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THE IMPORTANCE OF SEEDCANE QUALITY
Effective 50°C. 2 hour Hot Water Treatment of seed cane
against ratoon stunting disease (RSD).
For the Small, Medium and Larger Grower.
Profitable crop production partly depends on the quality of the seed planted. This principle applies to sugarcane as much as to any other crop. The potential cane yield that should be obtained will not be achieved if seedcane of poor quality is planted.
Seed cane quality is determined by freedom from diseases and pests, varietal purity and germination capacity. The need to control diseases is the main reason for adopting a planned system of seedcane production.
The most serious diseases in South Africa are ratoon stunting disease (RSD), smut and mosaic. These diseases are spread by planting infected seedcane. All these diseases can cause serious yield losses.
Healthy seedcane is the basis of disease control and is most easily produced in carefully managed seed cane nurseries.
One stage nurseries
For most growers a one-stage nursery system, which has a rotation of a plant crop, a first ratoon and a fallow break, is suitable. With this system, seedcane from the plant and the first ratoon crop is used for commercial planting.
A properly managed one stage nursery should be situated on a specially allocated area of land that has above average productivity potential and, ideally, should be irrigated. One third of the area must be fallow for a year, one third will carry plant cane and one third first ratoon cane.
When the plant and first ratoon harvests have been used as seedcane, the regrowth from the first ratoon section is eradicated and that third of the nursery is fallowed or planted to a break crop. Regrowth from the previous crop (volunteers) can be identified and eradicated. Volunteers are a major source of many important diseases. The section which was fallow will be planted and the plant cane section allowed to grow a first ratoon crop, and so on.
The plant cane section should always be established with seedcane that has been selected to be varietally pure and disease free, and which has then been hot water treated for two hours at 50�C. The plant cane section can also be established with transplants. These should be varietally pure, free from diseases and pests, and grown from hot water treated seed cane.
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If a break crop is planted in the fallow section of the nursery, it should be of a type that readily permits the identification and early elimination of volunteers.
Two stage nurseries
Seedcane schemes for large estates often include a two stage nursery. A two stage nursery should be established in an area which is completely free of any cane regrowth. It is planted with seed cane from a first stage nursery. Only the plant crop from a second stage nursery is acceptable as seedcane; the succeeding ratoons must only be used for milling.
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Nursery management
Both one and two stage nurseries must be kept weed free, adequately fertilized, and irrigated if possible to avoid any stress to the seedcane. An inspection once a month is essential, and all diseased cane and off-types must be rogued out immediately it is identified.
In most areas, seedcane from one stage nurseries should have less than 0,1% plants with smut, mosaic or off-types.
Timing and seed production
Because young seed cane germinates better than old, seedcane should ideally be about 9-12 months old when used, with limits of approximately 8 and 15 months.
For spring planting in most areas, the nursery should be planted in the previous spring or early summer.
Optimum age will vary according to bioclimatic region.
For example
8-10 months in the northern region (12 months is usually too old)
12-15 months in the midlands (20-24 months is too old).
Size of nursery
The size of the nursery required will depend on the expected yield of seedcane from the nursery, the extent of the replanting program and the rate of planting in commercial fields. Nursery size will therefore vary from farm to farm and area to area.
When planting fields with narrow row spacings, more seedcane is required per hectare planted, and therefore a greater area of nursery is needed. More seedcane is also required for low population varieties with thick stalks, such as N19.
Approximately 2-3 hectares of nursery are required for each 100 hectares of commercial cane. However, the size of the nursery required can be estimated more accurately according to farm circumstances.
Variety selection
Every grower should be aware of the advantages of different varieties on his farm, or even on different parts of his farm. Soil form, drainage, frost traps, aspect and topography play an important part in this, even within a particular locality. Forward planning to ensure replanting requirements for the following two years is therefore most important when varieties are selected for the nursery.
Consideration needs to be given to trying out new varieties, and provision must be made for these in the nursery. Don't forget that the varieties chosen will influence farm income for the next 10 years!
Hot water treatment
Seed cane for a one stage nursery MUST be subjected to heat treatment to ensure elimination of RSD.
Treatment in hot water is the method normally used in southern Africa. This treatment consists of maintaining a water temperature of 50�C for two hours. In single batch HWT tanks, the timing of the two hour period starts when the water temperature, which drops when the cane is immersed, has risen back to 50�C. Accurate temperature control and timing are essential; a slight drop in temperature or shortened treatment time may permit RSD to survive, whereas prolonged treatment will reduce germination.
Heat treatment eliminates the dominant effect of the apical bud and, as a consequence, each lateral bud is equally able to develop. This means that it is not necessary to cut heat treated stalks into setts to ensure good germination, as it is when planting nursery produced seed in commercial fields.
A source of fresh, clean water should be used for heat treatment. The water in the HWT tank must be renewed regularly because of a buildup of contaminants that eventually inhibit germination. For a HWT plant in normal daily use, the water must be changed at least weekly.
Inspections
While it is essential to have trained staff on the farm to manage seed cane nurseries properly by inspecting and roguing the cane monthly during the growing season, only the Local Pest, Disease and Variety Control Committees' inspection teams can certify whether the seedcane complies with the required standards.
Reproduced courtesy of SASA Experiment Station March 2002
