Rice is an important dietary grain but may be difficult to fortify with water-soluble vitamins due to the losses incurred during processing and preparation. Edible coatings can offer reasonable protection against folate processing losses in fortified rice, in particular pectin (Shrestha, 2003). However, pectin, an indigestible fibre, may entrap or bind added folate, decreasing its absorption efficiency. Healthy volunteers (n=26, 18-39 yrs) received oral 400??g [13C5]PteGlu doses in three separate test meals in randomized cross-over trials as follows: 1) aqueous 2) 200g white rice and 3) 200g of pectin-coated rice premix. A plasma AUC0-8 was conducted (0, 1, 2, 5 and 8 hrs postprandial). Subjects followed a low folate basal diet (112??12 ??g/day) - verified using L.casei microbiological assay - during the AUC and for 24 hours prior. Optimisation of the pectin-coated rice premix gave folic acid coating and cooking losses of 33.5% and 15.5% respectively. The mean test dose error per 400??g folic acid was ?? 26 ??g. Single- or tri- enzyme extraction of fortified rice extracts did not significantly increase the mean assayable folate content compared to the mean folic acid content. The levels of plasma [13C5]5-methyl-THF, [13C5]PteGlu and 5-methyl-THF were quantified using a validated HPLC-tandem MS method. The calibration curves indicated good response linearity in the 0-100 ng/mL range (R2&gt0.9978). Inter- and intra-assay variation of 5-methyl-THF (100 ng/mL) was 6.9% (n=6) and 5.2% (n=4) respectively. The mean recovery of 5, 20 and 50 ng/mL 5-methyl-THF in spiked plasma extracts was 98.6 ?? 8.7%, 89.3 ?? 2.8% and 92.6 ?? 3.7% (n=3) respectively. Standard Reference Material-1846, infant formula (129??28 ??g/100g) was measured at 110 ?? 15 ??g folic acid/100g. The relative bioavailability of the folic acid in meals 2 and 3 was measured by comparing their [13C5]5-methyl-THF AUC???s relative to meal 1. The relative bioavailabilities (Mean % ?? CI) of meals 2 and 3 were 86.5 ?? 4.6 % and 68.7 ?? 5.4 % respectively. It appears the pectin coat moderately reduces short-term folic acid bioavailability. These studies define the basis for calculating the amount of folic acid to be added to rice so that an adequate amount can be absorbed after coating and cooking losses. Pectin coatings may be a useful means of increasing the folate status of populations that rely heavily on rice as a staple.

Graduation date: 1976

Statistical analyses were used to develop predictive models of rice blast and to relate the favorability of environment to disease incidence and severity on different rice cultivars at five sites in Asia. The WINDOW PANE program was used to search for weather factors highly correlated with blast. Stepwise and r-square linear regression procedures were then applied to generate the predictive models at each site. Models developed at Icheon, South Korea included relative humidity and rainfall factors as the most important predictors of disease. Temperature, rainfall, wind speed, and relative humidity factors were components of models at Cavinti and the IRRI blast nursery in the Philippines. Rainfall, temperature, and solar radiation factors were important at Gunung Medan and Sitiung, Indonesia. Model validation was done to verify accuracy of models for predictions. Model predictions were also used to determine the effects on blast of sowing time, nitrogen amount, and increase in temperature. Limitations of the models are discussed. Path coefficient analysis was used to identify direct and indirect influences exerted by weather factors on blast. The largest direct influence on disease was exerted by humidity factors at Icheon; temperature, rainfall, and wind speed factors at Cavinti; temperature and humidity factors at IRRI; rainfall factors at Gunung Medan; and temperature factors at Sitiung. Although path coefficient values (Py) were estimated from the decomposition of correlation coefficients, factors that had a high correlation with disease parameters did not always give high Py. Multivariate analysis was used to determine the effects of sowing times on proneness of tropical rice to blast. Cluster analysis of 24 hypothetical sowing months at Cavinti, the IRRI blast nursery, and Sitiung sites revealed three blast proneness groups. Principal component analysis showed that IR50 cultivar would be susceptible at Cavinti at any time of the year. Sowing C22 cultivar at Cavinti in Group I and III months would make it prone to panicle and leaf blast, respectively. At the IRRI blast nursery, leaf and panicle infections on IR50 would be probable only in Group I and II months. This trend was also observed for C22 at Sitiung, although some months in Group III at this site had moderate to high degree of proneness to leaf blast. / Graduation date: 1994

