Root Regrowth Research Articles

Response on root regrowth potential to soil moisture in Sedum species during winter in Særheim, Norway

PurposeThe impact of winter moisture on root metabolism and root integrity has potential consequences for the geographical distribution of drought-adapted succulent species and for their long-term performance on green roofs. The interacting effects of soil characteristics and precipitation frequency on root mortality under winter conditions and the potential to grow new roots in spring were evaluated for six Sedum species under controlled conditions. MethodsTo test for the impact of soil moisture during winter on root regrowth potential in six Sedum species, we used a combination of two substrates with differing water-holding capacity and four contrasting watering regimes. Specially, for the fine and coarse substrates, total pore volume was 42 and 46 %, respectively, and maximum water-holding capacity (i.e. field capacity) was 0.50 and 0.33 kg water per L, respectively. The four watering treatments involved overhead watering to runoff (approx. 10 mm): once every second week, once a week, three times per week and three times per week with 1 cm standing water in trays from January to March 2019. ResultsIt was found that winter soil moisture had no major impact on root mortality or root regrowth potential in spring. Root mortality was not affected by watering frequency and regrowth potential showed no directional response to increased watering frequency, although species-specific responses were involved. Root diameter did not differ between the substrates, but there were some differences between the species. Sedum rupestre had on average the thickest roots (0.17 mm), followed by S. acre, S. anglicum and S. sexangulare (0.15–0.16 mm), while S. album and S. hispanicum had the thinnest roots (0.12–0.13 mm). Moreover, effects of watering frequency on root mortality and regrowth potential were not influenced by soil water-holding capacity across species. We concluded that winter soil moisture had no negative effects on root performance within the range of treatments tested here. ConclusionsRoot response to transient waterlogging or moist but unsaturated soil may not be an important mechanism for determining the survival and distribution of temperate Sedum species during winter.

Quercus virginianaMill. Root Regrowth Following Linear Trenching

AbstractBackgroundAs long-lived organisms, urban trees often encounter development and redevelopment activities during their lifespans. These activities can damage tree roots, often through methods like root severing during trenching or excavation.MethodsIn 2017, we simulated trenching damage on matureQuercus virginianaMill. trees at 3 different distances from the base (3, 6, or 12 times the stem diameter). After 5 years, we revisited these trees to assess root regrowth based on the cut root’s cross-sectional area (CSA) and distance from the base.ResultsWe observed regrowth in all but 38 (6.7%) of the 557 cut roots revisited. The lack of regrowth in some roots was not associated with our original treatments, the CSA of the roots at the time of trenching, or distance between the cut root end and the trunk (minimumP-value = 0.841). On average, the observed CSA of the regrowth was 22.2% of the original root’s CSA. Only our initial trenching treatments (P-value = 0.024) and the distance between the trunk and the cut root end (P-value = 0.002) significantly predicted the level of regrowth observed 5 years after pruning.ConclusionsIn summary, our findings indicate that root systems require many years to recover from trenching damage. Increasing the distance between trenching activities and trees may have a minor effect on root regrowth.

The Invasive Ailanthus altissima: A Biology, Ecology, and Control Review.

Tree of Heaven (Ailanthus altissima (Mill.) Swingle) is a tree native to China which has invaded disturbed areas in many regions worldwide. Its presence endangers natural ecosystems by displacing native species, modifying habitats, changing community structures, and affecting ecosystem processes. Its invasive nature is enhanced by its high ability to reproduce both vegetatively through root regrowth and sexually through seeds. Seeds, which are wind dispersed, are the main mechanism by which this species reaches new habitats. When they germinate and develop the root system, roots emit new shoots that contribute to a rapid increase in the tree density and the subsequent expansion of the population nearby. The contradictory results about the ecological requirements for seeds to germinate and their degree of dormancy and longevity indicate the complexity and difficulty of understanding the mechanisms that govern the biology and adaptability of this plant. The management of this weed aims at its eradication, with programs based on herbicide applications carried out by injecting the active ingredient directly to the trunk. But, not many active ingredients have shown total control, so new ones should be tested in order to increase the range of available herbicides. During the last few decades, some biological agents have been identified, but their efficacy in controlling the tree and their safety for the local flora have not yet been determined. A correct management strategy should take into account all these aspects in order to contain the expansion of this species and, ultimately, allow its eradication.

