Japonica-indica Hybrid Research Articles

Varietal Differences in the Growth and Dry-Matter Production during Vegetative Growth in Rice under Upland Cultivation Conditions with Water Stress. A comparison of Japonica, Indica and Japonica-Indica hybrid cultivars.

Since rice is highly susceptible crops to water stress, it is important to improve drought resistance to increase and stabilize the rice yield under upland cultivation conditions. This study was conducted to elucidate the morphological and physiological characteristics related to drought resistance in diverse rice germplasm. Six cultivars including Japonica, Indica and Japonica-Indica hybrid cultivars were grown in a pot, suffering the same soil water deficit conditions at a vegetative growth stage. The reduction in leaf area growth and in dry matter production under water stress was smaller in IR36 and two Japonica -Indica hybrid cultivars, Suweon 287 and Suweon 290 than Japonica and Indica upland cultivars, Toyohatamochi and IRAT109. The reduction in leaf photosynthetic rate was also smaller in Suweon 287 and Suweon 290. IR36, Suweon 287 and Suweon 290 showed a semi dwarf morphological characteristic with a large tiller number. The partitioning of the net production directed much to roots and less to leaves under the water stress conditions in all cultivars tested. IR36 and Suweon 287 partitioned more net production to leaf sheaths. Suweon 287 showed good recovery after rewatering and partitioned much assimilates to roots after released from water stress.

Response of differentiated and degenerated spikelets to top-dressing, shading and day/night temperature treatments in rice cultivars with large panicles

The presence of large panicles enables to reach a sufficient number of surviving spikelets per unit area for further increase of rice yield. However, the response of differentiated and degenerated spikelets to environmental factors in terms of number in cultivars with large panicles has not been elucidated. By applying top-dressing at different rates and frequencies, shading, and day/night temperature treatments in pot experiments, we observed the response of the main stem in two cultivars with large panicles: Yangdao 4 (Chinese indica) and Akenohoshi (Japanese japonica-indica hybrid). The results showed that top-dressing increased the number of differentiated spikelets per panicle and decreased the percentage of degenerated spikelets. Consequently, the number of surviving spikelets per panicle increased. Shading increased the percentage of degenerated spikelets, resulting in the decrease of the number of surviving spikelets per panicle. Higher day/night temperature treatments led to a higher percentage of degenerated spikelets. The treatments affected mainly the spikelets on the secondary branches, while the number of spikelets on the primary branches did not change appreciably, irrespective of the presence of differentiated, degenerated, and surviving spikelets. The influence on the number of surviving spikelets per panicle depended on the number of differentiated spikelets. Shading effect on the percentage of degenerated spikelets also depended on the number of differentiated spikelets per panicle. The decrease of the percentage of degenerated spikelets was associated with the increase of the shoot dry weight (SDW) at heading and the ratio of SDW-differentiated spikelets. The SDW and N absorption at heading affected more significantly the number of surviving spikelets compared to the ratio of surviving spikelets-SDW and surviving spikelets-N, respectively. The above results were similar in Akenohoshi and Yangdao 4. In Akenohoshi, the percentage of degenerated spikelets responded much more conspicuously to the change of SDW or the ratio of SDW -differentiated spikelets than that in Yangdao 4. So did the number of surviving spikelets to SDW and N absorption at heading. Akenohoshi showed a higher ratio of surviving spikelets-N than Yangdao 4. These differences may account for the fact that Akenohoshi showed a larger number of surviving spikelets per panicle than Yangdao 4, even at the same levels of SDW and N absorption.

Varietal Differences in the Number and Cross Area of Large Vascular Bundles at the Neck Internode of Rice.

