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28 September 2012, Volume 19 Issue 3 Previous Issue    Next Issue
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Molecular Regulatory Network of Flowering by Photoperiod and Temperature in Rice SONG Yuan-li, LUAN Wei-jiang 2012, 19(3): 169-176.  Abstract ( )   PDF (240KB) ( )   Plants have an ability to flower in optimal seasonal conditions to ensure reproductive success. Photoperiod and temperature are two important season-dependent factors of plant flowering. The floral transition of plants depends on accurate measurement of changes in photoperiod and temperature. Recent molecular biology and genetics work in Arabidopsis and rice reveals that the regulation of plant flowering by photoperiods and temperatures are involved in a complicated gene network with different regulatory pathways, and new evidence and understanding were provided in the regulation of flowering in rice. Here, we summarize and analyze different flowering regulatory pathways in detail in rice based on previous studies and our results, including short-day promotion, long-day suppression, long-day induction of flowering, night break, different light-quality and temperature regulation pathways.

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Research Advances in High-Yielding Cultivation and Physiology of Super Rice FU Jing, YANG Jianchang 2012, 19(3): 177-184.  Abstract ( )   PDF (137KB) ( )   In 1996, China launched a program to breed super rice or super hybrid rice by combining intersubspecific heterosis with ideal plant types. Today, approximately 80 super rice varieties have been released and some of them show high grain yields of 12–21 t/hm2 in field experiments. The main reasons for the high yields of super rice varieties, compared with those of conventional varieties, can be summarized as follows: more spikelets per panicle and larger sink size (number of spikelets per square meter); larger leaf area index, longer duration of green leaf, greater photosynthetic rate, higher lodging resistance, greater dry matter accumulation before the heading stage, greater remobilization of pre-stored carbohydrates from stems and leaves to grains during the grain-filling period; and larger root system and greater root activity. However, there are two main problems in super rice production: poor grain-filling of the later-flowering inferior spikelets (in contrast to earlier-flowering superior spikelets), and low and unstable seed-setting rate. Here, we review recent research advances in the crop physiology of super rice, focusing on biological features, formation of yield components, and population quality. Finally, we suggest further research on crop physiology of super rice.

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Ascorbate-Glutathione Cycle Alteration in Cadmium Sensitive Rice Mutant cadB-1 SHEN Guo-ming1, 2, ZHU Cheng3, DU Qi-zhen2, SHANGGUAN Li-na3 2012, 19(3): 185-192.  Abstract ( )   PDF (394KB) ( )   A rice cadmium (Cd) sensitive mutant cadB-1 was obtained using Agrobacterium tumefaciens mediated system. After exposure of cadB-1 and wild type (WT) rice seedlings to a range of Cd concentrations for 10 d, Cd accumulated to higher levels in roots, stems and leaves of both cadB-1 and WT with increasing external Cd concentrations, and the inhibition of seedling growth in cadB-1 was more serious than in WT. Hydrogen peroxide accumulation was higher in leaves and roots of cadB-1. The ratios of reduced glutathione (GSH)/oxidized glutathione (GSSG), ascorbate (ASC)/dehydroascorbate (DHA) and reduced nicotinamide adenine dinucleotide phosphate (NADPH)/oxidized nicotinamide adenine dinucleotide phosphate (NADP+) were lower in cadB-1 than in WT both in leaves and roots under high Cd levels. The activities of ascorbate peroxidase (APX), glutathione peroxidase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) were also lower in cadB-1 than in WT both in leaves and roots under the treatment of high levels of Cd. Our results suggest that under Cd stress, the ASC-GSH cycle was more seriously inhibited in cadB-1 than in WT, indicating that the mutant cadB-1 is less able to scavenge reactive oxygen species and sensitive to Cd.

