GB2291779A - Seed sterilisation treatment - Google Patents

Abstract

The present invention seeks to address the problem of providing an effective process and apparatus for surface sterilisation of seed in advance of field sowing of the seed. The process involves immersing the seed inside a porous vessel in a water bath containing a solution of inorganic sterilant and agitating the seed and/or solution to ensure substantially complete surface exposure of the seed to the solution for an adequate time to allow the sterilant to take effect without harming the seed, and subsequently drying the seed. Specified seeds are carrot and parsnip.

Description

SEED STERILIZATION TREATMENT Field of the Invention The present invention relates to a process and an apparatus for surface sterilization of seed in advance of field-sowing of the seed.

Background to the Invention Modern farming techniques rely heavily upon use of chemically synthesized pesticides to reduce the disease susceptibility of not only crop seedlings as they are grown in the soil by topical spraying or injection of the pesticide into the soil but also that of seeds both prior to and as they are sown into the ground by coating of the seed with the pesticide prior to sowing. As is now well appreciated, this wide spread use of organo-chemical pesticides is ecologically undesirable although perceived by many farmers as a necessity.

Furthermore there is now relentless pressure for an overall reduction of inputs in modern intensive farming operations, and this must be achieved with guaranteed quality and continuity of supply. It is whilst attempting to come to terms with these market forces that much attention is being focused on control of pest and disease pressure without having to rely on blanket spraying of crops. As a consequence substantial research and development is being directed to improve seed quality and seed technology in the hope that many pest and disease problems can be controlled at the level of seed selection.

It is becoming readily apparent to many in the horticultural industry, both vegetable and flower producers alike, that fluctuations in seed quality attributeable to variability in seed health is greatly influencing the profitability of the crop.

In addtion to this, many biological control agents are being considered for introduction from the surface of seed, and this has necessitated a high degree of seed processing before these biological control agents can be attached.

One known approach to disease management which does provide an alternative to use of organo-chemical pesticides to sterilize the seeds to kill surface pathogens, is to sterilise them with steam. This does, however, prove risky. Conditions for steam sterilization must, be very carefully regulated to minimise damage to the fragile seeds which are very heat sensitive and must not be exposed to temperatures in excess of 65"C for more than an instant.

In addition to use of steam to sterilize seeds prior to field sowing, it is also known to use hot water. However, both steam and hot water treatments are unreliable, risk damaging seed viability and do not ensure kill of heat tolerant bacteria. In response to these problems of the prior art, the present invention seeks to provide a large scale seed sterilization treatment process which is safe and straightforward to implement and avoids reliance upon organo-chemical pesticides but which is reliably effective to kill at least a substantial proportion of the surface microbe contaminants to reduce disease incidence and without seriously risking harm to the seed.

Summarv of the Invention According to a first aspect of the present invention there is provided a process for surface sterilization of seed prior to field-sowing which comprises the steps of: placing seed in a porous vessel; immersing the vessel at least partially in a water bath containing a solution of an inorganic sterilant; agitating the seed and/or solution to ensure substantially complete surface exposure of the seed to the solution for an adequate period of time to allow the sterilant to take effect without harming the seed; and subsequently drying the seed.

The porous vessel may be any suitable vessel which is adapted to hold the seed securely therewithin, in use, and has apertures to allow influx and efflux of the sterilant solution without egress of the seed.

Preferably prior to drying, the seed is rinsed to be substantially free of the solution.

Preferably following a first exposure to the solution and subsequent rinsing the seed is subjected to a second exposure to the solution, again followed by rinsing.

The duration of exposure to the solution is suitably of the order of 5 to 10 minutes. An operating concentration of 1-5%(w/v) is preferred.

The sterilant solution is preferably iodine and/or chlorine based. It is suitably acidic and preferably has a pH less than 1. The acid may, for example, be nitric acid, which has the added advantage of being reusable as a fertilizer when re-claimed by passing the solution over, for example, calcium carbonate to form calcium nitrate.

The solution most suitably incorporates interhalogen compounds.

One preferred example of sterilant solution comprises DEOSAN COLD THERM (Trade Mark), a solution of Iodine, Chlorine and Nitric acid that incorporates interhalogen compounds.