A greenhouse study was conducted to investigate the mechanisms causing diurnal variations in methane emission from rice plants (Oryza sativa L.). Methane emission was measured using a closed chamber system on individual rice plants at five stages of development. The role of the rice plant as the primary methane transport component was examined by comparing emission from intact plants to plants severed above and below the water. No diurnal variations were present in the severed plants and the emission was greatly reduced when compared to the intact plant. Results from the vascular transport experiment showed that transpiration is a major factor in methane emission. Emission dependence on soil temperature was examined to test the hypothesis that soil temperature affects emission. With some plants, soil temperature was held constant using a water bath, otherwise the soil temperature was allowed to vary with environmental conditions in the greenhouse. Diurnal variations in emissions were higher for plants with uncontrolled soil temperature than for plants with controlled soil temperature. Soil temperature at a 5 cm depth explained 46% of the emission variation. Soil temperature affects the source of methane in the soil while transpiration promotes the uptake of water and subsequently the emission of methane. Methane emission was negatively correlated with biomass, probably due to effects of root biomass on soil water methane concentration. Methane concentration in soil water was negatively correlated with root biomass, most likely due to increases in soil oxidation with increasing biomass in a fixed soil volume, and change in root conductance with age.

Amylose content is generally the most important factor determining rice eating and cooking quality. Commercial rice varieties are, in fact, placed into market classes based on having “zero” (0-7%), low (10-20), intermediate (20-25%), or high (>25%) apparent amylose. This study demonstrates that the single-nucleotide polymorphisms (SNP) in the exon 1 (G->T) and in exon 6 (A->C) of GBSS can be used as markers to efficiently distinguish the amylose classes. These two SNPs accounted for 89.2% of the variation in apparent amylose content in a pedigree of 89 US rice varieties and 93.8% of the variation among 279 accessions in a European germplasm collection. All low amylose varieties had the T allele of exon 1. All intermediate amylose varieties had the G allele of exon 1 and the C allele of exon 6. All high amylose varieties had the G allele of exon 1 and the A allele of exon 6. In contrast to previous reports, the amylose content of rice varieties in West Africa was also largely determined by GBSS alleles, which accounted for 93.3% of the variation among 77 samples from West Africa Rice Development Association. GBSS gene from O. glaberrima was found to lack a transposon in exon 10 and have an additional polymorphism (G->A) in exon 12, but these do not significantly alter amylose content. The study also shows that some GBSS genes from high amylose varieties contain an additional C->T polymorphism in exon 10. This SNP does not significantly alter amylose content, but alters rice starch pasting properties. Traditional RVA analysis of starch pasting properties is complicated by differences in the shear forces between samples. However a simple method was developed to overcome this problem and it was shown that starch granules from rice varieties with the T allele of exon 10 are notably more shear resistant. Amylose and the SNP in exons 1, 6 and 10 of GBSS also played a key role in starch re-association. They accounted for 81 and 71.5%, respectively, of the variation in “gel hardness” of RVA samples which have been allowed to incubate at room temperature for 24 hours.

