Genetic factors determining varietal differences in characters affecting yield between two rice (Oryza sativa L.) varieties,Koshihikari and IR64

The yield of Koshihikari, a Japanese premium rice variety, is relatively lower than that of modern high yielding varieties. IR64 carries several well-known genes such as GS3, an important gene for grain size, sd-1, a semi-dwarf gene, and NARROW LEAF1 (NAL1), a gene for small, narrow flag leaves. In this study, we used two sets of chromosome segment substitution lines (CSSLs), from Koshihikari and IR64, and attempted to evaluate the genetic factors that cause differences between parents by analyzing the function of chromosome regions affecting a trait (CRATs). For 28 traits, we identified 312 CRATs in the Koshihikari background and 275 in the IR64 background. In these, donor alleles had positive effects in 84 and 103 CRATs, respectively. Among these, the CRAT related to GS3 and those for grain number expanded the potential sink size in Koshihikari, although this did not affect final yield. The combination of CRATs that enhances source ability may increase grain yield. Although the sd-1 gene might improve resistance to lodging, the yield of CSSLs with sd-1 decreased by 28.7 %. These results suggest that the smaller biomass conferred by sd-1 might reduce canopy photosynthesis. In the Koshihikari background, the CRAT related to NAL1 and those located on chr. 6 increased SPAD value but had the opposite effect on leaf size. Two CRATs that were detected on chr. 6 and 7 increased leaf area without any effect on the SPAD value. The combination of these CRATs for area and SPAD value might improve source ability.     

Characterization of six varieties of Cucumis melo L. based on morphological and physiological characters, including shelf-life of fruit

Seventy-two accessions covering six varieties of Cucumis melo were characterized by using 35 morphological characters with emphasis on shelf-life, and the relationships between shelf-life and related characters was investigated. Principal component analysis (PCA) revealed that development period of plant and fruit, size of seed and fruit, shelf-life, stem hair, flesh juiciness, netting, abscission of peduncle, rapid yellowing of epidermis at maturity, Brix value, and color of flesh and epidermis etc. were the principal characters to discriminate melon accessions examined in the present study. According to the scatter diagram, vars. acidulusand makuwa, both of which belong to the Oriental melon, are closely related because of their short growth duration, small seed, thin pericarp and poor shelf-life, while American cantaloupe (var.reticulatus) and European cantaloupe (var. cantalupensis) are rather closely related due to their climacteric fruit with orange flesh, slipped peduncle and rapid yellowing of epidermis at maturity, which is closely related with their shelf-life. PCA also indicated that var. saccharinus was closer to var. inodorus than to the other varieties, due to their requirement of long period for development, large size of seed and fruit, and half- or non-slipped peduncle. Shelf-life of melon fruit was significantly correlated with the following characters: quality of flesh, size of seed and fruit, abscission of peduncle, development periods of plant and fruit, rapid yellowing of epidermis at maturity, Brix value and color of flesh and epidermis. Accessions with good shelf-life were mostly found in vars. saccharinus and inodorus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection and verification of QTLs associated with heat-induced quality decline of rice (Oryza sativa L.) using recombinant inbred lines and near-isogenic lines

Decline in the apparent quality of rice (Oryza sativa L.) grain due to high temperatures during ripening recently became a major concern in many areas in Japan. The occurrence of white-back kernels (WBK) is one of the main problems of heat-induced quality decline. We identified QTLs associated with the occurrence of WBK using recombinant inbred lines (RILs) and verified their effects using near-isogenic lines (NILs). The QTL analysis used F₇ and F₈ RILs derived from ‘Hana-echizen’ (HE), which is tolerant to high temperature, × ‘Niigata-wase’ (NW), which is sensitive to high temperature. Four QTLs were identified on chromosomes 3, 4, 6, and 9 (qWB3, qWB4, qWB6 and qWB9). To verify the effects of qWB6 and qWB9, we developed two NILs in which qWB6 or both were introduced from HE into the NW background. The HE allele at qWB6 significantly decreased WBK under multiple environments. The combination of qWB6 and qWB9 in an F₂ population derived from a cross between a NIL and NW showed that the NW allele at qWB9 significantly decreased WBK if the qWB6 allele was HE. These results will be of value in marker-assisted selection for the breeding of rice with tolerance to heat-induced quality decline.     

