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Ukai Y.,Institute of Radiation Breeding
Breeding Science | Year: 2010

The "Crossing-within-Spike-Progeny (CSP) method" is a method to efficiently screen for mutants in allogamous (cross-fertilizing) plants. This paper presents a theoretical analysis of how to minimize the total number of plants in the screening generation (T) and the total cost (Tc) required to detect one or more mutants with a given probability when using the CSP method. Tc depends on the number of plants per line in the screening generation (n), the number of plants per hill plot in the M2 generation (h), the ratio of the cost needed in non-screening generations to that in the screening generation (W), and the mutation rate per cell (p1). T was lowest when n = 1 (T = 47.93 × p1 -1), irrespectively of h. On the other hand, the value of n which gave minimum Tc (designated n*) was not constant, but varied with h. n* was 6 when h = 2, increased as h increased, and was 15 when h = 48, when W= 10. Unlike in the case of autogamous species, the presence of chimeras in the M1 inflorescences greatly increased both T and Tc. A method for estimating the mutation rate per cell is also presented.

Shirasawa K.,Tohoku University | Shirasawa K.,Kazusa DNA Research Institute | Sekii T.,Tohoku University | Ogihara Y.,Tohoku University | And 7 more authors.
Molecular Breeding | Year: 2013

An unusually high temperature during the grain-filling period, such as that caused by global warming, impairs the quality of rice (Oryza sativa L.) grains. This sensitivity to high-temperature stress is different among cultivars, suggesting the possibility of developing a high-temperature-tolerant cultivar. Since marker-assisted selection would reduce time and labor in breeding for such a quantitative trait, we determined the chromosomal region responsible for high-temperature tolerance during the grain-filling period. A high-temperature-sensitive japonica cultivar Tohoku 168 and a tolerant japonica cultivar Kokoromachi were selected as the parental lines of recombinant inbred lines (RILs) by high-temperature stress treatment from 5 to 10 days after anthesis, which was found to be the period most critical for grain quality. Using the RILs, whose genotypes were determined by analysis with 131 DNA markers which were selected as polymorphic markers between these two cultivars from 2,648 DNA markers tested, the quantitative trait locus (QTL) for the percentage of white-back grains was mapped on chromosome 6. The Kokoromachi allele of the QTL, which had a positive additive effect on the high-temperature tolerance, was introduced into the Tohoku 168 genome by repeated backcrossings with marker-assisted selection. Using high-temperature stress treatment of the near isogenic lines developed, the QTL on chromosome 6 was localized within a 1.9-Mb region between two DNA markers, ktIndel001 and RFT1. These DNA markers would be useful not only for breeding high-temperature-tolerant cultivars but also for map-based cloning of the QTL. © 2013 Springer Science+Business Media Dordrecht.

Ukai Y.,Institute of Radiation Breeding | Yamashita A.,Institute of Radiation Breeding
Breeding Science | Year: 2010

We recently presented a method for simultaneous estimation of relative biological effectiveness (RBE) of alpha particles and protons. Here, we evaluate RBE for chlorophyll mutation rate and four M1 effects in thermal neutron exposure of barley (Hordeum vulgare L.) seeds. RBEs of both alpha particles and protons were low for germination rate, seedling height, and number of spikes, and high for seed fertility and mutation rate. Thus, M1 effects are not necessarily accurate as a proxy for mutation rate in comparisons of different types of radiation. RBE of alpha particles for mutation rate was 130.3, much higher than values so far reported in plant materials. RBE of protons for mutation rate was 106.4; as far as we are aware, this is the first value reported for thermal neutron exposure of plant materials. RBEs of alpha particles and protons were significantly correlated (r = 0.939, P < 0.05).

Muramatsu N.,Institute of Radiation Breeding | Yamamoto M.,Kagoshima University | Nakano H.,Kagoshima University | Yamanouchi H.,Institute of Radiation Breeding
Scientia Horticulturae | Year: 2011

We compared hydraulic traits of 18 tropical/subtropical fruit-producing species plants and a further 18 from temperate zone. Plants were classified into four categories by height: tall tree (>10m), small tree (4-9m), shrub (1-4m) and vine. We measured ratios [(cross-section area of xylem)/(cross-section area of twig)], and the diameters and numbers of xylem vessels in microscopic images. We calculated the water flow index (WFI: Σr4S-1×xylem ratio, where, r is the vessel radius, and S is the xylem cross-section area) according to Hagen-Poiseuille's law. Vine had thick vessels and remarkably higher WFI than free-standing trees in both temperate and tropical fruit species. Vessel diameter increased as trees being taller in both in latitudinal groups. Xylem vessel number decreased with height in temperate fruit trees but not in tropical species. WFI increased with tree height of both latitudinal groups. There were no significant effects of latitude on WFI. © 2011 Elsevier B.V.

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