Life‐history traits and geographical divergence in wild rice (Oryza rufipogon) gene pool in Indochina Peninsula region

Indochina Peninsula is the primary centre of diversity of rice and lies partly in the centre of origin of cultivated rice (Oryza sativa) where the wild ancestor (Oryza rufipogon) is still abundant. The wild gene pool is potentially endangered by urbanisation and the expansion of agriculture, and by introgression hybridisation with locally cultivated rice varieties. To determine genetic diversity and structure of the wild rice of the region we genotyped nearly 1000 individuals using 20 microsatellite loci. We found ecological differentiation in 48 populations, distinguishable by their life‐history traits and the country of origin. Geographical divergence was suggested by isolation of the perennial Myanmar populations from those of Cambodia, Laos and Thailand. The annual types would be most likely to have lost genetic variation because of genetic drift and inbreeding. The growing of cultivated and wild rice together, however, gives ample opportunities for hybridisation, which already shows signs of genetic mixing, and will ultimately lead to replacement of the original wild rice gene pool. For conservation we suggest that wild rice should be conserved ex situ in order to prevent introgression from cultivated rice, along with in situ conservation in individual countries for the recurrent evolutionary process through local adaptation, but with sufficient isolation from cultivated rice fields to preserve genetic integrity of the wild populations.     

江永普通野生稻遗传多样性和籼粳基因频率监测分析

以栽培稻的8个籼-粳测验种为对照,采用39对SSR引物检测了江永野生稻居群在1982年、2008年、2017年的遗传多样性,采用38对In Del引物检测了江永野生稻居群在1982年、2008年、2017年的籼-粳基因频率。结果表明:在1982年取样保存在异位圃的40份样本的遗传多样性稍高于2008年、2017年原位保护区样本的遗传多样性;2008年取的样本数虽然比2017年多,但两次取的样本之间遗传多样性几乎没差异。不同年份取的样本之间的遗传分化系数Fst都很小,基因流Nm都较大,分化不明显。通过聚类分析和主坐标分析(PCo A),发现野生稻居群与4份栽培粳稻聚为一类,4份栽培籼稻单独聚成一类,显示江永野生稻与粳稻的血缘近于籼稻;籼-粳基因频率的分析表明,野生稻样本多属粳稻型,少数属偏粳稻型,原位保护区的偏粳稻类型单株数占取样单株总数的比例,2008年比1982年的增加了10.0%,2017年比2008年的增加了1.6%,显示江永野生稻原位保护区生境条件有利野生稻从粳稻型向偏粳稻型变异,随着野生稻产生环境适应性变异,籼型基因频率在提高。     

普通野生稻线粒体蛋白质编码基因密码子使用偏好性的分析

以普通野生稻(Oryza rufipogon Griff.)线粒体基因组为对象,分析其蛋白质编码基因的密码子使用特征及与亚洲栽培稻(O. sativa L.)的差异,探讨其密码子偏性形成的影响因素和进化过程。结果显示:普通野生稻线粒体基因组编码序列第1、第2和第3位碱基的GC含量依次为49.18%、42.67%和40.86%;有效密码子数(Nc)分布于45.32～61.00之间,其密码子偏性较弱; Nc值仅与GC_3呈显著相关,密码子第3位的碱基组成对密码子偏性影响较大;第1向量轴上显示9.91%的差异,其与GC_3s、Nc、密码子偏好指数(CBI)和最优密码子使用频率(Fop)的相关性均达到显著水平;而GC_3和GC₁₂的相关性未达到显著水平。因此,普通野生稻线粒体基因组密码子的使用偏性主要受自然选择压力影响而形成。本研究确定了21个普通野生稻线粒体基因组的最优密码子,大多以A或T结尾,与叶绿体密码子具有趋同进化,但是与核基因组具有不同的偏好性。同义密码子相对使用度(RSCU)、PR2偏倚分析和中性绘图分析显示,普通野生稻线粒体基因功能和其密码子使用密切相关,且线粒体密码子使用在普通野生稻、粳稻(O. sativa L. subsp. japonica Kato)和籼稻(O. sativa L. subsp.indica Kato)内具有同质性。     

