Agricultural scientists in the country are now embracing mutation breeding to develop plant varieties to achieve attributes of their choice.

In Uganda the scientists are already breeding cassava and rice at the National Agricultural Crop Resources Research Institute to obtain cassava resistant to cassava mosaic virus and brown streak virus as well tolerant to drought and rice varieties resistant to pests and diseases and good aroma.

According to the scientists much as Uganda is embracing this technology now in plant breeding, it has been used in other countries since World War I

Mutation breeding also referred to as variation breeding is a process of exposing seed of plant parts to chemical radiation or enzymes in order to generate mutants with desired traits.

In simple terms it the process where scientists expose plants to regulated radiation rate under using a machine because the natural radiation obtained from sunrays take a long process for a plant to develop with desired trait.

This was revealed to science journalists during the monthly biocafe by Hellen Apio a scientist at NaCRRI who currently breeding cassava using this technology to obtain attributes of pest and disease resistance and drought tolerance.

Background

The first scientists to use this technology were Muller and Standler in the year 1928.

This is after they demonstrated that exposer to X-rays can cause genetic mutations to the plants especially maize and barley in the case of the two founding scientists.

During 1950-1960 several countries took up the task of crop improvement through mutation breeding approaches particularly after establishment of the International Atomic Energy which started coordinated programmes on the use of the technology in various crops in a number of countries across the globe.

Compared to other breeding methods such as cross breeding and chemical mutagenesis, radiation mutation breeding has incomparable advantages.

To date 3,355 mutant varieties of crops have been registered in the mutant data base of the International Atomic Energy Agency (IAEA) and more than 1,000new varieties have been promoted worldwide

Over 3500 mutant varieties belonging to 240 plant species including cereals, pulses, oilseeds, vegetables, fruits, fibres and ornamentals that have been developed and released by 2022 are evidence of successful use of mutation technique in plant breeding.

Scientists using this technology are doing it to identify a wide range of characteristics including yield, flowering and maturity period, quality and tolerance to biotic and abiotic stress to improve the plant using mutation.

Most of the mutant varieties have been developed using physical mutagens with gamma rays alone accounting for the development of the varieties.

Since induced mutagenesis is gaining importance in plant molecular biology as a tool to identify and isolate genes and study their structure and functions, interest in mutation techniques has increased recently in several biological research.

This studies have enormous potential for future crop improvement programmes

How scientists go about mutation breeding

Apio explained that crops provide the most basic guarantee for human survival on Earth, its domestication plays an important role in developing wild plants to produce cultivated crops through the long-term screening of desirable characteristics caused by gene mutations

However, spontaneous mutation appears at an extremely low frequency in nature rendering the process of excellent variety cultivation screening tedious.

How to accelerate the frequency of breeding, the process has always been a key problem in crop variety development, with a long history from natural evolution to cross breeding and mutation breeding in crop breeding

Mutation breeding refers to the method of using artificial mutagenesis to obtain new biological cultivars, mainly through chemical or radiation mutagenesis

Chemical mutagenesis refers to the biochemical reaction between chemical agents and genetic material and the result is mostly point mutations in genes.

Although chemical mutagenesis is effective its environmental optimization and biological safety need to be improved.

Comparatively, radiation mutagenesis has the characteristics of more complex genetic mutation and more beneficial mutant phenotype.

This approach offers the possibility of inducing desirable attributes that either cannot be expressed in nature or have been lost during evolution.

Use of radiation in mutation breeding

A large number of new varieties widely used in production have been bred by classical radiation mutation technology

Radiation mutation breeding is generally divided into classical radiation mutation breeding, particle mutation breeding and space radiation mutation breeding.

Classical radiation mutation breeding methods mainly include X-ray and gamma ray applications.

As a commonly used method, classical radiation mutation breeding has been proven to be useful for crop variation which mainly refers to the process of using various rays to induce a large number of genomic mutations and speed up the production of mutant traits through energy deposition directly or indirectly onto the plant’s DNA.

Particle mutation breeding mainly uses accelerated particles, such as heavy-ions or protons. They have unique physical properties, such as diversified radiation parameters, complex track structure and depth dose distribution.

Accelerated particle has been considered a powerful mutagen for crop breeding because it induces excellent biological mutagenic effectiveness at relatively low radiation doses.

Source of radiation how scientists convert it in mutation breeding

Apio explained that scientists obtain radiation from different sources and this include cosmic radiation which obtained from space existing in the sun and stars

Terrestrial radiation exists in materials such as soil, water and vegetation and Internal radiation which exists in humans such as carbon dioxide.

However the sunshine is the most form of radiation used by scientists. They use a specific equipment to measure the volume radiation to which the plants are exposed.

In this case the scientists target gamma rays to enable the plants to mutate and 63% of the plants released were developed using gamma rays.

The advantage of mutation breeding using gamma rays is that the time for the plant to develop naturally is reduced and it helps in creating genetic diversity for desired traits.

One plant can have traits of pest and disease resistance, high yield as well as tolerance to drought.

Mutation breeding in vegetative crops

In the case of vegetative cops such as cassava on which Apio is working, the scientists usually obtain its stalk which is cut into different pieces and exposed to radiation.

There will be a mixture of solution which is placed in the machine called gamma bean cell that measures the radiation amount. Since the radiation rates differ some plants will end up growing well while others will die off.

The scientists will select those that have grown well and these will be taken to to the field for further growth.

The cassava research

Apio says since there is no facility to expose the plant in the initial breeding process, she went with a number of cassava stalk to Malaysia which has the chronic gamma green house facility. The stalk were exposed to radiation and allowed to grow in the green house.

She sampled those that are growing well and brought them to Uganda where currently they are growing in the green house before they are taken to the field after four months.

The research will take about four years for the product development to be complete ready for release to farmers

Some of the varieties include Narocas1 and other famer preferred varieties.

Since mutation breeding is not regulated, once the research is complete the products will be released to farmers.

According to Apio the regulated radiation allows the changes in plant to occur easily and these changes are for pest and disease resistance, drought tolerance and yield improvement.