穂重型日本稲(JP), 穂数型日本稲(JN), 中国産日本型稲(CJ), 日印交雑稲(JI), 長稈インド型稲(TI)および半矮性インド型稲(SDI)の計18品種をポット栽培して, 穂首節間を走向する大維管束の種類と数および横断面積を調査し, 品種(群)間で比較した.CJ, JI, TIおよびSDIでは, 大型(L1)および小型(L2)の大維管束が走向していた.L1の数(9.2～13.0)は品種群間で大差はなかった.L2の数(1.3～9.3)は品種群間差が大きかった.L1とL2の合計は, SDI>TI>JI>CJ>JP>JNの順に多かった.1次枝梗数に対する大維管束の数の比(維管束比)は, JPおよびJNでは1程度であったが, JI, TI, SDIではL2の数が加わった分, 1を大きく越えた.1つのL1における全体および師部横断面積は, JPおよびJNに較べて, JI, TI, SDIで大きい傾向にあった.穂首節間を走向するすべての大維管束の全体および師部の横断面積は, いずれも, SDI>TI, JI>CJ>JP>JNの順で品種群間差異が大きく, L2が走向する品種群で大きかった.水田でJP(コガネマサリ)およびDSI(桂朝2号)を穂肥窒素量を増やして栽培したところ, 穂首節間を走向するすべての大維管束の全体および篩部の横断面積が大きくなる傾向が認められた.今後の水稲育種では, 稲首節間を走向する大維管束の横断面積の拡大, ならびに小型の大維管束の走向による光合成産物の輸送体制の強化が1つの育種目標になると考えられた.

High Yielding Ability of Japonica-Indica Hybrid Rice

High Yielding Ability of Japonica-Indica Hybrid Rice

Cytogenetical gene mapping by reciprocal translocation and tertiary trisomic analyses in rice (Oryza sativa L.).

The orientation of RFLP linkage map and the assignment of RFLP markers to the restricted chromosomal segment were determined on seven pachytene chromosomes (1, 3, 4, 5, 8, 9 and 12) of rice. A total of 24 interchange breakpoints were detected by pachytene analysis of reciprocal translocation (RT) heterozygotes derived from crosses between 12 RT lines and normal diploid varieties. Further, 19 strains of japonica-indica hybrid tertiary trisomics were developed and provided for RFLP gene dosage analysis, resulting in locating 32 breakpoints of the extra tertiary chromosomes within genetic linkage segments defined by RFLP markers. From these results, the orientation of RFLP linkage groups on pachytene chromosomes and the assignment of 113 RFLP markers and four cloned rice genes to chromosome arms were conducted, together with the delimitation of centromeres on 6 RFLP linkage groups (1, 3, 4, 8, 9 and 12). Meanwhile, 15 groups of RFLP markers were incorporated with the restricted segments of pachytene chromosome. Compared with RFLP map, the physical distance of a part of the long arm of chromosome 1 was 5.4 to 8.8 cM/μm at the pachytene stage.

Characteristics of Dry Matter Production and Partitioning of Dry Matter to Panicles in High Yielding Semidwarf Indica and Japonica-Indica Hybrid Rice Varieties.

A field experiment was carried out to investigate the dry matter production characteristics before and after heading, the partitioning of dry matter to panicles, and some related factors in high yielding semidwarf indica (SDI) and japonica-indica hybrid (JI) varieties in comparison with those of japonica panicle weight (JP) and panicle number (JN) type varieties transplanted in early and late cropping seasons (ET and LT). Leaf area indices (LAIs) of the JI and SDI varieties in both ET and LT were higher at full heading, but decreasing percentages were much more prevalent in these varieties after heading, which resulted in much lower LAIs than those of japonica varieties at maturity. Total top dry weights at full heading of SDI and JI varieties were higher than those of JP and JN varieties in ET and LT, except for Akenohoshi in LT. However, the difference in dry matter increment during the period from full heading to maturity (LIM) among the varieties were not found to be significant. Crop growth rates (CGR) during HN of SDI varieties both in ET and LT were the lowest among thc varietal groups due to the highest decreasing percentage of LAIs and SPAD readings at the later grain filling stage. Panicle dry weights of SDI and JI varieties were about 125∼190gm-2 (20∼31%) and 105∼115gm-2 (18∼20%) higher than those of japonica varieties in ET and LT, respectively. Mean ratios of panicle dry weight to total top dry weight at maturity of the SDI and JI varieties in both ET and LT were about 56%, which were significantly superior to the corresponding mean ratios of JP and JN varieties (i.e., about 47%). These higher mean ratios resulted in panicle weight differences between the high yielding varieties and japonica varieties. The shoot dry matter partitioning percentages to panicles of SDI and JI varieties were more than two times higher in ET, and those of SDI varieties were about four times higher than those of the japonica varieties in LT. The panicle dry weight at full heading (sink capactiy) was found to be closely related to the panicle dry weight at maturity. When the sink capactiy was high, the increment in top dry weights during HM tended to be lower. It was also observed that the partitioning ratios of the accumulated assimilates in shoot to panicles were closely related to the sink capacity.