Fitness estimation through performance comparison of F1 hybrids with their parental species Oryza rufipogon and O. sativa

BACKGROUND AND AIMS: Introgression of crop genes into populations of wild relatives has important implications for germplasm conservation as well as for the persistence of novel transgenes in wild populations. Studies of hybrid fitness can be used to evaluate the potential for introgression to occur following episodes of interspecific hybridization. METHODS: This study estimated relative fitness of interspecific hybrids through performance comparison of F(1) hybrids with their parental species, a cultivated rice (Oryza sativa) Minghui-63 and perennial common wild rice (O. rufipogon) under the cultivation conditions. KEY RESULTS: Compared with their parents, the hybrids had the lowest values of seedling survival ability, pollen viability and seed production; intermediate values of seed germination, spikelet production and flag leaf areas; and the highest values of plant height, number of tillers and panicles. The hybrids performed poorly at the stage of sexual reproduction, although they had a slightly higher hybrid vigour at the vegetative growth stage and better tillering ability than their wild parent. There were no significant differences in composite fitness across the whole life-history between the hybrids and their wild parental species. CONCLUSIONS: Rice genes, including transgenes, might persist in wild rice populations through vegetative and sexual reproduction. Further studies are needed to examine whether the extent of gene flow from rice is sufficiently significant to influence genetic diversity in wild populations of O. rufipogon, a species that has become endangered in some regions of south-east Asia.     

Patterns of Allozyme Variation at Two Stages of the Life History in Wild Rice <Emphasis Type="Italic">Oryza rufipogon</Emphasis> and Conservation Genetic Implications

Oryza rufipogon Griff. occurs widely in aquatic ecosystem of tropics and subtropics of monsoon Asia as well as Southern China. It is a vital gene source for rice breeding programs. Many populations of the species, unfortunately, have drastically diminished because of the disappearance of aquatic habitats as a result of human disturbance. In order to determine patterns of genetic variation at two stages of the life-cycle in the wild rice species, we investigated allozyme variation of four natural populations in China. Two southern populations have significant asexual reproduction while two other northern marginal populations show a mixed reproduction in China. At 22 allozyme loci, a significantly lower genetic diversity was observed in the ratoons than in the seeds of the two southern populations, whereas a significantly higher genetic diversity was found in the ratoons than in the seeds of the two northern marginal populations. The results suggest that the variation of reproductive system is probably associated with their patterns of genetic variation in the species. Moreover, a significantly higher genetic differentiation among populations found in the ratoons than in the seeds may stem from pollen-mediated gene flow among them. Finally, we propose suggestions for conservation management of the endangered species.     

海南普通野生稻稻瘟病的抗性鉴定与评价

在苗期应用自然诱发鉴定法对海南普通野生稻(Oryza rufipogonGriff.)41个居群的410份材料进行了2年的稻瘟病(rice blast)抗性鉴定,结果表明:经过初鉴和复鉴,410份海南普通野生稻中有21份表现高抗,占5.1%,117份表现抗,占28.5%,说明海南普通野生稻具有较好的稻瘟病抗性。     

Genetic diversity and origin of weedy rice (Oryza sativa f. spontanea) populations found in North-eastern China revealed by simple sequence repeat (SSR) markers

BACKGROUND AND AIMS: Weedy rice (Oryza sativa f. spontanea) is one of the most notorious weeds occurring in rice-planting areas worldwide. The objectives of this study are to determine the genetic diversity and differentiation of weedy rice populations from Liaoning Province in North-eastern China and to explore the possible origin of these weedy populations by comparing their genetic relationships with rice varieties (O. sativa) and wild rice (O. rufipogon) from different sources. METHODS: Simple sequence repeat (SSR) markers were used to estimate the genetic diversity of 30 weedy rice populations from Liaoning, each containing about 30 individuals, selected rice varieties and wild O. rufipogon. Genetic differentiation and the relationships of weedy rice populations were analysed using cluster analysis (UPGMA) and principle component analysis (PCA). KEY RESULTS: The overall genetic diversity of weedy rice populations from Liaoning was relatively high (H(e) = 0.313, I = 0.572), with about 35 % of the genetic variation found among regions. The Liaoning weedy rice populations were closely related to rice varieties from Liaoning and japonica varieties from other regions but distantly related to indica rice varieties and wild O. rufipogon. CONCLUSIONS: Weedy rice populations from Liaoning are considerably variable genetically and most probably originated from Liaoning rice varieties by mutation and intervarietal hybrids. Recent changes in farming practices and cultivation methods along with less weed management may have promoted the re-emergence and divergence of weedy rice in North-eastern China.     