The sterilant suitably also has added thereto a detergent to enhance surface wetting of the seed.

According to a second aspect of the present invention there is provided a process for sowing of seeds in a field which comprises the steps of: placing seed in a porous vessel; immersing the vessel at least partially in a water bath containing a solution of an inorganic sterilant; agitating the seed and/or solution to ensure substantially complete surface exposure of the seed to the solution for an adequate period of time to allow the sterilant to take effect without harming the seed; and subsequently drying the seed; and sowing the seed in a field.

According to a third aspect of the invention there is provided an apparatus for surface sterilisation of seeds prior to field sowing, comprising a water bath and a vessel operatively rotatably mounted within the water bath, whereby seed may be loaded into the vessel and secured therewithin, the vessel having one or more apertures to allow influx of solution within the water bath into the vessel as the vessel is rotated, tumbling the seed, and to allow influx and efflux of the solution without egress of the seed.

The vessel suitably has a door in its circumferential wall and is suitably of polygonal transverse section and may be provided with one or more internal radially inwardly extending fins to ensure effective tumbling of the seeds.

The revolving vessel is suitably provided with a conduit extending thereinto to supply air for drying the seed within the vessel. This conduit preferably extends into the vessel along its axis of revolution and for substantially the length thereof and is preferably provided with a plurality of air outlet apertures along the length thereof.

Preferably at least a portion of the vessel is transparent to enable the contents of the vessel to be visually monitored.

The apparatus and method of the present invention have already demonstrated their broad range efficacy in large-scale surface sterilisation of carrot and parsnip seeds and it is reasonable to expect that they will have efficacy in surface sterilisation treatment of seeds of other plants, including not only root crop and other food crop plants but also, for example, floricultural plants.

Brief Description of the Drawings A preferred embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a transverse sectional view through apparatus embodying the second aspect of the invention; and Figure 2 is a transverse sectional view of the seed treatment drum of the apparatus illustrated in Figure 1, taken along the line II-II in Figure 1.

Description of the Preferred Embodiment As shown in Figure 1, the apparatus comprises a water bath constituted by an open-topped tank 1 having a gated drainage outlet and receiving delivery pipes for the sterilisation treatment solution.

A seed holding drum 2 preferaby moulded of a plastics material such as PTFE is partially filled with seed to be treated and lowered into place within the tank 1, rotatably supported above the floor of the tank 1 by a spindle 4 mounted, suitably detachably, at each end in a bearing 3.

An AC motor 5 to drive rotation of the drum 2 about its longitudinal axis is mounted atop a shelf 15 above the tank 1.

Referring to Figure 2, it will seen that the drum 2 has a hexagonal cross sectional configuration centred upon the spindle 4. An access hatch with a removable door 9 is provided in one of the six radial walls of the drum 2 to enable loading and unloading of the seed from the drum 2.

The door 9 is manipulated by handle 10 and is locked in place by a latch (not shown). As a refinement the door may be automatically locking to avoid spillage of the valuable seed. To enable monitoring of the contents of the drum 2 during the course of the treatment process the door 9 or another wall is suitably formed of a transparent plastics material.

Influx to and efflux from the drum 2 of the treatment solution is enabled by the provision of a plurality of apertures 11 extending through the door 9 and suitably (though not illustrated) also through the other walls of the drum 2.

The diameter of the apertures 11 is inevitably greater than the diameter of the seeds to be treated in the drum 2 and may be of the order of 2cm and accordingly a gauze or other filter mesh is suitably provided to cover each of the apertures 11. The mesh is most preferably a micro-mesh to prevent microbial contamination of the rinsing water.

As further illustrated in Figures 1 and 2, the apparatus of the invention also comprises a drying facility to dry the seeds within the rotatable drum 2 and comprising an air inductor fan 6 and conduit 7 to deliver air into the drum 2 via a pivotal coupling 8 with the hollow spindle 4.

As shown in Figure 2, the hollow spindle 4 is provided with a series of apertures 13 along its length to emit the pressurised air into the interior of the drum 2 passed the seed and out through the apertures 11 in the door 9.

