四霉素对茶藨子葡萄座腔菌Botryosphaeria ribis室内毒力测定及其田间防效试验

为确定四霉素对杨树溃疡病的防治效果,采用菌丝生长速率法测定四霉素水剂对茶藨子葡萄座腔菌Botryosphaeria ribis的室内毒力,采用刮治喷涂法对茶藨子葡萄座腔菌引起的杨树溃疡病进行田间应用效果研究。试验结果表明,四霉素对茶藨子葡萄座腔菌的EC_(50)和EC_(90)分别为114.82 a.i.mg/L、389.05 a.i.mg/L,对茶藨子葡萄座腔菌具有较好的抑菌效果,优于对照药剂多抗霉素。田间防效试验结果表明,刮治喷涂0.3%四霉素水剂可以有效防治真菌病原茶藨子葡萄座腔菌导致的杨树溃疡病,其有效成分浓度为60～150 a.i.mg/L时,田间防效达68.25%～82.41%,与室内毒力测定结果相符。     

Learning from methylomes: epigenomic correlates of Populus balsamifera traits based on deep learning models of natural DNA methylation

Epigenomes have remarkable potential for the estimation of plant traits. This study tested the hypothesis that natural variation in DNA methylation can be used to estimate industrially important traits in a genetically diverse population of Populus balsamifera L. (balsam poplar) trees grown at two common garden sites. Statistical learning experiments enabled by deep learning models revealed that plant traits in novel genotypes can be modelled transparently using small numbers of methylated DNA predictors. Using this approach, tissue type, a nonheritable attribute, from which DNA methylomes were derived was assigned, and provenance, a purely heritable trait and an element of population structure, was determined. Significant proportions of phenotypic variance in quantitative wood traits, including total biomass (57.5%), wood density (40.9%), soluble lignin (25.3%) and cell wall carbohydrate (mannose: 44.8%) contents, were also explained from natural variation in DNA methylation. Modelling plant traits using DNA methylation can capture tissue‐specific epigenetic mechanisms underlying plant phenotypes in natural environments. DNA methylation‐based models offer new insight into natural epigenetic influence on plants and can be used as a strategy to validate the identity, provenance or quality of agroforestry products.     

Biotechnological mechanism for improving plant remobilization of phosphorus during leaf senescence

Phosphorus enrichment of aquatic ecosystems through diffuse source pollution is an ongoing issue worldwide. A potential solution lies in the use of fast‐growing, multipurpose feedstocks, such as trees, to limit the flow of phosphorus into riparian areas through luxury consumption. However, the perennial nature of trees and their use of leaves as storage organs for excess phosphorus may reduce the effectiveness of contaminant removal during periods of leaf abscission. In an attempt to improve phosphorus remobilization during autumnal senescence, transgenic hybrid poplar P39 (Populus alba × Populus grandidentata) and Arabidopsis thaliana harbouring a constitutively expressed low‐affinity potato phosphate transporter (35S::StPht1‐1) were generated using Agrobacterium‐mediated transformation. For both species, the highest expressing 35S::StPht1‐1 lines were grown alongside wild‐type plants and subjected to increasing phosphate applications. StPht1‐1 expression in A. thaliana led to a reduction in biomass when grown under high‐phosphate conditions and had no effect on phosphate remobilization during senescence. In contrast, StPht1‐1 constitutive expression in P39 resulted in increased leaf phosphate content in the highest expressing transgenic line and minimal to no effect on P resorption efficiency. Surprisingly, sulphate resorption showed the greatest improvement in all three transgenic poplar lines, displaying a 31%–37% increase in resorption efficiency. These results highlight the complexity of nutrient resorption mechanisms in plants.     

Divergence of 3′ ends as a driver of short interspersed nuclear element (SINE) evolution in the Salicaceae

Short interspersed nuclear elements (SINEs) are small, non‐autonomous and heterogeneous retrotransposons that are widespread in plants. To explore the amplification dynamics and evolutionary history of SINE populations in representative deciduous tree species, we analyzed the genomes of the six following Salicaceae species: Populus deltoides, Populus euphratica, Populus tremula, Populus tremuloides, Populus trichocarpa, and Salix purpurea. We identified 11 Salicaceae SINE families (SaliS‐I to SaliS‐XI), comprising 27 077 full‐length copies. Most of these families harbor segmental similarities, providing evidence for SINE emergence by reshuffling or heterodimerization. We observed two SINE groups, differing in phylogenetic distribution pattern, similarity and 3′ end structure. These groups probably emerged during the ‘salicoid duplication’ (~65 million years ago) in the Salix–Populus progenitor and during the separation of the genus Salix (45–65 million years ago), respectively. In contrast to conserved 5′ start motifs across species and SINE families, the 3′ ends are highly variable in sequence and length. This extraordinary 3′‐end variability results from mutations in the poly(A) tail, which were fixed by subsequent amplificational bursts. We show that the dissemination of newly evolved 3′ ends is accomplished by a displacement of older motifs, leading to various 3′‐end subpopulations within the SaliS families.     

