Location: Sugarcane Field Station
2018 Annual Report
Objectives
1. Identify disease resistant sugarcane and energy cane clones for high yielding commercial production.
2. Develop methodologies to efficiently screen germplasm for resistance and to identify new molecular markers associated with resistance.
3. Identify pathogenic variation in sugarcane pathogens that are endemic and emerging within the United States.
Approach
Objective 1: Sugarcane clones in the cultivar development program for both sucrose and bio-energy will be screened for their disease reaction in artificial inoculation tests separate from the cultivar development plots with the major pathogens and ratings will be determined based on incidence and severity of disease.
Objective 2: For Sugarcane Yellowleaf Virus (SCYLV) existing markers will be tested against our known historical clones having both resistance and susceptible reaction. Two new populations will be screened for SCYLV resistance and genotyping by secuencing (GBS) to identify new markers. For ratoon stunt disease and smut two populations will be screened for disease reaction and GBS to identify markers. For orange rust we will test published markers and perform fine mapping using a larger population and whole genome sequencing of the parents and bulked progeny to identify markers for screening the whole population.
Objective 3: Orange rust spores have been collected over the last two years from different cultivars and locations in Florida and stored for determining possible pathogenic variation. Specifically, cultivars CP 80-1743 (the susceptible cultivar first observed with orange rust in Florida), CL 85-1040 (susceptible) and two cultivars CP 88-1762 and CP 89-2143 that were originally resistant but became susceptible will be used to evaluate pathogenic variation. The whorl inoculation technique (Sood et al. 2009) that is routinely used to evaluate brown and orange rust reactions will be used to evaluate variation between the isolates. The whorl technique has been shown to give consistent results, as seen by the sample data in Table 2 of the Appendix. These will be used along with the new collections described. Sentinel plots of orange rust susceptible and resistant sugarcane cultivars will be planted at 5 different locations and from grower’s fields where the “breaking down” of resistance is reported. Fields will be observed monthly from March to July when orange rust is most prevalent. Orange rust pustules that develop on previously resistant cultivars will be collected and compared using the whorl inoculation techniques to isolate the collected spores from different cultivars differing in susceptibility over several years. Mass rust spore collections from the field will be inoculated on plants of the same cultivar twice as a means to help purify the isolate. Variation in symptom development of isolates on specific cultivars will be used to identify pathogenic differences. Unfortunately, pathogen variation will be limited to isolates from Florida because isolates from outside the state are prohibited from introduction.
Progress Report
Progress was made on all three objectives. All Stages 3 and 4 genotypes (clones), total 338 clones in 2017, of the Canal Point sugarcane breeding and cultivar development programs (CP programs) were routinely screened and identified for major diseases by both natural infection in fields and artificial inoculation in greenhouses. Because economic losses caused by sugarcane diseases, especially sugarcane brown and orange rusts, mosaic, ratoon stunting disease (RSD), smut, and leaf scald, are substantial, it is important for the CP programs to develop disease resistant and high-yielding sugarcane cultivars. Data were obtained in natural infection and artificial inoculated trials and reported to breeders to ensure that disease resistant or tolerant clones were advanced and released from the CP programs for growers to use commercially in Florida. Because pathogenic changes occur over time, developing resistance is a continuous effort in the CP programs. Sugarcane orange rust appeared in the Western hemisphere in 2007 and impacted the Florida sugarcane industry as well as CP cultivar development programs. Two sugarcane populations derived from a cross between orange rust susceptible (brown rust resistance) and brown rust susceptible (orange rust resistance) cross and a reciprocal cross have been evaluated for their reaction to orange rust and brown rust for multiple years based on the whorl inoculation. The phenotypic disease data obtained from this segregating population have been used for marker development. Quantitative trait loci associated with orange rust resistance as well as with brown rust resistance have been found. Diagnostic markers have been developed for orange rust resistance and will be further tested for potential use in the CP programs.
Accomplishments
1. Screening all clones in the Canal Point Sugarcane Breeding and Cultivar Development Programs for major diseases. Canal Point (CP) Sugarcane Cultivar Development Programs have been releasing disease resistance/tolerance, high yielding cultivars for Florida sugarcane industry. All susceptible clones in the seedling, Stage I and Stage II of CP programs are eliminated if exhibiting disease symptoms based on natural infection. ARS researchers at Canal Point, Florida, screened two CP Cultivar Development Programs (Organic-soil CP program and Sand-soil CP program), clones in both the CP muck and sand programs annually in inoculation tests at Stage III (135 clones), Stage III increase (40 clones) and Stage IV (13 clones) for their resistance to ratoon stunt, smut, brown rust, orange rust, leaf scald and mosaic. All clones with acceptable resistance levels were advanced to other stages and released for commercial cultivation.
2. Released six sugarcane cultivars with disease resistance and high yields. In 2018, three cultivars CP 11-1314, CP 11-1956, and CP 11-2248 for Florida muck soils and three cultivars CP 10-1620, CP 10-1716, and CP 10-2195 for Florida sand soils were released by the Florida Sugarcane Variety Committee. ARS researchers at Canal Point, Florida, collaborated with the University of Florida and Florida Sugar Cane League for development of these new cultivars. The resistant cultivars have contributed greatly in a sustainable production of sugarcane in Florida. Also, these disease resistant and high yielding cultivars help Florida sugarcane growers to economically grow sugarcane and produce approximately 20% of the sugar consumed in the United States.
Review Publications
Islam, M.S., Yang, X., Sood, S.G., Comstock, J.C., Wang, J. 2018. Molecular characterization of genetic basis of Sugarcane Yellow Leaf Virus (SCYLV) resistance in Saccharum spp. hybrid. Plant Breeding. 137(4):598-604. doi:org/10.1111/pbr.12614.
Rott, P., Kaye, C., Naranjo, M., Shine, J., Sood, S.G., Comstock, J.C., Raid, R. 2018. Controlling sugarcane diseases in Florida: a challenge in constant evolution. International Sugar Journal. 2:274-279.
Yang, X., Sood, S.G., Glynn, N., Islam, M.S., Comstock, J.C., Wang, J. 2017. Constructing high-density genetic maps for polypoid sugarcane (Saccharum spp.) and identifying quantitative trait loci controlling brown rust resistance. Molecular Breeding. 37:116. doi:10.1007/s11032-017-0716-7.
McCord, P.H., Comstock, J.C., Zhao, D., Gordon, V.S., Sood, S.G., McCorkle, K.M., Davidson, R.W., Baltazar, M., Singh, M., Sandhu, H.S. 2018. Registration of ‘CP 07-2320’ Sugarcane. Journal of Plant Registrations. 12:52-59. doi:10.3198/jpr2016.09.0047crc.