To initiate the seed treatment process the preferred procedure begins with the removal of the drum 2 from the bearings 3, the detachment of the door 9 and partial filling of the interior of the drum 2 with seed to be treated. The door 9 of the drum 2 is then replaced and then the drum is re-mounted upon the bearings 3.

Removal of the drum 2 from the tank 1 for filling is not essential but may in some cases be more convenient. In the alternative a hopper chute may be provided to direct the seed into the drum 2 while it remains on its is bearings 3 within the tank 1.

The tank 1 is then filled with the treatment solution which suitably comprises an acidic solution of inorganic sterilant chemicals iodine and/or chlorine.

The preferred sterilant is a proprietary chemical known in the dairy industry for cleaning milking equipment, manufactured by Diversey and known as DEOSAN COLD THERM (TM). This sterilant is a solution of iodine and chlorine in the Nitric acid that forms interhalogen compounds and has wide range sterilising activity and is reliably effective in cold water solution. The applicant of the present invention has found that sterilant of this type may be used to safely treat seeds without adverse effect and to good advantage.

A supply of COLD THERM (TM) is diluted with cold water from another supply and with a detergent such as Triton-X-100 at a metered rate by a computerised supply control system and delivered into the tank 1 at a concentration of about 2% (w/v) to fill the tank to the required depth submerging a substantial proportion of the drum 2.

The drum 2 is then set in motion by actuation of the motor 5 suitably under control of the computerisation system and is set to revolve at rates of revolution most suitably between 5 and 10 revolutions per minute.

A rate of revolution in excess of 30 cycles per minute is highly undesirable since it will risk damage to the fragile seeds leading to a reduction in viability.

As the drum 2 revolves the planar internal faces and the fins 12 which project radially inwardly of the walls of the drum 2 ensure effective tumbling of the seeds and prevent it from simply slipping to the base of the drum 2 as the drum 2 revolves.

When the initial treatment step has taken place for the optimum length of time allowing for effective surface exposure without penetrating to the heart of the seed (normally about 10 minutes) the tank 1 is drained of the solution and filled with cold water to rinse and then drained again (this generally takes about 20 minutes), the seed is then dried over a period of one to two hours and the drum 2 is then removed and emptied into a suitable receptacle for the sterilised and now swollen seeds.

Through trials it has been found that two or more treatments with the sterilant solution separated by rinsing stages prior to drying and removal are desirable to minimise risk of overdosing the seeds while ensuring full surface exposure and killing any newly germinating microbial contaminant spores.

The second and subsequent treatments are suitably of a lower concentration than the first, eg 1% (w/v). Beyond realisation of this important procedural variation, the most suitable protocol for a given seed type may be determined by routine trials A secondary effect of the process is to partially hydrate the seeds which has an apparent effect of priming the seeds to enhance the subsequent onset of germination when the seeds are sown.

The immediately following tables 1A and 1B demonstrate the effects of the surface sterilisation process of the present invention using DEOSAN COLD THERM (TM) to treat two separate batches of parsnip seed. In the first batch examination of the seed revealed that the contamination was too deep seated in the seed to be removable by surface sterilisation. Where the microbial contaminants were not deep seated these were removed completely. Furthermore, with the first batch a marked advancement of germination onset was observed.

TABLE 1A Untreated Seed (5to) Treated Seed (%) First Batch WHK Code WHKPC1 Germination 95% after 21 days 95% after 10 days Incidence of Phoma complanata 20.0 17.0 Incidence of Itersonilia pastinacae 9.5 0 TABLE 1B Untreated Seed (%) Treated Seed (%) Second Batch WHK Code WHK700 Germination 78.7% after 28 days 72.5% after 28 days Incidence of Phoma complanata 5.0 0 Incidence of Itersonilia pastinacae 0 0 Both Phoma complanata and Itersonilia pastinacae are known to induce cankers which can lead to complete crop loss.

The process was developed further with experiments on carrot seed, where broadly similar results were obtained. In this study a range of concentrations and contact times were investigated. The results are summarised in Table 2.

It is clear that the contact of the carrot seed with solutions of COLD THERM (TM) greatly reduced bacterial contamination, and substantially reduced fungal contamination.

