are released.
Identification of disease resistant cultivars of sugarcane. Disease susceptible cultivars must be identified to prevent yield losses in the sugarcane industry. Sugarcane clones in Stage II (1500) Stage III (135) and Stage IV (18) in the variety development program were screened for their disease reactions to ratoon stunt, smut, brown rust, orange rust, leaf scald and mosaic. Clones with susceptibility levels that would sustain yield losses were discarded. Resistant cultivars will allow Florida sugarcane growers to continue to produce approximately 20% of the sugar consumed in the United States. Resistant sugarcane cultivars will provide growers with an effective means of controlling diseases.
Zhang, J., Nagai, C., Yu, Q., Pan, Y., Ayala Silva, T., Schnell Ii, R.J., Comstock, J.C., Arumuganathan, A.K., Ming, R. 2012. Genome size variation in three Saccharum species. Euphytica. 185:511-519. DOI: 10.1007/S10681-012-0664-6.