Indica-type Varieties Research Articles

Varietal differences in tiller and panicle development determining the total number of spikelets per unit area in rice

ABSTRACT Rice varietal differences were compared between japonica type (JAT) and indica type (INT) and between panicle number type (PNT) and panicle weight type (PWT) in terms of tiller and panicle development. Rice varieties PNT-JAT Hinohikari, PWT-JAT Akenohoshi, PNT-INT IR36, and PWT-INT Takanari were used in the field experiments. Tiller bud formation and tiller leaf emergence occurred slightly later in the PWT than in the PNT varieties. These parameters occurred slightly earlier in the INT than in the JAT varieties. The maximum number of tillers was greater in IR36 than in Takanari, Hinohikari, and Akenohoshi. The number of panicles per unit area (PN) was greater in IR36 and Hinohikari than in Akenohoshi and Takanari. The widths of the shoot apical meristem (SAM) just before panicle initiation were in the order of Akenohoshi > Hinohikari = Takanari > IR36. The number of spikelets per panicle (SN) was in the order of Takanari = Akenohoshi > IR36 > Hinohikari. In conclusion, the PWT varieties, which had relatively wider SAM, presented with the promotion of main shoot development and the suppression of tiller development. Consequently, PN decreased and SN increased in PWT varieties. INT varieties presented with the promotion of tiller and rachis branch development, which resulted in increases in both PN and SN. These developmental factors may determine varietal differences in the total number of spikelets per unit area. Abbreviations CGR: crop growth rate; DEL: differences between the numbers of emerged leaves in the tiller and those in the main shoot; DIL: differences between the number of initiated leaves in the tiller and those in the main shoot; INT: indica type; JAT: japonica type; MLAI: mean leaf area index; NAR: net assimilation rate; PN: the number of panicles per unit area; SN: the number of spikelets per panicle; PNT: panicle number type; PWT: panicle weight type; SAM: shoot apical meristem; TSN: the total number of spikelets per unit area

Rice Varieties in Archaic East Asia: Reduction of Its Diversity from Past to Present Times.

The Asian cultivated rice, Oryza sativa, is one of the most important crops feeding more than a third of global population. In spite of the studies for several decades, the origin and domestication history of rice varietal groups, japonica and indica, have not been fully unveiled. Genetic information of ancient rice remains is essential for direct and exclusive insight into the domestication history of rice. We performed ancient DNA analysis of 950- to 2,800-year-old rice remains excavated from Japan and Korea. We found the presence of both japonica- and indica-type varieties in the Yayoi period and the middle ages of Japan and the middle part of Korea Peninsula 2,000 years ago. It is popularly considered that japonica has been exclusively cultivated in northern part of East Asia including Japan and Korea. Our result disclosed unexpectedly wide diversity of rice varieties in archaic East Asia. The present results from ancient rice DNA reveal an exclusive insight for the domestication history of rice which is not provided as far as contemporary rice.

Comparison of molecular genetic utilities of TD, AFLP, and MSAP among the accessions of japonica, indica, and Tongil of Oryza sativa L.

Rice is one of the most important food crops in the world. Genetic diversity is essential for cultivar improvement programs. We compared genetic diversity derived from insertion–deletion (in–del) or base substitutions by amplified fragment length polymorphism (AFLP), from transposon transposition mutations by transposon display (TD), and from cytosine methylation by methylation-sensitive amplified polymorphism (MSAP) in japonica, indica, and Tongil type varieties of Oryza sativa L. Polymorphic profiles from the three marker systems allowed us to clearly distinguish the three types of varieties. The indica type varieties showed the highest genetic diversity followed by the Tongil and japonica type varieties. Of the three marker systems, TD produced the highest marker indices, and AFLP and MSAP produced similar marker indices. Pair-wise comparisons of the three marker systems showed that the correlation between the two genetic markers systems (AFLP and TD, r = 0.959) was higher than the correlations between the genetic and epigenetic marker systems (AFLP and MSAP, r = 0.52; TD and MSAP, r = 0.505). Both genetic marker systems had similar levels of gene differentiation (G ST ) and gene flow (N m ), which differed in the epigenetic marker system. Although the G ST of the epigenetic marker system was lower than the genetic marker systems, the N m of the epigenetic marker system was higher than in the genetic marker systems, indicating that epigenetic variations have a greater influence than genetic variations among the O. sativa L. types.

