Reduced Shoot Length Research Articles

Effects of growth retardants on sprouting and development of apricot (Prunus armeniaca L.) and neem (Azarchta indica A. Juss.) nodal buds

As a first step to the establishment of an in vitro conservation protocol for apricot and neem, the effect of several growth retardants on the sprouting and development from nodal buds of both species and meristem development at the histological level was evaluated. Nodal section bud sprouting was affected by growth retardants, ranged from 4 to 100 % in apricot and from 10 to 100 % in neem, depending on the retardant and its concentration. Retardants paclobutrazol (PBZ), flurprimidol (FMD), diniconazole (DIN), and acetyl-salicylic acid (ASA) produced a drastic reduction of shoot length in apricot. PBZ, DIN and ASA decreased the number of leaves, whereas 1-Aminocyclopropane-1-carboxylic acid (ACC) at 10−5 µM improved the number of leaves. Length of neem sprouted buds as well as the number of leaves was affected by all of the growth retardants, with the exception of ACC that only affected the number of leaves. Triiodobenzoic acid (TIBA) at 10−5 µM improved neem shoot length. PBZ, FMD, and DIN produced several effects as very thin, long, and dark green colored leaves in shoots from both species. Once growth retardants were removed from the proliferation medium the recovery of apricot bud growth was good from PBZ and FMD at low and medium concentrations and from ACC and ASA at all concentrations tested. In neem, the recovery was good only from TIBA and ASA at low concentrations; TIBA at 10−5 µM produced an increment of shoot length higher than the control. Histological changes observed in the meristems of apricot and neem buds during growth retardation induced by FMD and ASA could be related to some extent with those observed in the dormant shoot apex.

Improving fruit quality and tree health of Prunus persica cv. ‘Sandvliet’ through combined mineral and salicylic acid foliar applications

Foliar products that can address crop protection through systemic resistance and simultaneously also enhanced fruit quality will promote a reduction for the requirement of chemical applications in commercial orchards. Such products may include flavonoids and salicylic acid combined with mineral nutrients such as calcium, potassium, magnesium and boron which are widely linked to enhancing plant resistance to pathogens. In this study the efficacy of foliar formulations to improve fruit quality and enhance tree health of Prunus persica cv. ‘Sandvliet’ over two seasons were evaluated. Alexin™-containing foliar applications were effective in controlling Xanthomonas infection on both leaves and fruit of ‘Sandvliet’. The efficiency was however related to the infection incidence which varied between organs and seasons. During the second season, all treatments reduced shoot length compared to the unsprayed control. K-Max™ and Alexin™ treatments confirmed the role of potassium (K) in disease resistance. Xanbac™ reduced the severity of Xanthomonas infections, but the efficacy varied between seasons. Applications of Alexin™, Cropbiolife™ and K-Max™ significantly increased fruit size to the control.

Copper oxide nanoparticle toxicity in mung bean (Vigna radiata L.) seedlings: physiological and molecular level responses of in vitro grown plants

In this study, the toxic effect of copper oxide nanoparticles (CuONPs) at the physiological and molecular level was investigated in mung bean (Vigna radiata L.) plants. The seedlings were grown in half strength Murashige and Skoog medium supplemented with different concentrations of CuONPs (0, 20, 50, 100, 200 and 500 mg l−1) for 21 days under controlled growth conditions. Exposure to 200 and 500 mg l−1 of CuONPs significantly reduced shoot length and biomass. Significant reduction in root length and biomass was observed upon exposure to all concentrations of CuONPs. Retardation of primary and lateral root growth was observed upon exposure to different concentrations of CuONPs. At 100, 200 and 500 mg l−1 of CuONPs exposure, the total chlorophyll contents reduced significantly. Exposure to different concentrations of CuONPs has not resulted in any significant change in carotenoid contents. The proline content significantly increased upon exposure to 100, 200 and 500 mg l−1 of CuONPs. Significant increase in hydrogen peroxide content and lipid peroxidation was observed in roots upon exposure to 20, 50, 100, 200 and 500 mg l−1 of CuONPs. Histochemical staining with nitroblue tetrazolium and treatment with 3′-(p-hydroxyphenyl) fluorescein indicated a concentration-dependent increase in reactive oxygen species generation in roots. Exposure to CuONPs has resulted in excess lignification of roots cells as revealed by phloroglucionol-HCl staining. Gene expression analysis using real-time polymerase chain reaction showed modulations in the expression of CuZn superoxide dismutase, catalase and ascorbate peroxidase genes in roots of CuONPs exposed plants.

