Reduced effective population size in an overexploited population of the Nile crocodile (Crocodylus niloticus)

Unchecked exploitation of wildlife resources is one of the major factors influencing species persistence throughout the world today. A significant consequence of exploitation is the increasing rate at which genetic diversity is lost as populations decline. Recent studies suggest that life history traits affecting population growth, particularly in long-lived species, may act to moderate the impact of population decline on genetic variation and lead to remnant populations that appear genetically diverse despite having passed through substantial demographic bottlenecks. In this study we show that the retention of genetic variation in a partially recovered population of Nile crocodile is deceptive, as it masks the reality of a significant decline in the population’s effective size (N_e). Repeated episodes of unchecked hunting in the mid to late 20th century have today led to a five-fold decrease in the population’s N_e. Using current census data we estimate the contemporary N_e/N ratio as 0.05 and, in light of quotas that permit the ongoing removal of adults, simulated the likely effects of genetic drift on extant levels of variation. Results indicate that even if the current effective size is maintained, both allelic diversity and heterozygosity will decline. Our findings have complex implications for long-lived species; an emphasis on the retention of genetic variation alone, whilst disregarding the effects of population decline on effective size, may ultimately obscure the continued decline and extinction of exploited populations.     

三峡库区天然次生林凋落物森林水文效应研究

对三峡库区上游四面山4种天然次生林凋落物储量、分解强度及持水力进行了研究.结果表明,4种林分凋落物储量最大的是天然阔叶林(107.09 t/hm2),天然针阔混交林(70.18 t/hm2)和天然针叶林(66.65 t/hm2)次之,楠竹林(35.37 t/hm2)最小;凋落物最大持水量和持水力均呈现出天然针阔混交林(89.95 t/hm2,2.25)最大,天然阔叶林(67.33 t/hm2,1.89)次之,而天然针叶林(39.83 t/hm2,1.66)和楠竹林(28.07 t/hm2,1.85)较差的趋势.因此,从凋落物持水特征来分析,4种天然次生林中,天然针阔混交林的森林水文效应最好,其次是天然阔叶林,而楠竹林和天然针叶林均较差,不适宜在该区域内的水土保持植被建设中应用.     

种子大小对冬小麦苗势及其幼穗发育的影响

以中大粒品种郑引1号为试验材料,研究了不同粒重种子对幼苗长势及幼穗发育的影响.结果表明,大粒种子出苗迟,生长发育快,叶片分化持续时间短,幼苗长势壮;大粒种子的幼穗发育开始早,分化强度大,形成小穗数多.茎生叶分化总数不因粒重不同而发生变化.     

Identification of molecular markers associated with sugar-related traits in a <Emphasis Type="Italic">Saccharum</Emphasis> interspecific cross

The cultivated sugarcane (Saccharum spp. hybrids, 2n = 100–130) is one crop for which interspecific hybridization involving wild germplasm has provided a major breakthrough in its improvement. Few clones were used in the initial hybridization event leading to a narrow genetic base for continued cultivar development. Molecular breeding would facilitate the identification and introgression of novel alleles/genes from the wild germplasm into cultivated sugarcane. We report the identification of molecular markers associated with sugar-related traits using an F₁ population derived from a cross between S. officinarum ‘Louisiana Striped’ × S. spontaneum ‘SES 147B’, the two major progenitor species of cultivated sugarcane. Genetic linkage maps of the S. officinarum and S. spontaneum parents were produced using the AFLP, SRAP and TRAP molecular marker techniques. The mapping population was evaluated for sugar-related traits namely, Brix (B) and pol (P) at the early (E) and late (L) plant growing season in the plant cane (04) and first ratoon (05) crops (04EB, 04LB, 04LP, 05EB and 05EP). For S. officinarum, combined across all the traits, a total of 30 putative QTLs was observed with LOD scores ranging from 2.51 to 7.48. The phenotypic variation (adj. R²) explained by all QTLs per trait ranged from 22.1% (04LP) to 48.4% (04EB). For S. spontaneum, a total of 11 putative QTLs was observed with LOD scores ranging from 2.62 to 4.70 and adj. R² ranging from 9.3% (04LP) to 43.0% (04LB). Nine digenic interactions (iQTL) were observed in S. officinarum whereas only three were observed in S. spontaneum. About half of the QTLs contributed by both progenitor species were associated with effects on the trait that was contrary to expectations based on the phenotype of the parent contributing the allele. Quantitative trait loci and their associated effects were consistent across crop-years and growing seasons with very few QTLs being unique to the early season. When the data were reanalyzed using the non-parametric discriminant analysis (DA) approach, significant marker-trait associations were detected for markers that were either identical to or in the vicinity of markers previously identified using the traditional QTL approach. Discriminant analysis also pointed to previously unidentified markers some of which remained unlinked on the map. These preliminary results suggest that DA could be used as a complementary approach to traditional QTL analysis in a crop like sugarcane for which saturated linkage maps are unavailable or difficult to obtain.     