District specific, in silico evaluation of rice ideotypes improved for resistance/tolerance traits to biotic and abiotic stressors under climate change scenarios

Using crop models as supporting tools for analyzing the interaction between genotype and environment represents an opportunity to identify priorities within breeding programs. This study represents the first attempt to use simulation models to define rice ideotypes improved for their resistance to biotic stressors (i.e., diseases); moreover, it extends approaches for evaluating the impact of changes in traits for tolerance to abiotic constraints (temperature shocks inducing sterility). The analysis—targeting the improvement of 34 varieties in six Italian rice districts—was focused on the impact of blast disease, and of pre-flowering cold- and heat-induced spikelet sterility. In silico ideotypes were tested at 5-km spatial resolution under current conditions and climate change scenarios centered on 2020, 2050, and 2085, derived according to the projections of two general circulation models–Hadley and NCAR–for two IPCC emission scenarios–A1B and B1. The study was performed using a dedicated simulation platform, i.e., ISIde, explicitly developed for ideotyping studies. The ideotypes improved for blast resistance obtained clear yield increases for all the combinations GCM × emission scenario × time horizon, i.e., 12.1 % average yield increase under current climate, although slightly decreasing for time windows approaching the end of the century and with a marked spatial heterogeneity in responses across districts. Concerning abiotic stressors, increasing tolerance to cold-induced sterility would lead to a substantial yield increase (+9.8 %) only for Indica-type varieties under current climate, whereas no increases are expected under future conditions and, in general, for Japonica-type varieties. Given the process-based logic behind the models used—supporting coherence of model responses under future scenarios—this study provides useful information for rice breeding programs to be realized in the medium-long term.

Identification and characterization of quantitative trait loci for root elongation by using introgression lines with genetic background of Indica-type rice variety IR64

The root is the sole organ taking up water and nutrients from soils. Hence, root system architecture (RSA) is important for enhancing high-level and stable rice (Oryza sativa L.) production. However, the genetic improvement of RSA has received less attention than yield and yield components. Here, we aimed to identify and characterize quantitative trait loci (QTLs) for RSA by determining the maximum root length (MRL) of seedlings grown hydroponically under various concentrations of NH4+. We used a total of 280 introgression lines (ILs) with an Indica-type variety IR64 genetic background, consisting of ten sibling ILs groups, to detect the QTLs. Greater variation of MRL was found in three sibling ILs groups. In total, five QTLs were detected by single marker analyses: two each on chromosomes 5 and 6 and one on chromosome 7. Among them, the most effective QTL was detected on a segment derived from IR69093-41-2-3-2 (YP5), which was localized to the long-arm of chromosome 6. The QTL, designated as qRL6.4-YP5, concerned in root elongation. MRL and total root length of a near-isogenic line (NIL) for qRL6.4-YP5 were significantly (15.2–24.6 %) higher than those of IR64 over a wide range of NH4+ concentrations. Root number and weight of the NIL were the same as those of IR64. These results indicated that qRL6.4-YP5 was a constitutive QTL for root length in response to change in nitrogen concentrations. To enhance yield potential by improving RSA, qRL6.4-YP5 might help to improve root development in rice molecular breeding programs with marker-assisted selection.