Evaluation of genetic variation among wild rice populations in Cambodia

A total of 448 samples in five natural populations of wild rice (Oryza rufipogon) were collected in Cambodia. They were examined using 12 SSR and two chloroplast markers to evaluate the degree of variation among populations and the genetic structure within populations. In the two annual populations, the number of plants with homozygous alleles at all 12 SSR loci were high (66.3% and 79.5%), suggesting that these plants propagate mainly through self-pollination. In the three perennial populations, no individuals had all homozygous genotypes, but redundant genotypes resulted from clonal propagation were observed. Percentages of the redundant genotypes were highly varied (3.6%, 29.2% and 86.0%). This may be due to the different stable levels of environmental conditions. As for chloroplast genome, most of the wild plants showed the same chloroplast types as most Indica-type cultivars have. However, plants with different chloroplast types were maintained, even in the same population. In tropical Asian countries, many wild rice populations were observed under similar ecological conditions examined in this study. Therefore, the present results concerning population structure will be important to further elucidate genetic features of wild rice, and will also give strong clues to utilize and conserve wild natural genetic resources.     

Variation in heading date conceals quantitative trait loci for other traits of importance in breeding selection of rice

To identify quantitative trait loci (QTLs) associated with the primary target traits for selection in practical rice breeding programs, backcross inbred lines (BILs) derived from crosses between temperate japonica rice cultivars Nipponbare and Koshihikari were evaluated for 50 agronomic traits at six experimental fields located throughout Japan. Thirty-three of the 50 traits were significantly correlated with heading date. Using a linkage map including 647 single-nucleotide polymorphisms (SNPs), a total of 122 QTLs for 38 traits were mapped on all rice chromosomes except chromosomes 5 and 9. Fifty-eight of the 122 QTLs were detected near the heading date QTLs Hd16 and Hd17 and the remaining 64 QTLs were found in other chromosome regions. QTL analysis of 51 BILs having homozygous for the Koshihikari chromosome segments around Hd16 and Hd17 allowed us to detect 40 QTLs associated with 27 traits; 23 of these QTLs had not been detected in the original analysis. Among the 97 QTLs for the 30 traits measured in multiple environments, the genotype-by-environment interaction was significant for 44 QTLs and not significant for 53 QTLs. These results led us to propose a new selection strategy to improve agronomic performance in temperate japonica rice cultivars.     

Estimation of LAI in the forested watershed using ASTER data based on Price’s model in summer and winter

Leaf area index (LAI) is an important parameter to identify the water balance in forested watershed as a biological factor influencing directly on the evapotranspiration in the forest area. The purpose of this study was to estimate the LAI in a small forested watershed in summer and winter by applying the Terra/Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to the LAI estimation method. In this study, the estimation was based on the absorption and scattering processes of the solar radiation in the vegetation canopy and the spectral reflectance characteristics of soil vegetation. First, we estimated LAI based on Price’s model by application of ASTER data on the forested watershed located in the Tenzan Mountains of Saga, Japan. To validate the results of LAI estimation, secondly, we compared them to the measured LAI obtained by a plant canopy analyzer (LAI-2000) on the observation area inside the target region. This study showed that the LAI estimation method was a feasible and accurate method as indicated by the high relationship (r = 0.97) between LAI derived from ASTER data and LAI measured by LAI-2000. This paper is the first report on LAI estimation using Terra/ASTER data based on Price’s model and field investigation. This LAI estimation method is a reliable and applicable method.     