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Genetic Diversity of Tropical Hybrid Rice Germplasm Measured by Molecular Markers HE Zhi-zhou1, 2, XIE Fang-ming2, CHEN Li-yun1, Madonna Angelita DELA PAZ2 2012, 19(3): 193-201.  Abstract ( )   PDF (333KB) ( )   Investigation of genetic diversity and relationships among breeding lines is of great importance to facilitate parent selection in hybrid rice breeding programs. In this study, we characterized 168 hybrid rice parents from International Rice Research Institute with 207 simple sequence repeat (SSR) and 353 single nucleotide polymorphism (SNP) markers. A total of 1 267 SSR and 706 SNP alleles were detected with the averages of 6.1 (SSR) and 2.0 (SNP) alleles per locus respectively across all lines. Based on the genetic distances estimated from the SSR and SNP markers separately and combined, the unrooted neighbor-joining cluster and STRUCTURE analyses consistently separated the 168 hybrid rice parents into two major groups: B-line and R-line, which is consistent with known parent pedigree information. The genetic distance matrices derived from the SSR and SNP genotyping were highly correlated (r = 0.81, P < 0.001), indicating that both of the SSR and SNP markers have distinguishable power to detect polymorphism and are appropriate for genetic diversity analysis among tropical hybrid rice parents. A subset of 60 SSR markers were also chosen by the Core Hunter with 368 alleles, and the cluster analysis based on the total and subset of SSR markers highly corresponded at r = 0.91 (P < 0.001), suggesting that fewer SSR markers can be used to classify and evaluate genetic diversity among parental lines.

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Genetic Analysis of Stripe Disease Resistance in Rice Restorer Line C224 Using Major Gene plus Polygene Mixed Effect Model ZHENG Wen-Jing1, 2, LIU Zhi-Heng1, ZHAO Jia-Ming2, CHEN Wen-Fu1 2012, 19(3): 202-206.  Abstract ( )   PDF (211KB) ( )   The inheritance of stripe disease resistance in a rice restorer line C224 was analyzed using the mixed effect model of major gene plus polygene for quantitative traits. In addition, the resistance was investigated in seven crosses of C224 with maintainer lines. The results showed that the stripe resistance of C224 was controlled by two major genes with additive-dominance-epistasis effects plus polygenes with additive-dominance effects (E-1 model). These two genes had additive effects of -12.47% and -24.75%, respectively, showing negative dominance effects. There were significant epistasis and interaction effects between the two major genes. The heritability of the two major genes was 92.12%, while that of polygenes was 2.74%, indicating that the stripe resistance had dominant major gene effect. Of the seven crosses, five displayed high or medium resistance to the stripe disease.

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Involvement of Antioxidative Defense System in Rice Seedlings Exposed to Aluminum Toxicity and Phosphorus Deficiency GUO Tian-rong, YAO Peng-cheng, ZHANG Zi-dong, WANG Jiang-jia, WANG Mei 2012, 19(3): 207-212.  Abstract ( )   PDF (171KB) ( )   Plants growing in acid soils may suffer both phosphorus (P) deficiency and aluminum (Al) toxicity. Hydroponic experiments were undertaken to assess the single and combination effects of Al toxicity and low P stress on seedling growth, chlorophyll and proline contents, antioxidative response and lipid peroxidation of two rice genotypes (Yongyou 8 and Xiushui 132) differing in Al tolerance. Al toxicity and P deficiency both inhibited rice seedling growth. The development of toxic symptoms was characterized by reduced chlorophyll content, increased proline and malondialdehyde contents in both roots and leaves, and increased peroxidase and superoxide dismutase activities in roots, but decreased in leaves. The stress condition induced more severe growth inhibition and oxidative stress in Yongyou 8, and Xiushui 132 showed higher tolerance to both Al toxicity and P deficiency. P deficiency aggravated Al toxicity to plant growth and induced more severe lipid peroxidation.

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Physiological and Molecular Analysis of Applied Nitrogen in Rice Genotypes Khalid Rehman HAKEEM1, 2, Ruby CHANDNA1, Altaf AHMAD1, Muhammad IQBAL1, 3 2012, 19(3): 213-222.  Abstract ( )   PDF (415KB) ( )   Ten genotypes of rice (Oryza sativa L.) were grown for 30 d in complete nutrient solution with 1 mmol/L (N-insufficient), 4 mmol/L (N-moderate) and 10 mmol/L (N-high) nitrogen levels, and nitrogen efficiency (NE) was analyzed. Growth performance, measured in terms of fresh weight, dry weight and lengths of root and shoot, was higher in N-efficient than in N-inefficient rice genotypes at low N level. Of these 10 genotypes, Suraksha was identified as the most N-efficient, while Vivek Dhan the most N-inefficient. To find out the physiological basis of this difference, the nitrate uptake rate of root and the activities of nitrate assimilatory enzymes in leaves of N-efficient and N-inefficient rice genotypes were studied. Uptake experiments revealed the presence of two separate nitrate transporter systems mediating high- and low-affinity nitrate uptake. Interestingly, the nitrate uptake by the roots of Suraksha is mediated by both high- and low-affinity nitrate transporter systems, while that of Vivek Dhan by only low-affinity nitrate transporter system. Study of the activities and expression levels of nitrate assimilatory enzymes in N-efficient and N-inefficient rice genotypes showed that nitrate reductase (NR) and glutamine synthetase (GS) play important roles in N assimilation under low-nitrogen conditions.

