Location: Sugarcane Research
2018 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) 2018, progress was made in identifying sugarcane germplasm resistant to economically important diseases. Varieties (42) for possible release into commercial production within the next 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, sugarcane yellow leaf, smut and leaf scald diseases. Pathology recommendations were made at variety advancement and variety release meetings.
The genetic population to develop a molecular marker linked to smut resistance was established from seedlings of four crosses between smut susceptible and smut resistant parents. Among 96 clones selected for further testing, smut was recorded in approximately one-half of the clones. Clones were retested for smut susceptibility in FY 2018 and total deoxyribonucleic acid (DNA) extractions were collected. The DNA samples are being analyzed for the development of sequence characterized amplified region (SCAR) markers.
In FY 2018, populations of the viruses that cause mosaic in sugarcane were monitored for genetic diversity. Sorghum mosaic virus (SrMV) remained the predominant virus causing mosaic. A low percentage of the isolates (<1%) were identified as Sugarcane mosaic virus (SCMV), another virus that causes mosaic symptoms in sugarcane, were identified from samples collected among experimental varieties. The sequences of an increasing number of isolates of SrMV do not match those of strains characterized using host differentials. Sequence data suggest the SrMV population contains multiple genotypes. Current studies are being conducted to further characterize these isolates and their relationship to earler characterized strains.
Climatic conditions were favorable for orange rust among variety trials at the USDA-ARS research farm in Houma, Louisiana; however, no epidemics have been observed in commercial fields. Highly susceptible clones were not advanced to the next stage of the variety development program.
In collabative studies with the researchers in the Rio Grande Valley sugarcane production area of Texas, orange rust was observed for the first time in 2017. Orange rust was observed in variety trials, but was not observed in commercial plantings although the most widely grown variety, CP 89-2143 is known to be susceptible.
Sugarcane streak mosaic virus (SCSMV) was detected in two imported plants of Saccharum spontaneum. Because these clones have potentially beneficial traits that will benefit the sugarcane breeding program, they have been place in USDA's Animal and Plant Health Inspection Service (APHIS) quarantine for treatment to eliminate the SCSMV from the plants. Tissue samples of sugarcane plants on the USDA-ARS, Sugarcane Research Unit research farm, off-station test locations, and commercial planting have been analyzed for the presence of SCSMV. All samples have been negative for SCSMV.
Accomplishments
