Biochemical responses associated with induced resistance to Colletotrichum acutatum in Pinus radiata seedlings treated with methyl jasmonate and Trichoderma spp.

The effect of Trichoderma (T. atrobrunneumFCC320 and T. atrovirideLU633) and/or methyl jasmonate (MJ) on resistance to terminal crook (Colletotrichum acutatum) and on seedling biochemistry was investigated in radiata pine (Pinus radiata) seedlings. Seedlings were germinated and grown in Trichoderma‐amended or non‐amended media for 3 months and then sprayed with 2.25 mM MJ 1 week before inoculation with C. acutatum. The incidence and severity of terminal crook in the seedlings treated with MJ and Trichoderma+MJ were lower than in Trichoderma‐treated and Trichoderma‐untreated seedlings. The MJ‐induced resistance response was concomitant with an increase in the concentrations of the monoterpenes α‐pinene, β‐pinene, β‐phellandrene, camphene and myrcene in needles, and also α‐pinene, β‐pinene and camphene in stems. The concentrations of α‐pinene, β‐pinene and camphene were elevated from at least 1 week until 4 weeks after MJ application, compared with those in non‐MJ counterparts. Trichoderma alone did not affect monoterpenes, but the concentrations of α‐pinene, β‐pinene and camphene were greater in needles of Trichoderma+MJ than in MJ‐treated seedlings after 28 days. Total phenolic concentration in needles and peroxidase activity in stems were twofold greater in MJ‐treated seedlings than in non‐MJ seedlings over the same period. None of the treatments affected the activity of peroxidase in needles. It is proposed that the accumulation of monoterpene and phenolics and the induction of peroxidases contribute, in part, to MJ‐induced resistance to terminal crook in radiata pine seedlings.     

Enhancing resistance in Pinus radiata seedlings to terminal crook (Colletotrichum acutatum) using methyl jasmonate and ultraviolet‐C radiation

Colletotrichum acutatum is a fungal pathogen that causes terminal crook disease in radiata pine (Pinus radiata) seedlings in New Zealand forest nurseries. Symptoms of infection include malformation or death of the growing tip and a stiffening and thickening of the stem. Although the disease can be managed effectively using fungicides, the New Zealand forest industry is interested in alternative control options such as induced resistance. The aim of this study was to evaluate spray application of chitosan (1.4 g/l) or 2.25 mm methyl jasmonate (MeJA) and irradiation with UV‐C (2.16 kJ/m²) for their potential to induce resistance to terminal crook. The treatments were applied to 4‐month‐old seedlings at 1 week before pathogen inoculation. By the end of the experimental period (42 days after inoculation), there was 80% disease incidence in the controls, with 48% of seedlings exhibiting severe terminal crook symptoms. The most effective treatment (p < 0.05) was MeJA with 16% disease incidence and none with severe symptoms. UV‐C also significantly (p < 0.05) reduced infection with 52% incidence and 20% of seedlings exhibiting severe symptoms. Chitosan did not reduce disease incidence (72%) compared with the control (80%) but did significantly reduce (p < 0.05) disease severity with 28% exhibiting severe symptoms. MeJA was the only treatment that significantly (p < 0.05) reduced the detrimental effects of infection on seedling apical growth and stem diameter. To our knowledge, this is the first report demonstrating the potential for MeJA and UV‐C to control terminal crook in radiata pine.     

Changes in Ectomycorrhizal Colonization and Root Peroxidase Activity in Pinus sylvestris Nursery Seedlings Planted in Forest Humus

Plant biomass, root colonization by ectomycorrhizal (ECM) fungi and root peroxidase (POD) activity were monitored in Scots pine (Pinus sylvestris L.) nursery seedlings during the first growing season after planting (after 4, 8 and 16 weeks, in July, August and October, respectively) in forest humus in outdoor open-top chambers with gaseous atmospheric pollutants (combinations of low levels of ozone, sulfur dioxide and nitrogen oxides). The number of ECM morphotypes as well as root biomass increased towards the end of the growing season, while root POD activity decreased. Fungal biomass estimated as ergosterol concentration peaked in August, 8 weeks after planting. The seedling growth, mycorrhizal status and POD activity in the roots were not affected by the gaseous pollutants.     

