Location: Sugarcane Research2013 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.
3. Progress Report:
Varieties (42) 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 diseases. 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 were cut from each seedling and dip-inoculated in a suspension of smut spores and planted in the field. Of the 429 clones, there were 132 (31%) smut infections recorded. Ninety-six clones were selected for further inoculated testing, one in the greenhouse and the other in the field. Smut was recorded in one-half of the 96 in the first test. The first test was maintained for observation of smut in the first-ratoon crop. 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. In June 2012, lesions typical of orange rust caused by Puccinea kuehnii were observed on sugarcane variety Ho 05-961 (a complex hybrid of Saccharum L. spp.) on a farm near Schriever, LA. The causal agent was identified as Puccinea kuehnii based on the size, shape, and appearance of spores from the lesions and on a deoxyribonucleic acid (DNA) identity test. Although extensive surveys were conducted throughout 2012, observations of orange rust were limited to one variety, HoCP 05-961, a recently released variety with limited distribution. Initially, disease incidence and severity were low, increasing gradually throughout the growing season, becoming severe in November at two locations. In the spring of 2013, orange rust was observed and verified in a commercial field of CP 89-2143. Disease incidence and severity were high. Surveys will continue to determine further spread to other varieties or different geographical areas.
1. Spread of sugarcane orange rust in Louisiana. In June 2012, ARS scientists at the Sugarcane Research Unit (SRU) in Houma, LA, observed orange rust caused by Puccinea kuehnii for the first time in Louisiana on sugarcane variety Ho 05-961. Fungal spores from the infected sugarcane leaves were identified by ARS scientists at SRU and the Soybean/Maize Germplasm, Pathology, and Genetics Research Unit in Urbana, IL as Puccinea kuehnii based on the morphology of the spores and molecular analysis with quantitative polymerase chain reaction (qPCR). In cooperation with scientists from Louisiana State University and the American Sugar Cane League, Thibodaux, LA, orange rust was found in 17 of 38 fields of Ho 05-961 inspected. The incidence and severity were initially low; however, they both increased during the 2012 growing season and, in two of the infected fields of Ho 05-961, orange rust caused heavy leaf necrosis by December of 2012. Although extensive surveys of commercial and experimental varieties of sugarcane were conducted in Louisiana during the 2012 growing season, orange rust was found only on variety Ho 05-961. In June of 2013, a severe infection of orange rust was found in a commercial field of CP 89-2143. Surveys will continue throughout the 2013 growing season to monitor the geographic spread of the disease and infection of other varieties. Because of the potential for economic losses from orange rust infections, a program of screening test varieties and parents for orange rust has been established.