Inheritance of aluminium tolerance in sunflower (Helianthus annuus L.)

In acidic soil, aluminium (Al) toxicity is one of the foremost restraining factors which inhibit crop performance. Breeding for Al tolerance seems to be a vital approach for enhancing productivity of field crops including sunflower in acidic soil regions. In order to understand the inheritance pattern, tolerant genotypes NDLR-06 and EC601861 were crossed with susceptible genotypes MR-06 and RHA-298. P1, P2, F1, F2 and backcross populations were raised in nutrient solution and classified as tolerant/susceptible by observing root re-growth after staining with eriochrome cyanine R. Dominance nature of Al tolerance over susceptible was confirmed by the responses of F1’s which were similar to the tolerant parents. The segregation ratio for Al tolerance vs. susceptible in the F2 and backcross generations were 3:1 and 1:1, respectively. These outcomes indicated that inheritance of Al tolerance is governed by single dominant gene which can be transferred easily to desirable genotypes via backcross breedingmethod. This is the first report on inheritance of Al tolerance in sunflower.

Phenotypic plasticity in Cucurbita maxima and C. moschata seedlings as a measure of drought stress tolerance under pot screening

A pot screening approach was used to identify mannitol stress tolerance indicating traits that were reliable and easy to determine, in two Cucurbita species. A population of C. maxima seedlings with trimmed roots were exposed to 0–800 mM mannitol for 20 days and the mannitol concentration required to inhibit root regrowth by 50±0.51% was established through a linear regression analysis (LD50 = 453 mM, -1.11 MPa). The established LD50 was then used to screen a population of C. moschata seedlings in addition to a second population of C. maxima. When exposed to 453 mM mannitol for 10 days, both species were able to regrow roots, maintain biomass production, chlorophyll content, high water status, membrane stability and accumulate proline as an osmoprotectant. Even with a good water status, stress exposure for 20 days compromised the biomass production, chlorophyll content, membrane stability and encouraged a surge in proline content. Based on their phenotypic plasticity indices, traits such as root regrowth, fresh weight, dry weight, relative chlorophyll content, electrolyte leakage and proline content were identified as potential indicators of stress tolerance at day 10 of mannitol stress. Meanwhile, root regrowth and proline content were the only traits identified as good indicators of stress tolerance at day 20 of mannitol stress. The biochemical, morphological and physiological traits of tested populations had varying degrees of plasticity under stress and this should be considered when screening and identifying drought resilient seedlings prior to labourious field tests.

The harmfulness ofwestern corn rootworm (Diabrotica virgifera virgifera LeConte) under the conditions of perennial repeated maize sowing

Kukuruzna zlatica (Diabrotica virgifera virgifera LeConte) pripada najvažnijim štetnicima kukuruza. Istraživanje je provedeno u Gorjanima tijekom 2020. godine s ciljem utvrđivanja kako ponovljena sjetva kukuruza utječe na pojavu i brojnost kukuruzne zlatice, razinu oštećenja korijena, tolerantnost biljaka te prinos. Zasijan je hibrid kukuruza OS 378 u dva tretmana (ponovljena sjetva i monokultura tri godine). Štete uzrokovane hranidbom ličinaka utvrđene su očitanjem oštećenja korijena. Tolerantnost biljaka utvrđena je očitanjem veličine korijena i razvoja sekundarnoga korijenja, a let imaga pratio se žutim ljepljivim pločama. Prisutnost kukuruzne zlatice zabilježena je na objema istraživanim parcelama. Prosječna brojnost imaga po danu i mamcu u ponovljenoj sjetvi iznosila je 1,07, a u trogodišnjoj monokulturi 0,99. Oštećenje korijena ocijenjeno je prosječnom ocjenom 0,75 (ponovljena sjetva), odnosno 1,25 (trogodišnja monokultura). Veličina korijena ocijenjena je prosječnim ocjenama 2,50 (ponovljena sjetva) i 3,70 (trogodišnja monokultura), a prosječni porast sekundarnoga korijenja s 3,20 (ponovljena sjetva), odnosno 3,05 (trogodišnja monokultura). Lošije ocjene korijena bile su kod uzgoja kukuruza u trogodišnjoj monokulturi, što ukazuje kako dodatna godina monokulture može uzrokovati veće štete. Prinos kukuruza u ponovljenoj sjetvi bio je viši za 2,53 t/ha u odnosu na trogodišnju monokulturu. Preporuča se izbjegavanje daljnje sjetve kukuruza na ovim površinama te poštivanje višegodišnjega plodoreda.

