Root Sprouts Research Articles

Resprouting Control of Ailanthus altissima by Means of Cut and Stump Covering: Experimental Evidence for a Promising Technique

Ailanthus altissima is an invasive tree threatening the biodiversity in natural and disturbed habitats of temperate regions, primarily because of its high resprouting vigor. To test the effect of light exclusion on stem and root sprouting, black covers were applied on the cut stumps of 3-year-old saplings grown in pots. The treatments were as follows: SL, stumps exposed to light; SH, only stumps covered; SPH, the entire pot covered; C, intact control plants. The covers were removed when the root sprouts appeared. The emergence of stem and root sprouts was checked weekly, and their number and biomass were determined at the growth peak (cut I and III) and the end (cut II and IV) of two seasons after cutting. Stem sprouts were produced only in the first growth season in SL and SH and never in SPH and the controls. The number and biomass of the root sprouts were the highest in SH at cut I and in SL in the following cuts. In SH, the sprouting ceased completely after cut I, suggesting a rapid consumption of root reserves, while in SL and SPH, repeated cutting progressively reduced the sprouting vigor. We concluded that covering the stems after cutting is a promising technique to control ailanthus resprouting without the use of herbicides.

Insights into the Root Sprouts of Toona fargesii in a Natural Forest: From the Morphology, Physiology, and Transcriptome Levels

Toona fargesii (T. fargesii) is a deciduous tree of the Meliaceae family which is utilized for high-value timber. Interestingly, root sprouting is a typical reproductive pattern in T. fargesii. Nevertheless, the genetics underlying this phenomenon are still unclear. Here, three type of roots of T. fargesii were used for histological observation, plant endogenous hormone determination, non-structural carbohydrate (NSC) determination, and sequencing using the Illumina next-generation and PacBio SMRT platforms. Our results indicated that root sprouts originated from cork cambiums. Furthermore, indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellic acid 3 (GA3), and abscisic acid (ABA) content was significantly increased, while soluble sugar content was significantly decreased in the root sprouts. In addition, transcriptomic analysis suggested a total of 36.19 G of raw data from which 210 differentially expressed genes (DEGs) of were identified in RS vs. SR. Of these, the candidate DEGs were largely enriched in the citrate cycle, gluconeogenesis, starch and sucrose metabolism, and plant hormone signal transduction pathways. We therefore speculated that the accumulation of cytokinin and auxin might be induced by ATP-binding cassette-B 19 (ABCB19) and ABCG14, which were necessary for root sprouting. Additionally, transcription factors SQUAMOSA promoter binding protein-like 18 (SPL18) and NAM, ATAF1/2, and CUC2-14 (NAC14) were found in response to environmental water and epigenetic modification in RS. Overall, this study was to unravel the physiological and transcriptomic levels of the development of root sprouting in T. fargesii.

Acroptilon repens (L.) DC. in the flora in the interfluve of the lower Dnister–Tiligul rivers

Primary field floristic studies of synanthropic species with a high invasive capacity are an important basis for broad, generalizing analyzes of the problems of flora transformation of ecotopes of different levels of anthropogenic transformation. Acroptilon repens is one of the species that has a high invasive capacity and is a quarantine plant on the territory of Ukraine. The aim of the work was to identify the localities of Acroptilon repens in the in the interfluve of the lower Dnister–Tiligul rivers, to characterize the conditions for the growth of plants of this species. Acroptilon repens is a herbaceous perennial plant, a xerophyte and a heliophyte; comes from Central and Asia Minor. It reproduces well both generatively and vegetatively (by root sprouts). According to the degree of naturalization, it is an epecophyte, according to the chronotype, it is a kenophyte. According to the method of spreading, the seeds are anemochorous. It is able to grow in areas with a wide range of environmental conditions and different levels of anthropogenic transformation (from natural to fully transformed). Preventive, agrotechnical, chemical, biological control measures are used to combat this species. Ecotopes with different levels of ecotope transformation were examined. According to herbarium materials of the herbarium (MSUD) of Odesa National University named after I.I. Mechnikov the species had not previously been noted in the Odesa region. The author found four localities of Acroptilon. Three of them are on transformed sections of transport routes: the village of Avangard, on the side of the Odesa — Reni Road and in the vicinity of S. Yehorivka. These are sections of highways and abandoned railway tracks. Another one is on a natural steppe slope. On the transformed areas, the participation of other plant species in the «spots» with steppe mustard is small: up to four species. In the natural area (in the vicinity of the village of Kholodna Balka), a total of 44 species coexisted with steppe mustard. Among them, only 23 (or 52.27%) species are synanthropic and only three (Bromus squarrosus, Descurainia sophia, Sisymbrium loeselii) are invasive species. They are mainly represented by a small number of specimens, but among them there are two species of local protection level: Kohlrauschia prolifera, Ephedra distachya. In the spring, in the «contour of the spot» with Acroptilon repens, the following plants of state protection level were found: Gymnospermium odessanum, Crocus reticulatus. These plants are ephemerals, and the terms of their growth and the beginning of vegetation of Acroptilon repens do not coincide.

