Mutations are normally deleterious and recessive and therefore majority of them are of no practical? value. A. Gustafsson
estimated that less than one in 1,000 mutants produced may be useful in plant breeding. Some of the most important mutants for plant breeders will be summarised here. For a detailed account several books published by International Atomic Energy Agency (IAEA) and Food and Agriculture Organization (FAO) should be consulted.
In wheat, several useful mutations namely branched ears, lodging resistance, high protein and lysine content, amber seed colour and awned spikelets were obtained and utilized in plant breeding. The most remarkable mutation among these is that for amber seed colour in wheat which enabled the cultivation of red seeded Mexican wheat varieties in India. A variety Sharbati Sonora
resulted from this mutant and is widely grown. This mutant was obtained by Dr. M.S. Swaminathan
and his coworkers, while working at Indian Agricultural Research Institute (IARI), New Delhi.
In rice, one of the high yielding varieties Reimei
was developed through mutations isolated after gamma irradiation. Mutants were also obtained in rice for increased protein and lysine content. In some other mutants isolated in rice, duration of crop was reduced by as many as 60 days. Some of the japonica
strains of rice which are high yielding cannot be grown in India due to poor grain quality. Mutations in these 'japonica' strains could be induced to get indica
type grains liked by Indian consumers, so that it will be possible now to grow these 'japonica' strains in India.
In barley, mutations known as erectoides
have been induced. These mutants had high yields including several useful characters. Several new barley varieties, utilizing different useful induced mutations, were released in Sweden in the last 20 years.
Two very good examples of the use of induced mutations in crop improvement also include the development of : (i) Todd's Mitcham
variety of peppermint and (ii) Aruna
variety in castor plant. In Todd's Mitcham variety of peppermint, disease resistance could be combined with desired oil quality following mutagenic treatment. Similarly in Aruna variety, extreme earliness, a reduction from 270 days to 140 days was achieved by induced mutations. This has now been further reduced to about 110 days. Aruna and other early castor varieties are a breakthrough for this crop in India, because the crop is now harvested before the spread of insects and diseases. This has further allowed the farmer to utilize his land for another crop like rice.
Another valuable application of induced mutations is the increased yield of penicillin from the fungus Penicillium.
When penicillin was first discovered, the yield was very low and its production could not be commercially exploited. Millions of spores were irradiated and few colonies with higher yield of penicillin were selected.
Somatic mutations have also been found useful in many ornamentals. Many of our fruit varieties resulted from spontaneous somatic mutations. A late ripening peach has been developed at Brookhaven National Laboratory from gamma radiation.
In regular survey by joint FAO/IAEA Division of Atomic Energy in Food and Agriculture, it has been estimated that till October, 1973, 98 released crop varieties were known to have developed through the use of induced mutations. In addition to these, atleast 47 varieties were developed in ornamental crops through similar methods. Data were compiled from regular survey of results published in Mutation Breeding Newsletters published by IAEA (International Atomic Energy Agency) and are presented in Table 21.7. It can be seen that the number of varieties in crops developed through the use of induced mutations increased from 98 to 1019 and those of ornamentals increased from 47 to 553 during 1973-91. Varieties produced due to induced mutations during 1973-91 were therefore 1397, which suggests increased research activity in this area and demonstrates enormous potential of mutation breeding in crop improvement.