Polyploidy plays a key role in plant evolution and breeding, but the reproductive biology of polyploid rubber trees (Hevea brasiliensis) remains poorly understood. Here, we investigated microsporogenesis and pollen morphology in triploid and tetraploid rubber trees using acetic acid–magenta staining. Both polyploids displayed largely regular meiotic progression but exhibited abundant tetrad-stage abnormalities, including monads, dyads, triads, and unequal polyads. Tetraploids additionally exhibited chromosome misalignment, lagging chromosomes, asynchronous segregation, and multipolar spindles, with abnormal tetrads accounting for 24.52%. A total of more than 26,000 pollen grains (15,009 triploid and 11,774 tetraploid) were analyzed. In the triploid, 95.21% were normal-sized (30.7–43.3 µm), 2.21% were large (putative 2n; mean 47.2 µm), and 2.59% were super-large (putative 4n; mean 64.2 µm). In the tetraploid, 95.23% were normal-sized (31.7–46.7 µm), 4.75% were small (mean 19.6 µm), and only 0.025% were large (mean 55.3 µm). Normal-sized pollen from both polyploids was comparable to haploid pollen from diploids. Most large pollen grains exhibited wrinkled or irregular morphology, suggesting non-viability. Thus, functional male gametes in rubber tree polyploids are mostly reduced, and unreduced pollen is rare or nonviable. This study provides the first detailed description of the morphological sequence of microsporogenesis in triploid rubber tree and a cytological basis for understanding the low male fertility potential in breeding programs.

Polyploidization is a beneficial technique for enhancing the biomass of and secondary metabolite concentrations in plants. Java ginseng (Talinum paniculatum (Jacq.) Gaertn.) can be used as an alternative source of nutrition and has both ornamental and medicinal value. To improve the biomass and content of medicinal ingredients, this study established an in vitro system that was used to induce polyploidy of java ginseng. Tetraploids were successfully produced by exposing the axillary buds to colchicine. The most favorable medium for inducing polyploidy was Murashige and Skoog medium devoid of hormonal substances, while immersing stem segments in a solution of 1-3 mg/mL colchicine for 48 h could achieve tetraploidy induction with a maximum rate of 18.03%. Tetraploids were distinguished from diploids by flow cytometry, with the tetraploids exhibiting darker and thicker leaves, bigger fruit and pollen, and larger stomata but lower stomatal density, while the aboveground biomass yield was reduced significantly compared with that of the diploids. Tetraploidization also altered the metabolite profile, with 22 metabolite concentrations being significantly increased (p < 0.05) and 74 metabolite concentrations being significantly decreased (p < 0.05) in the leaves of the tetraploids. The autotetraploid produced in this study could provide novel insights into artificial polyploid breeding and could be utilized as a germplasm to generate new polyploids.

The rubber tree (Hevea brasiliensis) is an important species in global natural rubber production. However, the mechanisms regulating the height of rubber trees remain poorly understood. In previous work, the dwarf mutant MU73397 was obtained through ethyl methanesulfonate mutagenesis. Compared to the wild-type CATAS73397, MU73397 exhibited significantly reduced plant height and stem diameter, slower xylem development, and decreased cellulose and lignin content. Phytohormone analysis revealed that gibberellin levels were reduced in both the apex and stem of MU73397, while jasmonic acid was increased in the apex and auxin was reduced in the stem. These differences in hormone levels may contribute to the dwarf phenotype. Transcriptome analysis identified nine key genes related to cell wall biosynthesis and hormone signaling, namely, FLA11 (Fasciclin-like arabinogalactan protein 11), TUBB1 (Tubulin Beta 1), TUBB6 (Tubulin Beta 6), CESA7 (cellulose synthase A 7), TUBA4 (Tubulin Alpha 4), LAC17 (Laccase 7), CTL2 (Chitinase-like protein 2), IRX9 (Irregular xylem 9), and KOR (korrigan). Overexpression of HbFLA11 in transgenic poplar resulted in significant increases in plant height and stem diameter. Gibberellin signaling genes and cell wall biosynthesis genes were significantly upregulated in the transgenic lines. These results suggest that HbFLA11 is involved in gibberellin signaling and cell wall biosynthesis, thereby regulating plant growth. This study provides valuable genetic resources and research foundations for targeted trait breeding in rubber tree.