HPPD 저해 제초제에 대한 벼 품종별 약해 반응

The objectives of this study were to investigate the levels of phytotoxicity of rice varieties to HPPD (4-hydroxy phenylpyruvate dioxygenase)-inhibiting herbicides known for their efficiency to control the sulfonylureas-resistant weed species:mestrione, benzobicyclone, and tefuryltrione. The twenty-six rice varieties (8-Japonica × Indica-type varieties and 18-Japonica-type varieties) were grown for 25 days on seedling trays and then transplanted to paddy rice fields followed by herbicide treatment i.e. standard and double doses of there respective herbicides at 5, 10, and 15 days after transplanting. Although mestrione, benzobicyclone and tefuryltrione are all HPPD-inhibiting herbicides, the phytotoxicity symptoms of the different rice varieties based on the timing of application and doses of the herbicides were significantly different. The Japonica × Indica-type varieties showed much more phytotoxicity symptoms than Japonica- type varieties in all applied herbicides. Increasing herbicidal doses of mesotrione, and an earlier application of and increasing herbicidal doses of benzobicyclon caused severe phytotoxicity symptoms. On the other hand, phytotoxicity due to tefuryltrione did not exhibit significant differences between rice varieties in either the timing of application or dose of the herbicide. Regardless of timing of application and dose of the herbicides, Hangangchalbyeo-1, Hyangmibyeo-1 and high-yield rice varieties such as Namcheonbyeo, Dasanbyeo, Areumbyeo, and Hanareumbyeo, which belong to the Japonica × Indica-type varieties, showed 5 to 8 levels of phytotoxicity symptoms including albinism, browning, detached leaf, and necrosis to mesotrione and benzobicyclon whereas only 1 to 3 levels of phytotoxicity symptoms (chlorosis, albinism, and browning) were seen with to tefuryltrione application. The Japonica-type varieties exhibited only slight

Evaluation of parameterization strategies for rice modelling

In a previous study, the crop simulator CropSyst was evaluated against crop data collected on rice varieties grown in Northern Italy. The need of model re-parameterization became apparent after investigating new field data, as inconsistencies in the simulation of leaf area index emerged for Indica-type varieties. Key parameters (specific leaf area, stem-leaf partition, extinction coefficient, light-to-biomass conversion efficiency) derived from field measurements (respectively, 27 square m/kg, 3.6 square m/kg, 0.53, 3.2 g/MJ) considerably differed from those previously obtained via calibration (39 square m/kg, 1.5 square m/kg, 0.50, 3.0 g/MJ). Such new parameters are informative for suitable modelling of rice systems. The agreement between simulated and observed above ground biomasses was similar with both parameter sets: average general standard deviation = 25% (previous) and 26% (new); average modelling efficiency = 0.90 (previous) and 0.87 (new). Such comparisons demonstrate as the accumulation of aerial biomass in crop models can be depicted in different ways and reasonable estimations can be achieved by different pathways (not all acceptable). A check on parameters like the one performed here (field measurements versus calibrated parameters) is worth to give protection against spurious conclusions while indicating whether the parameterization is conceptually consistent and related to reality.

Diversity analysis for resistance of rice (Oryza sativa L.) to blast disease [Magnaporthe grisea (Hebert) Barr.] using differential isolates from the Philippines

AbstractA wide variation in resistance to blast disease caused by Magnaporthe grisea (Hebert) Barr. (Rossman et al. 1992) was found using 922 rice (Oryza sativa L.) varieties collected mainly from Asia. These were classified into six varietal groups, termed clusters A–F, according to Ward’s hierarchical cluster analysis, based on the reaction pattern to 20 standard differential blast isolates from the Philippines. The most susceptible two clusters, B and C, dominated in varieties from the Far East (Japan). Varieties from East Asia and Southeast Asia occurred less frequently in B and C clusters than those of Japan, and more frequently in E and F clusters, which were the most resistant of the cluster groups. Varieties from South Asia showed the widest variation, occurring in all clusters but less frequently in cluster B. The cluster B varieties dominated in Japan and showed a high frequency of isozyme type VI, corresponding to Japonica type. In contrast, the frequency of cluster B was low in the groups with isozyme types I, II, III and V, which dominated in South Asia. Isozyme type I corresponds to Indica type varieties. The distribution of resistance corresponded to the geographical distribution of rice varieties and might be related to differentiation into Indica and Japonica types. These findings will provide useful information for understanding the variation in blast resistance at the global level.