小麦籽粒产量及穗部相关性状的QTL定位

由小麦品种花培3号和豫麦57杂交获得DH群体168个株系,种植于3个环境中,利用305个SSR标记对籽粒产量和穗部相关性状(穗长、穗粒数、总小穗数、可育小穗数、小穗着生密度、千粒重和粒径)进行了QTL定位。利用基于混合线性模型的QTLNetwork 2.0软件,共检测到27个加性效应和13对上位效应位点,其中 8个加性效应位点具有环境互作效应。相关性高的性状间有一些共同的QTL位点,表现出一因多效或紧密连锁效应。5D染色体区段Xwmc215–Xgdm63,检测到控制籽粒产量、穗粒数、总小穗数、可育小穗数和小穗着生密度5个性状的QTL位点,各位点的遗传贡献率较大且遗传效应方向相同,增效等位基因均来源于豫麦57,适用于分子标记辅助育种和聚合育种。控制千粒重与穗粒数的QTL位于染色体不同区段,有利于实现穗粒数与粒重的遗传重组。     

利用Mudgo/武育粳3号F2群体分析水稻抗灰飞虱QTL

灰飞虱是我国水稻生产上的重要害虫。Mudgo是一个高抗灰飞虱的籼稻品种,对灰飞虱具有强的排驱性和抗生性抗性。利用Mudgo/武育粳3号F₂群体,构建了含有177个单株的F₂群体的遗传连锁图谱。该连锁图包含104个SSR标记和3个Indel标记,覆盖整个水稻基因组1 409.9 cM,每两个标记之间的平均距离为13.2 cM。采用改进的苗期集团筛选法对177个F_2:3家系进行了抗性鉴定,通过Windows QTL Cartographer 2.5进行复合区间作图分析,在第2、3、12染色体上分别检测到抗灰飞虱QTL Qsbph2b、Qsbph3d和Qsbph12a,分别位于标记RM5791~RM29、RM3199~RM5442和I12-17~RM333 1之间,单个LOD值分别为3.25、3.11和6.82,贡献率分别为17.3%、15.6%和35.8%,各QTL增强抗性的等位基因效应均来自Mudgo。其中Qsbph12a与标记RM3331和I12-17紧密连锁。结合表型鉴定的结果,Qsbph12a应为抗灰飞虱主效QTL,与该位点紧密连锁的标记可用于抗灰飞虱快速选择辅助育种。     