Rubber tree (Hevea brasiliensis) provides the sole commercial source of natural rubber, a crucial industrial raw material. Rubber yield and girth are widely considered as the most important agronomic traits of rubber tree. However, due to the delayed initiation of rubber tree research, the identification of quantitative trait loci (QTLs) and candidate genes for these traits remains limited. Here, QTL mapping analysis was conducted on the fullsibling progeny population derived from a cross between the clones of GT1 and CATAS8-79. Phenotypes of girth, dry rubber yield (DRY) and yield per centimeter girth (YCG) were measured annually for four consecutive years. Meanwhile, the resequencing of 238 offspring individuals identified 29,140,529 high-confidence SNPs, which resulted in the generation of 3147 non-redundant bin markers. Based on these bin markers, 18 highdensity linkage groups were constructed, with an average genetic distance ranging from 1.49 to 4.96 cM. Subsequently, a total of 37 environmentally stable QTLs were identified comprising 8 for girth, 16 for DRY, and 13 for YCG. These QTLs explained phenotypic variances spanning from 0.32 % to 17.71 %. The two most reliable QTLs, namely QGirth-4 and QGirth-7.2, were further investigated and 21 candidate genes were identified. Based on transcriptome sequencing and homologous annotation, a gibberellin receptor gene (GIBBERELLIN-INSENSITIVE DWARF1, GID1) was determined as the promising candidate for QGirth-7.2. Overexpression of HbGID1 led to early flowering and increased rosette-leaf branches in Arabidopsis, implying its significant role in girth development. These findings provide valuable insights into QTLs and target genes for enhancing growth and rubber yield traits, thereby contributing to molecular breeding of elite latex-timber rubber tree clones.

Unreduced megagametophytes via second-division restitution were confirmed through heterozygosity analysis, and four candidate physical centromeres of rubber were located for the first time. The evaluation of maternal heterozygosity restitution (MHR) is vital in identifying the mechanism of 2n gametogenesis and assessing the utilization value of 2n gametes. In this study, three full-sib triploid populations were employed to evaluate the MHR of 2n female gametes of rubber tree clone GT1 and to confirm their genetic derivation. The 2n female gametes of GT1 were derived from second-division restitution (SDR) and transmitted more than half of the parental heterozygosity. In addition, low recombination frequency markers were developed, and four candidate physical centromeres of rubber tree were located for the first time. The confirmation that 2n female gametes of rubber tree clone GT1 are derived from SDR provides insights into the molecular mechanisms of 2n gametogenesis. In addition, the identified centromere location will aid in the development of centromeric markers for the rapid identification of the 2n gametogenesis mechanism.

The expression levels of HbREF3 and HbSRPP1 positively correlate with dry rubber yield (DRY) and fresh latex yield (LY) in both F1 population at the juvenile stage and clonal population at the mature stage. Hevea tree is almost the sole commercial source of natural rubber, an indispensable industrial raw material. Conventional Hevea breeding is hampered by a long cycle of 25–30 years whereas the use of reliable yield-related molecular markers may efficiently shorten the breeding cycle. Here, carefully selected Hevea trees in an F1 population at juvenile stage and a clonal population at mature stage were exploited to identify the correlations between the expression levels of 26 latex regeneration-related genes and six yield-related latex physiological parameters. The correlations varied strikingly between the two populations or across the 2 years of experiment in the F1 population. Nevertheless, in both populations, the expressions of two rubber-biosynthesis pathway genes, HbREF3 and HbSRPP1, correlated positively with both dry rubber yield (DRY) and fresh latex yield (LY). Moreover, compared with the juvenile F1 population, the mature clonal population saw much more significant correlations for DRY and LY with the other latex parameters. In brief, our findings contribute to identifying reliable marker genes used in Hevea breeding for early selection.