Effects of Ethylene and 1-Methylcyclopropene on the Quality of Sweet Potato Roots during Storage: A Review

Sweet potato (Ipomoea batatas (L.) Lam.) is served as an important root crop worldwide due to its high yield, strong adaptability and nutrient richness. Sweet potato has played a significant role in ensuring food security and family income opportunities for local populations in China for years of experience. The storage roots, which provide abundant nutrition and health benefits to people, are the mainly harvested and consumed parts of sweet potato. However, after harvest, physiological disorders, such as sprouting, mechanical injury and infectious postharvest diseases, increase the magnitude of sweet potato root quality decline and nutritional compound losses. Ethylene and 1-methylcyclopropene (1-MCP) were considered to be effective commercial treatments in sweet potato postharvest. Exogenous ethylene and 1-MCP treatment could successfully inhibit root sprouts and reduce rot decay without affecting the storage quality of sweet potato. This review aims to summarize the latest available information on the effects of ethylene and 1-MCP with respect to enhancing or impairing sweet potato root quality. A better understanding of the influence of ethylene and 1-MCP on root quality parameters will be useful to further explore the role and mechanisms of action of ethylene in regulating the postharvest storage of sweet potato roots and contributions to technological development and innovation.

Fire reduces Russian olive seed germination and seedling survival with increasing fuel load

Elaeagnus angustifolia (Russian olive) is an invasive tree common within riparian areas in the western United States. Control methods can be expensive and regular monitoring is necessary to control stump and root sprouts, and newly established seedlings. Studies have assessed scarification and cold treatment effects on germination and establishment of Russian olive seeds. However, fire effects on seeds and newly emerged seedlings have not been documented. Russian olive seeds were subjected to fire at three fuel loads (1,500, 3,000, and 4,500 kg/ha) and a non‐burned control. With no fire, 40% of seeds germinated and fire at any of the three fuel loads reduced germination. Germination was reduced to one‐fifth of the non‐burned level with fire at the 1,500 kg/ha fuel load and did not differ from 0% at the 4,500 kg/ha−1 fuel load. The probability of at least one seed germinating from 50‐seed lots decreased as all measures of temperature and time–temperature increased. Fire killed all but one of the 250 seedlings tested, indicating Russian olive seedlings at 10 weeks old or younger were highly susceptible to fire‐induced mortality. However, some seedlings did not die immediately following fire and produced new axillary buds. Although all but one seedling died, bud production after fire was interpreted as an indicator of potential resistance to fire. Our results indicate that fire does not enhance Russian olive seed germination and is deleterious to seed viability. Fire could potentially kill most Russian olive seedlings that are less than 1 year old.

Spatial Distribution Pattern of Root Sprouts under the Canopy of Malus sieversii in a Typical River Valley on the Northern Slopes of the Tianshan Mountain