Development of New Sets of International Standard Differential Varieties for Blast Resistance in Rice (Oryza sativa L.)

The IRRI-Japan Collaborative Research Project has been developing new sets of differential varieties for resistance to blast disease (Pyricularia grisea Sacc.) in rice (Oryza sativa L.). The first international standard differential variety set composed of monogenic lines for 24 kinds of resistance genes (Pia, Pib, Pii, Pik, Pik-h, Pik-m, Pik-p, Pik-s, Pish, Pit, Pita, Pita-2, Piz, Piz-5 (= Pi2), Piz-t, Pi1, Pi3, Pi5(t), Pi7, Pi9, Pi11(t), Pi12(t), Pi19(t), and Pi20) was released and has been widely used in various countries. Furthermore, the project has been developing near-isogenic lines (NILs) for blast resistance with three kinds of genetic backgrounds, a Japonica-type variety Lijiangxintuanheigu (LTH), an Indica-type variety CO39, and a newly developed ‘universal susceptible’ line US-2 which was derived from a cross between Indica and Japonica-type susceptible varieties. A total of 23 lines for 14 kinds of resistance genes, Pia, Pib, Pik, Pik-h, Pik-s, Pita, Pita-2, Piz-5 (= Pi2), Piz-t, Pi1, Pi3, Pi5(t), Pi7, and Pi9, have been developed by the recurrent backcross method using the monogenic lines with the LTH genetic background. Twenty lines for 14 kinds of resistance genes, Pib, Pik, Pik-h, Pik-m, Pik-p, Pik-s, Pish, Pita, Pita-2, Piz-5 (= Pi2), Piz-t, Pi1, Pi5(t), and Pi7 have been developed with the CO39 genetic background. Moreover, a universal susceptible rice line, US-2, which has not been known to have any blast resistance genes in the genetic background, and can be cultivated easily under both tropical and temperate conditions, is also being used for the development of NILs as the next generation of differential varieties. These lines are offered as gene sources for breeding of blast resistance and as sets of international standard differential varieties used for the study of blast disease.

Evaluation of LAI-2000 for leaf area index monitoring in paddy rice

Leaf area index (LAI) is a variable of primary importance for crop monitoring and it is usually measured by labor intensive destructive field sampling. Indirect non-destructive estimates by optical instruments are a competitive alternative to direct methods for frequent measurements and over large areas. The work presented here evaluated the adequacy and the range of reliability of the LAI-2000 estimates for rice ( Oryza sativa L.) by comparison with LAI measurements derived by destructive sampling. Field data were collected in 2004 for an Indica type variety grown under different levels of nitrogen fertilization. The comparison showed that LAI-2000 estimates and destructive LAI measurements are well correlated ( R 2 > 0.8) whereas the correlation decreases when LAI values are lower than one ( R 2 < 0.6). Moreover, when LAI > 1, the estimates derived by discarding the wide angle reading (fifth ring) of the optical instrument are closer to the actual LAI values compared to the standard LAI-2000 outputs. The regression line is, in fact, not statistically different ( P = 0.25) from the 1:1 line. In these application conditions, LAI-2000 estimates are correct within ±32%. Therefore, if the range of applicability is restricted to LAI values greater than one and the wide angle readings are discarded, LAI-2000 is an appropriate instrument for in situ LAI estimation in paddy rice fields.