Understanding the genetic basis of rubber tree ( Hevea brasiliensis ) domestication is crucial for further improving natural rubber production to meet its increasing demand worldwide. Here we provide a high-quality H. brasiliensis genome assembly (1.58 Gb, contig N50 of 11.21 megabases), present a map of genome variations by resequencing 335 accessions and reveal domestication-related molecular signals and a major domestication trait, the higher number of laticifer rings. We further show that HbPSK5 , encoding the small-peptide hormone phytosulfokine (PSK), is a key domestication gene and closely correlated with the major domestication trait. The transcriptional activation of HbPSK5 by myelocytomatosis (MYC) members links PSK signaling to jasmonates in regulating the laticifer differentiation in rubber tree. Heterologous overexpression of HbPSK5 in Russian dandelion ( Taraxacum kok-saghyz ) can increase rubber content by promoting laticifer formation. Our results provide an insight into target genes for improving rubber tree and accelerating the domestication of other rubber-producing plants.

为探讨橡胶树(Hevea brasiliensis)叶片特征与营养物质含量对六点始叶螨(Eotetranychus sexmaculatus)螨口密度的影响,分析了橡胶树叶片特征和营养物质与六点始叶螨的相关性,为橡胶树抗六点始叶螨品系选育提供理论基础.结果表明:六点始叶螨在 7 个橡胶树品系上的螨口密度(3.44±0.11)～(9.03±0.10)头/片;RRIM600 上的螨口密度最大,热研 87-6-62 上的最低,热研 87-6-47 次之.7 个品系的叶片特征(蜡质含量和叶片厚度)及营养物质(叶片含水率、脯氨酸、可溶性糖、游离氨基酸和抗坏血酸)含量结果显示:热研 87-6-62 的蜡质含量最高,PR107 的叶片厚度最厚,RRIM600 的叶片含水率最高,热研 87-6-62 的脯氨酸和可溶性糖含量最高,PR107 的游离氨基酸和抗坏血酸含量最高.螨口密度与叶片厚度、游离氨基酸含量、抗坏血酸含量和叶片含水率呈极显著正相关,与蜡质含量、脯氨酸含量、可溶性糖含量呈极显著负相关,说明橡胶树叶片特征和营养物质对六点始叶螨的生长发育有一定影响.

In order to objectively select new rubber tree clones suitable for China’s rubber planting environment, the yield and secondary characters of four introduced clones ’Reshi 09-5’ ’Reshi 09-6’ ’Reshi 09-7’ and ’Reshi 09-10’ were systematically identified and evaluated. The results showed that among the four clones, just ’Reshi 09-7’ showed fast-growing, not yet in yield. Only ’Reshi 09-5’ was close to the control in the first taping year and was lower in other years. The results of latex physiological characteristics showed that, according to good latex stability, fast latex discharge and high sugar utilization rate, ’Reshi 09-5’ showed good rubber production potential, had higher thiol content and lower sucrose content than that of ’RRIM600’, and there was no significant difference in dry rubber yield and initial speed of latex discharge between them. ’Reshi 09-6’ had higher dry rubber content and plugging index, thicker original bark and more latex tubes number than ’RRIM600’, and there was no significantly differences in initial flow rate and sucrose content between them. It was considered that the variety had good rubber production potential, but the metabolic intensity of latex was low. It had better potential in latex production, but a low metabolic intensity, so the production could be increased by stimulated tapping. The results of raw rubber properties, physical and mechanical properties, molecular weight and molecular weight distribution of vulcanizates of different varieties showed that there were some differences among the four clones. ’Reshi 09-5’ showed the lowest in plastic initial value and Mooney viscosity, but the highest plastic retention rate. ’Reshi 09-6’ showed the highest Mooney viscosity. According to larger weight-average molecular weight, ’Reshi 09-7’ showed good physical and mechanical properties. In terms of stress resistance performance, ’Reshi 09-5’ had the lowest wind damage collapse rate and ’Reshi 09-10’ had the highest. The results of cold-resistant outpost data showed that under the condition of no cold injury in the control clone ’93-114’, the cold injury grade of ’Reshi 09-5’ was 1.00, and that of ’Reshi 09-7’ was 0.17. The comprehensive analysis results showed that the fast-growing traits of the four introduced clones were obvious. ’Reshi 09-6’ had good rubber production potential.’Reshi 09-5’ had better wind resistance than ’RRIM600’, ’Reshi 09-7’ had good adaptability in cold damage. Among the four clones, ’Reshi 09-6’ showed better performance in yield, girth growth, latex physiological characteristics and latex quality, and suitable to popularize and cultivate in same condition.