Maize Inbred Mp708 is Highly Susceptible to Western Corn Rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), in Field and Greenhouse Assays.

The western corn rootworm (WCR), Diabrotica vifgirera virgifera LeConte, (Coleoptera: Chrysomelidae) causes significant economic damage in corn production each year. Resistance to insecticides and transgenic corn with Bacillus thuringiensis (Bt), Berliner toxins have been reported throughout the United States Corn Belt. Corn breeding programs for natural resistance against WCR larvae could potentially assist in rootworm management. Root damage and root regrowth of eight corn lines were evaluated in field assays at three different locations. Results indicated the inbred 'Mp708' had the greatest root damage and was significantly greater than damage for the susceptible control, B37×H84. In greenhouse assays, we evaluated four of these lines plus a hybrid expressing the mCry3A Bt toxin for damage. The results indicated that Mp708 had significantly higher root damage when compared to 'CRW3(S1)C6' and 'MIR604'. Despite previous work suggesting otherwise, we conclude that Mp708 is highly susceptible to the WCR larvae based on root damage in field and greenhouse plant assays.

Genetic variability for aluminium tolerance in sunflower (Helianthus annuus L.)

Breeding for aluminium (Al) tolerance is a vital approach for enhancing the productivity of field crops in acidic soil regions where Al toxicity seems to be the most restraining factor for crop performance. Sunflower is generally considered extremely sensitive to Al toxicity; although no comprehensive information on the evaluation of sunflower genotypes for Al tolerance is available. In this study, 50 sunflower genotypes (set-I and set-II) were evaluated for Al tolerance at the seedling stage under hydroponic conditions. Substantial genetic variability in Al tolerance was observed among the studied genotypes. High estimates of heritability were obtained for both the total root length (TRL) and root regrowth (RRG), together with high estimates of genetic advance. A cluster analysis separated the genotypes into five different groups among the studied germplasm, the genotypes; NDLR-06 and EC-601861 were observed to be highly Al tolerant in terms of root regrowth under Al stress. In conclusion, the findings lreveal the complex mechanisms of Al tolerance in sunflower and may help to find new genetic resource for the improvement of Al tolerance in sunflower breeding.

Aluminum Stress Induces Irreversible Proteomic Changes in the Roots of the Sensitive but Not the Tolerant Genotype of Triticale Seedlings.

Triticale is a wheat–rye hybrid with a higher abiotic stress tolerance than wheat and is better adapted for cultivation in light-type soils, where aluminum ions are present as Al-complexes that are harmful to plants. The roots are the first plant organs to contact these ions and the inhibition of root growth is one of the first plant reactions. The proteomes of the root apices in Al-tolerant and -sensitive plants were investigated to compare their regeneration effects following stress. The materials used in this study consisted of seedlings of three triticale lines differing in Al3+ tolerance, first subjected to aluminum ion stress and then recovered. Two-dimensional electrophoresis (2-DE) was used for seedling root protein separation followed by differential spot analysis using liquid chromatography coupled to tandem mass spectrometry (LC-MS-MS/MS). The plants’ tolerance to the stress was evaluated based on biometric screening of seedling root regrowth upon regeneration. Our results suggest that the Al-tolerant genotype can recover, without differentiation of proteome profiles, after stress relief, contrary to Al-sensitive genotypes that maintain the proteome modifications caused by unfavorable environments.