Relation between Leaf Gas Exchange Rate and Stomate. I. Stomatal frequency and guard cell length in C3 and C4 grass species.

葉身の気孔密度および気孔サイズとガス交換速度との関係を明らかにする第一段階として, 本報ではイネ科植物の気孔密度および孔辺細胞長を調査し, 亜科およびC3, C4植物間の差異を検討した. その結果, C4植物の気孔密度は, スズメガヤ亜科では418.5, キビ亜科では243.9個mm-2あり, 夏型C3植物に比べ1/2～1/3であった. 一方, ウシノケグサ亜科に属する冬型のC3植物の単位面積当たりの気孔数は少なく, サイズは大きかった. イネ亜科に属する水稲は, イネ科植物の中で最も高い気孔密度を有していたが, サイズは小さかった. また, 最高分げつ期の最上位完全展開葉に比べ出穂期の止葉の気孔密度は高く, 特に, 日印交雑品種でその傾向が顕著に認められた. イネ科植物において, 気孔密度と気孔サイズは反比例の関係にあり, また, 散布図における各亜科の分布はイネ科の系統樹と対応した.

Root System Development of Japonica-Indica Hybrid Rice Cultivars. 1. Number and elongation direction of primary roots.

To characterize the root system of the Japonica-Indica hybrid rice cultivars (Milyang 23, Suweon 258), we compared the number and elongation direction of primary roots both per stem and shoot unit bases with the japonica type rice cultivars (Nipponbare, Koshihikari). The four cultivars were grown in 45-liter polyethylene containers with paddy field soil, and soil cores ( 15 cm in depth and 15 cm in diameter) were taken at the grain-filling stage. To estimate the number of primary roots of different elongation direction, soil cores were divided into four layers by different color markings. Stem numbers of the Japonica-Indica hybrids at the grain -filling stage were less than Japonica type cultivars, but the numbers of primary roots per stem were larger in the Japonica-Indica hybrid cultivars. In particular, the number of primary roots of Suweon 258 were the highest per shoot unit, per stem and per hill. The rate of primary roots of Japonica-Indica hybrid cultivars elongating deep into the soil were more than that of Japonica type cultivars. In the Japonica-Indica hybrid rice, the elongation direction of primary roots were very different between upper and lower roots in the higher shoot units of the main stem ; i.e. the upper roots elongate to the shallow layer, while the lower roots tend to elongate deep into the soil.

Root Growth and Distribution in Some Japonica-Indica Hybrid and Japonica Type Rice Cultivars under Field Conditions.

The development of rice root system has been studied in Japonica-Indica hybrid cultivars (J-IH), Milyang 23 and Suweon 264, and Japonica type cultivars (JT), Nipponbare and Koshihikari, grown in a paddy field. Soil cores were taken below (and between) hill(s) at the panicle initiation, the heading and the grain-filling stages. After the soil cores were divided into layers by soil depth and the roots were washed out, length and weight of the roots in each soillayer were measured to calculate root length density (RLD) and root weight density (RWD). At the panicle initiation stage, there were no significant differences in RLD and RWD in the 0-25 cm soil layer below hill of each cultivar. Thereafter, RLD and RWD markedly increased, especially in J-IH, and at the grain-filling stage RLD and RWD of J-IH both below and between hills were significantly larger than those of JT. Such increases of RLD and RWD in J-IH after the panicle initiation stage occurred mainly in shallow soil layers. The soil depth of the maximum value in RLD and RWD below hill were different from each other ; the 0-5 cm soil layer in RLD and the 5-10 cm soillayer in RWD. The specific root length in 5-10 cm soillayer below hill was smaller than those in the other soil layers below and between hills, especially in the later growth stage, which might depend on the distribution of root diameter and branching.

Characteristics for the Efficiency of Spikelet Production and the Ripening in High-Yielding Japonica-Indica Hybrid and Semidwarf Indica Rice Varieties.

