WO1982001297A1

WO1982001297A1 - Method for treatment of disease in plant material

Info

Publication number: WO1982001297A1
Application number: PCT/AU1981/000144
Authority: WO
Inventors: Douglas W Quick
Original assignee: Douglas W Quick
Priority date: 1980-10-10
Filing date: 1981-10-09
Publication date: 1982-04-29
Also published as: EP0062048A4; EP0062048A1

Abstract

A method for treatment of disease in plant material. The method involves subjection of the plant material, especially seed material, to elevated temperatures (less than 55`C) at pressures other than atmospheric. The method may also involve simultaneous treatment with suitable chemicals.

Description

METHOD FOR TREATIENT OF DISEASE IN PLANT MATER IAL BACKGROUND 0F THE INVENTION

1. Field of the Invention The present invention relates to a method for the treatment of plant material for purposes of the eradication therefrom, or at least a reduction in the degree of incidence therein, of damaging or potentially damaging disease.

2. Description of the Prior Art Plant material, regardless of type, is generally susceptible to the ravages of a number of diseases. Such diseases may manifest themselves in a manner which will serve to make the plant itself unsightly and hence effectively unsuitable for sale, display, use or other-rise. Generally speaking in such a situation a diseased plant will also not be suitable for purposes of propagation, by reason of the fact that the disease present in the so-called "parent" plant will more often than not be transmissible to subsequent generations. Investigation has also shown that, generally speaking at least, diseases of the type under consideration are transmissible from an infected to a previously "clean" or uninfected neighbouring plant, by means of wind action, water action, contact etc. Growers are therefore faced with the problem of effectively isolating infected growing areas from previously "clean" or uninfected areas - a difficult problem indeed. As the level or degree of infection increases, growers are also faced with the problem of locating "clean" growing areas, whereby to satisfy the demand for their crop. Investigations have shown that, with certain types of plant fungal diseases, a growing area once tainted will remain unusable for a substantial period of time (perhaps several growing seasons or mere) by reason of what may be termed a residual effect of the infection. This residual infection in turn increases the likelihood of subsequent infection in surrounding areas - by reason of water action etc. (as stated earlier). As such, it can be seen that the effect of disease in plant material is, generally speaking, rather far-reaching, involving insofar as the grower is concerned an immediate loss of revenue by reason of lost production, a future loss in terms of breeding or propagation potential, not to mention the loss of growing area and the need for the location and maintaining of new, infection-free areas. Insofar as retailers and consumers are concerned, the result will be a reduction in the quality and/or volume of material (product) available for sale and purchase, with the subsequent and inevitable increase in price etc. Throughout the ensuing description attention will be directed specifically to a method for the treatment of potatoes with a view to eradicating therefrom or reducing the degree of incidence therein of the disease commonly known as "powdery scab" (spongospora subterranea). It should be understood, however, that the invention is not to be restricted solely to such a usage. Indeed the method in accordance with the present invention would be equally suitable for the treatment in potatoes of diseases such as common scab, phoma, Blackleg, Fusariums, Rhizoctonia, Silver Scurf and other skin complaints. Furthermore it should be understood that the method in accordance with the invention will also be suitable for use in the treatment of disease in other plant material, be such material in the form of vegetables, fruit or any other plant matter.

Insofar as the especially preferred embodiment involving the treatment of "powder scab" in potatoes is concerned, it should be noted that such a disease is becoming increasingly prevalent on or in potato crops here in Australia. This disease manifests itself in unsightly "scab" areas on. the surface of the potato itself. This "scab" in itself has a three-fold effect. Firstly, the unsightly nature thereof reduces substantially the chances of sale, use etc. of infected articles. Secondly, it ultimately results in breaking of the skin of an infected potato, thereby allowing for ingress to the interior of the vegetable of other organisms which in their turn will lead to ultimate destruction, as for example by rotting, of the overall potato. Thirdly, the "scab" has been found in practice to be especially suited for "carrying", so to speak, a number of associated and more serious plant diseases, such as for example various forms of destructive blights, so-called mop-top virus, pink rot, and the dreaded Irish blight.

The disease known as "powdery scab" is further more significant by reason of its capability of being trans ported, as by wind, water etc., from an infected growing area to a previously untainted area, thereby spreading the disease. In addition, once an area is tainted or infected there is a residual effect, such that a previously infected area will remain tainted for a substantial period of time. In the long-term, therefore, the disease if allowed to go unchecked will result in effectively continuous infection in an ever-increasing area and on an ever-increasing scale. The consequences of this will be disastrous to the grower, not to mention the retailer and/or the consumer.