Ultrahigh-density genetic mapping is used extensively for gene discovery, mapping quantitative trait loci (QTL), and assisting in crop breeding. However, genetic mapping of rubber trees (Hevea brasiliensis) has hitherto been limited in terms of both types and resolution. In this study, 214 F1 progenies derived from a cross of IAN 873 & nbsp;x REYAN 106 were genotyped via a whole-genome resequencing-based (WGRS) approach. From the 44,438,656 single nucleotide polymorphisms (SNPs) obtained from the genotyping, an ultrahigh-density genetic map was constructed using 203,124 SNPs, which included 2099.12 cM across eighteen linkage groups of the entire rubber tree genome. To the best of our knowledge, an ultrahigh-density genetic map of a rubber tree constructed via the WGRS approach has not yet been reported in literature. Two phenotypes associated with growth, namely, the girth at breast height (GBH) and tree height (TH), were investigated under a six-month interval. A total of six QTLs were found, in which qGBH11 and qGBH18 were detected repeatedly. Based on the physical positions of the bin markers that flank the QTLs, 47 genes identified within the qGBH11 locus, as well as the gene HB11G00752, were selected as the candidate genes that encodes ent-kaur-16-ene synthase (KS), regulating gibberellin biosynthesis. The search results for the KS gene family in the genome indicated that six out of ten KS family members were located in the qGBH11 allele. Expression analysis further shed light on the differential expressions of the KS family genes between F1 individuals having fast and slow growth. These results are expected to provide new insight into the genomic regions that control growth in rubber trees, and also facilitate the development of more effective approaches for breeding fast-growing timber latex clones.

六点始叶螨(Eotetranychus sexmaculatuss)作为橡胶树的重要害螨,对橡胶树的生长发育产生巨大危害,严重影响橡胶树产量.为进一步明确六点始叶螨在不同橡胶树无性系上的发育和繁殖情况,以及不同螨态对杀螨剂的敏感程度.本研究以'热研87-6-62'热研87-6-47'热研93-59'热研87-4-19'热研89-4-51'PR107'RRIM600'7个橡胶树无性系稳定期叶片作为六点始叶螨的寄主,分析了各螨态的形态特征、发育历期以及繁殖能力.同时,采用浸叶蝶法、叶片残毒法、玻璃浸渍法测定了4种杀虫剂对六点始叶螨各螨态的活性.结果显示,在(28±1)℃、RH(75±5)％、光照[16(L):8(D)]条件下,六点始叶螨在以上7个橡胶树无性系上各螨态发育时间从长到短为:成螨期>后若螨→成螨>前若螨→后若螨>卵→前若螨,六点始叶螨各螨态在'RRIM600'无性系上的发育历期最短,在'热研87-6-62'和'热研87-6-47'无性系上的发育历期相对较长;六点始叶螨在7个橡胶树无性系上的单雌产卵量由多到少依次为:'PR107'>'RRIM600'>'热研89-4-19'>'热研93-59'>'热研89-4-51'>'热研87-6-47'>'热研87-6-62',其中'PR107'上单雌产卵量最多,平均单雌产卵量为12.17个,'热研87-6-62'单雌产卵量最少,平均单雌产卵量为7.33个.筛选不同化学药剂对六点始叶螨进行防效试验,结果表明4种药剂在药后15 d的校正死亡率均在80％以上,其中15％哒螨灵乳油和1.8％阿维菌素·高效氯氰菊酯乳油的速效性较好,在施药3 d后死亡率可达80％以上.

以37个橡胶树栽培品种为材料,利用SSR荧光标记技术进行DNA指纹图谱的构建和遗传关系分析,构建我国橡胶树栽培品种的SSR指纹图谱.共计筛选和确定出34对SSR引物作为构建橡胶树品种DNA指纹图谱库的核心引物,其中30对SSR引物可用于品种鉴定,4对SSR引物可作为备选引物用于后续新选育品种的鉴定.筛选和确定出的核心SSR引物表现出较高的多态性信息含量(PIC值),其中PIC值高于0.5的引物高达97％,PIC值大于0.7的引物多达12对,PIC值大于0.8的引物有2对.引物rbm28的多态性最高,可作为最佳引物用于鉴定中国橡胶树主栽品系的遗传多样性,其他4条引物HESR025、HESR163、H-084、H-122同时具备较高的杂合率和多态性,可考虑作为备选引物.34对核心SSR引物在37个橡胶树品种中共检测到161个等位变异,平均每对引物检测到5.4个等位基因,平均PIC值为0.65,表现出高度多态性.利用30对核心SSR引物对37份橡胶树品种进行扩增,得到相关品种的准确SSR位点信息,获得包含37个橡胶树品种的标准DNA指纹图谱库,其中33个橡胶树品种均具有唯一的DNA特征指纹,可作为各品种特定的图谱,为橡胶树品种鉴定和育种实践提供依据.

