Collins Kimbeng, Gravois, Kenneth, Pontif, Michael J.
Collins Kimbeng, Michael Pontif, Niranjan Baisakh and Kenneth Gravois
Sugarcane is a tall perennial grass of tropical origin that is cultivated for its ability to store sucrose in its stalks. Attempts to grow sugarcane in Louisiana began in the early 1700s. In the 1750s, the French Jesuits were among the first to successfully grow and harvest several crops of sugarcane at their New Orleans plantation. However, it was not until 1795 when Étienne de Boré, aided by experienced “sugar makers” from Haiti, successfully granulated about 100,000 pounds of sugar that Louisiana farmers recognized sugarcane as a potential cash crop.
Louisiana represents the northern-most latitude where sugarcane is grown. The cultivation of this tropical crop in a subtropical environment presents many challenges that affect its ability to be grown and processed into sugar. The seven-to-nine-month Louisiana growing season is short compared with tropical environments. Louisiana also faces extreme weather conditions, such as drought and hurricanes. The fear of a plant-killing freeze beginning in late November, which can result in the deterioration of sucrose quality, compels harvesting to commence early when the plant is not fully mature and continue even under unfavorably wet conditions. Following harvest, underground buds must survive the winter months and remain viable for shoots to emerge in early spring to produce the next crop.
Additionally, mosaic virus, smut, leaf scald, rust and strains of other diseases continue to evolve and remain an ever-present danger to the Louisiana sugar industry (Photo 1). Furthermore, insect pests, such as the sugarcane and Mexican rice borers, dictate the need for sugarcane varieties with a wider range of tolerance to both pests and diseases. Louisiana sugarcane breeders have overcome these challenges through the development and deployment of sugarcane varieties uniquely suited to Louisiana’s environment (Photo 2).
Almost all sugarcane industries and their corresponding variety development programs have benefitted from the free exchange of varieties and breeding material. The first sugarcane varieties planted in Louisiana came from Martinique and St. Domingue (now Haiti). However, sugarcane is indigenous to areas in Southeast Asia, including Papua New Guinea/Indonesia, India, and China. It is within these native areas that the greatest display of genetic diversity for traits of economic importance to cultivated sugarcane is observed.
Prior to the 1920s, most of the sugarcane varieties grown around the world consisted primarily of variants of the sugar-producing species, S. officinarum, which are commonly known as noble canes. In 1904, the Louisiana sugar industry was ravaged and nearly wiped out by the mosaic virus. Twenty-five years earlier, the sugar industry in Java, Indonesia, had experienced a similar fate with another viral disease, Sereh disease. Dutch breeders working in Java bred S. officinarum with its more resistant and widely distributed wild relative, S. spontaneum, which does not produce sugar, to obtain new interspecific hybrids of sugarcane. This process, termed nobilization, is perhaps the best example of the contribution of a wild species to the genetic improvement of its cultivated relative. These disease-resistant, interspecific hybrids were distributed worldwide and became the foundation clones for most sugarcane breeding programs. These varieties produced in Java, Indonesia, are credited with bringing the Louisiana sugar industry back from the brink of extinction as they allowed time for local breeding efforts to take hold.
In the mid-1950s, using recurrent selection techniques, Louisiana sugarcane breeders repeatedly selected and bred among varieties with high early sucrose content. This led to the development of early maturing varieties with sucrose levels comparable to those achieved in tropical environments. In the late 1950s, Louisiana sugarcane breeders began breeding successful Louisiana varieties with the wild S. spontaneum, a process known as introgression. The objective is to broaden the genetic base of cultivated sugarcane in Louisiana and introduce into Louisiana varieties novel genetic variation for disease resistance, cold tolerance, general hardiness, and other traits found in S. spontaneum.