Surveys for asymptomatic persistence of Sphaeropsis sapinea on or in stems of red pine seedlings from seven Great Lakes region nurseries

The fungus Sphaeropsis sapinea persists on or in stems of asymptomatic red pine (Pinus resinosa) nursery seedlings, and proliferates to cause collar rot and mortality after planting. In the spring of 2002, seven nurseries were surveyed to determine the potential range in frequency of asymptomatic persistence: three operated by Wisconsin Department of Natural Resources (DNR), two by Minnesota DNR, one by Michigan DNR, and one by USDA Forest Service (in Michigan). At each nursery five groups of 20 asymptomatic red pine seedlings were collected near an inoculum source (red pine windbreak), if present, and five groups of 20 asymptomatic seedlings were collected away from such a source (1400 seedlings total). A segment of the lower stem/root collar from each seedling was surface disinfested and incubated on tannic acid agar. Transfers were made from resulting colonies and the pathogen identified from pycnidia and conidia produced in culture. The pathogen was identified from asymptomatic seedlings collected in all Wisconsin and Minnesota nurseries, but was never detected from seedlings from the Michigan DNR or USDA Forest Service nurseries. Frequencies of detection were greater (as high as 88%) from asymptomatic seedlings near red pine windbreaks including diseased trees than from seedlings distant from such windbreaks. A subset of isolates from asymptomatic seedlings was characterized using inter‐simple sequence repeat–polymerase chain reaction analysis. Most isolates were the A group of S. sapinea, but B group isolates (recently named Diplodia scrobiculata) were also obtained from one nursery. One Minnesota nursery was more extensively sampled in 2003, with 17–44 groups of five asymptomatic red pine seedlings collected in four separate fields (525 seedlings total). The mean frequency of detection of the pathogen in these four fields ranged from 40 to 71%. Persistence of S. sapinea on or in asymptomatic seedlings continues to be problematic, not only because of the potential for subsequent seedling mortality, but also as a means by which a pathogen may be widely distributed.     

Sand pine (Pinus clausa) seedling distribution and biomechanics in relation to microsite conditions and proximity to potential nurse plants

We investigated the distribution of sand pine (Pinus clausa) seedlings in relation to the locations of hardwoods and palmettos that had resprouted in five recently clear-cut and one burned stand in sand pine scrub vegetation in Ocala National Forest (Florida, USA). We also studied how the shade and mechanical support provided by the taller resprouts affect the allometry and biomechanics of sand pine seedling stems. Although soil surface temperatures were higher and soil moisture contents (0–5 cm) were lower in open than in covered microsites, sand pine seedling densities did not vary in relation to proximity to resprouted hardwoods and palmettos. There was no apparent nurse plant effect on sand pine seedling distributions, but seedlings that grew up under the resprouts had larger whole stem flexibilities, greater height:diameter ratios, and less tapered stems. In response to the mechanical support and shade of neighboring plants, sand pine seedlings grow taller per unit investment in stem tissue, thereby shortening the period during which they presumably suffer from above-ground competition. This biomechanical plasticity increases the rates at which sand pine seedlings can overtop their resprouted competitors.     

Vascular cambial sucrose metabolism and growth in loblolly pine (Pinus taeda L.) in relation to transplanting stress

Sucrose synthase (SS) was the dominant enzyme of sucrose metabolism in both stem and root vascular cambial zone tissues of nursery-grown loblolly pine (Pinus taeda L.) seedlings. Acid invertase (AI) and neutral invertase (NT) activities were generally less than 10% of the SS activity in both tissues. In both cambial tissues, seasonal patterns of enzyme activity were observed for SS but not for AI or NI. The seasonal patterns of SS activity in stem and root cambia paralleled the periodic growth of stems and roots. Stems had high SS activity and growth during summer and early fall. Roots had substantial SS activity and growth during summer and fall, but SS activity and growth were even higher in winter. When seedlings were transplanted, about eight months elapsed before stem and root cambia resumed rates of growth and sucrose metabolism similar to those in control nontransplanted seedlings. Two months after transplanting, root SS was at its lowest, whereas AI activity in transplants was 50% higher than in control nontransplanted seedlings. In stems, SS activity decreased in response to transplanting, whereas AI and NI activities did not change appreciably. In loblolly pine tissues, SS was specific for uridylates, whereas the nucleotide triphosphate-dependent phosphofructokinase (NTP-PFK) had similar activity with either UTP or ATP. Except in winter, the NTP-PFK was less active than the pyrophosphate-dependent phosphofructokinase (PPi-PFK) during all seasons. The PPi-dependent PFK activity in nontransplanted seedlings followed similar seasonal and spatial patterns to those of SS activity. In actively growing tissues, such as stem cambial tissues in summer and root cambial tissues in winter, the measured total PFK to SS ratio ranged between 1.5/1 and 3/1. In contrast, in less actively growing tissues or transplanted seedlings, a greater decrease occurred in SS than in PFK activity, hence the ratio rose to as high as 12/1. It was concluded that: (1) SS was the dominant enzyme for sucrose metabolism in root and stem cambial tissues of loblolly pine seedlings; (2) both SS and PPi-PFK in the cambial tissues can be used as biochemical indicators of growth sink strength in stems and roots; and (3) both enzymes can be used as indicators of seedling stress caused by events such as transplanting and winter freezing.     

