Showing papers on "Mutation breeding published in 2001"

Mutation induction and tissue culture in improving fruits

Abstract: This review describes in vitro mutation induction methods in fruits and the in vitro selection procedures available for early screening. Results obtained through in vitro mutation techniques, including somaclonal variation, are reviewed and compared with the current achievements and future prospects of transgenic breeding. Plant improvement based on mutations, which change one or a few specific traits of a cultivar, can contribute to fruit improvement without altering the requirements of fruit industry. Induced mutations have well defined limitations in fruit breeding applications, but their possibilities may be expanded by the use of in vitro techniques. Tissue culture increases the efficiency of mutagenic treatments for variation induction, handling of large populations, use of ready selection methods, and rapid cloning of selected variants. Molecular techniques can provide a better understanding of the potential and limitations of mutation breeding e.g. molecular marker-assisted selection, which can lead to the early identification of useful variants. The relatively high number of research reports compared with the low number of cultivars released suggests that mutagenesis in combination with tissue culture is either ineffective or has yet to be exploited in fruits. Positive achievement recorded in other species seem to support the hypothesis that in vitro mutation induction has high potential also for fruit improvement. The possible contribution of a well-pondered and coordinated use of the numerous mutation induction, mutant selection, and field validation procedures available to advances in fruit breeding is discussed.

Breeding Bread Wheat for Tolerance to Aluminum Toxicity

Abstract: Seedlings originating from F2 hybrid populations, from 26 crosses between tolerant and sensitive wheat cultivars to aluminum toxicity and from 18 crosses between tolerant cultivars were evaluated for tolerance to 3 mg/liter of Al3+, using nutrient solutions. Crosses and backcrosses were also made between the semi-dwarf cultivars IAC-24 (tolerant) and Anahuac 75 (sensitive) and seedlings in different generations were evaluated in nutrient solutions containing 2 mg/liter of Al3+. The evaluations of the seedlings from the tolerant and sensitive crosses showed that the tolerance to Al3+ toxicity was dominant and in crosses the tolerant cultivars differed from the sensitive by one pair of alleles for the tolerance. Differences were not observed between the tolerant cultivars in relation to the pair of alleles for the tolerance. Considering that selection for tolerance to Al toxicity in early generations after crossing is effective and that there is no strong undesirable genetic correlation with tolerance, outstanding inbred lines that presented tolerance to Al in nutrient solutions and in acid soils were obtained by the pedigree selection, the backcross method and the mutation breeding using gamma irradiation. No genetic obstacles to transfering Al tolerance were found.

Release of a New Lodging-resistant Mutant Cultivar Produced by Gamma-rays in Glutinous Rice.

Abstract: To obtain short culm mutants with lodging resistance, while retaining the other desirable traits, such as an excellent quality of the original variety, dry seeds of a glutinous rice cultivar Mezuru were exposed to gamma-rays. In M3, thirty plants were selected from 4 020 plants, based on the short culm length. From the results of the subsequent yield and adaptability tests, a promising mutant line was called by the name of Sakata-Mezuru as a new cultivar in 1996. This mutant variety was mainly characterized by shortening of each internode, especially the lowest internode, and at harvest it was more adaptable to mechanical work due to the lodging resistance than its parent. It was demonstrated that the grain quality of the mutant equals to or slightly surpasses that of the parent. Sakata-Mezuru has been registered in February of 2001 and officially released.

Two approaches for induction and isolation of starch mutants in potato (Solanum tuberosum L.) : random versus gene targeted mutagenesis

Abstract: In this thesis two approaches were used to induce structural mutations in potato starch biosynthesis genes in potato. First production of new monoploid amf genotypes through parthenogenesis made it possible to initiate mutation breeding for amfae double mutants. Two amf monoploids were selected which fulfilled most of the prerequisites. By inducing a mutation in one of the branching enzymes in an amf -mutant it is possible to select a double mutant having less branched amylopectin. This mutation can easily be identified by iodine staining. Amylose-free starch will stain red and less branched amylopectin will stain blue, like amylose containing starch. Mutations were induced by X-ray irradiation of leaf explants followed by adventitious shoot regeneration and microtuber induction or followed by several rounds of multiplication of axillary buds and microtuber induction. In both cases the starch of microtubers was stained with iodine to screen for aberrant types. In 56 tuber samples blue or otherwise aberrant starch granules were found. With this kind of observations, the concept of mutation breeding for starch variants in monoploid potatoes is proven. A second way to induce structural mutations was the use of the Ac ( Activator )/ Ds ( Dissociation ) transposase system of maize in potato where the Ds transposon is activated by a transposase source. In this study the Ds element was linked to the GBSS gene, of which the phenotypic effect of deactivation is known i.e. red staining starch after iodine staining. The known amf mutation was used as a model system to gather more information about the transposition frequency of the Ds transposable elements in potato and to test the tagging of the wildtype GBSS gene. To activate the Ds element four Ds transposon containing plants were combined with the Ac transposase via cross combination or double transformation. Excision rates ranged from 14.8-48.4 %. Three phenotypic starch mutants were found after screening by iodine staining of tuber cut surfaces. These amylose-free mutants were analyzed by in vitro tests, Southern blot hybridization and sequencing. Strong indications were found that inactivation of the GBSS gene was caused by a transposable element.

Two approaches for induction and isolation of starch mutants in potato (Solanum tuberosum L.): random versus gene targeted mutagenesis = Twee benaderingen voor de inductie en isolatie van zetmeelmutanten in aardappel (Solanum tuberosum L.): ongerichte versus gen gerichte mutagenese

Abstract: In this thesis two approaches were used to induce structural mutations in potato starch biosynthesis genes in potato. First production of new monoploid amf genotypes through parthenogenesis made it possible to initiate mutation breeding for amfae double mutants. Two amf monoploids were selected which fulfilled most of the prerequisites. By inducing a mutation in one of the branching enzymes in an amf -mutant it is possible to select a double mutant having less branched amylopectin. This mutation can easily be identified by iodine staining. Amylose-free starch will stain red and less branched amylopectin will stain blue, like amylose containing starch. Mutations were induced by X-ray irradiation of leaf explants followed by adventitious shoot regeneration and microtuber induction or followed by several rounds of multiplication of axillary buds and microtuber induction. In both cases the starch of microtubers was stained with iodine to screen for aberrant types. In 56 tuber samples blue or otherwise aberrant starch granules were found. With this kind of observations, the concept of mutation breeding for starch variants in monoploid potatoes is proven. A second way to induce structural mutations was the use of the Ac ( Activator )/ Ds ( Dissociation ) transposase system of maize in potato where the Ds transposon is activated by a transposase source. In this study the Ds element was linked to the GBSS gene, of which the phenotypic effect of deactivation is known i.e. red staining starch after iodine staining. The known amf mutation was used as a model system to gather more information about the transposition frequency of the Ds transposable elements in potato and to test the tagging of the wildtype GBSS gene. To activate the Ds element four Ds transposon containing plants were combined with the Ac transposase via cross combination or double transformation. Excision rates ranged from 14.8-48.4 %. Three phenotypic starch mutants were found after screening by iodine staining of tuber cut surfaces. These amylose-free mutants were analyzed by in vitro tests, Southern blot hybridization and sequencing. Strong indications were found that inactivation of the GBSS gene was caused by a transposable element.