Analysis of rice sample size variability due to development stage, nitrogen fertilization, sowing technique and variety using the visual jackknife

The determination of sample size before collecting experimental data is fundamental to obtain reliable estimates of variables describing agroecosystem development. In order to analyze the influence of experimental factors (artificially-induced variability) on rice sample size, an experiment was carried out in 2004 in northern Italy. In particular, different sample size determinations were carried out for different fertilization levels, varieties (Indica and Japonica type), development stages, sowing techniques and typologies of the sampling unit. The obtained sample sizes were compared to investigate the influence of each factor, keeping the others constant (for example, we have compared the sample sizes computed for different fertilization levels within the same variety, the same phenological stage and the same sampling unit). Since original data were often not normally distributed and the variances of the original samples were not homogeneous, a new approach for sample size determination based on a visual evolution of the jackknife was preferred to classical techniques. Results (expressed as number of plants) showed that (i) sample sizes computed in an early phenological stage (between 21 and 27) are higher than those calculated for later stages (15–21); (ii) fertilization hides soil N content variability with the consequence that larger sample sizes are required for unfertilized plots (21–27) compared to fertilized plots (15–27) and (iii) for the early sampling, the Indica type variety required larger sample size (always 27) with respect to the Japonica type variety (21–24). For row-seeded rice, the number of plants instead of linear centimeters as the sampling unit led to lower sample sizes (18–27 versus 30–33). These results highlight the influence of experimental factors and development stage on within-plot variability, and therefore the importance of preliminary samplings for sample size determination.

Characterization of segregation distortion on chromosome 3 induced in wide hybridization between indica and japonica type rice varieties

We previously surveyed chromosomal regions showing segregation distortion of RFLP markers in the F2 population from the cross between a japonica type variety ‘Nipponbare’ and an indica type variety ‘Milyang23’, and showed that the most skewed segregation appeared on the short arm of chromosome 3. By comparison with the marker loci where distortion factors were previously identified, this region was assumed to be a gametophytic selection-2 (ga2) gene region. To evaluate this region, two near isogenic lines (NILs) were developed. One NIL had the ‘Nipponbare’ segment of this region on the genetic background of ‘Milyang23’ (NIL9-23), and the other NIL had the ‘Milyang23’ segment on the genetic background of ‘Nipponbare’ (NIL33-18). NIL9-23 and ‘Milyang23’, NIL33-18 and ‘Nipponbare’, and ‘Nipponbare’ and ‘Milyang23’ were respectively crossed to produce F1 and F2 populations. The F1 plants of NIL9-23 × ‘Milyang23’ and NIL33-18 × ‘Nipponbare’ showed high seed fertility and the same pollen fertility as their parental cultivars, indicating that ga2 does not reduce seed and pollen fertility. Segregation ratio of a molecular marker on the ga2 region in the three F2 populations was investigated to clarify whether segregation distortion occurred on the different genetic backgrounds. Segregation distortion of the ga2 region appeared in the both F2 populations from the NIL9-23 and ‘Milyang23’ cross (background was ‘Milyang23’ homozygote) and the ‘Nipponbare’ and ‘Milyang23’ cross (background was heterozygote), but did notin the F2 population from the NIL33-18 and ‘Nipponbare’ cross (background was ‘Nipponbare’ homozygote). This result indicates that ga2 interacts with a ‘Milyang23’ allele(s) on the different chromosomal region(s) to cause skewed segregation of the ga2 region. In addition, segregation ratio was the same between the F2 populations from NIL9-23 × ‘Milyang23’ and ‘Nipponbare’ × ‘Milyang23’ crosses, suggesting that the both genotypes, ‘Milyang23’ homozygote and heterozygote, of gene(s) located on the different chromosomal region(s) have the same effect on the segregation distortion.