Malus sieversii is a precious wild fruit tree resource, and its sustainable reproduction is of great significance to the conservation of wild fruit tree germplasm resources and the stability of wild fruit forest ecosystems. In recent years, the natural population number and area of distribution of the Malus sieversii have been declining due to pests, water limitations, and human activities. Root sprouts are a primary means of rejuvenation of the Malus sieversii. A reasonable spatial distribution pattern is conducive to the growth of Malus sieversii plants and the ecological restoration of wild fruit forest populations. However, the spatial distribution pattern of root sprouts still needs to be discovered, which constrains our understanding of the mechanisms underlying the damage and management of Malus sieversii. Therefore, this paper examines the study area of the Gilgalang River Malus sieversii forest in Gongliu County, Ili Valley, Xinjiang. The topographic data and high-resolution images were first obtained using ultra-low-altitude photogrammetry and total station measurement techniques, then spatial pattern analysis and standard deviation ellipse analysis were used to investigate the spatial distribution pattern of root sprouts, and, finally, the factors affecting the spatial distribution pattern of root sprouts were investigated by principal component analysis and grey correlation analysis. The results show that: (1) Under-canopy Malus sieversii root sprouts are clustered and randomly distributed along the root system, with the degree of clustering decreasing with increasing distance; (2) Spatial orientation and distance from the maternal plant are the main factor affecting the sprouting of Malus sieversii roots, explaining 73.69% of the total variance; (3) Under sediment accumulation and water erosion, the root sprouts under the canopy are mainly distributed in the downslope direction. The shape is similar to the “clover type”. The results of this study can provide a theoretical basis for conserving Malus sieversii germplasm resources and a solid scientific basis for the ecological restoration of plants under anthropogenic disturbance.

The Value of Hybrid Aspen Coppice Investment under Different Discount Rate, Price and Management Scenarios: A Case Study of Estonia

Hybrid aspen is one of the most promising tree species for short-rotation forestry in Northern Europe. After the clearcutting of hybrid aspen plantation, the next generation arises from root and stump sprouts. The economic feasibility of different management strategies of hybrid aspen coppice stands has not yet been comprehensively evaluated in Northern Europe. We compared the land expectation values (LEVs) of hybrid aspen coppice stands managed according to four scenarios: three early thinning methods (corridor, cross-corridor and single-tree) followed by conventional management and intensive bioenergy production (repeated harvests in 5-year rotations) over a 25-year period in hemiboreal Estonia. We considered the historic price volatility of aspen wood assortments under various discount rates (1–20%). We found that the 25-year rotation with different early thinning methods was more profitable than short bioenergy cycles in the case of low discount rates (<5%). The LEV of short coppice cycles for only bioenergy production became more profitable in comparison with those by thinning methods, when higher discount rates (>10%) were applied. Hybrid aspen coppice stands can be managed profitably, but more risks are taken when the management strategy focuses only on bioenergy production.

Genome-wide high-resolution mapping of DNA methylation reveals epigenetic variation in the offspring of sexual and asexual propagation in Robinia pseudoacacia.

We detected the genome-wide pattern of DNA methylation and its association with gene expression in sexual and asexual progenies of mature Robinia pseudoacacia trees. DNA methylation plays an important role in plant reproduction and development. Although some studies on sexual reproduction have been carried out in model plants, little is known about the dynamic changes in DNA methylation and their effect on gene expression in sexual and asexual progeny of woody plants. Here, through whole-genome bisulfite sequencing, we revealed DNA methylation patterns in the sexual and asexual progenies of mature Robinia pseudoacacia to understand the regulation of gene expression by DNA methylation in juvenile seedlings. An average of 53% CG, 34% CHG and 5% CHH contexts was methylated in the leaves of mature and juvenile individuals. The CHH methylation level of asexually propagated seedlings was significantly lower than that of seed-derived seedlings and mature trees. The intergenic regions had the highest methylation level. Analysis of differentially methylated regions (DMRs) showed that most of them were hypermethylated and located in the gene upstream and introns. A total of 24, 108 and 162 differentially expressed genes containing DMRs were identified in root sprouts (RSs), root cuttings (RCs) and seed-derived seedlings (SSs), respectively, and a large proportion of them showed hypermethylation. In addition, DMRs were enriched within GO subcategories including catalytic activity, metabolic process and cellular process. The results reveal widespread DNA methylation changes between mature plants and their progenies through sexual/asexual reproduction, which provides novel insights into DNA methylation reprogramming and the regulation of gene expression in woody plants.

