2011 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.
Varieties (57) 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 (approx. 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 (progeny) from seed produced by the selfing of the sugarcane variety, LCP 85-384. The population has been characterized for their response to several diseases including brown rust, ratoon stunting disease (RSD), and smut. Presently this information is being incorporated into the enriched LCP 85-384 genetic linkage map to identify qualitative trait loci (QTLs) associated with these diseases.
A mapping population of LCP 85-384 was rated for resistance with susceptibility to rust and ratoon stunt disease. For each disease, DNA from the five individuals showing the greatest resistance was combined into one sample and the five individuals with the greatest susceptibility to each disease was also combined. These four bulk samples along with DNA from the parent 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 to date. Sub-cloning and DNA sequencing of differential RGA or RAPD polymerase chain reaction (PCR) products are underway by the ARS cooperator in Pakistan.
In the 2010 surveys of sugarcane plants expressing mosaic symptoms, strain I of SrMV remained the predominant strain of virus causing mosaic. Strains H and M of SrMV and a few isolates of Sugarcane mosaic virus (SCMV) were also identified among the diseased plants.
The top rot symptoms of red stripe were observed on sugarcane during the 2010 growing season. To date, experiments demonstrate that this expression of the disease can cause measurable yield loss. Experiments also demonstrated that nutritional factors influence the severity of the disease.
The Louisiana sugarcane industry continues to be monitored for the presence of rust spores. Rust spores were collected from pustules on multiple sugarcane varieties located on commercial farms throughout the Louisiana in 2010. All were identified as spores that cause brown rust. Spore traps were set up at three locations to detect airborne orange rust spores. Orange rust spores were identified in three traps in late September or early October 2010. No established infections of orange rust were observed.
Release of disease-resistant sugarcane and energycane varieties. The success of the Louisiana sugarcane and the emerging bioenergy industries depends on the release of well adapted, high yielding sugar and energy cane cultivars with resistance to economically important diseases. ARS researchers at the Sugarcane Research Unit, Houma, LA, released a sugarcane variety (HoCP 04-838) and an energycane variety (Ho 02-113) for use by their respective industries. Each variety is resistant or moderately resistant to the economically important diseases of sugarcane in Louisiana. These new varieties will offer additional options to growers that equal or exceed presently available varieties in agronomic and pathological traits.
Gao, S., Pan, Y.-B., Chen, R.-K. 2010. Detection of sugarcane yellow leaf virus by direct antigen coated enzyme-linked immunosorbent assay. Chinese Journal of Tropical Crops. 31(8):1356-1361.