Induced tree response to herbivory influences the foraging preference and performance of a conifer‐defoliating sawfly

AbstractHerbivory often alters the growth and development of woody plants and can thereby render hosts less susceptible to subsequent herbivores. We carried out field surveys and experiments to investigate how previous herbivory influences adult egg lay, larval feeding preference, and associated survival of the yellowheaded spruce sawfly, Pikonema alaskensis (Rohwer) (Hymenoptera: Tenthredinidae), within crowns of black spruce, Picea mariana (Mill.) Britton et al. (Pinaceae). Pikonema alaskensis females laid nearly twice as many eggs, and late‐instar larvae consumed nearly twice as much foliar biomass, on undefoliated vs. defoliated branches. The major factor driving the lower incidence of egg lay on defoliated branches was a significant reduction in the availability of preferred size classes of shoots. In general, adult females preferred medium‐sized shoots, whereas late instars preferred large shoots; previous defoliation generally decreased the availability of medium and large shoots. In a field bioassay, late‐instar survival generally declined with increasing defoliation, which again corresponded to significant reductions in shoot length on defoliated branches. The tendency of P. alaskensis to avoid shoots on severely defoliated branches is likely to increase the time lag between herbivory and the feedback effects of induction and could thus contribute to fluctuations in sawfly population density during outbreak. Our results differ from numerous past studies of closely related diprionid sawflies in conifers, most of which have reported weak or positive effects of previous herbivory on host susceptibility; we attribute the observed responses of spruce to the unusual sawfly feeding preference of P. alaskensis for developing conifer foliage.

Chloroplastic and mitochondrial GPX genes play a critical role in rice development

Plant glutathione peroxidases (GPX) catalyze the reduction of H2O2 or organic hydroperoxides to water, mitigating the toxicity of these compounds to cells. In rice plants, the GPX gene family is composed of five members that are distributed in a range of sub-cellular compartments including cytosol, mitochondria, chloroplasts, or endoplasmic reticulum. Of these, OsGPX1 and OsGPX4 are located in mitochondria and chloroplasts, respectively. To understand the role of these GPX in rice, the effect of knockdown of OsGPX1 and OsGPX4 in rice plants was evaluated. Our data show that OsGPX4 was essential for in vitro rice regeneration because no plants were obtained from calli carrying a hairpin construct against OsGPX4. Although the knockdown of OsGPX1 did not impair plant regeneration, the plants with silenced OsGPX1 (GPX1s plants) showed reduced shoot length and a reduced number of seeds compared to the non-transformed rice plants. These results indicate that OsGPX1 and OsGPX4 are essential for redox homeostasis which leads to normal growth and development of rice.

Characterization of plant growth-promoting traits of Penicillium species against the effects of high soil salinity and root disease

This study investigated the plant growth promotion and stress mitigation effects of Penicillium species RDA01, NICS01, and DFC01 on sesame (Sesamum indicum L.) plants. The fungal isolates NICS01 and DFC01 significantly enhanced shoot length, root length, and fresh and dry seedling weight, due to the secretion of various concentrations of amino acids (Asp, Thr, Ser, Asn, Glu, Gly, Ala, Val, Met, Ile, Leu, Tyr, Phe, Lys, His, Try, and Arg). Penicillium sp. NICS01 increased the amount of chlorophylls, proteins, amino acids, and lignans in the sesame plants more so than in controls. Sesame plant growth was stunted by high soil salinity, and application of the three fungal isolates increased plant survival. The RDA01 and NICS01 strains significantly increased shoot length and fresh and dry seedling weights under salt stress conditions. In addition, an in vitro study of the Penicillium spp. revealed their antagonistic activity toward the pathogenic fungi Fusarium spp. Fusarium spp. reduce shoot length; co-inoculation with the NICS01 or DFC01 isolates significantly increased shoot length in infected plants. Our results suggest that exogenous application of the Penicillium sp. NICS01 can act as a biofertilizer and a biocontrol agent to improve plant growth and enhance plant survival against salt stress and Fusarium infection.

