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Results of RSD Survey
A survey carried out by the Institute over the last three months has resulted in detection of the organism associated with Ratoon Stunting Disease (RSD) in 9 fields of 64 sampled. In affected fields the level of infection tends to be low at this time. This marks the first time RSD has been recorded in Jamaica. Previous surveys, carried out by different methods, had all shown negative results. This last survey was done in collaboration with the French International Agricultural Research organisation known as CIRAD. Samples were analysed at their Guadeloupe Station under an agreement with the West Indies Central Sugar Cane Breeding Station, of which Jamaica is a member. In collaboration with CIRAD Montpellier, France, arrangements are being made for confirmatory tests using the well-established PCR method.
Estates showing infection so far are Worthy Park, Monymusk, Appleton, Frome and St Thomas Sugar. Negative results were obtained from samples taken at New Yarmouth, Bernard Lodge, Long Pond, Tulloch Estate and Rhymesbury. This survey was however not sufficiently comprehensive for us to say that a negative result means that RSD does not exist on any particular estate or farm. Follow-up, more intense surveys will now have to be done.
All the leading industries - Australia, Thailand, India, Mauritius, South Africa, Brazil, Cuba, USA etc - have been living with RSD for the longest while, without being ruined and so there is no reason to believe Jamaica should be any different.
There are no reliable visual symptoms that can be used to detect RSD. The disease is caused by a bacterium (known as Clavibacter xyli subsp. xyli)and its net effect is a stunting of growth (which could be caused by a number of other factors). Stunting is more pronounced in dry weather. With adequate moisture, visual detection is near impossible.
Experts say RSD may cause an estimated 5-15% yield loss without a grower even being aware of its presence. In Florida, for instance, it is reported that RSD may cause an estimated 5% yield loss in some years. Yield loss will vary depending on the degree of resistance in the variety. Impact is usually greater in older ratoons. There are reports that suggest that a drop in cane tonnage is often accompanied by an improvement in juice quality.
No variety in the world is completely immune but there are varying degrees of resistance. Results so far in the Jamaican tests show RSD presence in D14146, BJ8226, BJ7504, BJ7262, BJ7627, BJ82119 and BJ82156. The more susceptible seem to be D14146 and BJ8226. D14146 is planted only in St Thomas and is being phased out. BJ8226 was already being withdrawn because of smut susceptibility and only small pockets of BJ7262 remain in the industry.
RSD is transmitted primarily by human activity. The disease is spread during harvesting by contaminated machetes and mechanical harvester blades. Machines or tools that chop cane for planting may also contribute to spreading RSD. Rats are also thought to be capable of spreading the disease by biting a contaminated stalk and spreading the bacteria to other stalks.
The most popular form of control is by heat treatment of seed pieces to establish nurseries, then taking cane seed from such nurseries to plant commercial fields. Heat treatment is usually in a water bath held at 52 degrees Celsius for 2-3 hours. SIRI will conduct screening to ensure that the more susceptible varieties are not released to the industry.
One further measure that may be conducted to slow the spread is decontamination of cane knives and harvester blades before entering new fields. Decontamination requires use of chemical disinfectants such as Lysol, ethanol, Dettol etc. The chemical should be kept in contact with the cutting surface for at least 5 minutes to ensure proper disinfection.
The presence of RSD adds further to the challenge of providing the industry with disease resistant varieties that meet all the other desirable yield and agronomic characters. SIRI has had to deal with such challenges before, with diseases of even more severe impact, smut and rust being the more recent. There is no reason to believe the industry should not be able to handle this further challenge.
At this time, growers are not advised to do emergency removal of any variety. The ordered withdrawal of BJ8226 should continue. Meanwhile, SIRI will intensify the survey so that a more comprehensive picture may be obtained of the presence of RSD. Screening for RSD will now be added to the present programme, which now includes smut and rust.