Hybrid weakness is a reproductive barrier that is found in many plant species. In rice, the hybrid weakness caused by two complementary genes, Hwc1 and Hwc2, has been surveyed intensively. However, their gene products and the molecular mechanism that causes hybrid weakness have remained unknown. We performed linkage analyses of Hwc1, narrowed down the area of interest to 60 kb, and identified eight candidate genes. In the F(2) population, in which both Hwc1 and Hwc2 genes were segregated, plants were separable into four classes according to their respective phenotypes: severe type, semi-severe type, F(1) type, and normal type. Severe type plants show such severe symptoms that they could produce only tiny shoot-like structures; they were unable to generate roots. Genetic analyses using closely linked DNA markers of the two genes showed that the symptoms of the F(2) plants were explainable by the genotypes of Hwc1 and Hwc2. Weakness was observed in plants that have both Hwc1 and Hwc2. In Hwc1 homozygote, the symptoms worsened and severe type or semi-severe type plants appeared. Consequently, Hwc1 should have a gene dosage effect and be a semi-dominant gene. The dosage effect of Hwc2 was recognizable, but it was not so severe as that in Hwc1. These results are useful to elucidate the mechanism that causes the hybrid weakness phenomenon and the role of each causal gene in hybrid weakness.

Hybrid weakness is a reproductive barrier. In rice, the hybrid weakness caused by two complementary genes--HWC1 and HWC2--has been surveyed extensively. However, their gene products and the molecular mechanism that causes hybrid weakness have remained unknown. We first performed fine mapping of HWC2, narrowing down the area of interest to 19 kb. We thereby identified five candidate genes. Second, we performed haplotype analysis around the HWC2 locus of 33 cultivars. With 15 DNA markers examined, all the 13 Hwc2-1 carriers share the same haplotype for consecutive 14 DNA markers. As for hwc2-2 carriers, five out of 20 have the haplotypes relatively similar to those of Hwc2-1 carriers. However, the other haplotypes differ remarkably from them. These results are useful to identify the HWC2 gene and to study rice varietal differentiation.

Two methods, the Method of Effective Trajectories and the Method of Distorted Particle Flux, are suggested for calculation of cross-sections of n-n'transitions between Rydberg states of multicharged ions induced by electron impact. These methods are based on rectilinear trajectories with effective impact parameter and effective velocity. The difference between direct calculations of CoulombBom cross-sections and these methods for transitions with principal quantum numbers n,n' Q 6 is about 10-20%. Calculations of cross-sections 20 20 + An are given.

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We present production of silicon nano‐particles and their surface nitridation for efficient multiple‐exciton generation. Nitridated silicon nano‐particles were produced using double multi‐hollow discharge plasma CVD, where generation of silicon particles and their nitridation were independently performed using SiH4/H2 and N2 multi‐hollow discharge plasmas. We succeeded in controlling nitrogen content in a silicon nano‐particle by varying a number density of N radicals irradiated to the Si particle. We also observed strong photoluminescence (PL) emission around 300‐500 nm from silicon nano‐particles, where the PL peak energy is about 2.5 and 3.1 eV for pure Si nano‐particles, and 2.5, 3.1, and 4.1 eV for nitridated Si nano‐particles. The additional UV‐peak of 4.1 eV from nitridated Si particles is closely related to the nitridation surface layer on Si nano‐particles (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)