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Variations in Carbohydrate and Protein Accumulation among Spikelets at Different Positions Within a Panicle During Rice Grain Filling DONG Ming-hui1, 2, CHEN Pei-feng2, XIE Yu-lin2, QIAO Zhong-ying2, YANG Jian-chang1 2012, 19(3): 223-232.  Abstract ( )   PDF (687KB) ( )   The accumulation dynamics of kernel components for spikelets at different positions within a rice panicle were investigated during grain filling to understand the physiological reasons for the variation of grain quality. Two rice cultivars, Yangdao 6 (indica) and Yangjing 9538 (japonica), were field-grown, and the grain filling characters and contents of starch, soluble sugar, and protein of the spikelets at different positions were studied. There were significant differences in matter accumulation among spikelets at different positions during grain filling. The early-flowering spikelets presented dominance over the late-flowering spikelets in initial time and initial rate of accumulation. At the initial and mid filling stages, the contents and the rates of starch and amylose accumulation in spikelets decreased with the flowering sequence, but soluble sugar content (SSC) exhibited the opposite trend. The difference in SSC among the spikelets of Yangjing 9538 was greater than that of Yangdao 6, but amylose content in mature spikelets showed no obvious relationship to their flowering sequence. The crude protein content (CPC) of early-flowering spikelets decreased more rapidly than that of late-flowering ones at the initial filling stage, and CPC in the spikelets on the secondary branch was higher than that on the primary branch, but CPC in early-flowering ones was lower than that in late-flowering across the whole grain filling period. Grain water content (GWC) of early-flowering spikelets decreased more rapidly than that of late-flowering spikelets on the same branch at the initial and mid filling stages, especially for the top grain on each primary branch. The results suggested that poor grain filling of late-flowering spikelets may be attributed to their low biological activity rather than carbohydrate supply limitation.

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Leaf Construction Cost and Related Ecophysiological Parameters of Rice Crop and Its Important Weeds Vartika Singh, Hema Singh 2012, 19(3): 233-240.  Abstract ( )   PDF (303KB) ( )   To understand the reason for the success of weeds, we investigated the energetic cost of leaf construction, and certain ecophysiological traits of rice and its dominant weeds. On physiological basis among all weeds, Caesulia axillaris Roxburgh was found to be the most serious, followed by Echinochloa cruss-galli L. Beauv and Echinochloa colonum L. Link, while Fimbristylis miliaceae L. Vahl and Cyperus iria L. were moderate weeds of the rice fields. C. axillaris had the lowest leaf construction cost (LCC) both on a mass basis (1.15 g/g) and on a unit area basis (22.93 g/m2). Comparatively higher specific leaf area, photosynthetic rate, photosynthetic nitrogen use efficiency, leaf area ratio and leaf area index provided C. axillaris with further competitive advantage. Low LCC suggests that weeds utilize carbon resource more efficiently than the crop and potentially spend the saved energy on other competitive strategies viz. seed production, biomass production and high relative growth rate, which results in low crop yield and increase in weed seed bank.

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Pathogenic and Genetic Diversity of Magneporthe oryzae Populations from Sri Lanka Y J P K MITHRASENA1, W S S WIJESUNDERA2, R L C WIJESUNDERA3, D C WIMALASIRI2, R P N PRIYANTHI2 2012, 19(3): 241-246.  Abstract ( )   PDF (309KB) ( )   The present study was undertaken to determine the pathogenic and the genetic diversity of the isolates of M. oryzae collected from the wet, intermediate and dry zones of Sri Lanka with a view to develop rice varieties conferring durable resistance to rice blast. No significant morphological or growth variations existed amongst the isolates studied. The genetic diversity of isolates determined by carrying out Pot2 transposable element based on repetitive-PCR revealed that the majority of isolates (92%) clustered into a single group with 45.4% similarity. The existence of nine pathotypes was identified by observing the reaction type of isolates on 16 different rice lines. Pathotype 1 which was distributed in all zones affected only one differential line. Pathotype 2 which was able to infect six lines was restricted only to the dry zone of Sri Lanka. Of the 16 rice lines, seven lines, K3 (Pik-h), C101A51 (Piz5), K1 (Pita), C105TTP2L9 (Pita), K59 (Pit), Shin (Pish) and WHD-1S-75-1-127 (Pi9) had highly effective blast resistance. None of the isolates of the fungus showed any virulence against the seven lines. These seven blast resistant lines can be used in the breeding programmes in Sri Lanka for development of lines conferring durable resistance to rice blast.

