Hawaii Agriculture Research Center (HARC)
The cornerstones of HARC's sugarcane research program are to improve sugarcane varieties through breeding and selection, to develop sound agronomic practices, and to control insects and diseases.
HARC maintains a breeding and selection program to identify sugarcane cultivars with high yield potential and resistance to sugarcane diseases and test them for site adaptability.
Producing sugarcane seedlings each year from genetically diverse parents (breeding clones) is essential for developing high yielding disease and insect resistant sugarcane cultivars for commercial planting by the sugar industry. About 1,200 Hawaii-produced breeding clones and 800 imported breeding clones are currently maintained in field plots at the HARC Breeding Station at Maunawili on Oahu. Advanced selection and yield testing of seedlings is accomplished in cooperation with commercial plantations. It requires about 10 to 15 years of testing to identify a new sugarcane cultivar.
Genetic engineering and molecular techniques have been developed as plant breeding tools. These include genetic transformation, tissue culture, and molecular marker techniques.
It's important to control weeds in sugarcane fields as they compete for nutrients and water which can affect the sugarcane's vigor and ultimately the yield. Recently, field trials installed at the plantations yielded information on the most effective herbicide combinations of compounds that are registered for use in sugarcane and the rate required to give effective weed control. Several new herbicides that are not yet registered for use in sugarcane were also tested in small experimental plots. Mineral nutrition studies are also conducted to determine optimum rates and timing of fertilizer application.
Hawaii's sugarcane industry has successfully controlled sugarcane insect pests through biological control rather than using pesticides. This strategy has proved itself over 100 years and has been used as a model for many other crops.
Presently, yellow sugarcane aphid (YSCA) is a prevalent pest in sugarcane fields, although the extent of damage it causes has not yet been quantified. HARC and Dr. Messing of the University of Hawaii's Kauai Research Center are cooperating on a project to introduce effective aphid parasitoids into Hawaii. The first aphid parasitoid, Aphidius colemani (Viereck) (Aphidiidae: Braconidae) introduced in April 1996 was not effective on YSCA but was highly effective on the melon aphid. When an effective YSCA parasitoid which passes quarantine and host range studies is introduced, field release will be conducted on Maui and Kauai at sugar plantations.
Lesser cornstalk borer (LCB) is not currently causing substantial damage in plant cane; however, we expect damage to increase with greater emphasis on ratooning. (Good cultural practice, especially timely irrigation in ratoon fields, will help reduce damage.) In anticipation of this, the sugarcane cultivar 73-6110 was transformed with a Bt gene. Laboratory feeding studies indicated that LCB-resistance was conferred. A decision on whether to deploy the transformed cultivar is pending.
HARC's disease control program for the sugar industry develops assessment methods, identifies and controls disease problems, and screens breeding material for resistance to important diseases. Currently, several sugarcane diseases are of concern:
Eyespot Disease-is caused by the fungus Bipolaris sacchari and transmitted by air-borne spores which germinate and make leaf lesions resulting in yield lost due to reduced functional leaf area. New sugarcane clones are being screened for resistance to the pathogen using a toxin from the fungus to inoculate plants.
Smut Disease-is caused by the fungus Ustilago scitaminea which infects the plants systemically, stunting the shoots, and eventually killing the plant. New sugarcane varieties are screened for smut resistance by inoculating seed pieces of all clones with fungus spores and eliminating those that become infected. These are again tested for smut resistance under natural conditions by being planted among other infected plants and exposed to the airborne spores as they would be in nature. All seed cane is treated by soaking in hot water for 20 min at 52º C to kill the fungus. Seed farms are inspected periodically.
Yellow Leaf Syndrome-is-now a recognized virus disease of sugarcane which is transmitted by aphids and causes cane tonnage losses. The development of a tissue-blot immunoassay (TBIA) for detection of the causal virus (ScYLV) has made it possible to screen large numbers of plants accurately and quickly for the infection. All of the main commercial varieties were surveyed on the Hawaiian plantations and the virus was found to be more widespread than had been expected. Most infected sugarcane remains asymptomatic until it is placed under stress conditions. Inoculations with viruliferous aphid vectors determined that some sugarcane varieties are resistant to the virus. No specific control measures are practised.
Ratoon Stunting Disease-is a systemic bacterial infection that is generally symptomless, but results in cane tonnage losses which may be severe. The pathogen is Leifsonia xyli subsp. xyli. It is kept to a very low level in Hawaii by screening seed fields for infection using an immunological diagnostic technique and giving all seed a hot water treatment for 20 min at 52º C before planting.
Leafscald Disease-is caused by the bacterium Xanthomonas albilineans. Symptoms are white leaf streaks that coalesce and turn brown, eventually killing the plant. They appear on infected plants during cooler times of the year. In Hawaii, outbreaks occur during some years and not others. An immunological diagnostic technique can detect the bacterial infection in plants. However, control is maintained by giving seed a hot water treatment for 20 min at 52º C before planting. Some sugarcane varieties are resistant, but this cannot be counted upon for control because new strains of the bacteria occasionally appear.
HARC cooperates with many countries exchanging research findings and sending sugarcane varieties to them for disease testing. Sugarcane varieties developed in Hawaii are exchanged with other countries for breeding and all quarantine and disease protection protocols are strictly followed.
About the sugar industry in Hawaii.