Continuing Search for Ratoon Stunting Disease

by

Trevor Falloon & Errol Henry

Books up until the 1950’s had Jamaica listed as one of the many countries worldwide with ratoon stunting disease (RSD). Yet, a number of studies carried out since then have failed to confirm this. The major industry-wide survey, conducted by Dr Michael Davis of the University of Florida in 1987 using his then newly developed method known as the fluorescent antibody staining technique, failed to detect symptoms in any of 61 fields sampled.

However, a recent survey at the start of the 2004 crop, carried out on 64 fields, detected the organism associated with RSD in nine. 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. This then marked the first official confirmation of RSD in Jamaica.

The survey was done using a recently developed sampling technique called the tissue blot. A freshly taken core from the base of each stalk was pressed against a specially developed membrane, which was then packaged and sent to Guadeloupe for analysis.

From each field tested, 6 tissue blots were made (from 6 randomly selected stalks). Although 6 stalks would seem a small number, pathologists claim that RSD is of such a nature that this adequately determines the likelihood of the pathogen being present at any significant level in a field. The greater the number of stalks that are positive, the wider would be distribution within a field. There was just one instance, with D14146 at St Thomas Sugar, that all six stalks in a field sample were positive, Table 1. All other fields showed much lower distribution of the pathogen and only 6.88% of total stalks surveyed tested positive. In this survey, Worthy Park showed the highest number of fields with positive readings. It should be noted though that Worthy Park was averaging over 90 tc/ha, at the time of sampling, which would indicate that where good agronomic practices are maintained, the RSD effect might hardly be measurable.

Fresh samples, taken from some of the same fields where initial detection was made, at Appleton, Worthy Park and St Thomas, were sent to the CIRAD laboratory at Montpelier, France, for the more definitive test carried out by the polymerase chain reaction (PCR) process. This test failed to detect the pathogen in the Worthy Park and Appleton samples but confirmed RSD in two out of three stalk samples of D14146 from St. Thomas Sugar. The pathologist’s report stated that the samples were not as highly infected as known susceptible varieties available at CIRAD, since only a few vascular bundles were infected. Nonetheless, the findings were sufficiently clear-cut to leave no doubt that RSD was in Jamaica.

Locations 

Estates showing infection were Worthy Park, Monymusk, Appleton, Frome and St Thomas Sugar. Negative results were obtained from samples taken at New Yarmouth, Bernard Lodge, Long Pond and the SIRI Farm. This study was however not sufficiently comprehensive for us to say that a negative result meant that RSD did not exist on any particular estate or farm. Follow-up, more intense surveys would have to be done.

Symptoms 

There are no reliable visual symptoms that can be used to detect RSD. The disease is caused by a bacterium, known as Leifsonia (Clavibacter) xyli subsp. xyli)and its net effect is a stunting of growth (which could be caused by a number of other factors). Stunting tends to be more pronounced in dry weather. With adequate moisture, visual detection is near impossible.

Worldwide Distribution

All the leading industries - Australia, Thailand, India, Mauritius, South Africa, Brazil, Cuba, USA etc - have long ago recorded the presence of RSD.

Impact 

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. This is therefore added reason to maintain an appropriate replanting cycle. While it is usually cost effective to maintain ratoons for as long as possible, doing so now may be providing the best conditions for development and spread of RSD. Whereas the typical replanting cycle in Jamaica used to be a plant crop and 5 ratoons, lately this has drifted to a plant and 7 or 8 ratoons (where data are available). For many small farms, replanting cycle is even longer and it is not unusual to find fields that have been going for over 20 years. It should be noted that Australia, for instance, replants every three years.

Variety Preference

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. Another series of tests will be required in order to rank varieties according to degrees of tolerance.

Spread

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 the spread. Rats are also thought to be capable of spreading the disease by biting a contaminated stalk and taking the bacteria to other stalks. Recent reports suggest that it may also be possible to contaminate freshly planted setts by the bacterial ooze from old stumps remaining in a field.

Control

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. Many industries however find decontamination too tedious and shed the practice before long. As a precaution against possible infection during replanting, old cane stubble should be properly destroyed during land preparation. In reduced tillage operations, new plantings should be placed in the previous furrow and not on banks containing stubble.

Summary

It is unlikely that RSD should cause sudden sharp drop in cane productivity in Jamaica. That is because we suspect it might have been here all along – just that we failed to detect it. We have probably kept ahead of this disease by the speed with which we change varieties. In the 1960’s the industry was dominated by B4362 and B41227. By the seventies the picture changed radically to an industry built largely around HJ5741 and UCW5465. By the nineties, HJ5741 was completely removed and BJ7015 had moved to the fore. Today the slate of varieties is led by BJ7504 but there are at least half dozen others occupying significant areas – BJ7015, BJ7465, BJ82119, BJ82156, BJ7627, BJ78100 etc. This willingness on the part of growers to try the new varieties would have kept at bay this slow moving disease, spread in the manner described.

At this time, growers are not advised to do emergency removal of any variety. The few remaining fields of D14146 should be removed and the ordered withdrawal of BJ8226 should continue. Meanwhile, SIRI will do a more intense 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 disease-testing programme, which now includes testing for smut and rust, before varieties are released to the industry. Smut and rust are regarded as much more devastating diseases. The industry dealt successfully with those. There is no reason to believe it should not be able to handle this further challenge.

 

RSD Survey Data

Samples tested by CIRAD, Guadeloupe, using Tissue (stalk) Blot Technique

Estate/Farm	Varieties showing no RSD infection	Varieties Infected	No. Stalks Testing Positive out of 6	*Infected Vascular Bundles/20
St Thomas Sugar	BJ7465, B51129, BJ7314, BJ7314, BJ7465	D14146	6	10
Long Pond	BJ7452, BJ78100, BJ7015, BJ82119, BJ7548
Frome	BJ7465, BJ82156, BJ82119, BJ7355, BJ7015, BJ7938, BJ8252	BJ7504,	1	20
New Yarmouth	BJ8859, BJ82102, BJ8252, BJ8226, BJ7015, BJ7627, BJ7504
SIRI Expt Farm	BJ8783, BJ8859, BJ8534, BJ8708
Bernard Lodge	CR67400, BJ78100, BJ7555, BJ7504, BJ8226
Monymusk	BJ7015, BJ7504, BJ82119, BJ8252, BJ7627
Worthy Park	BJ7938, BJ7504	BJ7262	4	12
		BJ7452	1	2
		BJ82119	1	13
		BJ7627	2	9
		BJ82156	1	13
Appleton	BJ7465, BJ7015, BJ8226, BJ7452,	BJ7504	1	20
		BJ7262	1	5

* Applies only to the infected stalk(s)

Total number of stalks sampled                      = 378

Total number of stalks RSD positive               = 26 (6.88%)