Arsenic is not an essential element and can be toxic to both plants and animals in high concentration. There is a demonstrated association between soil arsenic (As) and the occurrence of straighthead (a physiological disorder in rice characterized by panicle sterility and yield loss); however, the relationship between grain-As accumulation and straighthead susceptibility in rice is not yet fully understood. The objective of the current study was to evaluate a set of diverse rice cultivars, including both indica and japonica subspecies, for total grain-As (TGAs) and As-species concentrations in 2004, 2005, and 2007, on a native (moderate As-concentration) paddy soil and an adjacent monosodium monomethylarsonate (MSMA) amended soil. Cultivars were evaluated under both continuously flooded and intermittently flooded (saturated) field conditions. The genotypic differences in the occurrence of straighthead, total grain-As (TGAs) and As-species concentrations, and their relationships with plant growth parameters, e.g., heading date, plant height, and yield were assessed. The cultivars exhibited a considerable range in both TGAs and grain-As species concentrations. In 2004 and 2005, twenty-one rice cultivars replicated on native soil under continuous flooding showed significant differences in TGAs and As-species concentrations by genotype and year. In 2005, heading was generally delayed in the rice cultivars, resulting in reduced yields that were likely associated with unusually high temperatures and prolonged exposure to stresses in the field, including prolonged flooding and associated soil-As induced stresses. Lower grain-As concentrations were generally associated with early maturing and high yielding genotypes, but with some exceptions. Total grain-As concentrations were not correlated to straighthead susceptibility suggesting that high As concentration in rice grain might not be a direct cause of the genotype-dependent panicle sterility associated with MSMA in soil. The rice cultivars grown on the MSMA-flooded treatment could be effectively differentiated for their relative straighthead susceptibility, with scores ranging from 1 to 8 for the most resistant to the most susceptible genotypes, respectively. In general, traits such as low grain-iAsIII concentration,early maturity, and high yield were correlated with straighthead resistance. In the MSMA-flooded treatment, very high grain-As accumulation resulted in elevated rice-grain dimethyl-AsV (DMAsV) concentration, whereas, the concentration of the more harmful inorganic-AsIII species was less affected. The TGAs and As-species concentrations were considerably higher in continuously--flooded soil than the intermittently-flooded soil. The variations in TGAs and grain-DMAsV concentrations were more highly influenced by water regime than by genotype, whereas, grain-iAIII concentrations were more highly genotype dependent. In the native soil with intermittent flooding, the concentrations of grain-DMAsV and the less desirable grain-iAIII concentrations were lowest. The study concluded that for attaining lower As accumulation in the rice grain both genotype selection and water management are potentially useful approaches.

A greenhouse study was conducted to investigate the mechanisms causing diurnal variations in methane emission from rice plants (Oryza sativa L.). Methane emission was measured using a closed chamber system on individual rice plants at five stages of development. The role of the rice plant as the primary methane transport component was examined by comparing emission from intact plants to plants severed above and below the water. No diurnal variations were present in the severed plants and the emission was greatly reduced when compared to the intact plant. Results from the vascular transport experiment showed that transpiration is a major factor in methane emission. Emission dependence on soil temperature was examined to test the hypothesis that soil temperature affects emission. With some plants, soil temperature was held constant using a water bath, otherwise the soil temperature was allowed to vary with environmental conditions in the greenhouse. Diurnal variations in emissions were higher for plants with uncontrolled soil temperature than for plants with controlled soil temperature. Soil temperature at a 5 cm depth explained 46% of the emission variation. Soil temperature affects the source of methane in the soil while transpiration promotes the uptake of water and subsequently the emission of methane. Methane emission was negatively correlated with biomass, probably due to effects of root biomass on soil water methane concentration. Methane concentration in soil water was negatively correlated with root biomass, most likely due to increases in soil oxidation with increasing biomass in a fixed soil volume, and change in root conductance with age.

Thesis (M. Sc.)--University of Hong Kong, 1968. / Typewritten.