Growth, Yield and Seed Nutritional Composition of Groundnut (<i>Arachis hypogaea</i> LINN) under Elevated Level of Soil Salinity

A field experiment was conducted to investigate the effect of salinity on growth, yield and nutritional composition of Arachis hypogaea L. (groundnut) to evaluate its tolerance level. Plants were irrigated with 0 (control), 25, 50, 100, 150 and 200 mM NaCl solution. Mortality 30% and 50% occurred only at 150 and 200 mM concentrations respectively. Salinity significantly reduced shoot length, collar diameter, leaf area, root length and relative growth rate (RGR). Number of leaves, branches, roots, primary branches and root nodules/plant declined with increasing NaCl concentration. Fresh and dry mass of plant parts were significantly lower under saline soil than in control, which culminated in reduced total biomass. Leaf total chlorophyll decreased significantly from 100 mM NaCl to higher concentrations. Plants grown in saline soil had slightly higher root: shoot ratio than in control. Yield parameters decreased with increasing salt concentration except number of seeds/pod. Number of pods/plant differed from control significantly except at 25 and 50 mM NaCl. Pods produced at 200 mM lacked seeds. Salinity reduced seed mineral content except phosphorus (P), while percentage sodium (Na) increased with increasing salinity. Cl - and Na + accumulated in the seeds of salt-treated plants, which resulted in elevated level of percentage ash. Percentage fibre was not affected while carbohydrate, protein and lipid were reduced by soil salinity but at a non-significant level. Arachis hypogaea can tolerate and produce reasonable yield up to 50 mM NaCl concentration, but not fit for soil above 150 mM NaCl.

EXOGENOUS APPLICATION OF PROHEXADIONE-CALCIUM PROMOTES FRUIT COLOUR DEVELOPMENT OF 'CRIPPS PINK' APPLE

The effects of various concentrations and number of sprays of prohexadione-calcium(ProCa) and summer pruning (SP) alone on fruit colour and other quality parameters of ‘Cripps Pink’ apple were investigated. The treatments were: (i) no spray as control, (ii) SP, (iii) 250 mg L-1 with two sprays (3 and 33 days after full bloom (DAFB), (iv) 500 mg L-1 with two sprays (3 and 33 DAFB), (v) 750 mg L-1 with two sprays (3 and 33 DAFB), (vi) 250 mg L-1 with three sprays (3, 33 and 63 DAFB),(vii) 500 mg L-1 with three sprays (3, 33 and 63 DAFB), and (viii) 750 mg L-1 with three sprays (3, 33 and 63 DAFB). Spraying was done on fruits of a whole treated tree. The reduction in shoot length was pronounced after the second spray application of ProCa regardless of concentration. The treatment of two sprays of500 mg L-1 ProCa and three sprays 500 and 750 mg L-1 of ProCa showed the highest reduction in the shoot length as compared to control. The SP alone, and three sprays of 500 and 750 mg L-1 ProCa at 3, 33 and 63 DAFB, respectively significantly improved percent red blush, percent fruit for export, higher a* value and lower b*,L* and hue angle values on the fruit as compared to control. The treatment of three sprays of 750 mg L-1 ProCa resulted the highest accumulation of cyanidin 3-ogalactosidein apple skin.