Effect of nitrogen application during ripening period on photosynthesis and dry matter production and its impact on yield and yield components of semidwarf iniica rice varieties under water culture conditions

A water culture pot experiment was conducted to analyze the effects of N application during the ripening period (RP) on photosynthesis, dry matter production, and its impact on grain ripening and yield in two semidwarf indica type varieties viz. Gui Zhao 2 (GZ) and BR3 (BR) compared with a japonica type variety Koganemasari (KO) under four N rates viz. 0 (N0), 10 (N10), 20 (N20), and 40 (N40) mg L−1. Results showed that N application enabled to maintain a higher leaf area and delay leaf senescence in both indica and japonica type varieties but the decrease in the rate, of leaf area was higher in the former than in the latter and the rate was reduced with increasing N rates. Flag leaf photosynthesis and SPAD values of N treated plants were higher throughout the RP, showing the presence of a significant correlation either for each variety or all the varieties together. Higher photosynthetic rate was supported by higher leaf chlorophyll (SPAD value basis) content, stomatai conductance, and N concentration in leaf blades. Top dry matter content increased with increasing N rates mainly due to mean leaf area rather than NAR except for BR during RP but it was higher in KO than in GZ and BR. Reduction of shoot weight due to translocation of dry matter to panicles during RP was suppressed by N rates both in GZ and BR while shoot weight increased in the N-treated plants in KO. The dependency of KO on current photosynthates for panicle weight was found to be almost hundred percent while the contribution of stored carbohydrates in shoot before heading to panicle weight in GZ and BR was in the range of 4-27 and 33-54%, respectively and the rest was contributed by current photosynthates. The percentage increased with increasing N rates. Percentage of ripened grains (PRG) increased with increasing N rates in GZ and BR due to the increase in dry matter production and in the photosynthetic rates of apex leaves, despite the larger spikelet number and larger hull size. However, KO showed almost no variation although it had the highest PRG among the varieties. Brown rice yield followed the same pattern as that of PRG in GZ and BR and the highest yield was produced by BR followed by GZ and KO. These results suggest that N application during RP was more effective in increasing yield in the semidwarf indica type varieties than in the japonica type variety.

Callus induction from indica rice coleoptiles

Rice coleoptiles have been used in tissue culture and genetic transformation, but reports on callus induction and subsequent plant regeneration from such explants in indica type varieties are scarce. We obtained significant improvements in callus induction from coleoptiles by testing different explant and culture media conditions. Mature seeds from the Perla rice cultivar were dehulled, sterilized, and the seedlings were grown on solid MS medium in the dark at 27°C. Coleoptiles were aseptically extracted with a scalpel from 3-, 4-, 5-, or 7-d-old seedlings and incubated in N6 medium supplemented with 2 mg 2, 4-D L -1 (N621, unless otherwise stated. In the first attempt for inducing callus from both apical and basal portions from coleoptiles (Fig. 1), apical sections did not render callus regardless of their age in culture. Basal portions from coleoptiles cultivated for 3, 4, or 5 d produced significantly more calli than did those from 7-d-old coleoptiles (Fig. 2a), so in all subsequent experiments only basal portions from 3-d-old rice coleoptiles were used. Figure 1 shows results of culturing coleoptile basal portions in N62 medium with NAA. Adding 0.1 mg NAAL -1 resulted in a significant increase in callus induction over N62 medium containing no NAA. Concentrations of 0.5 or 1 mg NAAL -1 also improved induction as compared with the N62 medium. Effects increasing sucrose concentration were also tested. While 4.5% sucrose increased callus formation very significantly, 6% gave results lower than the control (Fig. 2b). Effects of using 2, 4-D at 3, 4, or 5 mgL -1 were compared with those at 2 mgL -1 . Concentrations higher than 2 mgL -1 improved callus induction (Fig. 2b), but no significant differences were found among 3, 4, or 5 mgL -1 .

Classification of Japanese rice varieties into Indica and Japonica types by using isozyme genotypes.