Interlaboratory Validation of Toxicity Testing Using the Duckweed Lemna minor Root-Regrowth Test.

Simple SummaryDuckweed (Lemna minor) is commonly used as a phytotoxicity test organism, adopted by the main international standardization organizations (ISO, OECD, USEPA, ASTM). For duckweed tests, measurements of fronds or biomass are usually preferred with a standard exposure period of at least 7 days. The proposed root- regrowth test differs from other internationally standardized methods in several important aspects: (a) the test can be performed within 72 h; (b) the test vessel was a 24-well cell plate; (c) the required volume of test water samples was 3 mL; (d) roots were excised before exposure and newly developed roots then measured. The validation of the new test method by interlaboratory comparison tests confirmed that the Lemna root bioassay is valid and reliable. The root growth test is therefore a valuable tool for rapid toxicity screening of wastewater effluents and hazardous pollutants in natural waters because it is simple to perform, quick to conduct, cost-effective to operate, and can have operational benefits for testing time, since management decisions need to be made promptly in the event of unpredictable pollution events.The common duckweed (Lemna minor), a freshwater monocot that floats on the surfaces of slow-moving streams and ponds, is commonly used in toxicity testing. The novel Lemna root- regrowth test is a toxicity test performed in replicate test vessels (24-well plates), each containing 3 mL test solution and a 2–3 frond colony. Prior to exposure, roots are excised from the plant, and newly developed roots are measured after 3 days of regrowth. Compared to the three internationally standardized methods, this bioassay is faster (72 h), simpler, more convenient (requiring only a 3-mL) and cheaper. The sensitivity of root regrowth to 3,5-dichlorophenol was statistically the same as using the conventional ISO test method. The results of interlaboratory comparison tests conducted by 10 international institutes showed 21.3% repeatability and 27.2% reproducibility for CuSO4 and 21.28% repeatability and 18.6% reproducibility for wastewater. These validity criteria are well within the generally accepted levels of <30% to 40%, confirming that this test method is acceptable as a standardized biological test and can be used as a regulatory tool. The Lemna root regrowth test complements the lengthier conventional protocols and is suitable for rapid screening of wastewater and priority substances spikes in natural waters.

Efficient Protocol for Improving the Development of Cryopreserved Embryonic Axes of Chestnut (Castanea sativa Mill.) by Encapsulation-Vitrification.

An optimized cryopreservation protocol for embryonic axes (EAs) of chestnut (Castanea sativa Mill.) has been developed based on the encapsulation–vitrification procedure. EAs of mature seeds were aseptically dissected and encapsulated in alginate beads with or without 0.3% (w/v) activated charcoal (AC). Embedded EAs were dehydrated with Plant Vitrification Solution 2 for different treatment times up to 120 min, followed by direct immersion in liquid nitrogen. Cryopreserved embryonic axes encapsulated with AC showed higher survival (70%) compared to those encapsulated without AC (50%). Sixty-four percent of embryonic axes, from synthetic seeds with AC, subsequently developed as whole plants. Plantlet regrowth was faster in AC-encapsulated EAs and showed enhanced postcryopreservation shoot and root regrowth over 2 cm after five weeks from rewarming. Results indicate that encapsulation–vitrification with activated charcoal added to the beads is an effective method for the long-term preservation of Castanea sativa embryonic axes.

Straw Removal Effects on Sugarcane Root System and Stalk Yield

The sugarcane (Saccharum spp. L.) mechanical harvesting system leaves a large amount of straw mulch on the soil surface. The straw mulch may affect soil conditions, root regrowth, and sugarcane yield. Thus, this study assessed the response of sugarcane root system growth and stalk yield to different rates of straw removal. An experiment was conducted in a Rhodic Kandiudox with sand clay loam texture to test the impact of four rates of straw removal: no removal (18.9 Mg ha−1 of dry mass); moderate removal (8.7 Mg ha−1); high removal (4.2 Mg ha−1) and total removal on sugarcane root system and stalk yield. Higher concentrations of roots (60%) were found in the first 40 cm of soil. Moderate straw removal resulted in higher root mass (3.6 Mg ha−1) and stalk production (23 Mg ha−1 of dry mass). However, no straw removal reduced root mass by &lt;40% (2099 kg ha−1) and reduced stalk yield by &gt;20% (105 Mg ha−1). Through regression analysis, it was estimated that retaining between 8.5 and 13 Mg ha−1 of straw resulted in the highest root mass and stalk yield. Managing straw removal to retain a moderate amount enables producers to sustain suitable soil conditions for sugarcane root growth and stalk production while providing straw for industrial use.