Systematic Analysis of Branching Patterns of Three Almond Cultivars with Different Tree Architectures

Different almond (Prunus dulcis) cultivars have been characterized by their contrasting shoot branching patterns; however, the differences between patterns have been difficult to quantify. This study aimed to model the branching patterns of 2-year-old proleptic shoots on three almond cultivars (Nonpareil, Aldrich, and Winters) representing different tree architectures. The effects of branching pattern on flowering were also studied. The branching patterns of shoots of different length categories were assessed by a single hidden semi-Markov model for each cultivar. The models identified zones of homogeneous branching composition along shoots and were used to extract the occurrence and number of nodes of the zones according to shoot length categories. The numbers of flower buds were also determined for each shoot length category in each cultivar. The models of branching patterns of ‘Nonpareil’ and ‘Aldrich’ were similar and differed from the ‘Winters’ model. ‘Winters’ shoots produced more zones, but some of the zones had similar characteristics as previous zones and thus appeared to be repeated. This cultivar also had more spurs and sylleptic shoots than the other cultivars. The occurrence and node number of the central zones decreased along with reduction in shoot length in all the cultivars. ‘Aldrich’ tended to have more flower buds than comparable-length shoots of the other two cultivars. This study provides a quantitative description of the shoot branching patterns of three important cultivars and explains how branching changes in relation to shoot length, whereas production of flower buds varies despite similar branching patterns.

Effects of girdling on fruit abscission, yield and shoot growth in macadamia

In Australian macadamia (Macadamia integrifolia Maiden and Betche, M. tetraphylla Johnson and hybrids) orchards, trees are generally side-hedged in early spring to maintain the inter-row for efficient orchard management. Hedging at this time increases fruit abscission and decreases yield due to competition for carbohydrates between fruit and post-pruning shoot growth, and to the loss of photosynthetic area. Girdling increases fruit set in many crops and the possibility that girdling might mitigate the effect of pruning on fruit abscission and yield was investigated in this study. Girdling was also investigated for its potential to control shoot growth and tree size. In the first experiment, in early spring around anthesis, trees were pruned (P), pruned and girdled (PG), or were left as unpruned and ungirdled control trees. Fruit per raceme over time, percent of racemes with fruit at 20 weeks post anthesis, fruit number per tree, nut weight, yield, and the shoot length and number of the post-pruning flush were measured. In a second experiment, trees were pruned (P) or pruned and girdled (PG) in autumn, and the shoot length and number of the post-pruning flush were measured. In a third experiment, trees were girdled at anthesis in 3 years over a 4-year period and shoot growth, tree height, yield, fruit number and nut weight were compared with ungirdled control trees. Girdling mitigated the effect of pruning on fruit abscission and yield but the mitigation was slight with PG trees producing 28% less yield than unpruned control trees. Girdling reduced shoot length and number but more so on unpruned branches (26% and 28%, respectively) than on pruned branches (10% and 14%, respectively). The tree height increment in girdled trees was around half that of ungirdled trees. In the 4-year study, girdling increased yield by around 10% in two out of four seasons, and decreased it in one season. Cumulative yields were similar for girdled and ungirdled trees. This study has shown that girdling was not useful in mitigating the effect of pruning on yield. However girdling was effective in controlling shoot growth and tree size, with no reduction in cumulative yield, and may be useful as a tree size control strategy. Further monitoring of long-term effects of repeat girdling is required to confirm this.

Atividade alelopática de extrato acetato-etílico de folhas de Solanum cernuum Vell

The aim of this study was to evaluate the allelopathic action of an ethyl-acetate extract of the leaves of Solanum cernuum Vell (Solanaceae) relative to the inhibitory effect on seed germination and seedling vigour in Sorghum bicolor L. (sorghum), Lactuca sativa L. (lettuce) and Bidens pilosa L. (Spanish needle). The phytotoxic activity of the ethyl acetate extract was evaluated at concentration s of 0.00; 31.25; 62.50; 125.00; 250.00; 500.00; 750.00 and 1000.00 mg L -1 . The variables analyzed were: percentage of germination; germination speed index; length of shoot and root; and seedling dry weight. The results showed a phytotoxic effect for the ethyl acetate extract of S. cernuum on sorghum, lettuce and Spanish needle for at least one of the variables analysed. For Spanish needle, all the variables except dry mass suffered significant reductions (p<0.05). There are phytotoxic effects for the ethyl acetate extract of Solanum cernuum Vell on seed germination and seedling vigour in sorghum, lettuce and Spanish needle. From the species studied, Spanish needle is the most sensitive, with a 69% reduction in shoot length and an 88% reduction in root length in the presence of the extract of S. cernuum at 100mg L -1 .