Polyploidy is a potential way to breed new varieties with high yield and stress resistance in plants. In this study, we provided an efficient method for induction of tetraploid of Hevea brasiliensis by immerse somatic embryos in the liquid plant induction medium containing colchicine. The optimum concentration of colchicine is 5 mg/ml, and the optimum immersion time is 24–48 h. The highest average induction rate of tetraploid is 27.12% in Reyan73397 with 5 mg/ml colchicine for 48 h, and 38.89% in Reyan87662 with 5 mg/ml colchicine for 24 h. Finally, 82 tetraploids of Reyan73397 and 14 tetraploids of Reyan87662 were obtained. Compared to diploids, tetraploids exhibited less and lighter leaf veins, daker and thicker leaves, larger stomatal size and smaller stomatal density. These tetraploids have the potential to be used as parents to produce new triploid germplasms in Hevea brasiliensis breeding programs.

The mechanism of unreduced gametogenesis is of great significance for understanding and utilising 2n gametes in the breeding of new varieties. In this study, a cultivated rubber tree clone that can produce triploid progeny and unreduced pollen was found. The triploid frequency of the progeny was determined by flow cytometry. The cytological mechanisms of unreduced pollen production were revealed by microsporogenesis and pollen development observation. Ploidy detection of offspring showed that the frequency of triploid progeny was different in different regions and years, ranging from 0% to 13.64%. Cytological studies showed that tripolar spindles and nuclei fusion in meiosis II and cytokinesis failure after meiosis are the mechanisms of unreduced pollen production. The fraction of 2n pollen and 4n pollen producing male flower was 36% and 14%, respectively. The occurrence of 2n pollen and 4n pollen in single male flowers was 0.19% and 0.10%, respectively. The average diameter of n, 2n, and 4n pollen grains were 39.38 µm, 53.23 µm, and 66.59 µm, respectively. These results are the first to reveal the cytological mechanism of unreduced gametes production in Hevea brasiliensis and may have theoretical value for polyploidy breeding of rubber trees.

植物体细胞染色体数目减少是一种罕见现象.本研究以同一份橡胶树野生种质的四倍体和嵌合体为材料,通过流式细胞术分析嵌合体中四倍体细胞比例的位置效应,利用SSR分子标记分析四倍体和嵌合体的来源途径.结果表明,嵌合体植株四倍体细胞的比例在第一蓬叶处为80.50％,在第七蓬叶位置的比例为65.58％,嵌合体中四倍体细胞比例随着植株的生长而下降.18对引物在四倍体和嵌合体中扩增出的32条带完全一致,与嵌合体的二倍体砧木中的扩增结果有28条差异条带,表明嵌合体来源于四倍体体细胞的自然减倍.18个位点中1个位点的2个等位基因相对扩增产物量为3:1,表明该四倍体种质资源不是体细胞染色体加倍形成的同源四倍体,而是由2n卵细胞和2n花粉经有性多倍化途径形成的异源四倍体.本研究首次发现并证实了橡胶树异源四倍体体细胞减倍现象.

This study used SSR and AFLP markers to construct the genetic linkage map of Reyan5-11xPR107 population, integrated the published genetic linkage map and utilised the integrated map to perform QTL mapping of rubber yield-related traits. A genetic map consisting of 132 molecular markers (88 SSR and 44 AFLP markers) was constructed, and a joint map consisting of 143 molecular markers (99 SSR and 44 AFLP markers), which contained 19 linkage groups covering the rubber tree genome of 1298.5 cM, each linkage group containing 2-40 Mark, the average distance between the marks is 9.08 cM. Under the conditions of LOD >= 2.5, it was detected 2 QTLs related to girth, 3 QTLs related to dry rubber content, and 3 QTLs related to dry rubber yield per tree, 4 QTLs related to the unit secant length dry rubber yield, 5 QTLs related to the number of conducting phloem laticifer and 4 QTLs related to the number of yellow phloem laticifer.