A physical map of the highly heterozygous Populus genome: integration with the genome sequence and genetic map and analysis of haplotype variation

As part of a larger project to sequence the Populus genome and generate genomic resources for this emerging model tree, we constructed a physical map of the Populus genome, representing one of the few such maps of an undomesticated, highly heterozygous plant species. The physical map, consisting of 2802 contigs, was constructed from fingerprinted bacterial artificial chromosome (BAC) clones. The map represents approximately 9.4-fold coverage of the Populus genome, which has been estimated from the genome sequence assembly to be 485 ± 10 Mb in size. BAC ends were sequenced to assist long-range assembly of whole-genome shotgun sequence scaffolds and to anchor the physical map to the genome sequence. Simple sequence repeat-based markers were derived from the end sequences and used to initiate integration of the BAC and genetic maps. A total of 2411 physical map contigs, representing 97% of all clones assigned to contigs, were aligned to the sequence assembly (JGI Populus trichocarpa , version 1.0). These alignments represent a total coverage of 384 Mb (79%) of the entire poplar sequence assembly and 295 Mb (96%) of linkage group sequence assemblies. A striking result of the physical map contig alignments to the sequence assembly was the co-localization of multiple contigs across numerous regions of the 19 linkage groups. Targeted sequencing of BAC clones and genetic analysis in a small number of representative regions showed that these co-aligning contigs represent distinct haplotypes in the heterozygous individual sequenced, and revealed the nature of these haplotype sequence differences.     

杨树无性系PV曲线水分参数的研究

采用PV技术对8个杨树无性系(3、6、7、8、9、10、11、12号)的水分参数ψstlp、ψssat、RWCtlp、ROWCtlp、AWC、ξmax和b值等进行了研究,并采用抗旱性指数(DI)和模糊数学反隶属函数两种方法对各个无性系的抗旱性进行了综合评价.结果显示:8个无性系的ψstlp、ψssat、ROWCtlp、ξmax、b值不同,抗旱性也存在一定的差异.其中,11、7和8号维持膨压和渗透调节的能力比其余无性系强;11号具有很强的保持最大膨压和维持低水势的能力;7~9号无性系具有较强的忍耐水分胁迫和抗脱水的能力;3和6号细胞弹性最大,主要依靠其坚硬厚实的细胞保持体内的水分.结果表明,8个无性系分为3个类群:第一类群为无性系7、8、9、11、12号,抗旱性最强;第二类群为无性系10号,抗旱性居中;第三类群为无性系3号和6号,抗旱性最弱.     

白杨派树种雌蕊柱头可授性及其检测方法的研究

以银腺杨、毛新杨和银毛杨为材料,采用定期授粉观察以及联苯胺-过氧化氢染色等方法,对白杨派树种雌蕊柱头可授性进行了研究,结果表明:在温室水培条件下,白杨树种雌蕊柱头的可授期一般在1~3 d内,其中毛新杨雌蕊柱头可授期比银腺杨和银毛杨相对短些.但3个树种进入最佳授粉时期时的柱头开裂角度约为180°,此时柱头发亮且表面有大量分泌物存在;在适宜授粉时期内,用联苯胺-过氧化氢染色后柱头变蓝,并有气泡产生。在育种实践中,可根据柱头形态以及联苯胺-过氧化氢染色后柱头颜色变化和气泡产生情况及时判别有关白杨派树种最佳授粉时期。     

Age‐mediation of tree‐growth responses to experimental warming in the northeastern Tibetan Plateau

The trajectory of tree‐growth response to climate warming may be related to attributes like tree age. However, age‐mediation of temperature sensitivity of tree growth has received little attention. This study aimed to determine how age affects tree growth in a future warmer world. In a 2‐year ecosystem warming experiment in the northeastern Tibetan Plateau of China, we explored the response of Qinghai spruce saplings at two life stages to two warming levels. Our results indicated a significant interaction between warming and age for sapling growth of Qinghai spruce. In high‐level warming scenario, the experiment increased growing season air temperatures by approximately 1.0°C and annual growing degree‐days by 38%. In response, warmed saplings lengthened the growing season by 10 days on average and increased the final shoot length to a maximum of 104% compared to control groups. Comparison of age classes revealed that old saplings exhibited significantly higher temperature sensitivity than young saplings. This performance may be caused by the differences in adaptive strategy to the asymmetric warming occurring during the whole day. Increased daytime temperature was expected to significantly enhance leaf photosynthesis, whereas lack of obvious nighttime warming would effectively restrict autotrophic respiration, thus resulting in the higher growth rate of old saplings compared with young saplings. Moreover, lack of nighttime warming rendered young saplings to be still in high stresses of freezing injury at low temperatures. These findings highlight the need for additional research on the effects of further climate anomalies on tree species during their ontogenetic processes.     

Phytoextraction Potential of Poplar (Populus alba L. var. pyramidalis Bunge) from Calcareous Agricultural Soils Contaminated by Cadmium

To investigate the phytoextraction potential of Populus alba L. var. pyramidalis Bunge for cadmium (Cd) contaminated calcareous soils, a concentration gradient experiment and a field sampling experiment (involving poplars of different ages) were conducted. The translocation factors for all experiments and treatments were greater than 1. The bioconcentration factor decreased from 2.37 to 0.25 with increasing soil Cd concentration in the concentration gradient experiment and generally decreased with stand age under field conditions. The Cd concentrations in P. pyramidalis organs decreased in the order of leaves > stems > roots. The shoot biomass production in the concentration gradient experiment was not significantly reduced with soil Cd concentrations up to or slightly over 50 mg kg^–1. The results show that the phytoextraction efficiency of P. pyramidalis depends on both the soil Cd concentration and the tree age. Populus pyramidalis is most suitable for remediation of slightly Cd contaminated calcareous soils through the combined harvest of stems and leaves under actual field conditions.