Effects of an Innovative Strategy to Contain Grapevine Bois Noir: Field Treatment with Resistance Inducers

Grapevine Bois noir (BN) is a phytoplasma disease that is widespread in most viticultural regions of the world, and it can result in heavy reductions to yields and grape juice quality. At present, there is no effective strategy to reduce the incidence of BN-infected grapevines. However, phytoplasma-infected plants can recover through spontaneous or induced symptom remission. Five elicitors (chitosan, two glutathione-plus-oligosaccharine formulations, benzothiadiazole, and phosetyl-Al) were applied weekly to the canopy of BN-infected 'Chardonnay' grapevines from early May to late July. The best and most constant recovery inductions were obtained with benzothiadiazole and the two glutathione-plus-oligosaccharine formulations. The plants that recovered naturally or following the elicitors showed qualitative and quantitative parameters of production no different from healthy plants. In another vineyard, diseased plants showed reduced shoot length and production compared with healthy plants, and there were no negative effects on these parameters for grapevines sprayed with a glutathione-plus-oligosaccharine formulation. The application of resistance inducers promoted the recovery of BN-infected grapevines with no adverse effects on the plants. Therefore, grapevine can be used as a model species to test this innovative strategy to contain phytoplasma diseases.

Evaluation of Brassica species for resistance to Rhizoctonia solani and binucleate Rhizoctonia (Ceratobasidum spp.) under controlled environment conditions

Isolates of R. solani AG 2–1, AG 8, AG 10 and binucleate Rhizoctonia (Ceratobasidium spp.) were tested for virulence on Brassica crops in growth chamber experiments. Isolate virulence and genotype resistance were determined based on percent of seedling survival, shoot length reduction, and shoot fresh weight. Isolates had significant effects on all tested measurements, compared to the non-inoculated controls. Rhizoctonia solani AG 2–1 appears to be the most aggressive pathogen on all tested genotypes followed by R. solani AG 8, binucleate Rhizoctonia and R. solani AG 10, respectively. Genotype by isolate interaction effects were found to be significant for percent of seedling survival and shoot length reduction. None of the tested genotypes exhibited any level of resistance to R. solani AG 2–1, but three promising genotypes with moderate levels of resistance to R. solani AG 10, R. solani AG 8 and binucleate Rhizoctonia were identified. Moderate heritability (0.57) was observed for the percent of seedling survival in the resistant genotype KS4022.

Effect of Irrigation with Contaminated Water by Cloth Detergent on Seed Germination Traits and Early Growth of Sunflower (Helianthus annuus L.)

One of the sources for irrigation is sewage. Contaminated water may affect seed germination and plant growth. A laboratory experiment and a pot experiment were conducted in 2012 to determine the effect of different doses of detergent on seed germination traits and early growth of sunflower (Helianthus annuus L.). The experiments included eight doses of cloth detergent (0, 0.00002, 0.0002, 0.002, 0.02, 0.2, 2, 20 g/L). Results showed that 20 and 2 g/L of detergent severely reduced seed germination, plant height, leaf number per plant, total biomass and stem weight. 20 g/L of detergent reduced shoot length, root length, seedling weight and seed vigor. Seed germination stage was more sensitive to contaminated water than early growth stage. The results demonstrated that irrigating sunflower by contaminated water with household cleaning products at high concentration should be avoided.

Efficient micropropagation and chlorocholine chloride induced stevioside production of Stevia rebaudiana Bertoni

A promising method of micropropagation of Stevia rebaudiana Bertoni has been developed with an aim to increase the biomass, survivability of the plantlets and stevioside production, using chlorocholine chloride (CCC). Microshoots transferred to the MS medium containing different combinations CCC and IBA were found to be most effective in terms of growth pattern, hardening ability of the plantlets and stevioside content, compared to MS medium containing either IBA or CCC. Among other combinations tested, MS medium supplemented with 3mg/l CCC and 3mg/l IBA was found most effective in inducing significant changes like reduced shoot length, increased number of roots, higher leaf size, increased biomass and chlorophyll retaining capacity, higher survival percentage and most importantly the elevated stevioside content. Collectively, the major observations of this research indicate that application of CCC in micropropagation of S. rebaudiana Bertoni is a promising approach and has commercial prospects.