Clonal variation in coppiced and uncoppiced growth, root sprout stem formation, and biomass partitioning in Salix interior on two highly disturbed site types

Salix interior Rowlee (INT) is a wide-ranging North American willow from the small taxonomic group Salix section Longifoliae, notable for its ability to form multi-stemmed vegetative stem colonies arising via root sprouts (RS) from a shallow horizontal root network. This study quantifies biomass production for both 1-year-old coppiced plants and the original 4-year-old plants established from dormant, unrooted stem cuttings, as well as for the RS stems associated with each ortet (original mother plant) using eight selected INT clones established on two distinct site types. Significantly greater coppiced and uncoppiced ortet stem dry mass was recorded on coarse-textured, shale rock overburden (SO); possibly due to significantly greater fertility, compared to adjacent gravel outwash deposits (GD), which had greater RS stem mass. The total stem dry mass (ortet + associated RS) was comparable across the two different site types for both the 1-year-old coppiced plants and the 4-year-old uncoppiced plants, showing rapid recovery of biomass growth and yield in the year following coppicing. Significant clonal differences, as well as site type × clone interactions, were found for ortet stem dry mass, especially on SO sites, indicating that clonal selection might be useful to increase biomass production on different site types. When expressed as a fraction of total stem dry mass produced on 2 m × 2 m biomass plots, the RS component represented a significant 57% of total stem dry mass per plot (ortet + associated RS) on GD sites and only 18% on SO sites. The use of colony-forming willows such as INT minimizes the need for periodic replanting, providing a cost advantage over conventional short-rotation, coppice-based woody biomass plantations using species that do not have the ability to produce new stems via root sprouting. This root-sprouting trait enables INT to rapidly colonize and spread on difficult-to-manage sites, making it suitable for use in land reclamation.

The application of biopriming using trichoderma and Streptomyces spp. on the germination stage of soybean

Biopriming is one way to overcome the stunted plant growth due to a decline in the quality of seed physiology by using a combination of biological agents. This study aims to improve the quality of seed germination and vigor with a combination of biological agents in the form of Trichoderma harzianum and Streptomyces spp. This research was conducted at the Laboratory of Bio-Science and Plant Reproductive Biotechnology, Department of Agriculture Cultivation, Faculty of Agriculture, Hasanuddin University, which took place from January to April 2019. This study used a Split Plot Design, the main plot was the duration of biopriming consisting of four levels, 3 hours, 6 hours, 12 hours and 24 hours. Type of microbes as subplots consisting of three levels, namely water, Trichoderma harzianum and Streptomyces spp. The results show that the duration of biopriming 12 hours with Streptomyces spp. able to produce the highest average percentage of normal sprouts (96.48%). The duration of biopriming treatment for 12 hours with water produced the highest average percentage of abnormal sprouts (15.09%). Treatment duration of biopriming for 6 hours with Streptomyces spp. able to produce the highest average length of root sprouts (11.91 cm). Streptomyces spp. gave the highest yield at an average germination rate (90.42%).

Competition of biological agents of Streptomyces sp, Gliocladium sp, and Trichoderma harzianum to Fusarium oxysporum in Tomato Rhizophere

Fusarium oxysporum is a soil-borne fungus that attacks all stages of tomato plant from seedlings to mature plants. The disease occurrence on the tomato nursery can lead economically loss due to its fast and massive damage. Application of effective biological control agents is considered as promising control measure of the disease. The aim of this study was to evaluate the potential competitiveness of biological agents mixture consisting of Streptomyces sp., Gliocladium sp. and T. harzianum against F. oxysporum f. sp. lycopersici in the rhizosphere of the tomato plant. The experiment was arranged in completely randomized design with five treatment types of agents that a single biological agents Streptomyces sp. (S), a mixture of Streptomyces sp. and Gliocladium sp. (SG), a mixture of Streptomyces sp. and T. harzianum (ST), a mixture of Streptomyces sp., Gliocladium sp., and T. harzianum (SGT) and control without biological agents. Each treatment was replicated four times and consisted of 6 plants for observation purposes destructively. Descriptive analysis conducted on the pattern of colonization of the roots competition showed a growth pattern colonization of biological agents, Streptomyces sp , Gliocladium sp , T. harzianum and F. oxysporum pathogen (SGTF) was the same growth pattern of SGF and STF, where four of the microbes grew on the same side of roots as fungal pathogens, in all parts of the root sprouts. Given biological agent Streptomyces sp, Gliocladium sp., dan Trichoderma harzianum decreased fusarium wilt diseases severity of tomato. Weight root of tomato plants was applied by biological agents was 9.2 g greater than plant without biological agents, which were 2.5 g. The observation on tomato indicated root colonization occurs, especially on the base of the stem-roots by a mixture of biological agents T. harzianum and Gliocladium sp.