The release of LCP 85-384 in 1993 by our collaborative breeding and selection program marked the first milestone of success of the introgression program. In the variety name LCP 85-384, the LCP signifies that the cross was made at Canal Point, Florida (CP), and was evaluated, selected and assigned a permanent variety designation (L) and number (384) by LSU AgCenter personnel in 1985. Thereafter, the experimental variety was jointly evaluated and recommended for release to the industry by researchers from three organizations, the LSU AgCenter, the U.S. Department of Agriculture (based at Houma) and the American Sugar Cane League (representing Louisiana growers and processors). This variety, whose lineage can be traced to a S. spontaneum clone, US 56-15-8 from Thailand, remains significant to the history of modern sugarcane breeding in Louisiana. The variety ushered in unprecedented increases in cane yield, cold tolerance and crop longevity, which increased from two to four ratoon crops. LCP 85-384 was grown on more than 90% of the sugarcane acreage in Louisiana by 2004, when it succumbed to a new strain of brown rust disease (Photo 1). Positive attributes from LCP 85-384 have been bred into newer sugarcane varieties, such as HoCP 96-540 and L 01-283 (Photos 1 and 2), underscoring the continued success of the introgression program.
Earlier accomplishments were achieved using conventional breeding approaches. Nonconventional breeding approaches, such as DNA marker-assisted selection (MAS), now provide additional tools for variety development. DNA markers can be associated with the presence or absence of a gene or genes controlling traits of economic importance in a plant. The MAS technology allows breeders to use small amounts of plant leaf tissue to quickly identify varieties with such genes. Before MAS technology, this would require several years of variety evaluation in field trials. Using MAS, LSU AgCenter researchers have increased the frequency of Bru1, a brown rust resistance gene, in the breeding population from 5% in 2014 to 26% in 2020.
DNA markers are also being used to identify varieties with resistance to leaf scald, another sugarcane disease. Both diseases account for severe losses when present in the industry, but their sporadic occurrences make the task of developing resistant varieties difficult. Increasing the frequency of parents harboring these genes in the breeding population will increase the chances of developing varieties resistant to these diseases. LSU AgCenter researchers are also utilizing a novel MAS strategy called genomic selection. With this strategy, researchers use DNA markers to scan the entire genome of experimental varieties, and that information is used to estimate breeding values. Breeding values are then used to eliminate varieties likely to perform poorly early in the variety development process, thereby minimizing the need for time consuming and expensive field trials.
Evidence suggests that sugarcane has yet to achieve its physiological limit of performance in Louisiana. Combining recurrent selection and introgression, strategies fundamental to plant breeding, with new technologies such as DNA marker-assisted selection will likely lead to breakthroughs in designing future sugarcane varieties for the Louisiana sugar industry.
Collins Kimbeng is a professor, Michael Pontif is an assistant professor-research, and Kenneth Gravois is a professor and extension sugarcane specialist at the Sugar Research Station in St. Gabriel, Louisiana. Niranjan Baisakh is an associate professor at the School of Plant, Environmental and Soil Sciences.
(This article appears in the spring 2021 issue of Louisiana Agriculture.)
Photo 1. Previously resistant to brown rust, LCP 85-384, which was once a leading variety in the Louisiana sugar industry, became susceptible to a new strain of the disease in 2004 and was replaced with HoCP 96-540, pictured in the background. Moderately resistant to brown rust when it was released in 2003, HoCP 96-540 has slowly become more susceptible to the disease and is being replaced by other varieties. Photo by Kenneth Gravois
Photo 2. Fourth ratoon crop of experimental varieties of sugarcane in a selection trial at Bunkie, Louisiana. Bunkie is in the northern fringes of the Louisiana sugar industry and experiences colder temperatures than locations in southern Louisiana or tropical environments. Notice the difference in performance between experimental varieties in the first, second and third row. The variety in the third row, L 01-283, a progeny of LCP 85-384, was recommended for cultivation in the Louisiana sugar industry in 2008 after displaying superior characteristics including sugar yield, disease resistance, cold tolerance and ratooning ability. Photo by Kenneth Gravois