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28 March 2005, Volume 12 Issue 1 Previous Issue    Next Issue
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Practice and Thought on Developing Hybrid Rice for Super High Yield by Exploiting Inter-subspecific Heterosis LU Chuan-gen, ZOU Jiang-shi 2005, 12(1): 1-6 .  Abstract ( )   PDF (38KB) ( )   Since the breakthrough of grain yield owing to the development of dwarf rice and three-line system hybrid rice, rice breeding for high yield hardly had showed significant progress in the next successive two decades. It was considered that utilizing heterosis between subspecific varieties (Oryza sativa L.) would be an effective approach to increase yield further. During 1987-1993, an indica-japonica hybrid Yayou 2 yielded as high as 10.5 t/ha; however, it failed to be commercialized because of seed purity problem due to non-uniform emasculation by chemical agent in seed production, and sensitivity of seed setting in F1 plants to environmental conditions. In the past decade, two inter-subspeific hybrids, Liangyoupeijiu (Peiai 64S/9311, javanica/indica) and Liangyou E32 (Peiai 64S/E32, javanica/ japonica); both of them exhibited grain yield higher than 10.5 t/ha, and were widely judged as the pioneers of super hybrid rice. Liangyoupeijiu has been successfully popularized over 4 million hectare in wide climatic areas, while Liangyou E32 made a yield record and offered a model of plant ideotype for super hybrid rice. It was considered that in combination with plant ideotype, active physiological functions, and wide-range adaptability to ecological conditions, exploitation of indica-japonica heterosis would be the key approach for super hybrid rice breeding.

Research Paper

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Identification and Purity Test of Super Hybrid Rice with SSR Molecular Markers XIN Ye-yun, ZHANG Zhan, XIONG Yi-ping, YUAN Long-ping 2005, 12(1): 7-12 .  Abstract ( )   PDF (189KB) ( )   Five super hybrid rice combinations, i.e. HYS-1/R105, Pei’ai 64S/E32, Liangyoupeijiu (Pei’ai 64S/9311), 88S/0293, and J23A/Q611, and their parental lines were tested by means of SSR analysis. A total of 144 SSR primer pairs distributed on 12 rice chromosomes were used, out of which 47 detected polymorphism among the tested rice lines. Among all these primers, RM337 and RM154 produced polymorphic patterns in four or more of the tested experimental materials respectively, and they could distinguish among most rice genotypes tested. Twenty-four primer pairs, two on each rice chromosome, were selected to make a reference SSR marker-based fingerprinting for the rice lines. For most of the primer pairs, F1 hybrids mainly showed complementary pattern of both parents, which could be very useful to distinguish the F1 from its parental lines. In addition, 5 primer pairs were selected as special primer pairs for five hybrid rice combinations respectively. By combining the rapid, simple method on DNA extraction, it is suggested that SSR technique has wide prospective in variety authentication and purity identification.

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Machine Vision Analysis of Characteristics and Image Information Base Construction for Hybrid Rice Seed CHENG Fang, LIU Zhao-yan, YING Yi-bin 2005, 12(1): 13-18 .  Abstract ( )   PDF (115KB) ( )   Incompletely closed glumes, germination on panicle and disease are three important factors causing poor seed quality of hybrid rice. To determine how many and which categories should be classified to meet the demand for seed in rice production, the effects of various degrees of incompletely closed glumes, germination on panicle and disease on germination percentage at the harvest and after storage for six months were studied by standard germination percentage test. Six categories of seeds with germ (germinated seeds), severe disease, incompletely closed glumes, spot disease, fine fissure and normal seeds were inspected and then treated separately. Images of the five hybrid rice seed (Jinyou 402, Shanyou 10, Zhongyou 27, Jiayou 99 and Ⅱyou 3207) were acquired with a self-developed machine vision system. Each image could be processed to get the feature values of seed region such as length, width, ratio of length to width, area, solidity and hue. Then all the images of normal seeds were calculated to draw the feature value ranges of each hybrid rice variety. Finally, an image information base that stores typical images and related feature values of each variety was established. This image information base can help us to identify the classification limit of characteristics, and provide the reference of the threshold selection. The management of large numbers of pictures and the addition of new varieties have been supported. The research laid a foundation for extracting image features of hybrid rice seed, which is a key approach to future quality inspection with machine vision.

