European and Turkish rice varieties were analysed to identify the traits associated with low-temperature germination. The aim of the study is to develop new rice varieties that can use these traits to reduce greenhouse gas emissions in rice fields. The average low temperature germination ratio (GR) in the European and Turkish rice varieties was 89.0±14.1%. The speed of the germination rate (SG) in Korean early maturing varieties, ‘Jopyeong’ and ‘Baekilmi’ was 1.3 and 3.5, respectively, whereas the European and Turkish varieties had a SG of 6.6. In terms of germination energy (GE) by the date, the European and Turkish varieties started germination within 4 days, while ‘Jopyeong’ and ‘Baekilmi’ began to germinate after 8 and 10 days, respectively. The mean germination time (MGT) for the European and Turkish varieties was 9.9±1.2 days. Between 4 to 10 days after inoculation, the germination velocity coefficient (GVC) for the European and Turkish varieties increased moderately from 2.6 to 5.3. After 10 days, the GVC rose rapidly from 7.0 to 12.0. ‘Jopyeong’ and ‘Baekilmi’ had slower germination rates compared to the European and Turkish varieties, in which the GVC increased moderately to 3.2 and 2.3, respectively, between 7 and 9 days after inoculation. The average mesocotyl elongation ability was 4.0±0.4 cm, with a range from 1.3 cm to 7.3 cm.

Rice mesocotyl is the region between the coleoptile node and point of union of the culm with the root. The mesocotyl is one of the important factor contributing to rice seedling emergence from soil in direct seedling. Several quantitative trait loci (QTLs) for mesocotyl elongation of rice had been reported in few studies. However, association mapping of mesocotyl elongation QTL was not conducted. For that reason, we detected QTLs for mesocotyl elongation in agar and soil conditions and confirmed the potentials of QTLs using chromosome substitution lines (CSSLs). Backcross inbred line (BILs) and chromosome segment substitution lines (CSSLs) derived from a cross between Kasalath and Nipponbare were employed to detect QTLs for mesocotyl elongation in rice. A total of 12 QTLs for mesocotyl elongation were detected on chromosome 1, 3, 6, 7, 9 and 12 using 98 BILs in agar and soil conditions. Two QTLs, qMel-1 and qMel-3 were consistently detected in both conditions. For substitution mapping of qMel-1 and qMel-3, across was made between 2 CSSLs, CSSL-6 and CSSL-15. Our results showed that the qMel-1 was located between two markers RM5448 and RM5310 on chromosome1 and the qMel-3 was located between RM15859-RM15974 on chromosome3. To understand factors controlling mesocotyl elongation, cell expansion and division of rice mesocotyl were investigated. Moreover, microarray analysis was conducted to select candidate genes using near-isogenic lines for two QTLs. 194 genes were up- and down regulated in rice mesocotyl.

In direct-seeding cultivation of rice, the emergence and establishment of seedlings are important for determining the actual yield. These traits depend principally upon elongation of both the mesocotyl and coleoptile. Mesocotyl elongation in rice is controlled by several genetic factors and is also affected by environmental factors. In this study, we mapped QTL for mesocotyl elongation using F8 lines from a cross between the cultivated rice, Ilpumbyeo and a weedy rice, PBR. One of the Korean weedy rice, PBR showed the long mesocotyl length than that of cultivars, Ilpumebyeo under soil and agar media conditions. This weedy rice showed long mesocotyl than the elite japonica cultivars. After a phenotyping of 150 F7 lines for mesocotyl length, a subset of 20 lines selected from the two extreme phenotypic tails was used for the bulked segregant analysis. Two QTL were identified on chromosomes 1 and 3. These two QTL were confirmed using 120 F8 lines. Two QTL, qMel-1 and qMel-3 on chromosomes 1 and 3 accounted for 37.3% and 6.5% of the phenotypic variance, respectively. The PBR alleles were associated with an increase in mesocotyl elongation at both loci. It is noteworthy that two QTL for mesocotyl elongation were colocalized with the QTL for mesocotyl length reported in the previous QTL reports. These QTLs can be introgressed into cultivar background using marker assisted backcrossing in an effort to enhance the level of mesocotyl elongation.

Direct-seeding method on dry paddy soil could make rice farming large-scale cultivation and cost-saving, but it has still some problems on poor seedling establishment caused by low temperature and varying sowing depth. This research was carried out to identify weedy rice genetic resources that may help to poor seedling establishment in direct-seeded rice on dry paddy soil in temperate region. The genetic resources screened in this study were 128 accessions that consist of 92 japonica weedy rices, 24 indica weedy rices, and 12 Korean bred cultivars.The weedy rices on average have very superior abilities to emerge form depth than cultivated rice. The germplasm showed that the coleoptile or/and mesocotyl lengths were positively correlated with emergence rate to a high degree. Among the germplasm, WD-3, a japonica weedy rice, evidenced the highest level of emergence with the longest coleoptile and mesocotyl elongation. The emergence ability of WD-3 depending on the burial depth under low temperature condition was confirmed in both the phytotron and the field conditions. WD-3 showed 100% of emergence rate until a burial deptho f 7 cm in the dry soil in the phytotron, and 76.2 % of very high emergence rate in the total layer of paddy field where the seeds were sown from the surface to 10 cm depth. In the emerged plants in the field, the mesocotyl elongation increased with increasing burial depth in a logarithmic fashion, and the coleoptile extension increased exponentially. The total elongation lengths of the mesocotyl and coleoptile were similar with a plant burial depth, which indicated that they could induce the safe emergence of the main leaf of the seedling from the soil to thesurface. Conclusively, the elongation habit of mesocotyl and coleoptile of WD-3 could be one of the important characteristics to develop direct-seeding cultivars.