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Growth and Reproduction of Artificially Fed Cnaphalocrocis medinalis XU Jian1, #, LI Chuan-ming1, #, YANG Ya-jun2, QI Jian-hang1, ZHENG Xu-song2,HU Rong-li1,LU Zhong-xian2, LIU Qin1 2012, 19(3): 247-251.  Abstract ( )   PDF (258KB) ( )   The growth and reproduction of rice leaffolder, Cnaphalocrocis medinalis, fed on an artificial diet were studied. The results showed that the larvae were able to grow and pupate on the artificial diet. The durations of larvae and pupas of C. medinalis on the artificial diet were 28.1 d and 10.1 d, postponed 4.9 d and 1.7 d respectively, compared with those reared with rice leaves. The number of ovipositions was 41.6 per female, 26.2% higher than that fed on rice leaves. Survival rate curve of larvae was a descent function of mortality-age, with no significant differences from the curve of larvae fed on rice leaves. The net reproductive rate (Ro), intrinsic rate of increase (rm) and finite rate of increase (λ) of the population fed on diet were 17.6928, 0.0884 and 1.0924, respectively, and the mean generation time (T) and double time (td) were prolonged 4.9 d and 1.3 d in comparison with the treatment of rice leaves. Population trend index (I) was 3.26, indicating a growing number of the population of C. medinalis fed on artificial diet.

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Pathogenicity of Rice Blast Fungus Magnaporthe oryzae on Brachypodium distachyon WANG Jiao-yu1, WANG Xiao-yan1, 2, LI Ling1, ZHANG Xin1, WANG Yan-li1, CHAI Rong-yao1, SUN Guo-chang1 2012, 19(3): 252-258.  Abstract ( )   PDF (573KB) ( )   Inoculation methods for rice blast fungus Magnaporthe oryzae to Brachypodium distachyon were developed to investigate the infection process and symptom development in comparison with those on rice (Oryza sativa) and barley (Hordeum vulgare). M. oryzae could infect leaves, sheathes, stems and panicles of B. distachyon and cause blast disease. Spraying conidial suspension on either intact seedlings or leaf segments induced typical symptoms on B. distachyon. During the intact seedling inoculation, the symptom developed on B. distachyon leaves closely resembled that on rice; but the lesions on B. distachyon had better uniformity in shapes and sizes than those on rice or barley. In the leaf segments inoculation, only initial and low-developed lesions could be found on rice, while normal symptoms on B. distachyon and barley. Inoculated with low-virulent mutants of M. oryzae, B. distachyon produced low-level symptoms. The symptom level of each mutant on B. distachyon corresponded well to that on rice. In addition, typical infection processes presented on B. distachyon leaves: forming melanized appressoria, penetrating into host epidermis and then forming hyphae in epidermal cells. According to these results, B. distachyon can be used as a candidate for studying fungus-plant interactions and as a probable source of disease resistance.

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Boron Application Improves Growth, Yield and Net Economic Return of Rice Mubshar HUSSAIN1, M. Ayaz KHAN1, M. Bismillah KHAN1, Muhammad FAROOQ2, Shahid FAROOQ1 2012, 19(3): 259-262.  Abstract ( )   PDF (187KB) ( )   A field trial was conducted to evaluate the role of boron (B) application at different growth stages in improving the growth, yield and net economic return of rice at farmer’s fields during summer season, 2009. Boron was soil applied (1.5 kg/hm2) at the transplanting, tillering, flowering and grain formation stages of rice; foliar applied (1.5% B solution) at the tillering, flowering and grain formation stages of rice, and dipped seedling roots in 1.5% B solution before transplanting; while control plots did not apply any B. Boron application (except dipping of seedling roots in B solution, which caused toxicity and reduced the number of tillers and straw yield than control) substantially improved the rice growth and yield. However, soil application was better in improving the number of grains per panicle, 1000-grain weight, grain yield, harvest index, net economic income and ratio of benefit to cost compared with the rest of treatments. Overall, for improving rice performance and maximizing the net economic returns, B might be applied as soil application at flowering.