Effects of Hexaconazole on Growth and Antioxidant Potential of Cucumber Seedlings under UV-B Radiation

The present study was conducted to determine the effect of hexaconazole (HEX), a triazole fungicide, on the growth, yield, photosynthetic response and antioxidant potential in cucumber (Cucumis sativus L.) plants subjected to UV-B stress. UV-B radiation and HEX were applied separately or in combination to cucumber seedlings. The growth parameters were significantly reduced under UV-B treatment, however, this growth inhibition was less in HEX treated plants. HEX caused noticeable changes in plant morphology such as reduced shoot length and leaf area, and increased leaf thickness. HEX was quite persistent in inhibiting shoot growth by causing a reduction in shoot fresh and dry weight. HEX noticeably recovered the UV-B induced inhibition of biomass production. Significant accumutation in anthocyanin and flavonoid pigments in the leaves occurred as a result of HEX or UV-B treatments. HEX permitted the survival of more green leaf tissue preventing chlorophyll content reduction and higher quantum yield for photosystemⅡ under UV-B exposure. HEX treatment induced a transient rise in ABA levels in the leaves, and combined application of HEX and UV-B showed a significant enhancement of ABA content which activates H2O2 generation. UV-B exposure induced accumulation of H2O2 in the leaves, while HEX prevented UV-B induced increase in H2O2, indicating that HEX serves as an antioxidant agent able to scavenge H2O to protect cells from oxidative damage. An increase in the ascorbic acid was observed in the HEX treated cucumber leaves affecting many enzyme activities by removing H2O2 during photosynthetic processes. The activities of antioxidant enzymes including catalase(CAT), ascorbate peroxidase(APX), superoxide dismutase(SOD) and peroxidase(POD) in the leaves in the presence of HEX under UV-B stress were higher than those under UV-B stress alone. These findings suggest that HEX may participate in the enhanced tolerance to oxidative stress. From these results it can be concluded that HEX moderately ameliolate the effect of UV-B stress in cucumber by improving the components of antioxidant defense system.

Silicon significantly alleviates the growth inhibitory effects of NaCl in salt-sensitive ‘Perfection’ and ‘Midnight’ Kentucky bluegrass (Poa pratensis L.)

The study was conducted to clarify the effects of silicon on the salt-sensitive ‘Perfection’ and ‘Midnight’ Kentucky bluegrass (Poa pratensis L.). The 400 mM NaCl treatment reduced shoot length, fresh and dry weight of shoot and root as well as relative water content and chlorophyll and carotenoid content in both cultivars. The NaCl caused an increase in electrolyte leakage, malondialdehyde concentration and H2O2 in both cultivars. This physiological interferences and visually noticeable disturbances in Kentucky bluegrass were significantly alleviated by the addition of silicon after salt stress. In ‘Perfection’, for example, 0.1 mM silicon application after NaCl treatment significantly increased in the shoot length by 48%, the fresh weight of the shoot by 72%, the relative water content by 61%, and the total chlorophyll content by 57%. Compared to the NaCl-only treatment, significant reduction in the electrolyte leakage and the concentration of malondialdehyde and H2O2 were observed in silicon treatment.

