No abstract

Genetic mapping of centromeres has been a challenge for plant geneticists. The objective of this study was to develop a new strategy for determining the locations of centromeric regions on genetic maps by mapping centromere-associated sequences, to make it possible to define the centromeric region of each chromosome as a single Mendelian locus on the molecular linkage map. Two DNA probes containing sequences specifically associated with the centromeres of grass species were used for genetic mapping. The centromere-associated sequences for all 12 rice chromosomes were mapped on the molecular map with either or both of the probes, and flanking molecular markers on one or both sides were localized 0 to 8 cM away. The map locations of the centromere-associated markers corresponded very well with the positions of centromeric regions determined previously using trisomic analyses for 11 of the 12 chromosomes. The precise mapping of the centromeric regions using these probes makes the molecular map a more complete and informative tool for genomic studies, which will facilitate studies of the structure and function of the rice centromeres. The simplicity of this technique, together with the fact that these probes are also associated with the centromeric regions in other grass species, may provide a general approach to the mapping of centromeric regions in the genomes of other cereal crops.

Low-temperature-sensitive steriUty has become one of the major obstacles in indica-japonica hybrid rice breeding. The objectives of this paper were to evaluate the extent of the fertility reduction and to determine the genetic basis of low-temperature-sensitive sterility. Seventeen varieties were crossed in various ways to produce 21 F|S including 16 indica-japonica hybrids. Fertility of the F]S and their parents was examined under both high and low temperature conditions. Considerable reduction in spikelet fertility was observed under low-temperature conditions in the majority of the indica-japonica hybrids having at least one wide compatibility parent. However, the extent of fertility reduction varied greatly, depending on the parental genotypes. Data from five pairs of reciprocal crosses indicated that the cytoplasm had no effect on fertility reduction. The more-or-less bimodal distribution of the fertihty segregation of one BCiF, and two F^ populations under low-temperature conditions suggested that the lowtemperature-sensitive sterility was controlled by only one or a few genes. It was also shown that the low-temperature-sensitivity is not related to wide compatibility. We conclude that it is possible to develop indicajaponica hybrids with wide compatibility and also insensitivity to the low-temperature conditions.

To investigate the effect of Coriolus versicolor polysaccharides (CVPS) on the immune response of crucian carp (Corassius auratus gibelio), fish were fed diets containing CVPS at different concentrations including 0.5, 1.0 and 2.0 g kg À1 for 5 weeks. Other groups of fish were vaccinated by intraperitoneal injection (i.p.) against Aeromonas hydrophila with a killed bacterin at the beginning of the experiment and fed the same diets as described above. Additionally, control fish and vaccinated-only fish were fed basal diets without CVPS supplementation. The phagocytosis, lysozyme activity, complement components C3 and C4, E-C3bRR (Erythrocyte-C3b rosette rate) and E-CIRR (Erythrocyte-immune complex rosette rate) levels and circulating antibody titers in the serum were monitored. Five weeks after feeding the prescribed diet, fish were challenged with A. hydrophila and the mortalities recorded. Results showed that feeding non-vaccinated and vaccinated crucian carp with CVPS stimulated the phagocytosis of leukocytes, lysozyme, complement components C3 and C4, erythrocyte immune adherence, and circulatory antibody titers in serum in vaccinated crucian carp. Immune parameters increased to their highest levels after 3 weeks of feeding the diet containing 0.5 or 1.0 g kg À1 CVPS. These doses also resulted in the highest protection in the challenge experiment. Best survival (85%) was in the vaccinated group fed the diet containing 1.0 g kg À1 CVPS, whereas almost 80% of control fish (negative control) and 50% of vaccinated-only fish (positive control) died. FeedA normal balanced feed composed of 12% fish meal, 25% soybean meal, 25% rapeseed meal, 27% wheat flour, 2.2% soybean oil, 2.0% CaH 2 PO 4 , 0.1% vitamin mixture, 0.3% mineral mixture, 0.2% salt, 0.2% choline chloride and 1.0% sodium carboxymethyl cellulose was used as the basal diet (crude protein: 33.28%; crude lipid: 6.89%; moisture: 10.59; U.S.

Powdery mildew, caused byEryisphe graminis f. sp.hordei, is one of the most important diseases of barley (Hordeum vulgare). A number of loci conditioning resistance to this disease have been reported previously. The objective of this study was to use molecular markers to identify chromosomal regions containing genes for powdery mildew resistance and to estimate the resistance effect of each locus. A set of 28 F1 hybrids and eight parental lines from a barley diallel study was inoculated with each of five isolates ofE. graminis. The parents were surveyed for restriction fragment length polymorphisms (RFLPs) at 84 marker loci that cover about 1100 cM of the barley genome. The RFLP genotypes of the F1s were deduced from those of the parents. A total of 27 loci, distributed on six of the seven barley chromosomes, detected significant resistance effects to at least one of the five isolates. Almost all the chromosomal regions previously reported to carry genes for powdery mildew resistance were detected, plus the possible existence of 1 additional locus on chromosome 7. The analysis indicated that additive genetic effects are the most important component in conditioning powdery mildew resistance. However, there is also a considerable amount of dominance effects at most loci, and even overdominance is likely to be present at a number of loci. These results suggest that quantitative differences are likely to exist among alleles even at loci which are considered to carry major genes for resistance, and minor effects may be prevalent in cultivars that are not known to carry major genes for resistance.