TABLE 2 Run Treatment: W/V Initial Final Contact Repeat % % % No: Ratio Conc.: Conc. Time Interval Yeasts Filament Germination: q/l: Mins: Hrs: and Fungi: bacteria: 1 Polycote 0 0 0 0 0 100 4 n/a prime Poligandrum 0 0 0 0 0 96 58 n/a coated Natural seeds 0 0 0 0 0 94 76 n/a Wet Control 1:3 0 0 5 4 96 96 n/a Treatment 1 1:3 3 1 5 4 20 92 n/a 2 Dry 0 0 0 0 0 6 94 70 Control Wet Control 1:16 0 0 10 4 64 98 Treatment 1 1:16 3 1 10 4 2 42 40 Treatment 2 1:16 3 3 10 4 0 42 68 Treatment 3 1:16 3 1 10 4 0 60 64 TABLE 2 (continued) 3 Wet Control 1:16 0 0 10 12 98 96 82 Treatment 1 1:16 1 1 20 4 0 72 80 Treatment 2 1:16 1 1 20 12 0 70 88 Treatment 3 1:8 2 2 20 4 0 56 76 Treatment 4 1:8 2 2 20 12 0 42 74 4 Wet Control 1:16 0 0 30 24 94 80 n/a Treatment 1 1:16 2 2 20 4 0 24 n/a Treatment 2 1:16 2 2 20 24 0 30 n/a Treatment 3 1: :16 1 1 30 4 0 50 n/a Treatment 4 1:16 1 1 30 24 0 56 n/a

Claims (15)

1. CLAIMS: 1. A process for surface sterilisation of seed prior to field-sowing which comprises the steps of: placing seed in a porous vessel; immersing the vessel at least partially in a water bath containing a solution of an inorganic sterilant; agitating the seed and/or solution to ensure substantially complete surface exposure of the seed to the solution for an adequate period of time to allow the sterilant to take effect without harming the seed; and subsequently drying the seed.
2. 2. A process as claimed in Claim 1, wherein prior to drying the seed is rinsed to be substantially free of the solution.
3. 3. A process as claimed in Claim 1 or 2, wherein following a first exposure to the solution and subsequent rinsing the seed is subjected to a second exposure to the solution, again followed by rinsing.
4. 4. A process as claimed in any preceding Claim, wherein an operating concentration of 1 to 5% (w/v) sterilant is used.
5. 5. A process as claimed in Claim 4 wherein the duration of exposure to the solution is of the order of 5 to 10 minutes.
6. 6. A process as claimed in any preceding Claim, wherein the sterilant solution incorporates interhalogen compounds.
7. 7. A process as claimed in Claim 6, wherein the sterilant solution comprises DEOSAN COLD THERM (Trade Mark), a solution of Iodine, Chlorine and Nitric acid.
8. 8. A process as claimed in any preceding Claim, wherein the sterilant solution also has added thereto a detergent to enhance surface wetting of the seed.
9. 9. A process for sowing of seeds in a field which comprises the steps of: placing seed in a porous vessel; immersing the vessel at least partially in a water bath containing a solution of an inorganic sterilant; agitating the seed and/or solution to ensure substantially complete surface exposure of the seed to the solution for an adequate period of time to allow the sterilant to take effect without harming the seed; and subsequently drying the seed; and sowing the seed in a field.
10. 10. An apparatus for surface sterilisation of seeds prior to field sowing, comprising a water bath and a vessel operatively rotatably mounted within the water bath, whereby seed may be loaded into the vessel and secured therewithin, the vessel having one or more apertures to allow influx of solution within the water bath into the vessel as the vessel is rotated, tumbling the seed, and to allow influx and efflux of the solution without egress of the seed.
11. 11. An apparatus as claimed in Claim 10, wherein the vessel has one or more apertures in its wall facing radially outwardly from its axis of rotation.
12. 12. An apparatus as claimed in Claim 10 or 11, wherein the vessel is provided with a conduit extending thereinto to supply air for drying the seed within the vessel.
13. 13. An apparatus as claimed in any of Claims 10, 11 or 12 wherein at least a portion of the vessel is transparent to enable the contents of the vessel to be visually monitored.
14. 14. A process for surface sterilisation of seed substantially as hereinbefore described.
15. 15. An apparatus for surface sterilisation of seed substantially as hereinbefore described with reference to the accompanying drawings.