Hiroyuki Terao

Identification of quantitative trait loci associated with pre-harvest sprouting resistance in rice (Oryza sativa L.)

Abstract One of the most important agronomic problems in rice production (Oryza sativa L.) in high humidity climates is pre-harvest sprouting (PHS). This study was conducted to identify quantitative trait loci (QTLs) for PHS resistance using a recombinant inbred (RI) population derived from a cross between a japonica variety Asominori (relatively susceptible to PHS) and an indica variety IR24 (highly resistant to PHS). Knowledge of the genomic positions of QTLs for PHS resistance in rice could greatly simplify selection of the trait. A total of six QTLs for PHS resistance in rice were detected with 289 restriction fragment length polymorphism (RFLP) markers by both one marker analysis (P 2.0). The two QTLs, located on chromosome 1, accounted for 10.7–20.0% of total phenotypic variations, and the other four QTLs, located on chromosome 4, 5, 7 and 8, respectively, explained 12.3–25.3% of total phenotypic variation. As a result, four alleles from IR24 on chromosomes 1 (two QTLs), 5, 7 and two alleles from Asominori on chromosomes 4, 8 contributed to PHS resistance in rice, respectively. The RFLP markers tightly linked to PHS resistance in rice may be useful for breeding varieties with greater resistance to PHS and adaptable to high humidity climates during the maturation period through the use of marker-assisted selection.

Mapping of QTLs for leaf developmental behavior in rice (Oryza sativa L.)

Leaf developmental behavior in rice (Oryza sativa L.) is one of the important agronomic characteristics, which not only determines vegetative growth but also influences grain yield. This study was conducted to identify quantitative trait loci (QTLs) for total number of leaves (TNL), days to the emergence of flag-leaf (DEF) and the leaf emergence rates (LER) on main stem, which mainly represent leaf developmental behavior, using recombinant inbred lines (RILs) derived from a cross between a japonica variety, Asominori and an indica variety, IR24, cultivated in 2001 and 2002. The transgressive segregations in both parental directions and continuous variations of all three tested traits were observed. Significant correlations among these traits were detected. A total of fourteen QTLs for leaf development behavior were detected with 289 RFLP markers. Six QTLs controlling TNL were mapped to chromosomes 3, 5, 6, 8, 9, 12, and accounted for 5.6∼15.7% of the total phenotypic variations, and three QTLs for DEF were mapped to chromosome 3, 6, 8 and accounted for 10.7∼35.4% of total phenotype variation and five QTLs for LER were mapped to chromosome 1(two QTLs), 2, 4, 9 and explained 6.2∼17.5% of phenotype variation. The identification of QTLs for leaf developmental behavior in rice may be useful for selection of ‘fast growing genotype’ before heading using maker-assisted selection.

Potential biological control of weeds in rice fields by allelopathy of dwarf lilyturf plants

Dwarf lilyturf (Ophiopogonjaponicus Ker-Gawl), a medicinal plant, hasbeen used for sore throat therapy andinhibition of physiological thirst sinceancient times. Experimental studies wereconducted to determine the allelopathic effectsof dwarf lilyturf plants on germination andgrowth of three main weed species, viz.,barnyardgrass (Echinochloa crusgalli L.),monchoria (Monocharia vaginalis P.) andsmallflower umbrella (Cyperus difformisL.), in rice production and on emergence andgrowth of weeds in rice fields in Japan. Theseresults showed that all aqueous extracts (1, 2,4, 8%, w/v) from the dried powders ofunderground parts of dwarf lilyturf containedwater-soluble substances that significantlyinhibited seed germination and seedling growthfor monchoria and smallflower umbrella. Withrespect to barnyardgrass, all aqueous extractshad less effect on germination, but lowconcentrations (<2%, w/v) had stimulatoryeffects on growth. However, higherconcentrations (>4%, w/v) had significantinhibitory effects. In a glasshouse experiment,all treatments (50, 100, 150 g m−2) of thedried powders significantly inhibited theemergence and dry weights of weeds in ricepaddy fields and the inhibition became strongeras the concentration increased, except that50 g m−2 concentration had slightstimulatory effects on the emergence ofbarnyardgrass. The 150 g m−2 concentrationmarkedly inhibited emergence (77.6%) and dryweight (91.1%) of rice field weeds. Inaddition, all treatments had no inhibition oninitial rice plant growth. Dwarf lilyturfplants may have inhibitory potential on weedsas a natural rice field herbicide.