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Mapping Quantitative Trait Loci for Palatability of Milled Rice TANG Shao-qing, HU Pei-song, JIAO Gui-ai, ZHAI Hu-qu, WAN Jian-min, 2005, 12(1): 19-24 .  Abstract ( )   PDF (58KB) ( )   Quantitative trait loci (QTLs) controlling palatability in rice were identified using a set of 98 backcross inbred lines (BILs) population derived from a cross between a japonica variety Nipponbare and an indica variety Kasalath. The palatability scores of the population measured by RQ1/Plus Rice Analyzer, showed a continuous and transgressive segregative distribution with a range from 66 to 92. Four putative QTLs for palatability, qPAL-5, qPAL-7, qPAL-8a and qPAL-8b, were detected on chromosome 5, 7 and 8, and they accounted 7.83, 7.03, 11.58 and 7.19% of the total phenotypic variation, respectively. Three alleles qPAL-5, qPAL-7 and qPAL-8b from Kasalath increased the palatability score, whereas only one Nipponbare allele qPAL-8a increased the score . Eight transgressive lines in palatability were selected to make a comparison between phenotypic and genotypic classes. The result explained the possibility of positive QTLs pyramiding through marker-assisted selection of highly palatable rice.

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Inheritance and QTL Mapping of Salt Tolerance in Rice YAO Ming-zhe, WANG Jian-fei, CHEN Hong-you, ZHAI Hu-qu, ZHANG Hong-sheng 2005, 12(1): 25-32 .  Abstract ( )   PDF (69KB) ( )   An F2 population derived from the cross between Jiucaiqing (japonica) and IR36 (indica) was used to analyze the inheritance of salt tolerance in rice by genetic model of major-genes plus polygenes, and to map the corresponding QTLs by SSR molecular markers. Rice plants of P1, P2, F1 and F2 at 5- to 6- leaf stage were treated under 140 mmol/L NaCl for 10 days. Three indices representing the ability of salt tolerance of rice seedlings were measured, including salt tolerance rating (STR), Na+/K+ ratio in roots and dry matter weight of shoots (DWS). STR, Na+/K+ and DWS were all controlled by two major genes with modification by polygenes. Heritability of these traits from major genes was 17.8, 53.3 and 52.3%, respectively. The linkage map constructed by 62 SSR molecular markers covered a total length of about 1 142 cM. There were three QTLs detected for STR located on chromosome 1, 5 and 9, two QTLs for DWS on chromosomes 8 and 9, and two QTLs for Na+/K+ on chromosomes 2 and 6, one on each chromosome respectively. Single QTL accounted for 6.7 to 19.3% of phenotypic variation. Identification method of salt tolerance in rice and breeding of rice varieties with salt tolerance based on molecular markers assisted selection had been discussed.

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Mapping QTL for Heat-Tolerance at Grain Filling Stage in Rice ZHU Chang-lan, XIAO Ying-hui, WANG Chun-ming, JIANG Ling, ZHAI Hu-qu, WAN Jian-min, 2005, 12(1): 33-38 .  Abstract ( )   PDF (53KB) ( )   A mapping population of 98 lines (backcross inbred lines, BILs) derived from a backcross of Nipponbare/Kasalath// Nipponbare was planted at two experimental sites, Nanjing and Nanchang, and treated with high and optimal temperature during grain filling, respectively. The grain weight heat susceptibility index [GWHSI= (grain weight at optimum temperature－grain weight at high temperature) / grain weight at optimum temperature×100] was employed to evaluate the tolerance of rice to heat stress. A genetic linkage map with 245 RFLP markers and a mixed linear-model approach was used to detect quantitative trait loci (QTLs) and their main effects, epistatic interactions and QTL×environment interactions (Q×E). The threshold of LOD score=2.0 was used to detect the significance of association between marker and trait. A total of 3 QTLs controlling heat tolerance during grain filling were detected, on chromosomes 1, 4 and 7, with LOD scores of 8.16, 11.08 and 12.86, respectively, and they explained the phenotypic variance of 8.94, 17.25 and 13.50 %, correspondingly. The QTL located in the C1100–R1783 region of chromosome 4 showed no QTL×environment interaction and epistatic effect, suggesting that it could be stably expressed in different environments and genetic backgrounds, and thus it would be valuable in rice breeding for heat tolerance improvement. This QTL allele, derived from Kasalath reduced 3.31% of the grain weight loss under heat stress. One located between R1613–C970 on chromosome 1 and the other between C1226–R1440 on chromosome 7, with additive effect 2.38 and 2.92%, respectively. The tolerance alleles of both these QTLs were derived from Nipponbare. Both of these QTLs had significant QTL×environment interactions, and the latter was involved in epistatic interaction also. Eight pairs of epistatic effect QTLs were detected, one pair each on chromosomes 1, 2, 3, 5, 7, 8, 10 and 12. The results could be useful for elucidating the genetic mechanism of heat-tolerance and the development of new rice varieties with heat tolerance during grain filling phase.