Three high-yielding japonica-indica hybrid (JIH) and semidwarf indica (SDI) rice varieties, and ten japonica (J) rice varieties, including different plant types, were cultivated under sparse (30×30 cm) and dense (20×20 cm) conditions to clarify the characteristics for the efficiency of spikelet production and the ripening in these high-yielding rice varieties in comparison with japonica rice varieties. 1) Brown rice yields in JIH and SDI were generally higher than those in J in both planting densities, because the number of spikelets per m2 of JIH and SDI, which mainly depended on the number of spikelets per panicle, especially those on the secondary rachis-branch, were greater than those of J. 2) The number of spikelets per m2 for the same level of leaf area index, top dry weight or top nitrogen content at heading stage was greater in JIH and SDI bearing bigger panicles than in J bearing smaller ones. 3) The number of spikelets per m2 of JIH and SDI, or that of J showed significant negative correlation with the percentage of ripened grains. Although the decline of percentage of ripened grains in each varieties was due to the increase of spikelets on the secondary rachis-branch, the percentage of ripened grans in JIH and SDI was higher than that in J at the same level of the spikelets number. 4) From the results mentioned above, it was suggested the high-yielding character in JIH and SDI was based on the greater spikelets per m2 due to the higher number of spikelets per panicle, and the less decline of percentage of ripened grains at this greater spikelets, in spite of the increase of the spikelets on the secondary rachis-branch, as compared with J.

Study on applicability of nitrogen-deep placement culture from the view point of productivity of various rice cultivars in warmer area.

An applicability of nitrogen-deep placement culture (NDPC) in warmer area suffered from poor number of spikelets and low sink-source ratio, and responsibilities of NDPC for not only japonica rice cultivars (Tsukushibare, Hiyokumochi), but also japonica-indica rice hybrids (Milyang 23, Suweon 258) and indica rice cultivar (IR 661) were studied. Results were as follows : 1) The ratio of ear culm length of rice cultivars was not significant between NDPC and ordinary culture (OC) . 2) All cultivars on NDPC enlarged leaf area index due to increase of tiller numbers and leaf elongation. 3) Dry matter production during 30 days after heading of japonica-indica rice hybrids increased, but that of the others decreased on NDPC. Canopy of japonica-indica rice hybrids didn't reach rank growth. 4) All cultivars on NDPC increased spikelet numbers, but decreased ripened grains. Therefore, yield was not significant between NDPC and OC. But the yield of Japonica-indica rice hybrids increased. 5) The sink-source ratio of rice cultivars was not significant between NDPC and OC. 6) It was concluded that the rice cultivar with high fertilizer responsiveness like japonica-indica hybrid was suitable to increasing the yield on NDPC in warmer area.

Leaf conductance in japonica and indica rice varieties. I. Size, frequency, and aperture of stomata.

Varietal differences in leaf conductance were studied in field conditions using 51 rice varieties, including japonica, indica, and japonica-indica hybrid. Leaf conductance of indica and japonica-indica hybrid was clearly larger than that of japonica at panicle formation stage. Cuticular conductance was much lower as compared to leaf conductance, indicating the stomata is the major path of water loss. Thus, we measured size, frequency, and aperture of stomata, and evaluated the relative importance of these factors to leaf conductance. Only slight differences were observed in length of the pore and the guard cells of stoma among rice varieties. By contrast, stomatal frequency of japonica-indica hybrid and semidwarf indica was clearly higher than that of japonica and tall indica. In addition, stomatal aperture of indica and japonica-indica hybrid was remarkably larger than that of japonica. Analysis of relative importance of frequency and aperture of stomata to leaf conductance showed that the leaf conductance was strongly affected by stomatal aperture, whereas it was slightly influenced by stomatal frequency in rice. It is concluded that the stomatal aperture is the major factor which causes the difference of leaf conductance between japonica and indica or japonica-indica hybrid.

Growth response to nitrogen in Japonica and Indica rice varieties. II. Differences in the rate of increase in culm length and leaf area due to nitrogen fertilization.