Seedling regeneration and spatial correlation between seedlings and seed trees in Castanopsis hystrix plantation by large diameter wood cultivation in south subtropical China

Using the paired correlation equation g(r) in the spatial point patterns, we investigated the regeneration characteristics and spatial patterns of Castanopsis hystrix seedlings and the spatial correlation with the seed trees in the plantation by large diameter wood cultivation in south subtropical China. The results showed that natural seedling regeneration in C. hystrix plantation was good, which were widely distributed in the whole plantation. The seedling regeneration were mainly contributed by root sprouts, accounting for 73.6% of the total. The number distribution of C. hystrix seedlings in different age classes showed a pyramidal shape, with the contribution of diameter class1, 2 and 3 being 64.3%, 29.3% and 6.4% of the total, respectively. The C. hystrix seedlings mainly presented aggregated distribution in small scale (<15 m). With the increases of size classes and spatial scales, the aggregation strength gradually weakened and finally presented random distribution. The spatial correlation between seedlings and seed trees was not significant with the increases of size classes or spatial scale.

Effects of Storage Temperature and Packaging Combinations on the Storage Quality of Fresh Yacon [Smallanthus sonchifolius (Poepp.) H. Rob.

The yacon tuber has gained interest due to its health-promoting components, such as high amounts of fructooligosaccharides (FOS) and phenolic compounds with strong antioxidant properties. However, the high water content and the soft, delicate internal tissues render it highly perishable, leading to significant losses during postharvest handling. The packaging and storage temperatures, two important factors in maintaining quality when storing fresh yacon tubers, were studied. The results showed that modified atmosphere packaging (MAP) combined with low temperature (10°C) had positive effects on the visual quality of yacon. Weight loss and shriveling were reduced in MAP compared to the unpacked yacon under room and 10°C storage temperatures. The use of MAP under room temperature for an extended storage period was limited by the development of disease and the occurrence of root sprouts and surface cracks in yacon, which reduced its visual quality. FOS hydrolysis by fructan exohydrolase occurred during storage, leading to higher amounts of fructose, glucose, and sucrose. The use of MAP regardless of storage temperature delayed the onset of rapid FOS decline. The total phenolic contents in the range of 4.84-5.98 mg Gallic acid equivalent per gram dry sample and antioxidant activity of yacon did not decrease relative to its initial content. Yacon could be stored at 10°C in conjunction with MAP to maintain quality and extend the shelf life of fresh yacon tubers.

Structural dynamics of Populus euphratica forests in different stages in the upper reaches of the Tarim River in China

We selected four Populus euphratica Oliv. forest plots (100 m × 100 m) in the upper reaches of the Tarim River in the Xinjiang Uygur Autonomous Region of China. Each of the four forest plots was chosen to represent a different growth and death stage of P. euphratica forest: juvenile forest, mature forest, dying forest, and dead forest. In each plot, we measured the coordinates, DBH, height, and status of all P. euphratica individuals. We used (1) spatial pattern analysis to explore spatial distribution patterns and associations of live trees and dead trees, (2) a random mortality model to test whether the tree death was random or non-random, and (3) a generalized linear mixed-effect model (GLMM) to analyse factors related to tree survival (or death). In the juvenile plot, live trees were significantly aggregated at all scales (p < 0.05); while in the mature and dying plots, live trees were more aggregated at small scales and randomly distributed at larger scales. Live trees and dead trees showed a significantly positive association at all scales in the juvenile plot (p < 0.05). While in the mature and dying plots, live trees and dead trees only showed a significantly positive association at scales of 0–3 m (p < 0.05). There was significant density-dependent mortality in the juvenile plot; while mortality was spatially random at all scales in the mature and dying plots. The distance from the river showed significantly negative correlations with tree survival (p < 0.01). DBH and height had significantly positive associations with tree survival in the juvenile, mature, and dying plots (p < 0.05). In extreme drought, dying trees appeared to be shape-shifting into more shrub-like forms with clumps of root sprouts replacing the high canopies. The shift under extreme drought stress to more shrub-like forms of P. euphratica may extend their time to wait for a favourable change.