Tomorrow Never Dies: biodegradation and subsequent viability of invasive macrophytes following exposure to aquatic disinfectants

Aquatic invasive alien species (IAS) negatively impact freshwater ecosystems worldwide. As suppression and eradication of established invader populations are often complex, costly and resource-intensive, the prevention of further invader spread is considered a key aspect of proactive management measures. Although broad-spectrum aquatic disinfectants have been suggested as a suitable decontamination mechanism to enhance invader spread-prevention strategies, inconsistencies concerning their effectiveness are reported within the literature. Here, we examine the use of two aquatic disinfectants, which were developed to kill damaging microbes, to induce substantial degradation of the apical fragmentary propagules of five invasive macrophytes: Crassula helmsii (Kirk) Cockayne; Egeria densa Planchon; Elodea canadensis Michx; Hydrocotyle ranunculoides Linnaeus; Lagarosiphon major (Ridley) Moss. Apical fragments were exposed to 0% (0 g L-1), 2% (20 g L-1) or 4% (40 g L-1) solutions of Virkon® Aquatic and Virasure® Aquatic, for submergence treatments of five, fifteen, thirty or sixty minutes. After 28 days, degradation of treated fragments was significantly greater than that of control groups, particularly for 4% solutions and longer exposure times. Despite this, sustained viability in relation to shoot and/or root regrowth was exhibited by almost all plant species. However, new shoot growth rates were significantly reduced following exposure to all treatments. At matched concentrations, there was no significant difference between the two disinfectants. Overall, it appears that the examined aquatic disinfectants will not curtail the spread of these invasive macrophytes. Yet, longer submergence times, multiple applications and synergistic effects of different biosecurity treatments may enhance preventative measures against further spread and this requires investigation.

Comparative Paraquat Sensitivity of Newly Germinated and Mature Fronds of the Aquatic Macrophyte &amp;lt;i&amp;gt;Spirodela polyrhiza&amp;lt;/i&amp;gt;

Here, we compared the intrinsic characteristics of 3-day-(newly germinated; “young”) and 8-week-old (“mature”) fronds of the aquatic plant Spirodela polyrhiza and their sensitivity to paraquat, a toxic herbicide. Endpoints measured were frond area and fresh weight, root length, chlorophyll a and b contents, and chlorophyll a fluorescence. Significant differences were detected in the intrinsic physiological traits between young and mature fronds. Young fronds showed higher root length, chlorophyll contents, maximum quantum yield (Fv/Fm), maximal relative electron transport rate (rETRmax) and saturating photon flux density (PFD), whereas mature fronds exhibited greater frond area and fresh weight. After a 72 h exposure to paraquat, root length and rETRmax were identified as the most sensitive endpoints of paraquat toxicity for both frond types, with EC50 values of 0.66 and 0.76 μg·L-1 for young fronds, respectively, and 5.53 and 2.28 μg·L-1 for mature fronds, respectively. Young fronds of S. polyrhiza showed significantly higher sensitivity to paraquat than mature fronds. A survey of other studies on paraquat toxicity to Lemna species revealed that EC50 values of paraquat-induced inhibition of root regrowth and rETRmax in both stages were the lowest, indicating that these two endpoints were the most sensitive to paraquat. In addition, EC50 values of both endpoints of mature fronds of S. polyrhiza appear to be similar to the current allowable concentrations in drinking water set by the World Health Organization (WHO), indicating that these values may have application for the assessment of toxicity risk of paraquat in aquatic ecosystems.