Field experiments on the growth response to nitrogen were conducted for three years (1983-1985) using 49 rice varieties including japonica, indica and japonica-indica hybrid. Rates of increase in culm length and lower internodes as a result of nitrogen fertilization to japonica, japonica-indica hybrid and semidwarf indica were large, intermediate and small, respectively. The rate of decrease in dry weight of the leaf sheath and culm per unit culm length was larger in japonica than that in japonica-indica hybrid and semidwarf indica. The ratio of leaf area to the spikelet number was obviously smaller in japonica-indica hybrid and semidwarf indica compared to that in japonica. However, the ratio of the rate of increase in leaf area to that in the spikelet number due to nitrogen fertilization was larger in these groups than that in japonica. Furthermore, the rate of increase in single leaf area and specific leaf area of japonica-indica hybrid and semidwarf indica were larger than those of japonica. The obtained results suggested that one of the reasons of higher lodging resistance of japonica-indica hybrid and semidwarf indica was ascribed to a little changes in the culm length due to nitrogen fertilization compared to that of japonica. It was also suggested that these groups had a tendency of over-luxuriant growth due to nitrogen fertilization compared to japonica. This characteristic should be improved for breeding high-yielding varieties by using japonica-indica hybrid or semidwarf indica as genetic resources.

Growth response to nitrogen in Japonica and Indica rice varieties. I. Varietal differences in the rate of increase in straw weight and number of spikelet due to nitrogen fertilization.

Experiments on the growth response to nitrogen were conducted in 41 (1981) and 51 (1982) rice varieties including japonica, indica and japonica-indica hybrid. The ratio of the number of spikelet to straw weight of japonica-indica hybrid and semidwarf indica was larger than that of japonica. However, the ratio decreased greatly as a result of nitrogen application in these groups, although it did not change in japonica. The rate of increase in dry weight of the leaf blade due to nitrogen application was larger than that in dry weight of the culm and leaf sheath, and the ratio of the rate of increase in dry weight of the leaf blade to that in the number of spikelet was larger in japonica-indica hybrid and semidwarf indica than in japonica. Coefficient of variation of the number of spikelet in a hill of japonica-indica hybrid and semidwarf indica was larger than in japonica, and several varieties of these groups with a large mean number of spikelet per panicle had a large percentage of the number of spikelet on the secondary and tertiary rachis branches. Japonica-indica hybrid and semidwarf indica, which were thought to have high-yielding characteristics, had a large ratio of spikelet number to straw weight, but, this advantageous characteristic decreased when nitrogen was applied. Moreover, these groups also had disadvantageous characteristics for ripening. It was concluded that these characteristics should be improved for breeding high-yielding varieties by using japonica-indica hybrid or semidwarf indica as genetic resources.

Study on productive ecology of a high yielding Japonica-Indica hybrid rice cultivar "Suweon258".

日射量, 移植期および栽植密度を多様に変えた圃場条件下で水原258号(日印交雑稲), アケノホシ(日印交雑稲)およびレイホウ(日本稲)の3品種を栽培し, 処理に対する各品種の物質生産の反応特性を比較, 解析する中で, 水原258号の多収機構を明確にした. 水原258号の特徴の一つは, 1穂粒数が多く, しかも, 環境の変化にともなう粒数の変動が小さいことであった. このため, 単位面積当たり茎数が増加する密植条件では, 単位面積当たり粒数も顕著な増加を示した. また, この品種は分げつ数が多く, かつ, 茎数が経時的に大きく変化する特徴を有しており, 収穫期の茎数は最高分げつ期茎数の60%前後であった。なお, 本品種は直立的草型を特徴とするため, 密植条件下においても過繁茂の弊害が見られず, 登熟歩合が比較的高かった. さらに, 移植(稚苗)から出穂までの期間(80日間前後)およびこの間の積算気温(2,000℃前後)がほぼ一定となる特徴を有していた。そのため, 出穂日が移植日の早晩に平行して変動するので, 移植時期を移動することによって登熟期を最適気象条件の時期に合致させることが容易であった。水原258号は, 800kg/10aを超える玄米生産力を有する品種であることが確認された。なお, 多収穫栽培には早期移植と密植が前提条件であった.

Effect of casamino acids on the growth of excised seminal root in several parent varieties of Korean Japonica-Indica Hybrids, and in asian rice cultivars.