Predicting seedling biomass of radiata pine from allometric variables

Allometric equations predict tree seedling biomass from non-destructively measured variables such as stem diameter (D), height (H) and seedling silhouette area (A), measured by digital imaging. This study investigates whether one general allometric equation can predict biomass of radiata pine (Pinus radiata D.Don) seedlings grown under three levels of photosynthetic photon flux density (PPFD). It also identifies which commonly used variables (A, D ² H or D ²) were the best for predicting seedling biomass under these conditions. Radiata pine seedlings were grown with constant daytime (12 h d⁻¹) PPFD = 500, 250 or 125 μmol m⁻² s⁻¹ for 11 weeks. Seedlings were randomly selected every 10 d for measurement. Analysis of covariance tested whether the relationship between seedling biomass and A, D ² H or D ² varied for each PPFD level. PPFD levels influenced the relationship between biomass and A, D ² H or D ². As a result, “full” allometric models which varied with PPFD levels were more accurate and precise at predicting biomass than “reduced” models which did not vary with PPFD level, although a “reduced” model using D ² also performed well.     

Influence of Stem Diameter on the Survival and Growth of Containerized Norway Spruce Seedlings Attacked by Pine Weevils (Hylobius spp.)

Pine weevils (Hylobius spp.) feeding on stem bark of young conifer seedlings pose a serious threat to forest regeneration-planting programmes in Nordic countries. This study was designed to determine the threshold diameter for planted, untreated containerized seedlings, above which pine weevils cause little or no damage. The effects of sublethal weevil damage on seedling growth were also assessed. In total, 5320 containerized spruce seedlings were planted on scarified and unscarified plots on three sites in southern Sweden. Seedlings in six size classes, which differed with regard to age (1.5-3.5 yrs) and cultivation density (28-446 seedlings m 2) were grown using the Combicell system. None of the seedlings was treated with insecticides, except for those in the smallest class, where both untreated and treated seedlings were used. Inspections were made periodically during the first 3 yrs and after both 5 and 7 yrs. A statistically significant relationship was found between seedling losses due to pine weevil attack and seedling stem-base diameter at the time of planting out, on both scarified and unscarified plots. For seedlings with a stem-base diameter of around 10 mm, mortality due to pine weevil attack on scarified plots was low enough to be considered negligible. This threshold diameter was several millimetres greater for seedlings planted on unscarified plots. An analysis of the relationship between the extent of weevil damage and seedling growth rate showed that among surviving seedlings, those that grew fast tended to show low levels of damage. On unscarified plots, the mortality rate amongst seedlings treated once with a permethrin insecticide was only one-third that of untreated seedlings. On scarified plots, the corresponding difference was somewhat smaller. Repeated insecticide treatment resulted in a pronounced reduction in seedling mortality on the unscarified plots, whereas the effect was weaker on scarified plots.     

