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28 January 2019, Volume 26 Issue 1 Previous Issue    Next Issue
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Research Progress on Heat Stress of Rice at Flowering Stage Yaliang Wang, Lei Wang, Jianxia Zhou, Shengbo Hu, Huizhe Chen, Jing Xiang, Yikai Zhang, Yongjun Zeng, Qinghua Shi, Defeng Zhu, Yuping Zhang 2019, 26(1): 1-10.  DOI: 10.1016/j.rsci.2018.06.009 Abstract ( )   HTML ( )   PDF (1753KB) ( )   Global warming has caused frequent occurrence of heat stress at the flowering stage of single-season rice in the Yangtze River region of China, which results in declines of spikelet fertility and yield in rice. Rice flowering stage is the most sensitive period to high temperatures, and therefore, the key for heat stress happening is the flowering stage coinciding with high temperature, which causes spikelet fertility decreasing in heat-sensitive varieties, and is the major factor for heat injury differences among various rice planting regions. With the development of rice breeding, temperature indexes for heat stress has been converted from daily maximum temperature of 35 ºC to 38 ºC with the stress duration of more than 3 d. During the flowering stage, anther dehiscence inhibition and low pollen shedding onto the stigma are two main reasons for spikelet fertility reduction under high temperatures. At panicle initiation stage, high temperatures aggravate spikelet degeneration, and destroy floral organ development. Various types of rice varieties coexist in production, and indica-japonica hybrid rice demonstrates the highest heat resistance in general, followed by indica and japonica rice varieties. In production, avoiding high temperature is the main strategy of preventing heat stress, and planting suitable cultivars and adjustment of sowing date are the most effective measures. Irrigation is an effective real-time cultivation measure to decline the canopy temperature during the rice flowering stage. We suggested that further study should be focused on exploring heat injury differences among different rice variety types, and innovating rice-planting methods according to planting system changes in rice planting regions with extreme heat stress. Meanwhile, high temperature monitor and warning systems should be improved to achieve optimal heat stress management efficiencies.

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Functional Analysis of Three Rice Chloroplast Transit Peptides Lei He, Guang Chen, Sen Zhang, Zhennan Qiu, Jiang Hu, Dali Zeng, Guangheng Zhang, Guojun Dong, Zhenyu Gao, Deyong Ren, Lan Shen, Longbiao Guo, Qian Qian, Li Zhu 2019, 26(1): 11-20.  DOI: 10.1016/j.rsci.2018.12.001 Abstract ( )   HTML ( )   PDF (1908KB) ( )   Chloroplast transit peptides (CTPs) can be used to transport non-chloroplastic proteins into the chloroplasts. Here, we studied the CTPs of three rice (Oryza sativa L.) chloroplast-localized proteins and found that their CTPs could be used to transport non-chloroplast-localized proteins into the chloroplasts. Fusion proteins lacking the CTP remained located in the cytoplasm. Furthermore, we constructed green fluorescent protein fusion vectors with the three CTPs and three non-chloroplast-localized proteins, Ghd10, MULTI-FLORET SPIKELET1 (MFS1), and SHORTENED UPPERMOST INTERNODE 1 (SUI1). After transforming these constructs into rice protoplasts, the fusion proteins all localized in the chloroplasts. Collectively, our results showed that these CTPs can transport non-chloroplast-localized proteins into the chloroplasts, and more importantly, these CTPs can be applied to engineer chloroplast metabolism.