为探明巴西橡胶树不同品种在叶片结构、光合生理方面的差异,以橡胶树热研106,热垦628等5个主栽品种幼苗为参试材料,观测其光合参数与叶片解剖特征,分析叶片结构对光合生理的影响.结果 表明:不同品种间叶片解剖结构、光合参数及光合色素之间均存在着显著差异,净光合速率与叶片厚度、栅栏组织厚度极显著相关,与叶绿素不显著相关.IAN873、PR107、RRIM600叶片较厚,栅栏组织发达,净光合速率与水分利用率较强,RRIM600的组织致密度与水分利用率均较高.橡胶树叶片厚度,栅栏组织的厚度等可作为筛选高光效基因型的重要参考指标.

[目的]分析6个国外引进橡胶树品种的产排胶特性,为丰富橡胶树产排胶理论和品种的扩大种植提供依据.[方法]以国外引进的6个橡胶树品种为研究对象,RRIM600为对照种,测定树皮次生乳管数量、刀次胶乳产量、干胶含量、排胶初速度及蔗糖、无机磷、镁离子和硫醇等参数指标.[结果]热试11-107平均株次干胶产量73.9 g,树皮次生乳管平均16.3列,蔗糖含量8.58 mmol/L,同时有较高的硫醇含量、排胶初速度和较低的堵塞指数;热试11-9平均株次干胶产量14.5 g,为所有品种中最低,蔗糖含量15.32 mmol/L,显著高于其他品种,硫醇含量和排胶初速度均显著低于其他品种;热试11-39各测定参数分析结果与热试11-9相近;热试11-1、热试11-2和热试11-3株次干胶产量与对照种相当,硫醇含量0.64～0.70 mmol/L,显著高于对照种,蔗糖含量4.37～5.17 mmol/L,显著低于对照种.[结论]热试11-107具有较好的产排胶特性,产胶潜力大;热试11-9和热试11-39胶乳再生不足;热试11-1、热试11-2和热试11-3胶乳稳定性良好,排胶顺畅,糖的利用效率高,但产胶潜力一般.

以3个橡胶树引进品种为研究对象,'热研73397'和'RRIM600'为对照,测定胶乳产量、干胶含量、排胶初速度及胶乳中蔗糖、无机磷、镁离子和硫醇等生理参数,比较分析不同品种的产排胶特性.结果 表明,各测定参数在品种间存在较大差异.'热试09-5'干胶产量高,蔗糖含量、排胶初速度低于'热研73397',干胶含量、硫醇含量、无机磷含量差异不显著,认为该品种产胶潜力大,胶乳稳定性好,排胶快,糖利用率高;'热试09-6'干胶产量一般,与'RRIM600'相比,干胶含量、堵塞指数高,排胶初速度和蔗糖含量差异不显著,认为该品种有较好的产胶潜力,但胶乳代谢强度低,可考虑通过刺激提高代谢强度,达到增产;'热试09-7'干胶产量低,与'RRIM600'相比,干胶含量高,排胶初速度低,蔗糖含量相当,认为该品种排胶障碍,糖的利用效率低,是否可以通过刺激割胶增加产量还需要进一步的试验验证.

倍性鉴定是橡胶树种质资源鉴定评价的基础工作之一.本研究利用流式细胞仪对国家橡胶树种质资源圃内的橡胶树种质资源进行全面的倍性鉴定,对嵌合体的四倍体细胞比例进行分析,并比较不同倍性的气孔性状差异.从5177份野生种质中发现三倍体11份,四倍体1份.从552份魏克汉种质中发现,三倍体9份,四倍体2份,嵌合体14份.14份嵌合体的四倍体细胞比例在49.06％～78.26％之间.不同倍性间的气孔长度、宽度和密度差异均极显著,气孔长度和宽度的排序为四倍体>三倍体>嵌合体,气孔密度的排序相反.研究结果对利用四倍体种质资源开展橡胶树倍性间杂交育种具有重要应用价值.