基于GYT双标图对西北内陆棉区国审棉花品种的分类评价

西北内陆棉区是我国最重要的主产棉区,对该棉区历年国审棉花品种进行科学分类和综合评价有利于国审品种资源的合理利用和棉花生产效率的提升。本研究采用GYT双标图分析对2003—2019年期间西北内陆棉区37个国审棉花品种的产量与霜前花率、纤维长度、比强度、马克隆值、枯萎病指数和黄萎病指数等性状的组合水平进行了综合分析和品种分类评价。结果表明,西北内陆棉区37个国审棉花品种可划分为3个特征明显的品种类型。其中,I型品种包括新陆早13号、中棉所49、新陆早21号、巴13222、新46、天云0769、Z1112、新石K18、J206-5、新石K21、禾棉A9-9、创棉508、H33-1-4、金科20、新K28、创棉512和J8031等17个品种,是产量与其余性状组合协调最好的品种类型,在生产上推广应用价值最高。II型品种产量和纤维品质表现一般,抗病性差,在当前生产上应用价值有限。III型品种的抗枯萎病性表现最好,但在其余性状上表现略差,综合生产应用价值有限,也许可作为抗病亲本应用。同时,根据各品种的理想指数筛选出创棉512、J8031、新K28、H33-1-4、金科20、新陆早13号和创棉508等综合表现优良的品种,也鉴别出新陆棉1号、新陆早33号、创棉501号和新陆早51号等综合表现相对略差的品种。本研究采用的GYT双标图分析方法是基于“产量-性状”组合水平对品种进行综合评价和分类研究,产量-性状组合之间的相关关系更加简单,多数组合间表现显著正相关,更适用于品种的多性状直观选择和综合评价,通常比先前的GT双标图解释的变异比率高,双标图模型拟合度更好,结果更可靠。本研究采用GYT双标图分析方法对西北内陆棉区国审品种的分类研究揭示了该棉区国审棉花品种的分类特征和应用价值,为本区的国家棉花品种试验审定提供了借鉴,也为其他作物品种的类似研究提供了范例。     

Development and evaluation of pyramiding lines carrying early or late heading QTLs in the indica rice cultivar ‘IR64’

The heading date is an important trait for determining regional and climatic adaptability in rice. To expand the adaptability of the indica rice cultivar ‘IR64’, we pyramided multiple early or late heading quantitative trait locus (QTLs) in the ‘IR64’ genetic background by crossing previously developed near-isogenic lines (NILs) with a single QTL for early or late heading. The effects of pyramiding QTLs were observed in three different climatic zones of the Philippines, Madagascar, and Japan. The early heading pyramiding lines (PYLs) headed 6.2 to 12.8 days earlier than ‘IR64’ while the late heading PYLs headed 18.8 to 27.1 days later than ‘IR64’. The PYLs tended to produce low grain yield compared to ‘IR64’. The low yield was not improved by combining SPIKE, which is a QTL that increases the number of spikelets per panicle. Conversely, ‘IR64-PYL(7+10)’ carrying Hd5 and Hd1 headed earlier, produced more tillers, and more panicles per m² than ‘IR64’, and mitigated the yield decrease in early heading. These results suggest that the effects of pyramided QTLs on heading date were consistent across various environments and PYLs could be used to enhance the adaptation of ‘IR64’ in other rice growing environments.     

利用SNP高密度遗传连锁图谱定位甘蓝型油菜种子硫苷含量的QTL

种子硫苷在甘蓝型油菜中有着重要的生物学作用和经济价值。本文旨在通过复合区间作图法利用高密度SNP遗传连锁图谱定位种子硫苷的QTL。用近红外扫描获得种子硫苷含量,每株系扫描3次,取平均值。所用的高密度SNP遗传图谱包含2795个SNP多态性标记位点,图谱总长1832.9 cM,相邻标记间平均距离为0.66 cM。定位了2年的种子硫苷含量QTL,其中有5个在2年内被重复检测到,分别分布在A03、A09和C02染色体上,LOD阈值在2.90~10.40之间。这些QTL在2011和2012年试验中分别解释了56.9%和55.1%的表型变异。另外有5个QTL仅在其中一年被检测到,这些QTL能够解释4.1%~7.9%的表型变异,QTL阈值在2.53~3.83之间。