Modification of the droplet-vitrification method of cryopreservation to enhance survival rates of adventitious roots of Panax ginseng

Panax ginseng Meyer is an important medicinal plant producing bioactive compounds. A droplet-vitrification method was developed for cryopreserving adventitious root cultures of mountain ginseng, and variations of this procedure were tested to determine their effects on regrowth rates and osmotic stress responses. Root regrowth rates were examined after exposing root segments to two pre-culture treatments, three loading solutions, and two vitrification solutions with different exposure periods. Pre-culturing excised segments of adventitious roots with 0.3 M sucrose produced the highest rate of regrowth after cryopreservation. Loading for 20 min with 17.5% (w/v) sucrose and 17.5% (w/v) glycerol at room temperature increased the regrowth rate of cryopreserved adventitious roots fourfold, compared with non-loaded samples. Treatments involving different vitrification solutions and exposure periods were compared, and the highest rate of regrowth (15%) after cryopreservation was achieved by incubating adventitious roots in modified plant vitrification solution 3 containing 40% (w/v) glycerol and 40% (w/v) sucrose for 10 min at room temperature, suggesting that ginseng adventitious root tips were sensitive to osmotic stress. Further study is necessary to develop optimal vitrification solutions that enhance the survival rate of cryopreserved adventitious roots of mountain ginseng.

An in vitro screening system to assess aluminum toxicity in sugarcane (Saccharum spp.) cultivars

Mutagenic breeding is an approach being developed especially for those characteristics that are not inherited through conventional genetic hybridization. Soil acidity and aluminum (Al3+) toxicity limit sugarcane production, particularly in leached soils in the coastal cultivation regions in South Africa. An in vitro screening procedure was developed based on plantlet re-rooting in Al3+-containing medium to select putative Al3+ tolerant variants produced by induced mutagenesis. A preliminary test did not show any difference among three cultivars in their ability to re-root in the presence of Al3+. Subsequent work focused on Saccharum sp. ‘NCo376’ and two Al3+ concentrations (15 and 45 mM), representing LC50 and LC90 re-rooting inhibition. In an attempt to increase the stringency of the selection conditions, the possible effects of inorganic nitrogen (N) forms in the culture media on Al3+ toxicity were investigated. The form of N affected root regrowth and citrate exudation. Sugarcane plantlets showed an uptake preference for ammonium (NH4+) over nitrate (NO3−), and 10 and 20 mM NH4+ appeared to alleviate Al3+ toxicity compared with NO3−. Although in agricultural soils NO3− is the dominant form of N, it can readily leach into the sub-soil, in which deep roots encounter Al3+ toxicity in the presence of NO3−. Therefore, the ability to withstand the toxic effects of Al3+ in the presence of NO3− could be beneficial for N use efficiency and access to water at depths during drought.

Impacts of Wire Basket Retention and Removal on Fraxinus americana ‘Autumn Purple’ Growth Nine Years After Transplanting

The topic of wire basket removal during planting remains an area of contention among nursery growers, landscapers, and arborists who work with balled-and-burlapped planting material. Those in favor of removal fear that the burlap and wire surrounding a tree’s root ball will impede root regrowth and eventually lead to the girdling of any roots that do penetrate into the surrounding soil. Those opposed to removal believe the advantages to tree and root system stability during transplanting and establishment outweigh any negatives to leaving the root ball intact. In 2008, 45 Fraxinus Americana ‘Autumn Purple’ were randomly assigned one of three transplanting treatments: 1) transplanted by tree spade without burlap/wire; 2) transplanted as balled-and-burlapped with only burlap and string removed; or 3) transplanted as balled-and-burlapped with all packaging materials (i.e., string, burlap, wire basket) removed. All trees survived regardless of treatment. In addition to survival, trunk diameter and tree height were measured annually for nine years. Marginal differences were noted for the two growth responses over the course of the trial (min P-value = 0.0599).

