Showing papers on "Mutation breeding published in 1998"

Mutation Breeding: Theory and Practical Applications

Abstract: Preface 1. General introduction 2. History of mutation breeding 3. Nature and types of mutation 4. Induction of mutations 5. In vitro techniques for mutation breeding 6. Mutation breeding in seed propagated crops 7. Mutation breeding in vegetatively propagated crops References Index.

Somaclonal Genetics of Forest Trees

Abstract: In addition to conventional mutation breeding approaches to increase genetic variation for crop improvement, plant tissue cultures also offer opportunities for recovering regenerants with genetic variability. Nearly all types of genetic change detected in plants following irradiation or chemical treatments have also been observed in plant tissue cultures. However, in plant tissue cultures the spectrum of genetic variation may be additionally enhanced by treatment of cultured cells with chemical and physical mutagens (Ahloowalia, 1995; Skirvin et al., 1994). Variation has been observed for phenotypic traits, chromosome number and structure, and biochemical traits in planttissues/regenerants derived from cells, protoplasts, anthers, or other tissues. However, it must be stated at the outset that somaclonal variation has not considerably enhanced the spectrum of useful mutations that have been produced by mutation breeding. Not all the variation produced in tissue cultures is due to mutations; some of it results from paragenetic (epigenetic) changes. Although, variation in plant tissue cultures has been observed for a long time, only in recent years was it categorized and its importance recognized. Plants regenerated from callus have been termed ‘calliclones’ (Skirvin, 1978), and those regenerated from protoplasts as ‘protoclones’ (Shepard, 1981). Larkin and Scowcroft (1981) proposed a more general term, ‘somaclones’, for plants derived from any type of somatic cell culture, and genetic variability originating from such cultures as ‘somaclonal variation’.

Induced Mutations and Somaclonal Variation in Sugarcane

Abstract: Mutation breeding as a methodology for crop improvement is based on the possibility of altering genes by exposing vegetative propagules, gametes or seeds to chemical and physical mutagens. The methodology is considered particularly useful in improving vegetatively propagated crops, as the mutated character can be maintained through asexual propagation. Many cultivars of this group of crops represent unique adaptive gene complexes which when passed through a sexual cycle for improvement of specific characters are bound to be irrevocably lost. All sugarcane cultivars grown today are highly heterozygous and complex polyploids, produced through interspecific hybridization involving three or four species of Saccharum. Consequently a considerable time is taken to improve sugarcane varieties for specific desirable traits through a conventional breeding programme. In this context, sugarcane breeders explored the possibility of mutation breeding to rectify specific defects or to improve a specific desirable trait of highly adapted and genetically balanced sugarcane cultivars, without involving a sexual cycle. The ability of maintaining the mutant genotype through vegetative propagation was also seen as an added advantage.

Mutation Breeding in Cereals and Legumes

Abstract: During the past more than 50 years, mutation breeding has been successfully utilized for crop improvement, to supplement the efforts made using conventional methods of plant breeding. As early as 1942, the first mutant for disease resistance was reported in barley showing resistance to powdery mildew (Freisleben and Lein, 1942). This encouraged further work on mutation breeding, leading to the release of mutant cultivars in several crops. The FAO/IAEA Mutant Varieties Database contained 1790 accessions in June 1996. Among these varieties, 854 were of cereals and 216 of legumes. The majority of varieties among the cereals came from rice (324), barley (256) and bread wheat (146). Many of these mutant varieties were released during the past 10 years (Maluszynski et al., 1991, 1992, 1995). Although, one may not accept that all the listed mutant cultivars really resulted from induced mutations, there is no doubt about the potential which mutation breeding offers for crop improvement. The attributes which are reported to have been improved by mutation breeding include a wide range of characters, including tolerance to biotic and abiotic stresses, duration of flowering and maturity, and other yield-contributing characters (Micke, 1984, 1988, 1991). Due to recent interest in new biotechnology, induced mutations have also proved useful in the preparation of genetic maps (Schwarzacher, 1994) that will facilitate molecular marker-assisted plant breeding in the future.

Micropropagation and mutation breeding techniques for the improvement of bananas

Abstract: Micropropagation, using shoot-tip meristems, has been used for commercial production of banana planting materials in Malaysia. Somaclonal variation, which is known to occur in such in vitro plants, has been exploited for the improvement of banana cultivars. Continuous selection of early fruiting individuals with desirable bunch weight following micropropagation has resulted inplanting materials of Pisang Berangan (cv. Intan) being relatively early in flowering (i.e. 63% of the plants have flowered by the end of eight months after field planting compared to 16% in the unselected materials). A selection of Pisang Rastali (AAB) derived from tissue culture was also found to be resistant to Fusarium wilt with plants apparently showing a hypersensitive reaction to the pathogen. In vitro mutation induction by gamma irradiation has resulted in the selection of an early flowering Cavendish banana called Novaria as well as the generation of diversity in Pisang Berangan. The plants produced following irradiation of Pisang Berangan are being evaluated for desirable agronomic traits and resistance to Fusarium wilt disease.