2010 Annual Report
1a.Objectives (from AD-416)
The long-term objective of this project is to reduce the impact of diseases on the productivity of the domestic sugarcane (Saccharum hybrids) industry by providing assistance to sugarcane breeders in identifying parental clones with resistance, improving the efficiency of selection for disease resistance traits, and providing the industry the information needed to guard against more virulent strain shifts and/or new pathogens. Our primary objectives will be to identify and develop germplasm with resistance to the major diseases affecting sugarcane, to identify the genetic variability among endemic pathogen populations, and to monitor the Louisiana sugarcane industry for the emergence of new pathogens. Disease resistant germplasm will be sought from among different taxa of Saccharum and related genera. Molecular markers that are linked to genes for disease resistance will be identified. Molecular approaches will be used to enhance the studies of host and pathogen genetics.
1b.Approach (from AD-416)
To identify and develop germplasm with resistance to the major diseases affecting sugarcane in the United States, highly domesticated and wild clones of sugarcane and near relatives will be evaluated for resistance to the major sugarcane diseases following either natural and infections or artificial inoculation. To identify molecular markers that are linked to genes for disease resistance, polymerase chain reaction (PCR) based methods such as AFLP, SSR, or TRAP will be used to identify genetic markers closely linked to the resistance genes. Priority will be given to finding markers for smut, then ratoon stunting disease (RSD) and mosaic. Genotypic and phenotypic expressions of variability within populations of pathogens will be used to identify the genetic variability among pathogen populations and determine the distribution of races, strains, or other biotypes. The domestic sugarcane industry will be monitored for the introduction of exotic pathogens.
Project receives support from the American Sugar Cane League (6435-21000-012-04T) through a Trust Funded Cooperative Agreement. Additional details of research can be found in the reports of the subordinate and parent projects.
Varieties (83) for possible release into commercial production in the next five years were screened through artificial inoculation in the field for susceptibility to smut and leaf scald. Candidate varieties (750) that could be released in 8 years were screened in the field by artificial inoculation for susceptibility to Ratoon Stunting Disease (RSD). In other ARS breeding trials and nurseries, candidate varieties were observed for natural infection by pathogens that cause mosaic, rust, smut and leaf scald diseases. Pathology recommendations were made at variety advancement and variety release meetings.
A linkage map was constructed using a population of offspring from seed produced by the selfing of the sugarcane variety, LCP 85-384. The map contained 108 co-segregation groups with a map length of 5,384 cM covering 42% of LCP 85-384 genetic makeup. The offspring have been been characterized for their response to several diseases including brown rust, ratoon stunting disease (RSD), and smut.
Two bulked DNA samples were prepared from five selfed offspring each of the LCP 85-384 mapping population that were rated either highly resistant or highly susceptible to the brown rust and/or RSD. These bulk samples along with LCP 85-384 were tested for trait-specific markers by either resistant gene analogue (RGA) for RSD or random amplified polymorphic DNA-sequence characterized amplified region (RAPD/SCAR) for brown rust. Sub-cloning and DNA sequencing of differential RGA or RAPD PCR products are underway.
In the recent surveys of sugarcane plants expressing mosaic symptoms, strain I of SrMV remained the predominant strain of virus causing mosaic. Strains H and M were also identified among the diseased plants. For the first time in over 25 years, isolates causing mosaic were identified as Sugarcane mosaic virus (SCMV).
The Louisiana sugarcane industry continues to be monitored for the potential introduction of orange rust (Puccinea kuehnii). Rust spores were collected from pustules on multiple sugarcane varieties located on commercial farms throughout Louisiana. All were identified as spores that cause brown rust (P. melanocephala), a rust that has been present in Louisiana since 1981. Spore traps were set up at three locations to detect airborne orange rust spores. No orange rust spores have been discovered to date.
Use of Leaf Reflectance to Detect Sugarcane Yellow Leaf Virus (SCYLV) Before Visual Symptoms Appear. SCYLV is capable of reducing yields of sugarcane in Louisiana. Visible symptoms of this disease are seldom evident when fields are being identified by growers to serve as seedcane fields to expand the vegetative planting of a variety. As a result, growers unknowingly spread the disease to new fields. High-resolution, hyperspectral reflectance data from SCYLV-infected and non-infected leaves of two sugarcane varieties, LCP 85-384 and Ho 95-988, were measured on three dates during the growing season. No symptoms were observed in any of the experimental plants. Analysis of the data showed that leaf reflectance was effective at predicting SCYLV infection in 73% of the cases in both varieties across all sampling dates. Predictive equations were improved when data from sampling dates were analyzed individually. SCYLV infection influenced the concentration of four leaf pigments. The results of this study demonstrate the potential application of hyperspectral remote sensing as a rapid, field-based method of identifying SCYLV-infected sugarcane plants prior to symptom expression.
Grisham, M.P., Johnson, R.M., Viator, R.P. 2009. Effect of ratoon stunting disease on yield of recently released sugarcane cultivars in Louisiana. Journal of the American Society of Sugar Cane Technologists. 29:119-127.
Grisham, M.P., Johnson, R.M., Zimba, P.V. 2010. Detecting Sugarcane yellow leaf virus infection in asymptomatic leaves with hyperspectral remote sensing and associated leaf pigment analysis. Journal of Virology. 167:140-145.