云南野生稻叶茎根组织结构特性的比较研究

采用徒手切片法对云南3种野生稻和栽培稻的叶片、茎秆及根的组织结构进行比较研究,以明确野生稻的内部结构,为进一步揭示其结构与云南野生稻的生长势旺盛、营养吸收能力强、抗某些病虫害能力强的关系奠定基础。结果表明,(1)云南野生稻与栽培稻叶片主脉、茎秆及根的组织结构差异显著,其中景洪疣粒野生稻、景洪药用野生稻与栽培稻的差异最明显。(2)在叶主脉结构中,景洪疣粒野生稻无气腔结构,维管束数量少、面积小;景洪药用野生稻、3个普通野生稻材料存在多个维管束和气腔结构,维管束、束内导管直径及气腔面积较栽培稻大,而栽培稻中的气腔均为2个。(3)在茎秆结构方面,景洪疣粒野生稻茎秆最小,维管束数量最少,其茎壁内的维管束排列方式与栽培稻不同;景洪药用野生稻和普通野生稻茎秆及茎壁较栽培稻粗厚,维管束数量也较栽培稻多,普通野生稻的茎壁中有通气组织。(4)在根的组织结构中,3种野生稻的导管数量较多,导管直径及中柱面积较栽培稻大,外皮层出现了具有凯氏带功能的凯氏点等。     

东乡野生稻耐冷渐渗系的细胞学观察及SSR分析

以前期鉴定筛选的2个东乡野生稻强耐冷渐渗系(IL5243和IL5335)为试材,研究其减数分裂时期的染色体行为特征及外源基因的渗入分子证据。结果表明:(1)IL5243和IL5335中正常减数分裂的花粉母细胞分别达89.93%和90.22%,最终形成正常的成熟花粉粒,花粉离体萌发率分别为(83.03±2.82)%和(81.96±1.73)%,与受体亲本无显著性差异。(2)在减数分裂I中,2个耐冷渐渗系均观察到低频率异常染色体行为,如单价体、"8"字型二价体、多价体,以及后期I有少数花粉母细胞(3.95%～5.15%)存在落后染色体等,表明其染色体组之间发生了交换和重组;在粗线期,2个强耐冷渐渗系均观察到较高频率(IL5243和IL5335分别为27.0%和38.9%)的双核仁,而其双亲都是单核仁。(3)SSR标记和Structure分析进一步证实了栽培稻和野生稻染色体组间发生了交换重组,东乡野生稻部分DNA片段已渗入到强耐冷渐渗系中,这为水稻耐冷基因的挖掘与利用奠定了重要基础。     

栽培稻与其野生近缘种的可交配性研究

通过人工授粉方法研究栽培稻与二倍体和四倍体野生稻之间的可交配性.以栽培稻为对照,用光学显微镜观察不同野生稻花粉在同一栽培种柱头上的萌发生长情况.结果表明,在栽培稻柱头上普通野生稻(AA)花粉萌发最好,与对照萌发情况相近.药用野生稻(CC)萌发差,表现为柱头上花粉附着量少,开始萌发时间迟,萌发量少,花粉管扭曲、缠绕、伸长慢等.四倍体野生稻未观察到有萌发现象.说明普通野生稻与栽培稻亲缘关系近,可交配性好;药用野生稻与栽培稻可交配性差;四倍体野生稻与栽培稻可交配性极差.由此推断,转基因水稻与普通野生稻通过花粉途径发生基因漂移的可能性很大,而与药用野生稻和其他基因组野生稻发生基因漂移的可能性很小.