|Hoy, J - LSU AGRICULTURE CENTER|
|Damann, K - LSU AGRICULTURE CENTER|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 26, 1999
Publication Date: N/A
Interpretive Summary: New sugarcane fields are planted with stalks from which multiple annual harvests of stalks are made before replanting. Following the first harvest of stalks, a ratoon or second-year crop is allowed to develop from the buds on the stubble remaining in the ground. A field in Louisiana is typically harvested three times over 3 years before it is replanted. Ratoon stunting gdisease (RSD) caused by a bacterium that infects the water and nutrient vessels of the plant is spread to new fields in infected cuttings and from plant to plant within a field on the cutting blades of harvester. The disease causes stunting that tends to be progressively more severe in successive ratoon crops. Yield of second ratoon crops can be reduced more than 50 percent. The disease is controlled by planting healthy stalks. Identifying healthy stalks for planting however is difficult because RSD causes no visible external symptoms. Rates of RSD spread to new fields and dwithin fields along rows were compared. Additionally, the reliability of five RSD detection methods was determined. The spread and increase of RSD varied among the cultivars and, in most, reflected the susceptibility of the cultivar. The increase of RSD between fields was greater than the increase within a field, emphasizing the need for disease-free stalks for planting. Among the diagnostic methods, tissue-blot immunoassay was the most accurate. Sample handling is more difficult however because stalk pieces are needed. The advantage of two other methods that approached the level of reliability of tissue-blot is that they only require a small sap sample that can be extracted from a stalk in the field. The sap samples are more easily transported and can be frozen for long-term storage.
Technical Abstract: The spread and increase of ratoon stunting disease (RSD) resulting from two mechanical harvests was compared in eight sugarcane cultivars at two locations. RSD spread and increase was detected in the ratoon crops grown after each harvest and varied among cultivars and locations. Disease spread and increase were greater in plants grown from stalks collected at the first harvest than in the first ratoon growth from the harvested field RSD infection was determined using five disease detection methods: alkaline induced metaxylem autofluorescence (AIMA); microscopic examination of xylem sap; and dot-blot, evaporative-binding, and tissue-blot enzyme- immunoassays. The dot-blot and evaporative-binding enzyme immunoassays were the least sensitive for detection of RSD-infected stalks, and AIMA was least accurate for correct identification of noninfected stalks. The tissue-blot enzyme-immunoassay was the most accurate RSD detection method. The results indicate that disease spread and increase is variable even among cultivars susceptible to yield loss due to RSD, and the greatest threat of disease spread and increase occurs at planting.