Using seven parent varieties of Japonica-Indica hybrid bred in Korea, 16 aman, 17 aus, 10 boro, 15 bulu and 15 tjereh rice varieties, excised seminal roots (root-tips) were cultured in modified White's medium containing 0% or 0.2% casamino acids. The excised roots were cultured at 28°C in the dark for two weeks. The results obtained were as follows. 1. In Japonica type parents, the excised seminal root growth was better in the 0.2% casamino acids lot than in the 0% lot. In Indica type parents, on the other hand, main root length was almost same between the two lots of casamino acids concentration in each of three varieties, while the length was shorter in the 0.2% casamino acids lot than in the 0% lot in two varieties. But, dry root weight was larger in the former than in the latter in every variety (Table 1). 2. In all the varieties belonging to aman and tjcreh ecotypes, main root length was shorter in the 0.2% casamino acids lot than in the 0% lot. In each ot aus, boro and bulu ecotypes, the length in the above half of varieties was shorter in the 0.2% casamino acids lot than in the 0% lot and it was opposite in the rest. Dry root weight, on the other hand, was larger in the 0.2% casamino acids lot than in the 0% lot in all the varieties in every ecotype (Table 2).

Comparison of the excised seminal root growth between Japonica and Japonica-Indica hybrid rices under different components of culture media.

In order to study the difference in the growth of excised seminal roots (root-tips) in vitro culture between Japonica and Japonica-Indica hybrid rices, different concentrations of sucrose, casamino acids (casein acid hydrolysate) or vitamins (thiamin, pyridoxin and nicotinic acid) in the culture medium were investigated. Effect of cultural temperature and degree of pH value of the medium on the excised seminal root growth were also tested. Unless otherwise mentioned, a Japonica rice cultivar (Nipponbare) and a Japonica-Indica hybrid rice cultivar (Milyang 30) were used as materials. All the experimental procedures were same with those described in the previous paper5). 1. Under the temperatures of 19° to 34°C, the excised seminal root growth of the Japonica-Indica hybrid rice was better than that of the Japonica rice (Fig. 1). 2. The optimum pH value of culture medium for the excised seminal root growth were 4.0 to 4.5 in the Japonica rice and 4.5 to 5.5 in the Japonica-Indica hybrid rice (Fig. 2). The optimum concentrations of sucrose for the root growth were 6 to 8% in the former and 4 to 6% in the latter (Table 1). On the other hand, effect of concentrations of vitamins on the root growth remained unclear in the both type of rices (Table 4). In all the culture media, however, the excised seminal root growth were better in the Japonica-Indica hybrid rice than in the Japonica rice. 3. In the Japonica rice, the excised seminal root grew well with increasing of concentration of casamino acids in the culture medium. On the other hand, in the Japonica-Indica hybrid rice, the dry root weight increased with increasing the concentration of casamino acids in the medium, while the main root length decreased with the casamino acids concentration (Table 2). When the excised seminal roots of each 20 cultivars of Japonica and Japonica-Indica hybrid rices were cultured in the medium containing 0% and 0.2% casamino acids, the root growth of all the Japonica rice cultivars and that of about one-third of Japonica-Indica hybrid rices were better in the 0.2% casamino acids medium than in 0% casamino acids. In the two-thirds of Japonica-Indica hybrid rices, however, the main root length was longer in the 0% casamino acids than in the 0.2% casamino acids, but the dry root weight was larger in the latter than in the former (Table 3). Thus, the effect of casamino acids on the excised seminal root growth clearly differed between the Japonica rice cultivars and the majority of the Japonica-Indica hybrid rices.

Genotypic variability for callus formation and plant regeneration in rice (Oryza sativa L.)

Sixty rice varieties (Oryza sativa L.), belonging to three subspecies, japonica, indica and javanica (some japonicaXindica hybrids were included), were compared for their capacity for callus growth and plant regeneration. Tissue cultures initiated from mature seeds on Murashige and Skoog's (1962) medium with 2 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) were transferred to a medium containing 0.02 mg/l 2,4-D and 10 mg/l kinetin, from which plantlets were regenerated. Large variabilities in callus growth and plant regeneration potentials were revealed among the varieties tested. Most japonica varieties formed a callus that weighed more than 100 mg per seed 30 days after inoculation, and showed a relatively high regenerative potential, whereas indica varieties, japonica-indica hybrids and javanica varieties showed poor callus growth and plant regeneration, although considerable varietal variation was observed in each subspecies. The callus growth potential was not correlated with the plant regeneration potential. Histological observations revealed that the epithelium cells of the scutellum mainly proliferated to form a callus, from which shoot and root primordia were differentiated independently from each other. The shoot primordia developed into plantlets when roots were formed adventitiously. In a few cases, shoots and roots were bilaterally initiated from a single primordium.

Comparison of the growth of rice seminal roots between Japonica and Japonica-Indica hybrids by the use of root-tip culture method.