English

In order to study performance of mungbean to salinity stress, a laboratory experiment was carried out to investigate salinity tolerance of two mungbean varieties (Kawmy-1 and IV 2010) to eight salinity levels i.e. 0, 2, 4, 6, 8, 10, 12 and 14 dS/m of NaCl concen- trations. Mungbean (Vigna radiata (L.) Wilczek) varieties were compared for germination efficiency and seedling characters. Results indi- cated that mungbean IV 2010 variety recorded the highest percentages of final germination, germination index %, seedling vigor index, energy of germination, mean germination time (day), coefficient velocity, abnormal seed percentage, root and shoot length, root fresh and dry weight and seedling height reduction. Whilst, mungbean Kawmy-1 variety recorded the highest weight of fresh and dry shoot and relative dry weight. Highest germination parameters and seedling characters of the two studied varieties under control treatment. The obtained results suggested that the two varieties registered a decrease in the percentage of germination and seedlings growth at higher NaCl concentrations. Results clearly indicated that mungbean Kawme-1 variety appeared to be more tolerant to salt stress than IV 2010 variety recording higher germination parameters and seedling characters. Increasing salinity concentrations significantly reduced germi- nation percentage, seedling vigor index, coefficient of velocity, mean germination time, shoot and root length, shoot and root fresh and dry weight. It could be concluded that germination efficiency i.e. final germination percentage, germination index, energy of germination, mean germination time, abnormal seed percentage, root and shoot length, seedling total fresh and dry weight, dry weight reduction and shoot length reduction were gradually decreased significantly when salinity increased.

EFFECT OF RED-, FAR-RED- AND BLUE-LIGHT-EMITTING DI-ODES ON IN VITRO GROWTH OF FICUS BENJAMINA

The effects of monochromatic blue, red and far-red light from commercial available light-emitting diode modules on the in vitro growth of Ficus benjamina ‘Exotica’ were compared with the effect of fluorescent light. The plants were micropropagated on a basal medium with 0.5 mg/L IAA and 2 mg/L BA. Our study showed that monochromatic blue, red and far-red and their combinations are suitable to manipulate the number of shoots, shoot length, shoot/callus weight ratio and leaf length/width ratio in Ficus benjamina. In general, the presence of blue light had a stimulating effect on the number of shoots, but also reduced shoot length. Grown under red light, the explants produced less but more elongated shoots. Blue light stimulated callus growth even in the presence of red light. Far-red had a negative effect on biomass production in general with a reduction in total number of shoots and both shoot cluster and callus weight. Under red and far-red light conditions, the morphology of the leaves was different from blue light conditions with an increase in relative leaf length as the most prominent characteristic.

Epiphytic bryophytes near forest edges and on retention trees: reduced growth and reproduction especially in old‐growth‐forest indicator species

Summary Epiphytes are an important component in many forest ecosystems. The proportion of threatened epiphyte species is high, and the impact of clearcuts on key demographic processes via edge‐influence is still poorly understood. There are few studies on epiphyte growth, and even less is known about how reproduction is affected by proximity to forest edges. For retention trees, demographic studies are even scarcer. Based on the results from a 6‐month transplant experiment and a 3‐year study of natural colonies, we modelled growth and reproduction of epiphytic bryophytes used as indicators of old‐growth forests and widespread epiphytes in relation to distance from the forest edge. We also modelled growth and reproduction on retention trees within the clearcut. Species responses were linked to variation in canopy openness. Unlike the widespread species, the old‐growth‐forest indicators grew exponentially with distance from the edge, and this response was more pronounced at the south‐east than north‐west forest edge. In one red‐listed species, reproduction was thoroughly inhibited near the edge, whereas the reproductive rate of the widespread species tended to increase. However, the widespread species also showed reduced shoot lengths on the retention trees. Reduced growth and inhibited reproduction of sensitive epiphytes near edges decrease the number of dispersing diaspores and may, in combination with lower local connectivity and increased tree fall rates close to edges, increase the risk of metapopulation extinction. Synthesis and applications. Two general management implications for boreal forests are drawn. First, retention trees may not have the capacity to act as a ‘lifeboat’ for epiphytic bryophytes and support their populations during the regeneration phase. Second, the creation of buffer zones is a useful conservation strategy for bryophytes. The exact width of zones depends on the forest structure and should be orientated in relation to the requirements of the most sensitive species. For the rather dense experimental forest, a width of at least 30 m was required for the south‐facing buffer, whereas for the north‐facing buffer 10 m was sufficient.