Evaluation of cytokine messenger RNA expression in peripheral blood mononuclear cells from dogs with canine demodicosis

Using RT-PCR and semi-quantitative PCR, mRNA expression for canine interferon (IFN)-gamma, interleukin (IL)-2, IL-4, IL-5, IL-10, tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta in peripheral blood mononuclear cells (PBMCs) was examined in dogs with or without demodicosis. mRNA expression for IFN-gamma as well as TNF-alpha in dogs with demodicosis (localized (LD) and generalized (GD)) was slightly lower than those in dogs without demodicosis (healthy controls). Expression of IL-5 mRNA in dogs with demodicosis was higher than that in control dogs, but there were no significant differences in IL-4 and IL-10 mRNA expression levels among the three groups. On the other hand, expression levels of TGF-beta mRNA in dogs with GD were higher than those in control dogs and dogs with LD. The expression levels of IL-5 and TGF-beta mRNA decreased in all three dogs with GD which showed resolution of the clinical signs. Taken together, these results suggest that the Th2-like response in PBMCs from dogs with demodicosis is up-regulated, and that subsequent increased expression of IL-5 and TGF-beta mRNA in dogs with GD is reversible after treatment. Therefore, these cytokines, particularly IL-5, might be a useful clinical index of the clinical course in demodicosis. Also, increased TGF-beta mRNA expression might be a key factor for revealing the difference in the mechanism of onset between LD and GD.     

In vitro evaluation of the growth inhibitory activities of 15 drugs against Babesia gibsoni (Aomori strain)

The in vitro growth inhibitory activities of 15 drugs against Babesia gibsoni were evaluated following establishment of a continuous culture isolate (Aomori isolate). The culture was successfully continued in an RPMI-1640 medium supplemented with 20% normal canine serum or fetal bovine serum in a humidified atmosphere containing 5% CO(2) and 5% O(2) at 37 degrees C. We used this isolate to evaluate the growth inhibitory effect of naphthoquinone (atovaquone), aromatic diamidine (diminazene and pentamidine), artemisinin compounds (artesunate and dihydroartemisinin), an iron chelator (deferoxamine), quinoline-containing compounds (quinine and chloroquine), macrolide antibiotics (azithromycin), lyncomycin antibiotics (clindamycin), tetracycline antibiotics (doxycycline and minocycline), imidazole antifungals (clotrimazole and ketoconazole), and a nitroimidazole antiprotozoal (metronidazole). Atovaquone and aromatic diamidine showed the highest activity; they were followed by artesunate compounds with nanomole levels of IC(50). Metronidazole did not exhibit activity against the parasite. Other drugs exhibited intermediate in vitro activities with micromole levels of IC(50). This is the first report to screen drug activities against B. gibsoni in vitro. The results of our study may support further in vitro drug evaluation for the establishment of therapeutic strategies against canine B. gibsoni infections.     

Evaluation of intestinal intramucosal pH,arterial and portal venous blood gas values,and intestinal blood flow during small intestinal ischemia and reperfusion in dogs

OBJECTIVES: To determine whether small intestinal ischemia and reperfusion affects intestinal intramucosal pH (pHi), arterial and portal venous blood gas values, and intestinal blood flow (IBF) and to investigate relationships between regional intestinal tissue oxygenation and systemic variables in dogs. ANIMALS: 15 healthy adult Beagles. PROCEDURE: Occlusion of superior mesenteric artery (SMA) for 0, 30, or 60 minutes, followed by reperfusion for 180 minutes, was performed; IBF, pHi, arterial and portal venous blood gas values, arterial pressure, and heart rate were measured at various time points; and intestinal mucosal injury was histologically graded. RESULTS: Occlusion of the SMA induced significant decreases in pHi and IBF. After the release of the occlusion, IBF returned rapidly to baseline values, but improvement in pHi was slow. Arterial and portal venous blood gas analyses were less sensitive than tonometric measurements of pHi, and there was no correlation between results of blood gas analyses and tonometric measurements. Histologic score for intestinal mucosal injury increased significantly, depending on duration of ischemia, and there was a correlation between tonometric results and the histologic score. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that it is difficult to accurately evaluate local oxygenation disorders by monitoring at the systemic level, whereas clinically pHi is the only reliable indicator of inadequate regional intestinal tissue oxygenation in dogs.