Factors influencing reversion from virus infection in sweetpotato.

Viruses limit sweetpotato (Ipomoea batatas) production worldwide. Many sweetpotato landraces in East Africa are, however, largely virus-free. Moreover, some plants infected by the prevalent Sweet potato feathery mottle virus (SPFMV) may be able to revert to virus-free status. In this study, we analysed reversion from SPFMV, Sweet potato virus C, Sweet potato mild mottle virus, Sweet potato chlorotic stunt virus (SPCSV) and Sweet potato leaf curl Uganda virus using the indicator plant I. setosa and PCR/reverse-transcriptase PCR. We also investigated environmental factors (temperature and soil nutrients) that may influence reversion from virus infection. We tested reversion in the East African cultivars New Kawogo, NASPOT 1 and NASPOT 11, and the United States cultivars Resisto and Beauregard. Reverted plants were asymptomatic and virus was undetectable in assayed parts of the plant. After graft inoculation, only the East African cultivars mostly reverted at a high rate and from most viruses though cultivar Beauregard fully reverted following sap inoculation with Sweet potato virus C. None of the tested cultivars fully reverted from single or double infections involving SPCSV, and reversion was only observed in co-infections involving potyviruses. Root sprouts derived from SPFMV-reverted plants were also virus free. Reversion generally increased with increasing temperature and by improved soil nutrition. Overall, these results indicate variation in reversion by cultivar and that the natural ability of sweetpotato plants to revert from viruses is malleable, which has implications for both breeding and virus control.

Managing Understory Fagus grandifolia for Promoting Beech Bark Disease Resistance in Northern Hardwood Stands

AbstractMany Allegheny hardwood stands contain dense understories of very shade-tolerant American beech, resulting from partial disturbances that have accelerated root sucker development. The low-shade produced by these sprouts hampers silvicultural regeneration efforts to maintain species diversity in new cohorts. An increasing proportion of sprouts result from stressed trees infested with beech bark disease. The clonal sprouts also have a genetic affinity for the disease. A mixture of Accord® and Oust® herbicides, applied to understory vegetation after shelterwood establishment cuts, can significantly reduce understory beech density. Yet, retention of some overstory beech, with demonstrated disease resistance, is ecologically desirable. The root sprouts from these parent trees should also have resistance to the disease. We used broadcast herbicide application to kill understory vegetation after shelterwood harvests in three stands, and tested the effect of herbicide on beech sprouts associated with resistant trees. Eight years after treatment, plots that had received herbicide had similar densities of beech to no-herbicide plots. However, there were significant differences in seedling densities among stands (P = .0303) and species (P = .0014). Our results indicate that there is much temporal variability in regeneration dynamics after treatment. Resistant beech sprouts are still competitive in the long term, even after herbicide application.

Virus Movement from Infected Sweetpotato Vines to Roots and Reversion on Root Sprouts

Sweetpotato is usually propagated in Uganda by vine cuttings from mature crops, but sometimes sprouts from storage roots are used, especially in drought-prone areas. No information is available on whether the storage of roots of Ugandan cultivars are infected with the viruses and whether the sprouts on them express symptoms so that farmers can eliminate diseased ones. Information on root sprout reversion from virus infection is also lacking. The storage roots of five sweetpotato cultivars was sourced either by random selection of roots from already harvested roots or obtained from symptomless plants selected before harvest at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK), and the National Semi Arid Resources Research Institute (NaSARRI). Roots were also generated in a screenhouse after being inoculated with Sweet potato feathery mottle virus (SPFMV) and/or Sweet potato chlorotic stunt virus (SPCSV). More than 70% of sprouts from roots of all the cultivars selected after harvest at MUARIK and NaSARRI were infected with the viruses. For roots obtained from symptomless plants, 64% and 21% of the sprouted roots from MUARIK and NaSARRI were infected with the viruses, respectively. Most of the root samples from MUARIK had visible virus symptoms on sprouts and tested positive for both SPFMV and SPCSV, whereas those from NaSARRI did not show symptoms and were infected primarily with SPFMV. Plants graft-inoculated with either SPCSV or SPFMV alone produced both infected and noninfected roots, whereas all the root sprouts from dually infected plants showed virus symptoms. Reversion from virus infection was observed on root sprouts infected singly with SPFMV, whereas those infected with SPCSV showed recovery only, and none of the root sprouts infected by both viruses showed recovery. This study proves that roots are good reservoirs for viruses, and reversion occurs only when singly infected with SPFMV. Therefore, there is a need to establish seed channels in which seedstock is cleaned continuously and made available to farmers.

