USE OF RADIATION AND SOIL

STERILIZATION IN PLANT PROTECTION

BY : JAYANT YADAV, CCSHAU, HISAR, HARYANA

RADIATIONS

O Radiation is the emission of energy as electromagnetic waves or as moving subatomic particles, especially high- energy particles which cause ionization.

O Direct transmission of electromagnetic energy through space or another medium.

Uses of radiation in agriculture field

O Food irradiation: kills bacteria insects and parasites that can cause food borne diseases. It exposes food to gamma rays.

O Radioisotopes are usually used as tracers.O Radiation sterilisation as used in biological

preparations like tissue grafts.O For development of resistant varieties against

various insect-pest.O Sterile Insect TechniqueO Cobalt-60 made radioactive by neutron irradiation,

have been used during recent years for investigating the radiation susceptibility of insect-pests.

Sterile Insect TechniqueO Also known as SIT and sterile insect

release method (SIRM).O It is a biologically- based method for the

management of key insect pests of agriculture and medical/ veterinary importance.

O It is defined “ as method of pest control using area-wide inundative releases of sterile insects to reduce reproduction in a field population of same species”.

O It is therefore a type of “Birth Control” in which wild female insect of the pest population do not reproduce when they are inseminated by released, radiation sterilised males.

O Sexual sterility is induced with radiation emitted from radioisotopes such as caesium-137 and cobalt-60.

O The dosage of radiation has no adverse effect on the males ‘ longevity, searching and mating ability.

O Mating of sterile males with wild females do not yield offspring and hence reduce population in next generation when large no of sterile male is released in population. The proportion of sterile male against wild male should be 10:1.

O The SIT was first time used to eradicate New World Screworm.

Screworm

Soil SterilizationO Importance of soil sterilization: It provide quick relief

of soils from substances and organisms harmful to plants such as:O Bacteria O VirusesO FungiO Nematodes and other pestsO Further positive effects are:O All weed and weed seeds are killedO Significant increase of crop yieldsO Relief from soil fatigue through activation of chemical – biological

reactions.O Blocked nutritive substances in the soil are trapped and made

available for plants.O Alternative to Methyl Bromide and other critical chemicals in

agriculture.

SOIL STERILIZATIONO In simplest terms soil sterilization consist in getting rid of the organisms harmful to

plant growth or atleast, in reducing their numbers to a point where they are no longer of consequence without permanently eliminating or disturbing the balance of those organisms essenstial for fertility.

O Basically it is treatment of soil of glasshouses , greenhouse and other horticultural soils in order to kill weed, seeds, plant disease organisms, and pests.

O Under this soil is sterilized in greenhouses or polyhouses and also in nurseries by steam or hot water/air.

O Soil treated with hot water or steam at about 50°C – To inactivate or kill majority of nematodes, some oomycetes fungi

60-70°C – most of plant pathogenic fungi and bacteria 82°C – Most of weeds and plant pathogenic bacteria and insects Some heat tolerant weed seeds and virus like tobacco mosaic virus are killed at near boiling point depend upon pressure.O It causes their cell structure to physically degenerateO Sterilization can be achieved with one or more of the following: heat, chemicals,

irradiation, high pressure, and filtration.O Sterilisation is distinct from disinfection, sanitization and pasteurization in that

sterilization kills, deactivates, or eliminates all forms of life and other biological agents.

O Example: Molya disease of wheat caused by Heterodera avenae White tip disease of rice caused by Aphelenchoides besseyiO Soil borne pathogens like Fusarium, Rhizoctonia, Sclerotia can be controlled by

this.

Types of sterilizationA.Heat Sterilization

O Heat is used to destroy all forms of life present in soil. It is thorough, quick- acting and clean. And heated soil can be used immediately after it has cooled.

O Heat sterilization is of two types wet/moist and dry heat sterilization.

O i) MOIST HEAT STERILIZATION: It utilizes hot air that is heavily laden with water vapour and where this moisture plays the most imp role in sterilization. Steam sterilization is non-toxic, inexpensive, rapidly microbicidal, sporicidal and rapidly heats.

O A widely used method for steam sterilization is the autoclave, sometimes called a converter or steam sterilizer.

O Autoclaves use steam heated to 121-134°C under pressure for a specific period of time.

O A general cycle is 15-20 mins at 121°C at 100 kPa. It inactivate all resistant bacterial spores in addition to fungi, bacteria and viruses but not eliminate all prions.