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Identification of New Resistance Loci Against Sheath Blight Disease in Rice Through Genome-Wide Association Study Zongxiang Chen, Zhiming Feng, Houxiang Kang, Jianhua Zhao, Tianxiao Chen, Qianqian Li, Hongbing Gong, Yafang Zhang, Xijun Chen, Xuebiao Pan, Wende Liu, Guoliang Wang, Shimin Zuo 2019, 26(1): 21-31.  DOI: 10.1016/j.rsci.2018.12.002 Abstract ( )   HTML ( )   PDF (1462KB) ( )   Sheath blight (SB) caused by the soil borne pathogen Rhizoctonia solani is one of the most serious global rice diseases. Breeding resistant cultivar is the most economical and effective strategy to control the disease. However, no rice varieties are completely resistant to SB, and only a few reliable quantitative trait loci (QTLs) linked with SB resistance have been identified to date. In this study, we conducted a genome-wide association study (GWAS) of SB resistance using 299 varieties from the rice diversity panel 1 (RDP1) that were genotyped using 44 000 high-density single nucleotide polymorphism (SNP) markers. Through artificial inoculation, we found that only 36.5% of the tested varieties displayed resistance or moderate resistance to SB. In particular, the aromatic and aus sub-populations displayed higher SB resistance than the tropical japonica (TRJ), indica and temperate japonica sub-populations. Seven varieties showed similar resistance levels to the resistant control YSBR1. GWAS identified at least 11 SNP loci significantly associated with SB resistance in the three independent trials, leading to the identification of two reliable QTLs, qSB-3 and qSB-6, on chromosomes 3 and 6. Using favorable alleles or haplotypes of significantly associated SNP loci, we estimated that both QTLs had obvious effects on reducing SB disease severity and can be used for enhancing SB resistance, especially in improving SB resistance of TRJ sub-population rice varieties. These results provided important information and genetic materials for developing SB resistant varieties through breeding.

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Introgression of Two Drought QTLs into FUNAABOR-2 Early Generation Backcross Progenies Under Drought Stress at Reproductive Stage Okechukwu Anyaoha Christian, Fofana Mamadou, Gracen Vernon, Tongoona Pangirayi, Mande Semon 2019, 26(1): 32-41.  DOI: 10.1016/j.rsci.2018.04.006 Abstract ( )   HTML ( )   PDF (1587KB) ( )   FUNAABOR-2 is a popular Ofada rice variety grown in a large area under rainfed upland condition across western states of Nigeria. We used the combination of phenotypic and marker-assisted selection (MAS) to improve grain yield of FUNAABOR-2 under drought stress (DS) at the reproductive stage via introgression of two drought quantitative trait loci (QTLs), qDTY12.1 and qDTY2.3. Foreground selection was carried out using peak markers RM511 and RM250, associated with qDTY12.1 and qDTY2.3, respectively, followed by recombinant selection with RM28099 and RM1261 distally flanking qDTY12.1. Furthermore, BC1F2-derived introgressed lines and their parents were evaluated under DS and non-stress (NS) conditions during the 2015-2016 dry season. Overall reduction of grain yield under DS compared to NS was recorded. Introgressed lines with qDTY12.1 and qDTY2.3 combinations showed higher yield potential compared to lines with single or no QTL under DS, indicating significant positive interactions between the two QTLs under the FUNAABOR-2 genetic background. Pyramiding of qDTY12.1 and qDTY2.3 in the FUNAABOR-2 genetic background led to higher grain yield production under DS and NS.

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Identification of QTLs and Validation of qCd-2 Associated with Grain Cadmium Concentrations in Rice Wenqiang Liu, Xiaowu Pan, Yongchao Li, Yonghong Duan, Jun Min, Sanxiong Liu, Licheng Liu, Xinnian Sheng, Xiaoxiang Li 2019, 26(1): 42-49.  DOI: 10.1016/j.rsci.2018.12.003 Abstract ( )   HTML ( )   PDF (1294KB) ( )   Cadmium (Cd) is one of heavy metals harmful to human health. As rice is the main staple food in Asia and Cd is easily contaminated in rice, the molecular regulation of Cd accumulation should be explored. In this study, a recombinant inbred population derived from Xiang 743/Katy was grown in Cd-polluted fields and used to map the quantitative trait loci (QTLs) for Cd accumulation in rice grains. We identified seven QTLs distributed on chromosomes 2, 3, 6, 7, 8 and 10. These QTLs displayed phenotypic variances of 58.50% and 40.59% in 2014 and 2015, respectively. Two QTLs, qCd-2 and qCd-7, were identified in both the two years. qCd-2 was detected on the interval of RM250-RM207 on chromosome 2, with an LOD of 2.51 and a phenotypic contribution of 13.75% in 2014, and an LOD of 3.35 and a phenotypic contribution of 14.16% in 2015. qCd-7 co-localized with the cloned qCdT7 on chromosome 7 and may represent the correct candidate. The other five QTLs were detected only in one year. To further confirm the effects of qCd-2, a residual heterozygous line designated as RHL945, with a heterozygous interval of RM263-RM207 on chromosome 2, was selected from the recombinant inbred population and used to develop an F2 population consisting of 155 individual plants. By incorporating further simple sequence repeat markers into the segmental linkage map of the target region, qCd-2 was delimited in the interval of RM5404-RM3774, with an LOD value of 4.38 and a phenotypic contribution of 15.52%. These results reflected the genetic regulation of grain Cd in rice and paved the way for the future cloning of qCd-2.