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Performance and Inheritance of Rice Starch RVA Profile Characteristics YAN Chang-jie, LI Xin, ZHANG Rong, SUI Jiong-ming, LIANG Guo-hua, SHEN Xin-ping, GU Shi-liang, GU Ming-hong 2005, 12(1): 39-47 .  Abstract ( )   PDF (87KB) ( )   The classification and inheritance of rice starch RVA profiles were studied by testing RVA profiles of F2 clonally propagated population and some varieties, including japonica, indica, and glutinous types. All the RVA profiles of accessions could be divided into six kinds based on the cluster analysis, that is A, B, C, D, E and F. Feature profile of sticky variety was type A. The profiles of indica varieties could be presented as B, C, D, E and F types and that of japonica varieties fell into D, E and F types. RVA profiles of the rice were mainly affected by apparent amylose content (AAC), but the difference of RVA profiles could also be detected in the varieties with similar AAC. The close relationship between RVA profile indices and sensory of low or middle AAC varieties suggested that the RVA profiles can be used as indirect index to evaluate eating and cooking quality. In four hybrid combinations, the component indices of RVA profiles of F1 were between those of its parents except peak viscosity and pasting temperature. Also, in F2 clonally propagated population, all the components of the RVA profiles showed continuous segregation, suggesting that all of them were controlled by a series of minor genes, although Wx gene may play an important role in determining the RVA profiles. These results may provide some new information useful for rice quality breeding program.

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Effect of Grain Position within a Panicle and Variety on As, Cd, Cr, Ni, Pb Concentrations in japonica Rice CHENG Wang-da , ZHANG Guo-ping , YAO Hai-gen , TANG Mei-ling 2005, 12(1): 48-56 .  Abstract ( )   PDF (156KB) ( )   Two japonica rice varieties, a compact panicle (CP) Xiushui 63 and a loose panicle (LP) Xiushui 11 were grown in a slightly contaminated paddy field, to determine the effect of grain positions within a panicle and variety on grain As, Cd, Cr, Ni and Pb concentrations. There was a significant difference in grain As, Cd, Cr, Ni and Pb concentrations among grain positions, and the extent of the difference was variety- and metal-specific; Xiushui 63 showed greater difference than Xiushui 11, and As, Cd, Cr and Pb being greater than Ni. The top grains (TG) of a panicle had higher As, Cd and Ni concentrations than the middle ones (MG), and the bottom ones (BG) contained the lowest. With regard to Cr and Pb, the case was opposite. Significantly positive correlations were found between grain weight and As, Cd, Ni concentrations, but there was a negative correlation between grain weight and Cr, and Pb concentrations. There was a remarkable variation in grain filling pattern among grains within a panicle, and between Xiushui 63 and Xiushui 11. In comparison with MG and TG, BG had the lowest grain filling rate and grain weight, leading to obvious difference in grain weight among grains within a panicle, and a greater difference for Xiushui 63 than for Xiushui 11. The regression analysis showed that grain As and Cd concentrations were positively correlated with the maximum grain filling rate (GRm),while negatively correlated with the required time for reaching the maximum grain filling rate (Tpoi). Concerning Cr and Pb, the case was just reverse. It is suggested that As and Cd accumulation in grains might be accompanied by the carbohydrate accumulations, while Cr and Pb accumulation displayed a different pattern.

