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 | | Johnson, Saimone Sabakera .
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|  | Distribution, assessment and loss caused by ratoon stunting disease (Leifsonia xyli subsp. xyli) of sugar cane in the Fiji sugar industry
Author:Johnson, Saimone Sabakera .
Institution: University of the South Pacific.
Award: M.Sc.
Date: 2006.
Call No.: Pac SB 608 .S9 J66 2006
BRN: 1128820
Copyright:This thesis may NOT be copied without the authors written permission.
Abstract: New sugarcane varieties are developed and provided to the Fiji Sugar cane farmers by the Fiji Sugar Corporation through its Sugar Cane Research Centre at Lautoka. Currently, the average cane yield in Fiji is 45 – 70 tonnes/ ha. Due to the low cane yield in Fiji, research has been directed at increasing the cane yields. One of the causes of low cane yield is the ratoon stunting disease. The objective of this study was to determine the distribution, assessment and loss by ratoon stunting disease (Leifsonia xyli subsp. xyli) of sugar cane in the Fiji sugar industry. A nationwide survey was conducted and positive samples were identified using two diagnostic technique, phase contrast microscopy and Evaporative-Binding immunoassay. A difference of 23% was observed with the results with EB-EIA being more sensitive. Positive samples were cultured in the laboratory. Cultured stocks were used in inoculating the cane plant for yield loss trial and resistance screening trial. The epidemiology of the ratoon stunting disease in the Fiji sugar industry showed that the disease is widespread in all the sugarcane sectors with varying amounts of infection averaging 29% and 6.6% based on evaporative-binding immunoassay and phase contrast microscopy respectively.The difference in cane yield was seen with all the treatments in the cane yield loss experiment but the difference was not statistically significant. It was observed that the only notable effect of the disease was on the cane yield but very little effect on the sugar and percent of pure obtainable cane sugar (% pocs). The cane yield for the plant (first crop) and subsequent ratoon crops (third year, fourth year, etc.) differed with an average reduction of 37% but the average loss caused by RSD was 29%. The best duration of hot water treatment was identified as 2 hours at 50ºC because it gave a higher average yield compared to the control (untreated) and 3 hours at 50ºC. In the screening of the fifteen commercial varieties; Vatu, Homer and Galoa varieties were susceptible to ratoon stunting disease based on reading of greater than 0.1nm on the ELISA reader while Kaba, Vomo, Yasawa, Naidiri, Ragnar, Ono, Waya, Mana, Spartan and LF82-2252 varieties were resistant to ratoon stunting disease with a reading of less than 0.05nm on ELISA reader. Only two varieties, Beqa and Aiwa were moderately susceptible to ratoon stunting disease. To control the disease to manageable levels, an integrated approach including resistant varieties with hot water treated nurseries with best farming practices are recommended.
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