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Effects of Rice-Fish Co-culture on Oxygen Consumption in Intensive Aquaculture Pond Fengbo Li, Zhiping Sun, Hangying Qi, Xiyue Zhou, Chunchun Xu, Dianxin Wu, Fuping Fang, Jinfei Feng, Ning Zhang 2019, 26(1): 50-49.  DOI: 10.1016/j.rsci.2018.12.004 Abstract ( )   HTML ( )   PDF (1925KB) ( )   Rice-fish co-culture has gained increasing attention to remediate the negative environmental impacts induced by intensive aquaculture. However, the effect of rice-fish co-culture on oxygen depletion has rarely been investigated. We constructed a rice-fish co-culture system in yellow catfish (Pelteobagrus fulvidraco) and freshwater shrimp (Macrobrachium nipponense) ponds using a new high-stalk rice variety, and conducted a field experiment to investigate the effect of rice-fish co-culture on water parameters and oxygen consumption. The results showed that rice-fish co-culture reduced the nutrients (total nitrogen, ammonia-N, total phosphorous and potassium) and the dissolved oxygen content in fish and shrimp ponds. However, they showed similar seasonal change of dissolved oxygen in the water of fish and shrimp ponds. Rice-fish co-culture reduced the total amount of oxygen consumption and optimized the oxygen consumption structure in pond. The respiration rates in water and sediment were significantly reduced by 66.1% and 31.7% in the catfish pond, and 64.4% and 38.7% in the shrimp pond, respectively, by additional rice cultivation. Rice-fish co-culture decreased the proportions of respiration in sediment and water, and increased the proportion of fish respiration. These results suggest that rice-fish co-culture is an efficient way to reduce hypoxia in intensive culture pond.

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Infection and Colonization of Pathogenic Fungus Fusarium proliferatum in Rice Spikelet Rot Disease Lei Sun, Ling Wang, Lianmeng Liu, Yuxuan Hou, Yihua Xu, Mengqi Liang, Jian Gao, Qiqin Li, Shiwen Huang 2019, 26(1): 60-68.  DOI: 10.1016/j.rsci.2018.08.005 Abstract ( )   HTML ( )   PDF (895KB) ( )   Rice spikelet rot disease (RSRD), caused by Fusarium proliferatum, is an emerging disease. So far, the effects of diseased rice floral organs as well as the primary infection sites and stages of this pathogen are not determined. We investigated changes in the floral organs, along with the infection processes of the pathogen in plants inoculated with F. proliferatum and labelled with a green fluorescent protein during different growth stages of rice. The results showed that RSRD is not a systemic infectious disease, which has negative effects on the fertility of the infected rice. F. proliferatum caused brown colored anthers, crinkled pistils and ovaries, pollen grain deformities and anther indehiscence. The number of pollen grains on the stigmas decreased significantly in the infected spikelets, and the anther dehiscence and seed-setting rate successively declined by 69% and 73%, respectively, as a result of the infection. The initial infection stage occurred at the pollen cell maturity stage, and the primary invasion sites were determined to be the anthers of rice. It was noted that the pathogen mainly damaged the pollen cells, and with the exception of the filaments, proceeded to colonize the pistils and endosperm.