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Canopy Spectral Reflectance Characteristics of Rice with Different Cultural Practices and Their Fuzzy Cluster Analysis XUE Li-hong , CAO Wei-xing , LUO Wei-hong , YANG Lin-zhang 2005, 12(1): 57-62 .  Abstract ( )   PDF (101KB) ( )   The influence of major cultural practices including different nitrogen application rates, population densities, transplanting leaf ages of seedling, and water regimes on rice canopy spectral reflectance was investigated. Results showed that increased nitrogen rates, water regimes and population densities and decreased seedling ages could enhance reflectance at NIR (near infrared) bands and reduce reflectance at visible bands. Using reflectance of green, red and NIR band and ratio index of 810–560 nm could distinguish the different type of rice by fuzzy cluster analysis.

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Differential Expression of Whitebacked Planthopper Resistance in the japonica/indica Doubled Haploid Rice Population under Field Evaluation and Seedbox Screening Test Kazushige SOGAWA , QIAN Qian , ZENG Da-li , HU Jiang , ZENG Long-jun 　 2005, 12(1): 63-67 .  Abstract ( )   PDF (38KB) ( )   Whitebacked planthopper (WBPH) -resistance in a japonica / indica doubled haploid (DH) rice population established from a cross between WBPH-resistant japonica Chunjiang 06 and susceptible indica TN1, was comparatively evaluated through a field experiment based on the WBPH immigrant density and standardized seedbox screening test (SSST). All the susceptible DH lines in the field experiment behaved accordingly in SSST. However, 35 of resistant 66 lines (53%) in the field, were categorized to susceptible groups in SSST. Likewise, there were no significant differences in WBPH immigrant densities among 70 DH lines that were highly resistant to susceptible in SSST. The results revealed that SSST could not evaluate properly WBPH resistance in the DH lines. Four QTLs for WBPH-resistance phenotyped by the immigrant density were detected on chromosomes 2, 3, 4, and 11. Of them, the QTL on chromosome 4 was the most effective (LOD 21.8, variance 78%). Five QTLs associated with seedling mortality were mapped on chromosomes 2, 3, 4, 5 and 6. In addition to the QTL (LOD 10.5, variance 68%) on chromosome 4, there was another major QTL (LOD 12.7, variance 71%) located on chromosome 5, which was SSST-specific but might be irrespective of the WBPH resistance traits.

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Sensitivity Detection Technique and Resistance Risk Assessment of Magnaporthe grisea to Tricyclazole ZHANG Chuan-qing, ZHOU Ming-guo, XUE Na 2005, 12(1): 68-74 .  Abstract ( )   PDF (63KB) ( )   In vitro detection method for the sensitivity of Magnaporthe grisea to tricyclazole was studied, and the potential resistance risk of blast disease to tricyclazole was assessed. Both EC50 of hyphal melanization (EC50-H) and minimum inhibitive concentration of melanization in appressorial (MIC-A) by inhibitor tricyclazole showed positive correlation to the EC50 of tricyclazole against blast disease tested in vivo, with relative co-efficiency (R2) of 0.8995 and 0.8244, respectively. However, stability and reproducibility of EC50-H were better than those of MIC-A, suggesting that it could be used to detect the sensitivity of M. grisea to tricyclazole in vitro. Tricyclazole sensitivity of the progenies derived from single spores of the most sensitive isolate DY2 and the least sensitive isolate GY6 detected in sensitivity monitoring in 2000 was not stable, with mean EC50 values of 4.4968 μg/mL and 5.4010 μg/mL, respectively, indicating that the difference in EC50 between DY2 and GY6 was not caused probably by resistance variation. EC50 of GY6 did not increase significantly when continuously selected for twenty generations under the selection pressure of tricyclazole in vivo. However, the sensitivity of DY2 was decreased by 10-fold after selected for twenty generations. The results suggested that tricyclazole was still low resistance risk for M. grisea in China.