Sixty Asian varieties (Oryza sativa L.) which had been classified into Indica and Japonica types based on diagnostic characters (OKA 1958), were investigated for the genotypes of 10 isozyme species including 17 Ioci (Fig. 1 and 2, Table 1, 2 and 4). Genotypic frequencies at 11 loci, Acp-1. Amp-2. Cat-1. Est-2, Mal-1, Pgd-1. Pgi-1. Pboi-2, Pgi-3. Pox-2 and Sdh-1 were significantly different between Indica and Japonica types (Table 5). Discriminant scores (D scores) for Indica and Japonica varieties were calculated for the above eleven loci. However, the alleles at Pgd-1 and Sdh-1 Ioci were not enough to discriminate between Indica and Japonica types. D score averaged over the nine loci excluding Pgd-1 and Sdh-1, appeared to be more useful than that based on the eleven loci (Table 7). Thus, the Asian varieties were classified by using D scores averaged over the nine loci (Fig. 3A). Japonica varieties except for one and Indica varieties classified by OKA (1958) showed D scores ranging from 0.12 to 0.30 and from 0.69 to 0.94, respectively. Only one Japonica variety showed D scores with a value of 0.6. Because the variety carried alleles frequently found in Japonica type varieties, only at Acp-1, Mal-1 and Pgi-1 and alleles frequently found in Indica type varieties at other six loci, it appeared to be a 'recombinant type' between Indica and Japonica varieties. Based on these results, varieties with D scores ranging from 0.0 to 0.4 and from 0.6 to 1.0 were confirmed to be Japonica and Indica types, respectively, and newly used Pgi-3 and Mal-1 were also confirmed to be useful for discriminating the varieties.

A new gene, developed through mutagenesis, for resistance of rice to bacterial leaf blight (Xanthomonas campestris pv. oryzae)

SUMMARYAn induced mutant of rice, designated M41, resistant to several races of bacterial leaf blight, obtained after irradiation with thermal neutrons, was crossed with the original variety, Harebare. Test crosses revealed that the resistance of M41 to the Japanese races I, II, III and IV is controlled by a single recessive gene, considered to be different from four previously identified dominant resistance genes of japonica-type varieties and from three recessive genes in indica-type varieties for resistance to Philippine races. The gene in M41 was tentatively designated xa-nm(t).

On the photosynthetic characteristics of high yielding rice varieties. I. Leaf photosynthetic rate.

The leaf photosynthetic rate of pot-cultivated rice plants was measured under the condition of artificial lighting and, at the same time, its relations to their some relevant characters were examined with five different varieties of rice plants, Musashikogane, Akenohoshi, Sweon 262, Nanking 11, and RP 9-3. In the case of low light intensity (10 klx), no striking difference in the photosynthetic rate among the varieties was found in the period from the maximum tiller number stage till the heading stage, whereas in the ripening stage the rate of all the varieties dropped remarkably. In the case of high light intensity (60 klx), the photosynthetic rate decreased as the growing stages proceeded.The japonica type varieties had a high photosynthetic rate at the maximum tiller number stage, while the indica-japonica hybrid variety had high rate in the booting stage. Nanking 11, an indica type variety, showed a photosynthetic rate similar to that of the japonica type varieties. Sweon 262, an indica-japonica hybrid variety, seems to have a high photosynthetic ability compared with the japonica type varieties. In the change of respiration rate according to the number of days after transplanting, it was observed that the respiration rate of the japonica type and the indica-japonica hybrid type varieties decreased more than that of the indica type varietics. The respiration rate of all the varieties tested decreased according to the number of days after transplanting. A close correlation was observed between chlorophyll contents and the photosynthetic rate at 60 klx.

Differences in the photosynthetic response to air humidity among rice varieties with special reference to the xylem-vessel size.

Photosynthetic response to air humidity and leaf characters were observed in fourteen rice varieties. In the indica type varieties the water-conduction system relative to their specific leaf weight and leaf nitrogen content was found to be more developed than in the japonica type varieties. The water-conduction system in the leaf was evaluated based on the ratio of the total cross-sectional area of xylem-vessels at the leaf blade, base to the leaf area (RVA). Higher positive correlations between the photosynthetic rates and the RVA, and specific leaf weight were detected under dry than humid air conditions. The present study suggests that RVA may be related to varietal differences in the photosynthetic rate, at least under low air humidity conditions, and that RVA can be used as an index for evaluating the development of the water supply system. The well-developed water conduction svstem of indica type varieties may have evolved as an adaptation to high temperature conditions.