Shoot and Root Growth in Common Bean (Phaseolus vulgaris L.) Exposed to Gradual Drought Stress

Drought condition during the dry season is a major constraint for intensifying agricultural activities at riparian wetlands in Indonesia, particularly for annual vegetables, including common bean (Phaseolus vulgaris L.). Besides inhibiting growth and reducing yield, drought also causes alteration of the shoot and root growth and development. The objective of this study was to evaluate responses of common bean to three durations of drought stress and the bean ability to recover after termination of the stress treatments. Gradual drought stress treatments were imposed by withholding all water sources to the treated plants. Three durations of drought stress imposed were 4, 8, and 12 days. The ability of the stress-treated plants to recover was evaluated at 7 days after termination of each treatment. The result of this study revealed that common bean was able to tolerate and recover from gradual water deficit for up to 8 days; however, prolonged water deficit for 12 days inhibited the growth of above-ground organs in common bean. Despite root regrowth during the recovery period, plants previously treated with 12 days of drought were unable to recover but those treated with shorter drought stress period were able to recover.

Molecular mapping of aluminium resistance loci based on root re-growth and Al-induced fluorescent signals (callose accumulation) in lentil (Lens culinaris Medikus).

Development of aluminium (Al) resistant genotypes through molecular breeding is a major approach for increasing seed yield under acidic conditions. There are no available reports on mapping of Al resistance loci and molecular breeding for Al resistant varieties in lentil. The present study reports a major quantitative trait loci (QTL) for Al resistance using simple sequence repeat (SSR) markers in F2 and F3 mapping populations derived from contrasting parents. Phenotypic response to Al was measured on the bases of root re-growth (RRG), fluorescent signals (callose accumulation) and Al contents in hydroponic assay. After screening 495 SSR markers to search polymorphism between two contrasting parents, 73 polymorphic markers were used for bulk segregation analysis. Two major QTLs were identified using seven trait linked markers, one each for fluorescent signals and RRG mapped on linkage group (LG) 1 under Al stress conditions in F2 mapping population of cross BM-4 × L-4602. One major QTL (qAlt_fs) was localised between PLC_88 and PBA_LC_373, covering 25.9cM with adjacent marker PLC_88at a distance of 0.4cM. Another major QTL (qAlt_rrg) for RRG was in the marker interval of PBA_LC_1247 and PLC_51, covering a distance of 45.7cM with nearest marker PBA_LC_1247at a distance of 21.2cM. Similarly, in F3 families of BM-4 × L-4602 and BM-4 × L-7903, LG-1 was extended to 285.9 and 216.4cM respectively, having four newly developed genic-SSR markers. These QTLs had a logarithm of odd (LOD) value of 140.5 and 28.8 along with phenotypic variation of 52% and 11% for fluorescent signals and RRG respectively, whereas, qAlt_rrg had LOD of 36 and phenotypic variance of 25% in F3 population of BM-4 × L-4602. Two major QTLs identified in the present study can be further dissected for candidate gene discovery and development of molecular markers for breeding improved varieties with high Al resistance.

Use of short-day treatment in the production of Norway spruce mini-plug seedlings under plant factory conditions

ABSTRACTMini-plug transplant seedlings of Norway spruce have been cultivated in closed growth systems, so-called plant factories, for few years. The aim of the experiment was to define a short-day treatment (SD) that harden seedlings to sustain 3 months of cold storage, but does not have adverse effects on growth, morphology, and vitality. The seedlings were subjected to one of the following treatments: (1) 12 h photoperiod + 3 weeks duration; (2) 8 h photoperiod + 3 wk duration; (3) 12 h photoperiod + 5 wk duration; and (4) 8 h photoperiod + 5 wk SD. All the SD treatments yielded healthy seedlings that grew well after the cold storage. The frost hardiness of the seedlings improved when the photoperiod was reduced from 12 to 8 h, and when the SD duration was increased from 3 weeks to 5 weeks, but reducing the photoperiod from 12 h to 8 h caused growth reductions. The root and shoot regrowth after cold storage was highest in seedlings that had received 12 h photoperiod and 5 wk duration. However, 12 h photoperiod and 3 wk duration may be an adequate practice for nurseries that treat multiple crops in their SD facilities.