Commercially grown sugarcane in Louisiana is a large grass with a complex genetic background derived from four different species within the genus Saccharum. The stalks of sugarcane store sucrose, which has pleased the palate of humankind for countless generations.
By Ken Gravois
The temperate climate for growing sugarcane in Louisiana differs from most other areas because sugarcane is a tropical crop. A plant-killing freeze can occur each year in Louisiana, but below-ground stalk portions harbor buds for next season growth. A variety grown in Louisiana must survive a cold and wet winter, re-establish in the spring and produce a profitable crop within a seven-to-nine-month period. This unique challenge has been successfully met by the Louisiana sugarcane breeding effort.
Simple at its beginning and complex today, technology has always been at the forefront of Louisiana sugarcane variety introduction and development. Over time, Louisiana has obtained new sugarcane varieties in a number of ways. The first sugarcane varieties grown in Louisiana arrived by boat as early as 1699 upon Pierre Le Moyne d’Iberville’s explorations in the lower Mississippi River Delta. Louisiana’s first approach to acquiring new sugarcane varieties was importation, and varieties were introduced from as far away as Indonesia and India.
As scientists unravelled the mysteries of sugarcane flowering and the production of true seed, the Louisiana Sugar Experiment Station at Audubon Park in New Orleans began importing true seed from tropical regions around the world. The U.S. Department of Agriculture collected sugarcane flowers and shipped true seed for germinating to experiment station greenhouses. The age of modern sugarcane breeding in Louisiana began with the release of the variety L 511 in the early 1900s as its first success.
Leaders within the Louisiana industry during the mosaic and stalk rot disease outbreaks of the 1920s realized that a more proactive, local sugarcane breeding effort was needed. Early sugarcane breeding efforts in Louisiana relied on crosses made in the warm climate of Canal Point, Florida, where sugarcane flowered under natural conditions. Germination of true seed sent to state and federal research stations in Louisiana starts the 12-year selection process. The first locally developed sugarcane varieties, such as CP 807, were released during the 1930s. Sugarcane varieties used during this period had improved sucrose content and yield along with early maturity for the short Louisiana growing season. There was some level of mosaic resistance in these locally bred varieties, but resistance was quickly overcome when new mosaic strains developed that would continue to rob sugarcane of its yield potential.
In the 1940s, breeders in South Africa worked out artificial photoperiod scheduling that created the opportunity for sugarcane flowering and crossing in temperate environments. An LSU scientist, St. John Chilton, adapted artificial photoperiod schedules in 1953 to fit Louisiana conditions and induce flowering for crossing in Louisiana.
Industry and scientific leaders pushed for a long-term solution to local disease and yield problems, and introgression breeding began in the late 1950s at the U.S. Department of Agriculture-Agriculture Research Service facilities in Houma, Louisiana. US 56-15-8 from Asia, a clone of Saccharum spontaneum, was targeted to broaden the genetic base among sugarcane parents used for crossing in Louisiana. The benefit of introgression breeding was first realized with the release of LCP 85-384, which extended the crop cycle in Louisiana from three or four crops to four or five crops. Other benefits included improved cold tolerance, leaf scald resistance and sugar yield.
Sugarcane breeding programs generate large amounts of data. Older records resided in ledger books and field notebooks. Retrieving and making sense of large amounts of data were daunting and difficult. Enter bits and bytes. Beginning in the 1970s, breeders had access to mainframe computers on the LSU campus that catalogued, stored and analyzed data with modern statistical packages. Analyses-guided crossing and selection decisions are now available at the press of a button.
As knowledge of DNA increased, the world of molecular biology was born. DNA fingerprinting was an early application for identifying varieties. Much like a person’s fingerprint, the DNA of each sugarcane variety is unique. For identifying a sugarcane variety, DNA is extracted, cut into pieces at known regions and catalogued by either gel bands or base sequence. Variety names can be re-established when identity has been lost and parents can be verified in the case of new crosses.
Marker-assisted selection is another useful tool developed by molecular biologists. A genetic marker is a short sequence of DNA used to identify a chromosome or to locate genes on a genetic map. The map shows a graphical representation of chromosomes that includes the position of the genes or gene regions. The first useful genetic marker in sugarcane is referred to as Bru1, which is associated with brown rust disease resistance, an intermittent disease that occurs only after mild winters. Sugarcane breeders cannot discard experimental clones for susceptibility to brown rust in years when the disease is not present. However, DNA can be extracted from sugarcane clones of interest and marker-assisted selection can indicate the presence of the Bru1 marker. LSU AgCenter scientists also have developed genetic markers for leaf scald disease. Much like brown rust disease, leaf scald is an important but intermittent disease of Louisiana sugarcane.
Sugarcane breeding has made remarkable progress in Louisiana. Sugar yields per acre have doubled since the 1970s. From boats to bytes, sugarcane improvement through new varieties has taken advantage of technology.
Kenneth Gravois is the LSU AgCenter sugarcane specialist and holds the Denver T. Loupe Sugar Heritage ASSCT Professorship in Sugarcane Research.
This article appears in the spring 2019 issue of Louisiana Agriculture.