The elongation of mesocotyl and coleoptile plays important roles in the seedling emergence and stand establishment of dry direct-seeded rice. Experiments were carried out to elucidate the effects of seed-presoaking treatments of GA3 and some inorganic salts on the mesocotyl, and coleoptile elongation of rice. Seed-soaked GA3 promoted the elongation of mesocotyl, but little effect on the coleoptile elongation. The stimulation effects of GA3 were found to be enhanced by addition of CaCl2 However, the sole treatment of CaCl2 showed no stimulating effect on the mesocotyl and coleoptile elongation. Mesocotyl elongation was most prominent in the combined treatments of 50ppm GA3 with 100 mM CaCl2 . The synergistic effects of GA3 and CaCl2 on mesocotyl elongation varied with varietal groups. The stimulating effects of GA3 were enhanced significantly by the addition of CaCl2 in japonica varieties, Dongjinbyeo, Ilpumbyeo and Milyang 95, and tall indica variety, Labelle, but not in semidwarf Tongil type varieties, Tongilbyeo, Milyang 23, and Nampungbyeo, and semi-dwarf indica, Short Labelle. The promoting effects of GA3 on the mesocotyl elongation were decreased in proportion to the lowered osmotic potential by PEG 6000 on the contrary to CaCl2 This implies that the synergistic effects of CaCl2 with GA3 on mesocotyl elongation was not caused by osmotic potential lowered by CaCl2 addition but by the salt itself. Salts such as Ca(NO3 )2 , MgCl2 BaCl2 , NaCl, KCl and KNO3 showed the synergistic effects with GA3 on mesocotyl elongation as well. The degree of synergistic effects showed no differences among salts tested, implying that there is no specificity of ions constituting the salts.

벼 건답직파재배에서 온도와 파종심도를 달리 하여 벼 품종의 출아와 중배축 신장을 조사한 결과를 요약하면 다음과 같다. 1. 온도가 높고 파종심도가 얕을수록 출아율이 높았으며 출아소요기간이 짧았다. 2. 각 처리온도 별로 파종심도 3cm이하에서는 출아율이 큰 차이가 없었으나 5cm이상이 되면 현저히 낮아졌다. 3. 파종 30일 후의 초장과 엽수는 온도가 낮을수록 감소하였고 파종심도가 5cm 이상이 되면 생육이 현저히 저하하였다. 4. 온도가 높고 파종심도가 5cm 이상일 때는 중배축과 하위절간의 신장이 컸다. 5. 파종심도 6cm에서 벼 품종들 중 출아율이 높았고 품종은 오수벼, 탐진벼이었고 중배축의 신장은 품종간 차이가 현저하여 5～16mm의 분포를 나타내었으며 제 1본엽의 출현이 지중 3～4cm에 이루어져서 파종심도는 지중 3～4cm가 적당한 것으로 판단되었다.

전보 10)의 경과 품종, 종자숙도의 차이에 따라 중배축 신장성 정도가 다르게 나타난 것이 유전 또는 생리적 특성의 차에 기인한 것인지를 구명하기 위해 수행하였던 바 실험결과를 요약하면 다음과 같다. 1. 습윤.고온처리에 의한 중배축 신장 효과는 처리구가 무처리구보다도 7배 이상 크게 신장하여 그 효과가 현저하였다. 2. 토양수분 함량에 따른 중배신장은 수분함량 8%구에서 최고치를, 16%구에서 최저치를 나타내 토양수분함량이 높을수록 작아지는 경향이었다. 3. 식물 Hormone중 중배축신장 효과는 cis-ABA 처리구가 GA3 , IAA 및 Kinetin 처리구보다도 그 효과가 현저하게 컸다. 4. 중배신장과 분리근장과는 어떠 뚜렷한 경향을 찾을 수 없었으나 중배축장과 분리근의 건물중간에는 중배축장이 클수록 건근중이 크게 나타났다.

수도의 직파재배에 있어서 가장 취약점인 출아.입묘율을 향상시키는데 많은 영향을 미치는 중배축 신장에 대하여 검토하였던 바 그 결과를 요약하면 다음과 같다. 1. 품종의 기원별 중배축장은 다수형 품종이 9.6mm로 재래종과 일본형 각각 4.4, 3.2mm 보다도 훨씬 컸다. 2. 생태형별 중배축 신장은 tjereh, aman, aus, boro 및 bulu 순으로 tjereh가 29.3mm로 buld의 5.4mm에 비해 약 5배나 컸다. 3. 품종간 중배축장은 재래종에서 백경조, 다다조 및 해조가, 일본형은 상풍벼, 팔달 및 간량도가, 다수형 품종에서는 원풍벼, 가야벼, 밀양30호 및 수정벼가 컸다. 4. 종자 숙도별 중배축장은 개화 1주후 채종 종자가 39.3mm로 가장 컸고, 성숙일수가 길어짐에 따라 중배축장은 점차 작아졌다. 5. 종자 저장기간이 길어질수록 종자숙도와 관계없이 중배축장은 점차 감소하는 경향이었고, 저장온도 5℃ 구가 15℃ , 25℃ 에 비하여 중배축장의 감소정도가 작았다.