Effects of soil temperature on biomass production and allocation in seedlings of four boreal tree species

One-year old seedlings of trembling aspen (Populus tremuloides Michx.), black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), and jack pine (Pinus banksiana Lamb.) were subject to seven soil temperatures (5, 10, 15, 20, 25, 30 and 35 °C) for 4 months. All aspen seedlings, about 40% of jack pine, 20% of white spruce and black spruce survived the 35 °C treatment. The seedlings were harvested at the end of the fourth month to determine biomass and biomass allocation. It was found that soil temperature, species and interactions between soil temperature and species significantly affected root biomass, foliage biomass, stem biomass and total mass of the seedling. The relationship between biomass and soil temperature was modeled using third-order polynomials. The model showed that the optimum soil temperature for total biomass was 22.4, 19.4, 16.0 and 13.7 °C, respectively, for jack pine, aspen, black spruce and white spruce. The optimum soil temperature was higher for leaf than for root in jack pine, aspen and black spruce, but the trend was the opposite for white spruce. Among the species, aspen was the most sensitive to soil temperature: the maximum total biomass for aspen was about 7 times of the minimum value while the corresponding values were only 2.2, 2.4 and 2.3 times, respectively, for black spruce, jack pine and white spruce. Soil temperature did not significantly affect the shoot/root (S/R) ratio, root mass ratio (RMR), leaf mass ratio (LMR), or stem mass ratio (SMR) (P>0.05) with the exception of black spruce which had much higher S/R ratios at low (5 °C) and high (30 °C) soil temperatures. There were significant differences between species in all the above ratios (P<0.05). Aspen and white spruce had the smallest S/R ratio but highest RMR while black spruce had the highest S/R but lowest RMR. Jack pine had the highest LMR but lowest SMR while aspen had the smallest LMR but highest SMR. Both LMR and SMR were significantly higher for black spruce than for white spruce.     

Grass interference limits resource availability and reduces growth of juvenile red pine in the field

The effects of competing grasses on resource availability, growth and ecophysiological characteristics of 3-0 red pine (Pinus resinosa Ait.) seedlings were examined the first two years following outplanting in Anoka County, Minnesota, USA. Equal numbers of seedlings were planted into suppressed and undisturbed grass communities in a sandy soil. Grass suppression was maintained throughout the first growing season, but partially discontinued thereafter on the site. During the first field season interference from grass reduced pine seedling root collar diameter, needle length, number of new root tips, and lateral root length by over 40%. Mean pre-dawn needle water potential was 0.55 MPa lower in undisturbed grass plots during a brief drought in year one, but otherwise water stress was not significantly (p=0.05) influenced by grass interference. The presence of grass also reduced, up to 50%, the photosynthetically active radiation reaching the seedling canopy. At the end of year one, total biomass N, P, K, and Ca content were significantly (p=0.05) less in seedlings growing in the undisturbed grass community. Nitrogen was deficient in seedlings growing in grass. After two growing seasons, seedling shoot length (p=0.03), root collar diameter (p=0.001), and needle length (p=0.001) were significantly less (40, 54 and 20%, respectively) for seedlings growing in undisturbed grass. Seedling growth reductions induced by grass competition were associated with multiple environmental stressors in the field and not restricted to water stress as was observed in earlier studies with pine species at low and mid-latitude sites.     

Adventitious root formation of two <Emphasis Type="Italic">Abies</Emphasis> species on log and soil in an old-growth subalpine forest in central Japan

We assessed stem burial and adventitious root formation of two late-successional species, Abies mariesii and A. veitchii, in central Japan. In a plot (5 × 5 m), all seedlings between 8 and 24 cm tall were excavated: six A. mariesii seedlings in soil, and six and four A. veitchii seedlings in soil and on logs, respectively. For each sampled seedling, the number of terminal bud scars (TBS) was counted on the aboveground and belowground stems. Stem length was measured, and divided into aboveground and belowground stems. Among the three groups (A. mariesii seedlings in soil and A. veitchii seedlings in soil or on logs), there was no significant difference in height or total root weight (sum of adventitious roots and primary roots), but diameter at ground level and number of TBS were significantly different. Counting TBS on the aboveground stem of seedlings in soil underestimated seedling age, whereas the estimate was much closer to the true age for seedlings on logs. Seedlings in soil formed more adventitious roots than seedlings on logs. A large proportion of the stem was buried in humus for seedlings in soil, while most of the stem was not buried in humus for seedlings on logs. These results suggest that substrate affects adventitious root formation, the formation of which is important to shade tolerance. Thus, our preliminary results suggest that consideration of adventitious root formation is necessary to understand seedling bank dynamics and estimate seedling ages of these Abies species in spatially heterogeneous old-growth subalpine forests.     