Using a culture method of excised root tip reported by KAWATA et al., the growth of seminal root tips of Japonica and Japonica-Indica hybrids were compared. Plant materials used were 20 cvs. of Japonica-Indica hybrids bred in Korea, 10 cvs. of Korean paddy rice and 10 cvs. of Japanese paddy rice. The 1 cm long root tips were excised from seminal roots and two root tips were grown in each flask containing 15 ml of the culture solution. They were grown at 27° or 3O°C in the dark for three weeks. The results obtained were as follows ; 1. Root length at 27°C varied from 10.9 to 18.0 cm in the Japonica and from 13.2 to 19.7 cm in the Japonica-Indica hybrids. At 30°C, it was from 9.1 to 19.0 cm in the former and from 16.7 to 27.3 cm in the latter (Table 1). 2. At 27° and 30°C, Japonica-Indica hybrids had more number of the primary branched roots than the Japonica (Table 2). Root dry weight was from 0.9 to 2.0 mg in the Japonica and from 3.2 to 5.7 mg in the Japonica-Indica hybrids at 27°C (Fig. 4), while it was from O.9 to 2.3 mg in the former and from 4.2 to 10.1 mg in the latter at 30°C (Fig. 5-b). 3. Excised root growth of the Japonica were better at 27°C than 30°C, while in the case of the Japonica-Indica hybrids this was reverse (Fig. 5-a, 5-b).

On the formation and development of abscission layer in rice plants, Oryza sativa L.

Variation of grain shedding among rice varieties may be attributed to the morphological and physiological characteristics of abscission region formed between pedicel and rachilla, i.e. no abscission layer, uncracking abscission layer or cracking abscission layer. In the present study, to clarify the varietal difference in the formation and development of abscssion layer during boot stage, change of histological peculialities in the tissue between pedicel and rachilla was observed. Varieties used were two Japonica-Indica hybrids bred in Korea (Yushin and Milyang 23) with cracking abscission layer, two Korean local varieties with uncracking abscission layer (Jojeongjo and Nengjo), and a Japanese paddy rice variety without abscission layer (Akibare). The results obtained were summarized as follows. 1. Rapid growth of panicle and spikelet were observed from 16 to 4 days before heading (Fig. 1). At 16 days before heading, when the panicle length was 20 to 30 mm and spikelet length was 2 mm, abscission layer could be observed by elongation of cells in the pedicel and rachilla (Fig. 2-D and E). 2. At 12 days before heading, when panicle length was 50 to 80 mm and spikelet length was 3 to 4 mm, abscission layer was clearly distinguished from the sclerenchymatous cells in the pedicel with thickened cell wall. Further, the cracking abscission layer of Japonica-Indica hybrid was composed by two layers of parenchymatous cell, while that of uncracking abscission layer of Korean local rice by one layer (Fig. 2-G, H). 3. At six days before heading, when panicle length was 120 to 190 mm and spikelet length was 7 to 8 mm, cell division was observed in the abscission layer of Japonica-Indica hybrid but not in the layer of Korean local rice. In both rice plants with abscission layer, cell walls of all the sclerenchymatous cells were lignified (Fig. 2-J, K). 4. In the rice plants with abscission layer, diameter of the parenchymatous cell composing abscission layer varied from 6 to 8 μm at heading time. This result seemed to show that little elongation of the cell occured after cell division. In another variety without abscission layer, on the other hand, cell was about 16 μm in length and cell wall was lignified at heading time (Figs. 2-O and 3). 5. At the heading time, length of sclerenchymatous cells in the protrusion at the top of pedicel was 70 to 110 μm. This result showed that remarkable elongation of scleren-chymatous cell has occured during boot stage as compared with parenchymatous cell in the abscission layer or with sclerenchymatous cell in the abscission region (Fig. 4). 6. From the above results, no clear differences in the formation and development of abscission layer and its around tissue was observed between the both rice plants with cracking and uncracking abscission layers. At harvest time, however, the former had one or two layers of parenchymatous cell and the latter had one layer of parenchymatous cell in the abscission layer. Further, activity of cell division seems to be higher in rice plant with cracking abscission layer than that with uncracking one. On the other hand, in a Japanese paddy rice cultivar, no abscission layer was observed during boot stage (Fig. 2-M, N, O).