In the past a number of different methods have been tried to overcome, that is eliminate altogether or at least reduce, the problems posed by the disease known as "powdery scab". However, these prior art methods have proven not particularly successful for a variety of reasons, as will be explained in more detail hereinafter.

One method previously employed involves the use of chemicals, to be sprayed or otherwise disposed over a crop-growing area. Such a procedure was found to produce non-uniform results and indeed to provide only transient relief from the problem at hand. Furthermore this method was found to be both wasteful of chemicals and accordingly expensive, in fact uneconomical. Experience also has shown that the effectiveness of such treatment was very much dependent upon timing, in that the disease has been shown to be in some ways impervious to chemical attack except at certain specific stages during its life cycle . In addition with such a method there always exists the possibility of danger to human and animal life by the spraying of chemical material. Another method tried employs a dipping process, with seed potatoes (for example) being dipped in a chemical bath, involving chemicals considered destructive to the relevant disease micro-organisms. Such a dipping procedure has also been found to be unsatisfactory in that generally speaking the chemicals employed were found not to have penetrated sufficiently far into the potatoes being treated to destroy the disease-causing micro-organisms, this despite the fact that diseases such as, for example, "powdery scab", manifest themselves primarily if not solely in the outermost surface layers of a potato.

Attempts are being made to breed varieties of potatoes exhibiting an increased resistance to the disease. However, success with such attempts is seemingly a long way off yet, and meanwhile the disease is spreading in a substantially uncontrolled manner. Furthermore, there is every chance that any such resistant varieties evolved will provide only a temporary solution to the problem, with future generations bred from such varieties exhibiting less and less resistance to the disease, or alternatively with different strains of the disease itself evolving, strains against which the so-called resistant varieties of potatoes would not be proof. SUMMARY OF THE INVENTION The problem is, therefore, to devise a method for treating tainted or infected seed potatoes, for example, such that the contamination is eliminated or at least greatly reduced, whereby to allow for planting in previously untainted ground. Furthermore the invention seeks to provide a method of treatment which will allow for planting even in previously contaminated ground without risking later contamination of the crop with the disease. The present invention seeks to provide, therefore, a method for the treatment of plant material which is responsible for both an immediate (or short-term) and a long term result. To be more specific the present invention relates to a method for the treatment of plant material which will result in a reduction in the incidence of disease, and preferably total eradication of that disease, from a first generation plant, at the same time making such a first generation plant suitable for purposes of breeding or prop agating subsequent generations of at least equivalently disease-free plant material.

The present invention furthermore seeks to provide a method for the production of a substantially disease-free variety of plant material, exhibiting a resistance (of sorts) to plant disease, thereby allowing for the planting thereof even in previous "tainted" or infected growing areas. As such, the method in accordance with the present invention will provide propagating material suitable not only for use in "clean" growing areas, but also in previously tainted areas, thereby allowing such tainted areas to be restored to growing condition or utility.

In accordance with the present invention there is provided a method for the treatment cf plant seed material, said method involving the subjection of the plant seed material to elevated or reduced temperatures, at a pressure other than atmospheric.

In order that the invention may be more clearly understood, and put into practical effect there shall now be described in detail an especially preferred method of treatment of plant material in accordance with the invention. The description is given by way of non-limitative example only and is specifically directed to the treatment of so-called powdery scab in potatoes. As stated earlier in this specification, however, the method in accordance with the present invention will be equally well suited to the treatment of various other plant diseases. When used in relation to potatoes, for example, the expression "seed material" can refer to whole potatoes, out potatoes, mini-tubers etc.

In a preferred embodiment the method in accordance with the present invention involves the subjection of seed material to a temperature in the vicinity of 50°C and a pressure of the order of 200 lbs. per square inch, for a period of approximately 5 minutes. It should be noted, however, that in practice the parameters involved in the method in accordance with the present invention will be varied to suit specific requirements, as for example variations in the size of the articles being treated, variations in the level of infection in the articles being treated etc. Indeed the temperature of treatment, pressure of treatment and treatment time may be varied to suit such specific requirements. It should, be noted, however, that tests have shown that treatment for any substantial period of time at temperatures above 55ºC is responsible for too great a loss of plant life - the seeds will be effectively killed. Tests have also shown that the incidence of diseases such as powdery scab is substantially reduced in less temperate climates, for example at temperatures below 20ºC. It should furthermore be noted that experience has revealed the existence of an upper ceiling or limit to the pressure which can be applied to potatoes, for example. To be more specific, pressures in excess of 230 pounds per square inch have been found to give rise to cell rupture in potatoes and the like, thereby resulting in loss of plant life (as well as destruction of disease spores). In a further preferred embodiment the subjection of tainted material to a pressure substantially less than atmospheric may also have a marked effect on the degree of infection of the material being treated. In this regard it should be noted that the spores responsible for the disease known as powdery scab are in fact air-breathing, so to speak. It therefore stands to reason that subjecting such spores to the effects of substantial Vacuum will result in the effective destruction of those spores.