O For prions, 121-132°C for 60 mins or 134°C for atleast 18 mins.

O Action on microorganisms: Moist heat causes destruction of microorganisms by denaturation of macromolecules, primarily proteins.

ii) Dry heat sterilization:

O It is one of the earliest form of sterilization used.O Dry heat utilizes hot air that is either free from

water vapour or has very little of it, and where this moisture plays a minimal or no role in the process of sterilization.

O In this process heat is absorbed by the exterior surface of an item and then passed inward to next layer. Eventually, the entire item reaches the proper temperature needed to achieve sterilization.

O The proper time and temperature for dry heat sterilization is 160°C (320°F) for 2 hours or 170°C (340°F) for 1 hour. Instrument should be well dried before used since water will interfere the process.

Generally there are 2 type of hot-air convection sterilizers:O A) Gravity ConvectionO B) Mechanical Convection

A) Gravity Convection Process: O As air is heated, it expands and

possesses less density (weight per volume) than cooler air. Therefore the heated air rises and displaces the cooler air (the cooler air descends). It produces inconsistent temperatures within the chamber and has a very low turnover.

B) Mechanical Convection Process:O It contains a blower that actively

forces heated air throughout all areas of chamber.

O The flow created by the blower ensures uniform temperatures and the equal transfer of heat throughout the load.

O It is more efficient.

Instruments used for dry heat sterilization

O Hot Air OvenO Incineration or BurningO FlammingO RadiationO MicrowaveO Bunsen burnerO Glass Bead Sterilizer

Application of hot steam

O In horticulture as well as nurseries for sterilization of substrates and top soil.

O In agriculture for sterilization and heating of molasses.

O In Mushroom cultivation for pasteurization of growing grooms and sterilization of top soil and combined application as heating.

Hot Air OvenO These are electrical devices which

use dry heat to sterilize.O Originally developed by Pasteur.O Generally, they can be operated

from 50-300°C, using a thermostat to control the temperature.

O Process involves heating the oven to the required temperature, maintaining that temperature for the proper time interval for that temperature, turning the machine off and cooling the articles in the closed oven till they reach room temperature.

O The standard settings for a hot air oven are:

O 1.5 to 2 hours at 160°C (320°F)O 6 to 12 mins at 190°C (374°F)

B.Chemical SterilizationO In these chemicals either as gases or in liquid form,

can be used as sterilants.O Ethylene oxide:O This gas is used to sterilize objects that are sensitive

to temperatures greater then 60°C and radiation.O Ethylene oxide treatment is generally carried out

between 30°C and 60°C with relative humidity above 30% and a gas concentration between 200 and 800 mg/l.

O It penetrates well through paper, cloth and some plastic films.

O Ethylene oxide can kill all known viruses, bacteria and fungi.

O However it is highly flammable, toxic, and carcinogenic with a potential to cause adverse reproductive effects.

O Two most important ethylene oxide sterilization methods are: the gas chamber method and the micro dose method.

O It is delivered by flooding a large area with a combination of ethylene oxide and other gases (CFCs or carbon dioxide )as diluents.

O Other chemicals used are nitrogen oxide, formaldehyde and hydrogen peroxide.

Methods of sterilizationSteaming with superheated steam

O Superheated steam at 180-200°C an optimal soil disinfection can be achieved.

O Soil only absorbs a small amount of humidity.

O Micro organisms become active once the soil has cooled down.

O Different types of such steam application are also available in practice, including substrate steaming and surface steaming.

Surface SteamingO Sheet steaming O The steaming hood O Depth steaming with vaccumO Combined surface and depth

injection of steam (Sandwitch steaming)

Sheet SteamingO Surface steaming with

special sheets in order to steam large areas reaching from 15 to 400 m sq. in one step using a steam injector.

O Use of two polythene sheets are highly effective one is used for steaming and other one for steam injection.

Steaming with hoodsO It is a mobile device consisting of

corrosion-resistant materials such as aluminium, which is put down onto the area to be steamed.

Depth steaming with vacuum

O Steaming with vacuum which is induced through a mobile or fixed installed pipe system in depth of area to be steamed, is the method that reaches best penetration.

Combined Surface and Depth Injection of Steam

O It represents combination of both surface and depth steaming.

O For this area to be steamed must be equipped with deep steaming injection system, is covered with a steaming hood. The steam enters the soil from the top and the bottom at the same time.

THANKS