Location: Sugarcane Research
2017 Annual Report
Objectives
Objective 1: Identify germplasm of hybrid sugarcane and wild relatives of sugarcane for resistance to economically limiting diseases that breeders can use for parental clones.
Sub-objective 1.A. Classify available clones from different taxa for disease resistance.
Sub-objective 1.B. Identify DNA markers that are closely 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 sugarcane.
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.
Approach
To identify and develop parental germplasm with resistance to the economically limiting 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 SCAR (Sequenced Characterized Amplified Region) and or single-nucleotide polymorphism (SNP) 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.
Progress Report
In fiscal year (FY) 2017, progress was made in identifying sugarcane germplasm resistant to economically important diseases. Varieties (43) for possible release into commercial production in the next four to five years were screened through artificial inoculation in the field for susceptibility to smut and leaf scald. In other Agricultural Research Service breeding trials and nurseries, candidate varieties were observed for natural infection by pathogens that cause mosaic, brown and orange rust, smut and leaf scald diseases. A screening trial was also established to monitor susceptibility of candidate varieties to Sugarcane yellow leaf virus. Pathology recommendations were made at variety advancement and variety release meetings.
Among 96 clones selected from a smut resistance mapping population, smut was recorded in one-half of the clones. Clones were retested for their phenotypic response to the smut pathogen in FY 2016. Deoxyribonucleic acid (DNA) extractions were collected in FY 2017 and are being analyzed for the development of sequence characterized amplified region (SCAR) markers.
From tissue samples collected among sugarcane plants expressing mosaic disease symptoms, Sorghum mosaic virus (SrMV) was the predominant virus recovered from these plants. A low percentage of the virus isolates (<1%) were identified as Sugarcane mosaic virus (SCMV), the other virus that causes mosaic symptoms in sugarcane. Analysis of the nucleic acid sequences among the SrMV isolates indicated genetic diversity. Strain identification within SrMV and SCMV have been identified based on nucleic acid sequence; however, the sequences of an increasing number of isolates of SrMV do not match those of characterized strains. A study has been initiated to further characterize these isolates and their relationship to identified strains.
Candidate clones in the variety development program continue to be rated for natural infection by the fungi that cause brown rust and orange rust. Brown rust continues to affect commercial production fields of susceptible varieties. Orange rust has been observed among susceptible experimental clones on the research farm; however, no epidemics were observed in commercial production fields.
Accomplishments