Rice is the staple food for nearly one half of the ever growing world's population. Phosphorus (P) deficiency commonly constrains crop productivity on a large area of arable land worldwide. P fertilizer is a finite resource and an expensive input, so it must be used efficiently. The main objective of this study was to investigate plant and soil P interaction in P deficient conditions and understand plant mechanisms that could enhance P uptake efficiency throughout two main research approaches: Firstly, investigating plant and soil microbes' interaction that promotes plant growth in Plimited conditions. Secondly, evaluating the P uptake efficiency of a number of rice genotypes in a high throughput screening systems in order to understand genotypic variations in P uptake mechanisms. The genotypes used were genotyped for the allelic variation in the Pup1 locus and the effect of this QTL on the plant growth was also investigated. In an experiment investigating the influence of soil microbes on rice growth in P deficient conditions, an experimental system where pots were filled with a mix of 95% low P Insch subsoil and 5% Insch topsoil, where the subsoil was sterilized by autoclaving and the top soil was either sterilized or live. Non-autoclaved (live) topsoil caused a significant increase in shoot dry weight (SDW) for IAC 25 compared to autoclaved soil while the opposite was true for Azucena suggesting that the presence of soil microbes is needed for IAC 25 to access soil-bound P under P-limiting condition while for Azucena it is not. Most importantly, a very strong cultivar x treatment interactions on almost all growth parameters and elements in the shoot except for Mn were found. In a dose experiment investigating whether there is a general toxic effect for autoclaving Insch topsoil being used in this study on the growth of IAC 25, a strong positive correlations of plant growth parameters with the percentage of sterile topsoil vi levels were observed indicating that the autoclaved topsoil was not toxic. The influence of soil wash (distilled water added to the soil then extracted) and different types of soil as sources of inocula on the plant growth of rice cultivars were also studied. Soil wash inoculation did not affected plant growth but soil inocula increased the biomass of all rice cultivars (Azucena, IAC 25 and Lemont) tested suggesting that if it is microbes that are important they must be remaining in the soil and are not transferable by washing. Two autoclaved soils did not behave similarly in terms of affecting plant growth of rice cultivars (Azucena and IAC 25). Moreover, the live treatment of a new soil stimulated the growth of both cultivars and the cultivar x treatment interaction that was found in earlier experiment was lost with the use of this new soil. The implication is that the cultivar by autoclave treatment interaction is soil specific. The fluctuating results between the experiments indicate that it is unlikely that such studies can be extended into plant genetics. So, the second approach of the study focused on examining simpler plant/soil P interaction in P limiting conditions. A 25/75% subsoil/sand mix was determined as a P deficient and used to screen 30 rice genotypes in two experiments: the first when watered with Yoshida's nutrient solution (YNS) either with (YNS+P) or without P (YNS-P) to assess whether rice genotypes differ in extracting P added in liquid form while the second was designed to test if shallow and deep-rooted genotypes differ in extracting P present in soil by using rock phosphate in three treatments: when rock P was absent or embedded either in a shallow 10 cm layer or distributed homogenously in soil mix. For both experiments, P treatment x genotype interaction was significant on SDW. On average, YNS-P treatment significantly reduced the SDW for genotypes compared to that of plants grown in YNS+P treatment while the addition of rock phosphate greatly stimulated plant growth where SDW of plants grown in homogenous P and shallow P significantly outgrew vii those in zero P treatment. In both experiments, rice from the aus subgroup grown in -P treatment accumulated significantly more SDW than indica and japonica genotypes. In -P treatment, the genotypes that accumulated higher SDW relative to the others were Black Gora, Rayada, Kasalath, Azucena, IAC 25, Dom Sufid, Aux1Wild type, FR 13A and especially Sadu Cho. In the rock phosphate experiment, both P treatment and genotype affected RDW and root/shoot ratio significantly. Most importantly, two root angle traits (the mean root direction and the weighted average of the unsigned root angles) measured in rhizotrons were correlated with the relative SDW in shallow P (SDW in shallow P/SDW in zero P) slightly stronger than with relative SDW in homogenous P (SDW in homogenous P/SDW in zero P) indicating that the relationship between plant growth and root distribution with depth was altered by the distribution of rock phosphate in soil. In both experiments, the presence of Kasalath alleles in the Pup1 QTL significantly increased SDW of the genotypes. However, some genotypes, especially Dom Sufid and Sadu Cho performed well in these experiments despite lacking the Pup1 allele suggesting that Pup1 QTL is not the only determinant for tolerance to P deficiency. The system appears to be suitable for high throughput screens of rice genotypes.

No description available.