Trisomic genetic analysis of aroma in three Japanese native rice varieties (Oryza sativa L.)

Information on the genetics of aroma in rice facilitates breeding and selection of new aromatic varieties with high yield and good quality. Objective of the present study was to make clear the number of genes controlling aroma, and the allelism of aroma genes and the location of aroma gene(s) on the chromosome in three Japanese native aromatic rice varieties (Kabashiko, Shiroikichi and Henroyori). Lack of leaf aroma in all F1 plants of non-aromatic/aromatic crosses indicated the recessive nature of aroma, and the segregation ratios (3:1) of non-aromatic to aromatic plants in its F2 populations from Nipponbare/aromatic varieties crosses revealed that each of the three aromatic varieties contains a single recessive gene for aroma. Through trisomic analysis, the segregation of non-aromatic and aromatic plants in all F2 populations from the crosses between trisomics lines NT8, with an extra chromosome 8, and aromatic varieties deviated significantly from disomic segregation of 3:1 ratios, and fitted to trisomic segregation, however, in other F2 populations derived from other 7 types of trisomic F1 plants, the segregation ratios of non-aromatic to aromatic were 3:1, indicating that the single recessive aroma gene was located on chromosome 8 in three aromatic varieties.

Molecular genetic analysis of QTLs for ferulic acid content in dried straw of rice (Oryza sativa L.).

Phenolic acids are secondary metabolic organic compounds produced by plants and often are mentioned as allelochemicals. This study was conducted to determine the genetic basis controlling the ferulic acid content of rice straw in a recombinant inbred (RI) population derived from a cross between a japonica variety, Asominori, with a higher content of ferulic acid, and an indica variety, IR24, with a lower content, using 289 RFLP markers. Continuous distributions and transgressive segregations of ferulic acid content were observed in the RI population, which showed that ferulic acid content in rice straw was quantitatively inherited. Single marker analysis and composite interval mapping identified three quantitative trait loci (QTLs) for ferulic acid content with LOD values of 2.03 (chromosome 3), 3.16 (chromosome 6), and 3.06 (chromosome 7); all three had increased additive effects (13.5, 18.3, and 18.1 μg g −1) from the Asominori parent and accounted for 5.5, 16.9, and 12.8% of total phenotypic variation, respectively. This is the first report on the identification of QTLs associated with ferulic acid and their chromosomal localization on the molecular map of rice. The tightly linked molecular markers that flank the QTLs might be useful in breeding and selection of varieties with higher phenolic acid content.

Elementary Identification of Phenolic Allelochemicals from Dwarf Lilyturf Plant (Ophiopogon japonicus K.) and Their Growth-Inhibiting Effects for Two Weeds in Paddy Rice Field

Abstract Dwarf lilyturf (Ophiopogon japonicus K.), used as a weed-suppressing cover crop and a medicinal plant, was suggested to be a promising natural herbicide to control weeds in the rice field through its allelopathic potential. Allelopathic chemicals from the dwarf lilyturf were identified and their growth-inhibiting effects on two major weeds in the rice field in Japan were examined. High pressure liquid chromatograph (HPLC) analysis showed the existence of at least six allelopathic chemicals, viz., salicylic acid, syringic acid, syringaldehyde, vanillic acid, ρ-hydroxybenzoic acid and sinapic acid in dwarf lilyturf plant. The chemical detected at the highest concentration was salicylic acid (251.04 ¼g g-1), which occupied more than half of total allelopathic chemicals detected (317.16 ¼g g-1), followed by syringic acid (37.30 ¼g g-1), syringaldehyde(13.30 ¼g g-1) and sinapic acid (11.03 ¼g g-1). The chemicals detected at the lowest concentration was vanillic acid (1.69 ¼g g-1). Salicylic acid displayed the most inhibitory effects on germination and growth of both barnyardgrass (Echinochloa crusgalli L.) and monchoria (Monochoria vaginalis P.). This compound might play a key role in dwarf lilyturf allelopathy.

Effect of low water potential of the culture medium on mesocotyl elongation of rice seedlings

At a soil water content of water potential of ca. -3.1 to -6.2 bars, mesocotyl elongation of both indica and japonica type rice was extremely stimulated. It was also stimulated in an aseptic culture medium (2.5-4.0% mannitol, water potential ca. -3.5 to -5.5 bars). The stimulation of the mesocotyl may be caused by cell multiplication.