2012 Annual Report
1a.Objectives (from AD-416):
The goal of this project is reduce the impact of diseases on the production of sugarcane and energycane by assisting breeders in identifying disease resistant germplasm.
Objective 1: Identify germplasm of hybrid sugarcane and wild relatives of sugarcane for resistance to economically limiting diseases that breeders can use for productive sugar and energy cane parental clones.
Sub-objective 1.A. Classify available clones from different taxa for disease resistance. Cultivars and near-release cultivars of sugarcane and energycane and wild clones of Saccharum spp. and genetically related genera that may be used as parents will be characterized for resistance to important diseases.
Sub-objective 1.B. Identify DNA markers that are linked to genes for disease resistance.
Objective 2: Determine molecular and biological characteristics of economically important sugarcane pathogens that can be applied to effective diagnostic protocols.
Objective 3: Develop useful methods to monitor potential emergence of exotic pathogens and identify genetic diversity among pathogen populations that affect sugar and/or energy cane.
Sub-objective 3.A. Characterize races, strains, or other biotypes of endemic pathogens and determine their distribution.
Sub-objective 3.B. Monitor the Louisiana sugarcane industry for the emergence of new pathogens.
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 disease resistance following either natural infections or artificial inoculation. To identify molecular markers that are linked to genes for disease resistance, Random Amplification of Polymorphic DNA (RAPD), Amplified fragment length polymorphism (AFLP), and Simple Sequence Repeats (SSR) markers in combination with the bulk segregant analysis (BSA) will be used to screen potential DNA markers for resistance to smut and other important diseases. Variations among the DNA sequences of polymorphic DNA fragments will be analyzed and used to design new pairs of specific primers to develop Sequenced Characterized Amplified Region (SCAR) markers. 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 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 Agricultural Research Service 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.
The genetic population to be used to develop a molecular marker linked to smut resistance was established in the field from seedlings of four crosses, namely, CP 01-2390 (smut susceptible female parent) X Ho 05-961 (resistant male parent) and the reciprocal cross of Ho 05-961 (resistant female parent) X CP 01-2390 (smut susceptible male parent), and L 97-128 (smut susceptible female parent) X Ho 05-961 (resistant male parent) and the reciprocal cross of Ho 05-961 (resistant female parent) X L 97-128 (smut susceptible male parent). Natural infection of the seedlings was recorded. Two stalks cut from each seedling were cut and dip-inoculated in a suspension of smut spores and planted in the field. Smut infections will be recorded.
In the recent surveys of sugarcane plants expressing mosaic symptoms, strain I of sorghum mosaic virus (SrMV) remained the predominant strain of virus causing mosaic. Strains H and M of SrMV were also identified among the diseased sugarcane plants.
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 (Puccinea 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. Orange rust spores were identified in each of the three traps in late September or early October. Sporulating pustules (pustules where spores are produced) with symptoms matching those described for orange rust were found in May 2012. Spores were examined by light microscopy to determine morphological characteristics. Lesions and surrounding tissues were analyzed by quantitative polymerase chain reaction (qPCR).
First observation of sugarcane orange rust in Louisiana. Following the discovery of orange rust in Florida in 2007, surveys were made of the Louisiana sugarcane industry to determine if the pathogen was present in the state using spore traps and sentinel plots. Orange rust spores were found in spore traps in the fall of 2010; however, no disease was observed on sugarcane in FY 2011. Orange rust was observed for the first time in Louisiana on sugarcane variety Ho 05-961 in May 2012. Fungal spores from the infected sugarcane leaves were identified as Puccinea kuhnii based on the morphology of the spores and molecular analysis with quantitative polymerase chain reaction (qPCR). Because of the potential for economic losses from orange rust infections, a program of screening test varieties and parents for orange rust will be established.
Grisham, M.P., Maroon-Lango, C.J., Hale, A.L. 2012. First report of Sorghum mosaic virus causing mosaic in Miscanthus sinesis. Plant Disease. 96:150.