A further variation of the method in accordance with the present invention again involves the subjection of seed material to elevated temperatures (less than 55ºC) for a specified period, but this time at varying pressure levels. By way of example, seed material could just be subjected to a temperature of, say, 50°C for a certain period at a pressure of, for instance, 200 pounds per square inch, the pressure then reduced to, say, 150 pounds per sπuare inch for a further period, and then returned to the original 200 pounds per square inch for an additional period. Treatment such as this has been found to fracture, rather than rupture, the spore balls without any catastrophic damage to plant cells, thereby increasing the degree of penetration of any treating chemicals and hence increasing the susceptibility to chemical attack.

In an especially preferred embodiment the method in accordance with the invention involves the treating of tainted or infected seed material with appropriate chemicals at elevated temperatures and perhaps varying pressures. Such a hot, pressurized chemical dipping process has been found to result in an increase in the degree of suffusion of the disease-destructive treating chemicals into the material being treated. Indeed it is suspected that such a procedure will result in "daughter" tubers or the like from treated seed material themselves including therein chemical material of a level sufficient to prevent infecting micro-organisms remaining in previously infected soil from attacking such "daughter" tubers or the like. In other words such so-called "daughter" tubers will exhibit a degree of resistance to the infection. Such a situation will allow for the replanting of previously infected frowing areas with substantially untainted plant material without risking subsequent infection of future generations of the growing crop by micro-organisms residual in the soil.

In the preferred usage for the method of the invention as described herein, that is the treatment or control of "powdery scab" in potatoes, chemicals considered suitable for the afore-mentioned hot-pressurized dipping process include mercury, formalin, a mixture of mercury and formalin, alcohol, hypo-sodium hypo-chloride, Ridomil, Difolatan, Benlate, Dithane H45, Pine Oil, Triuzin, BU-FOS, CaptanA, Diclone, Rovral, carbolic acid and/or hydrochloric acid. Generally speaking, however, such chemicals are rather expensive, hence the preferred method involving the subjection of plant material to elevated temperatures at elevated or reduced pressures in the absence of any additional chemical material.

It should be borne in mind that, whilst the aforegoing description refers merely to the treatment of "powdery scab" in potatoes, the method in accordance with the present invention could be employed for the simultaneous treatment of, for example, potatoes as proofing against a variety of skin complaints.

An apparatus for carrying out the method in accordance with the invention may include a pressure vessel having means associated therewith for raising or reducing the temperature and/or pressure existing in the vessel to suit particular requirements. Such variation in internal temperature and pressure of the vessel may be achieved in any known manner. The actual size of the pressure vessel itself will of course be dependent on projected demand. Such an apparatus will also include means allowing for the introduction of treating chemicals thereinto.

"Powdery scab" in particular, has been found to be susceptible to elevated temperatures. Preferably, in order to ensure uniformity of temperature with a pressure vessel, the vessel itself may be immersed - wholly or partially - in a suitable fluid, such as for example water, which may then be heated by any known means. As a further precaution against the formation of localized "hot spots" or "cool spots" be provided for circulating the heated fluid. In the instance of chemicals in the form of a bath being included within the pressure vessel whereby to constitute a chemical dip for the articles to be treated, means may also be included for regular stirring of the chemicals whereby to ensure uniformity of the treatment.

Finally, it should be understood that the aforegoing description refers merely to preferred embodiments of or usage for the method and apparatus in accordance with the present invention, and that variations and modifications are possible without departing from the spirit and scope of the invention, the ambit of which is to be determined from the following claims.

Claims

1. A method for the treatment of plant seed material, said method involving the subjection of the plant seed material to elevated or reduced temperatures, at a pressure other than atmospheric.

2. The method as claimed in claim 1, wherein said plant material is potatoes.

3. The method as claimed in claim 1 or claim 2, wherein said treatment occurs in a temperature range of from 20°C to 55°C.

4. The method as claimed in any one of claims 1 to 3, wherein said treatment takes place at pressures greater than atmospheric but less than 230 pounds per square inch.

5. The method as claimed in claims 1 to 3, wherein said treatment takes place in a substantial vacuum.

6. The method as claimed in any one of the preceding claims, wherein said method includes treatment of said seed materials with disease destroying chemicals.

7. The method as claimed in any one of the preceding claims, including the subjection of the plant seed material to elevated temperatures and varying pressures for a specified period of time.