Morphology, gas exchange, and chlorophyll content of longleaf pine seedlings in response to rooting volume, copper root pruning, and nitrogen supply in a container nursery

Few pine species develop a seedling grass stage; this growth phase, characterized by strong, carrot-like taproots and a stem-less nature, poses unique challenges during nursery production. Fertilization levels beyond optimum could result in excessive diameter growth that reduces seedling quality as measured by the root bound index (RBI). We grew longleaf pine (Pinus palustris), a grass stage species, in containers of four different volumes (60–336 ml) either coated with copper oxychloride or left untreated and fertilized at low, medium, or high levels of nitrogen (N). In general, N concentration of tissues rose as N rate increased, with larger changes in concentration occurring between low and medium levels than between medium and high levels. N rate influenced root tissue N concentration less than it did stems and needles. Subtle needle color differences caused by N rate were significant, suggesting its potential utility during nursery production. As expected, seedlings grew larger as container volume increased and as N rate increased. Copper treatment, which we posited could influence the RBI, tended to increase root-collar diameter and tap root biomass and decrease total root volume. Chlorophyll abundance was affected more by N rate than by container volume or copper treatment, but photosynthesis was affected more by copper treatment than N rate or container size. Although RBI was 25 % greater for seedlings grown in small containers with high N rates than those grown in large containers with low N rates, RBI ranged only from 11 to 15 %, well below the critical 27 % threshold.     

Covariances between morphological characteristics in bareroot Pinus sylvestris nursery stock

In this study an attempt was made to gather information on the relationships of morphological attributes of bareroot Pinus sylvestris seedlings in order to determine the possible use of these attributes for grading purposes. The covariance structure of different morphological variables was studied in commercially produced crops. From each selected batch of Scots pine seedlings, 300 seedlings were sampled, three successive living seedlings from each of the 100 systematically selected sampling points ("clusters"). Variance in the seedlings crop was described using a linear model: total covariance was divided into variance between batches, between clusters and between individual seedlings (error).

Most of the correlations between different plant parts were large and positive. Only needle length and root length seemed to vary independently of other “length”; variables. Within one batch, at the end of the growing season, height‐diameter was more clearly size‐independent than shoot‐root ratio. Needle biomass increased exponentially with seedling height but the smallest seedlings had relatively less needle biomass than the biggest seedlings. It is not necessary to include dry mass in the requirements for seedling quality since it correlates well and can be described with other variables that can be measured more easily. Of the principal components for morphological characteristics, the “stem”; component explained 69% of the height variation and 77% of the diameter variation, the “needle”; component explaining 79% of the variation in current needle length, and the “root”; component 58% of the variation in root length. Together the three components explain 76% of the total variance in the original crops.     

Long-term prescribed burning increases nutrient uptake and growth of loblolly pine seedlings

Loblolly pine (Pinus taeda L.) seedlings were grown from seed in a greenhouse on A1 horizon soil collected from field plots that have been burned each winter or maintained in an unburned condition for 33 years. Soils from burned and unburned plots were treated with phosphorus (P), P and calcium (Ca), or left untreated. After 32 weeks, height, biomass, and nitrogen (N) and P uptake were greater on soil from burned versus unburned plots, although application of P masked these effects. Addition of P increased plant biomass, seedling height, and uptake of N and P, but depressed levels of soil NH₄N. These results suggest that long-term prescribed burning may have a positive effect on nutrient availability that will benefit seedlings of the next stand.     

Aggressiveness of Fusarium oxysporum and F. verticillioides isolates on stone and scots pine under greenhouse conditions

Scots pine (Pinus sylvestris) and Stone pine (Pinus pinea) are two important species used in re-forestation that are subject to damage by damping-off fungi in forest nurseries. Twenty-two isolates of Fusarium oxysporum and F. verticillioides from diseased seedlings of eight different hosts were tested for aggressiveness on seeds and seedlings of both pine species, including the effects on seedling emergence and mortality. Scots pine was more susceptible to damping-off than Stone pine, as indicated both by reduced seedling emergence and elevated seedling mortality. The impact of F. oxysporum and F. verticillioides on seeds and seedlings did not differ significantly for either pine species. Our findings support previous studies that found that these are damping-off pathogens on the studied pines. Whereas most isolates proved to be pathogenic, some isolates of both Fusarium species showed to be non-pathogenic.     