Effect of seed presoaking in acetone containing ABA on plumule elongation of rice seedlings.

When rice plants of japonica type were grown on the agar medium containing ABA in darkness, the elongation of mesocotyl was strikingly simulated but that of coleoptile and seminal root was inhibited. In this experiment, the rice seeds presoaked in acetone containing ABA were used for ascertaining the direct effect of ABA on the elongation of mesocotyl and coleoptile. A japonica type variety "Koshijiwase" and an indica type variety "Peta" were uscd. After presoaking seeds in acetone containing ABA at 25°C, they were dried for two hours in a vacuum desiccator and stored for two days at room temperature. In all the experiments, each lot consisted of 60-80 plants. The results obtained were as follows: 1. In the plants grown from the presoaked seeds in acetone contatining 10-2M or 2×10-3M of ABA, not only the elongation of mesocotyl but also that of coleoptile was sitmulated, reaching the plateau at the soaking of 24 hours. Thus the soaking for about 48 hours may be enough to examine the effect of ABA (Fig. 1). 2. By the 48 hours soaking in ABA, the stimulation of mesocotyl elongation occurred between the concentration of 10-3M to 2×10-2M. The length of mesocotyl in ABA treated plants was from 3 to 16 times longer than that of control treated with pure acetone, while the coleoptile length was from 1.0 to 1.5 times longer than that of the control. Accordingly, the morphology of plumules was almost similar those from the high temperature pre-treated seed and those of indica type rice. On the other hand, elongation of seminal root was somewhat inhibited even at 10-3M of ABA, and the inhibitory effect increased with increasing ABA concentration (Fig. 2). 3. When the seeds presoaked with acetone containing ABA were again soaked in pure acetone, the stimulatory effect of ABA on the elongation of mesocotyl and coleoptile and inhibitory effect on that of seminal root disappeared. When the seeds of high temperature pre-treated japonica rice and those of nontreated indica rice were soaked in pure acetone, whereas, no effect was detected in the elongation of either mesocotyl or coleoptile (Fig. 3). 4. Parenchymatous cell length and number in a longitudinal section of mesocotyl with about 23 mm long in each experimental lot were measured. The plumules grown from the presoaked seeds in acetone containing 2×10-2M of ABA were almost similar to those from the high temperature pre-treated seeds, 40°C for 10 days. On the other hand, the plumules grown on agar medium containing 2×10-6M ABA were almost similar to those from immature seeds, harvested 15 days after anthesis (Table 1). 5. Considering the similarities of plumules between those originated from seeds presoaked with 2×10-2M ABA and those originated from seeds pre-treated with 40°C for 10 days, about 1.6 μg of ABA was estimated to be synthesized in a seedling originated from the latter, if the assumption that the mesocotyl elongation is based only on ABA is adopted (Fig. 4).

Physiological Studies on Photochemical Oxidant Injury in Rice Plants : IV. Effect of nitrogen application on endogenous abscisic acid (ABA) production and ozone injury of rice plants

In order to determine the effects of nitrogen application on ABA content of rice plants and their ozone-sensitivity, ABA production and ozone injuries were observed under different levels of nitrogen application with two Japonica and two Japonica × Indica type varieties. 1. In all varieties, endogenous ABA content decreased with the increasing level of nitrogen applied, although total nitrogen content increased with the increasing level of nitrogen applied. 2. Ozone injury was found to increasing level of nitrogen applied and to change depending on the varieties. Ozone injury was found to occure seriously with increasing nitrogen content in Jinheung and Nongback, however less pronounced in Tongil and Milyang No. 23. 3. Endogenous ABA content and ozone-sensitivity were related to the nitrogen content in the rice plants.