Phenotypic Expression and Stability in a Large-Scale Field Study of Genetically Engineered Poplars Containing Sexual Containment Transgenes.

Genetic engineering (GE) has the potential to help meet demand for forest products and ecological services. However, high research and development costs, market restrictions, and regulatory obstacles to performing field tests have severely limited the extent and duration of field research. There is a notable paucity of field studies of flowering GE trees due to the time frame required and regulatory constraints. Here we summarize our findings from field testing over 3,300 GE poplar trees and 948 transformation events in a single, 3.6 hectare field trial for seven growing seasons; this trial appears to be the largest field-based scientific study of GE forest trees in the world. The goal was to assess a diversity of approaches for obtaining bisexual sterility by modifying RNA expression or protein function of floral regulatory genes, including LEAFY, AGAMOUS, APETALA1, SHORT VEGETATIVE PHASE, and FLOWERING LOCUS T. Two female and one male clone were transformed with up to 23 different genetic constructs designed to obtain sterile flowers or delay onset of flowering. To prevent gene flow by pollen and facilitate regulatory approval, the test genotypes chosen were incompatible with native poplars in the area. We monitored tree survival, growth, floral onset, floral abundance, pollen production, seed formation and seed viability. Tree survival was above 95%, and variation in site conditions generally had a larger impact on vegetative performance and onset of flowering than did genetic constructs. Floral traits, when modified, were stable over three to five flowering seasons, and we successfully identified RNAi or overexpression constructs that either postponed floral onset or led to sterile flowers. There was an absence of detectable somaclonal variation; no trees were identified that showed vegetative or floral modifications that did not appear to be related to the transgene added. Surveys for seedling and sucker establishment both within and around the plantation identified small numbers of vegetative shoots (root sprouts) but no seedlings, indicative of a lack of establishment of trees via seeds in the area. Overall, this long term study showed that GE containment traits can be obtained which are effective, stable, and not associated with vegetative abnormalities or somaclonal variation.

Excluding deer increases the proportion of beech saplings originating from seed versus those of root sprout origin

Abstract American beech (Fagus grandifolia Ehrh.) regenerates both from seed and also clonally via root sprouts. Regenerating beech saplings often form dense and depauperate understories that cast deep shade and displace co-occurring species. The relative proportion of saplings that originate from seed versus root sprouts varies widely throughout the range of beech. Although the cause for that variation remains unclear, it may be linked to canopy or soil disturbances, the spread of beech bark disease (BBD), or overabundant deer. Here, we asked whether the long-term exclusion of deer and the absence of BBD would favor the regeneration of saplings (20–150 cm tall) of seed origin versus those of sprout origin. We addressed this question using deer exclosures (16 and 60+ yr old) and paired controls in one forest in Pennsylvania where BBD had caused major adult mortality and another where BBD was not present. We found that excluding deer significantly decreased the relative proportion of root sprouts from appr...

Clear-Cuts Are Not Clean Slates: Residual Vegetation Impediments to Savanna Restoration

ABSTRACT In response to widespread losses of savanna ecosystems worldwide, many restoration efforts are underway. For savannas degraded by fire suppression and hardwood invasion, a first step towards restoration typically involves removal of unwanted trees and shrubs, but after invasive nonnative woody plants are top-killed, savanna restoration is often impeded by their resprouts. To evaluate patterns of vegetative recovery following clear-cuts and to explore their implications for ecosystem restoration, we determined the origins of the vegetation that develops after a clear-cut in hardwood-invaded sites being restored to pine savanna in Florida. We excavated stumps and other sprout sources, characterized the soil seed bank, and estimated seed production by early-to-mature species during the first growing season after treatment. In twenty 100-m2 plots, there was approximately one source of woody plant sprouts per square meter. Root sprouts were more abundant than sprouted stumps, and most of the stumps t...