Mutation techniques for plant breeding
Nuclear technology is used in plant breeding to develop new varieties by means of induced mutations and related biotechnologies. With the aid of IAEA and UNDP, China has been able to develop new, higher-yielding rice cultivars and extend them to farmers across the country as they strive to produce more food from the 33 million hectares under cultivation with rice. Mutation techniques have produced some promising cytoplasmic male sterile lines which significantly increase the seed set, making the hybrid seed production more economical. Some new early season lines with better grain quality and disease resistance have also been developed in this way.
As part of an IAEA Model project, which began in 1995, Chinese scientists examined a number of mutant rice lines and selected two for large-scale trials. The 'Zehfu' lines have performed so well that over 10% of the rice acreage in five Chinese provinces is now planted to these varieties. Chinese scientists are now seeking to develop a variety that can survive in rugged, mountainous areas, where malnutrition is common. The final phase of the project in China will involve introducing newer complementary approaches, such as the double haploid technique (which is used to obtain reliable variety in 3-4 generations) and DNA fingerprinting procedures, to enhance the mutant development process.
Improved rice varieties have also been produced by mutation breeding in West Africa, where gamma irradiation of African rice (Oryza glaberrima) has produced varieties with white instead of red kernels. These new white varieties are much preferred by consumers and sell for more than double the usual market price. However, important evolutionary adaptations of African rice, such as its ability to withstand flooding and tolerance of drought stress, have been conserved.
Another important staple of West Africa, sorghum, is also undergoing
irradiation treatment and, in field trials, some of the new mutant varieties
produced have demonstrated increases yield of 30-50%, higher protein content
and earlier maturation compared to local cultivars.
Some
varieties demonstrated an improved tolerance to drought and the new plants also
maintained the important characteristics favoured by farmers. Thus, using this
technique, local cultivars can be conserved but also upgraded with one or two
improved characteristics.
Conventional breeding techniques can be used to introduce disease resistance to crops but usually at the expense of other important characteristics. However, in Ghana, disease resistance to Cassava Mosaic Virus (CMV) has been introduced to mutated cassava material produced by irradiation, which has also been selected for its improved taste and cooking qualities.
In summary, over the last thirty years more than 1800 crop varieties worldwide have been developed from selected mutations to provide increased yield, better quality, and combined pest and disease resistance and irradiation has become one of the plant breeders' most valuable tools. Mutant breeding, combined with in vitro and molecular techniques (DNA fingerprinting), is an appropriate technology for many countries which are not prepared for more advanced biotechnology methods (e.g. genetic engineering), offering an affordable way of striving for food security whilst conserving genetic diversity.