Effects of soil temperature on biomass and carbohydrate allocation in Scots pine (Pinus sylvestris) seedlings at the beginning of the growing season

We studied effects of soil temperature on shoot and root extension growth and biomass and carbohydrate allocation in Scots pine (Pinus sylvestris L.) seedlings at the beginning of the growing season. One-year-old Scots pine seedlings were grown for 9 weeks at soil temperatures of 5, 9, 13 and 17 degrees C and an air temperature of 17 degrees C. Date of bud burst, and the elongation of shoots and roots were monitored. Biomass of current and previous season roots, stem and needles was determined at 3-week intervals. Starch, sucrose, glucose, fructose, sorbitol and inositol concentrations were determined in all plant parts except new roots. The timing of both bud burst and the onset of root elongation were unaffected by soil temperature. At Week 9, height growth was reduced and root extension growth was much less at a soil temperature of 5 degrees C than at higher soil temperatures. Total seedling biomass was lowest in the 5 degrees C soil temperature treatment and highest in the 13 degrees C treatment, but there was no statistically significant difference in total biomass between seedlings grown at 13 and 17 degrees C. In response to increasing soil temperature, below-ground biomass increased markedly, resulting in a slightly higher allocation of biomass to below-ground parts. Among treatments, root length was greatest at a soil temperature of 17 degrees C. The sugar content of old roots was unaffected by soil temperature, but the sugar content of new needles increased with increasing soil temperature. The starch content of all seedling parts was lowest in seedlings grown at 17 degrees C. Otherwise, soil temperature had no effect on seedling starch content.     

Relationship of site and stand characteristics to Armillaria root disease incidence on ponderosa pine in the Black Hills,South Dakota

Ponderosa pine (Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole‐size trees and large‐diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large‐diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha^?1 and basal area infected.     

Nutrient element contents of cutting seedlings of hybrid species （ Liriodendron chinense x tulipifera）

The cutting seedlings ofLiriodendron chinense xtulipifera were treated with the different concentrations of auxin (treatment₁: IBA of 50 g·kg⁻¹+NAA of 300 g·kg⁻¹; treatment₂; IBA of 100 g·kg⁻¹+NAA of 300 g·kg⁻¹). The biomass nutrient element contents for different organs (root, stem, leaf) of cutting seedling ofLiriodendron chinense xtulipifera were measured by the dry method, Kjeldahl method and Atomic Absorption Spectroscopy method. The result showed that the biomass of root, stem, and leaf of the cutting seedling treated with auxin was all remarkably increased. The contents of element C in root, stem and leaf had no significant difference between the control and auxin treatments, while the contents of N, P, K and Ca in stem were much lower than that in leaf and root. Variance analysis showed that for the same organ with different concentration treatment of auxin, the four nutrient elements (N, P, K, and Ca) had no significant difference in contents, while there existed significant or very significant difference in contents of the four nutrient elements in different organs with the same concentration auxin treatment. The N, P, K and Ca contents were very low in cutting seedlings; as a result, additional fertilizer should be applied to the seedlings when they were planted in the field. Foundation item: This paper was supported by Jiangsu Province Science Foundation (BE96350). Biography: ZHANG Xiao-ping, (1972-), female, Ph. Doctor in Nanjing Forestry University. Nanjing 210037, P. R. China. Responsible editor: Zhu Hong     

Can methyl jasmonate treatment of conifer seedlings be used as a tool to stop height growth in nursery forest trees?

A plant's induced defense system can be triggered by the application of the plant hormone methyl jasmonate (MeJA), and recent research suggest that MeJA treatment may become a tool for protection of conifer seedlings against insect herbivory (e.g. by the pine weevil Hylobius abietis). A side-effect of MeJA application is temporarily reduced height growth. This has generally been considered as negative, but in forest tree nurseries this could instead be beneficial since it is commonly desired to stop the growth of nursery seedlings in late summer. Artificially longer dark periods (long nights/short days) are widely used in high-latitude nurseries to terminate height growth and induce freezing tolerance. However, long night treatment requires specialized nursery equipment and are labor intensive. Therefore alternatives are sought after. We compared long-night and MeJA treatments by following the growth of Norway spruce (Picea abies) seedlings throughout one season. The regulatory effect of MeJA on height growth was similar if not even better than that of long nights, i.e. it was terminated faster. However, MeJA treatment also reduced root growth and delayed the development of freezing tolerance. MeJA may therefore not replace long-night treatments, but it could facilitate a more flexible application of long nights by gaining a longer time interval during which this treatment can be used without risking the seedlings growing too large.