First-order Laterals Research Articles

Maize lateral root developmental plasticity induced by mild water stress. II: Genotype-specific spatio-temporal effects on determinate development.

Maize lateral roots exhibit determinate growth, whereby the meristem is genetically programmed to stop producing new cells. To explore whether lateral root determinacy is modified under water deficits, we studied two maize genotypes (B73 and FR697) with divergent responses of lateral root growth to mild water stress using an experimental system that provided near-stable water potential environments throughout lateral root development. First-order laterals of the primary root system of FR697 exhibited delayed determinacy when grown at a water potential of -0.28 MPa, resulting in longer and wider roots than in well-watered (WW) controls. In B73, in contrast, neither the length nor width of lateral roots was affected by water deficit. In water-stressed FR697, root elongation continued at or above the maximum rate in WW roots for 3 days longer, and was still 45% of maximum when WW roots approached their determinate length. Maintenance of root elongation was associated with sustained rates of cell production. In addition, kinematic analyses showed that reductions in tissue expansion rates with aging were delayed in the longitudinal, radial and tangential planes throughout the root growth zone. Thus, this study reveals large genotypic differences in the interaction of water stress with developmental determinacy of maize lateral roots.

A re‐assessment of sucrose signaling involved in cluster‐root formation and function in phosphate‐deficient white lupin (Lupinus albus)

Apart from substrate functions, a signaling role of sucrose in root growth regulation is well established. This raised the question whether sucrose signals might also be involved in formation of cluster-roots (CRs) under phosphate (Pi) limitation, mediating exudation of phosphorus (P)-mobilizing root exudates, e.g. in Lupinus albus and members of the Proteaceae. Earlier studies demonstrated that CR formation in L. albus was mimicked to some extent by external application of high sucrose concentrations (25 mM) in the presence of extremely high P supply (1-10 mM), usually suppressing CR formation. In this study, we re-addressed this question using an axenic hydroponic culture system with normal P supply (0.1 mM) and a range of sucrose applications (0.25-25 mM). The 2.5mM sucrose concentration was comparable with internal sucrose levels in the zone of CR initiation in first-order laterals of P-deficient plants (3.4 mM) and induced the same CR morphology. Similar to earlier studies, high sucrose concentrations (25 mM) resulted in root thickening and inhibition of root elongation, associated with a 10-fold increase of the internal sucrose level. The sucrose analog palatinose and a combination of glucose/fructose failed to stimulate CR formation under P-sufficient conditions, demonstrating a signal function of sucrose and excluding osmotic or carbon source effects. In contrast to earlier findings, sucrose was able to induce CR formation but had no effect on CR functioning with respect to citrate exudation, in vitro activity and expression of genes encoding phosphoenolpyruvate carboxylase, secretory acid phosphatase and MATE transporters, mediating P-mobilizing functions of CRs.

Ability to Acclimate to Sedimentation Gradually Decreases with Burial Time in Two Emergent Macrophytes from Dongting Lake Wetlands in China

Growth, below/above-ground mass ratio (BG:AG ratio), root morphology, carbohydrate content, and alcohol dehydrogenase (ADH) activity in the low-elevation species Phalaris arundinacea and the high-elevation species Miscanthus sacchariflorus buried under 0, 5, and 10 cm of sediment were investigated one, two, and three months after burial. Biomass accumulation, BG:AG ratio, and the starch content of both species generally decreased with increasing burial depth and burial time, except for higher biomass accumulation in P. arundinacea in the first month. In the first month, adventitious roots of both species, and first-order laterals of P. arundinacea, were shorter and thicker in the buried plants than in the controls. The ADH activity in both species and the soluble sugar content of P. arundinacea increased with increasing burial depth in the first month. Only the diameter of adventitious roots and the soluble sugar content of P. arundinacea were affected by burial depth after two or three months. It is concluded that P. arundinacea is more tolerant to sedimentation than M. sacchariflorus due to more efficient acclimation strategies in root morphology and soluble sugar content. However, the ability to acclimate becomes weaker over time due to consistently decreasing starch content and the trade-off between tolerance to sedimentation and plant growth.

Iranella inopinata Gollestaneh 1965, a puzzling dasycladalean alga from the Lower Cretaceous shallow carbonate shelf deposits of the Zagros fold-thrust belt, SW Iran

Iranella inopinata gen. and sp. nov. was first described in the unpublished thesis of Gollestaneh (1965), as an incertae sedis from the Lower Cretaceous carbonate rocks of the Zagros fold-thrust belt. More recently, the taxon was formally, although provisionally described by Hosseini and Conrad (Geol Croat 61:215–237, 2008), as a dasycladalean alga named Salpingoporella? inopinata. Here, based on the interpretation of quite-abundant although scattered fragments, it is assigned to Iranella, a large-sized, stalked, and capitulum-shaped new genus of Dasycladales. The lower, stalked part of the thallus is cylindrical, strongly calcified, with first-order laterals only, while the large capitulum is only partly calcified, showing one or two orders of laterals. Traces of cysts (reproductive organs) are present in the basal stalk, either in the stipe or the laterals. Iranella inopinata looks to be endemic to the southwestern part of the Tethyan realm, in the Zagros area and also south of the Persian Gulf. In the Zagros Mts., it extends from the Berriasian to the Aptian, with an Acme Zone in the Valanginian. Sequential interpretation proves the presence of this species in the late transgressive and early highstand stages of system tracts, and reveals a low-energy, restricted, lagoonal or back-reef depositional environment, in an inner-platform setting.

Allometry of root branching and its relationship to root morphological and functional traits in three range grasses.

The study of proportional relationships between size, shape, and function of part of or the whole organism is traditionally known as allometry. Examination of correlative changes in the size of interbranch distances (IBDs) at different root orders may help to identify root branching rules. Root morphological and functional characteristics in three range grasses {bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Löve], crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.×A. cristatum (L.) Gaert.], and cheatgrass (Bromus tectorum L.)} were examined in response to a soil nutrient gradient. Interbranch distances along the main root axis and the first-order laterals as well as other morphological and allocation root traits were determined. A model of nutrient diffusivity parameterized with root length and root diameter for the three grasses was used to estimate root functional properties (exploitation efficiency and exploitation potential). The results showed a significant negative allometric relationship between the main root axis and first-order lateral IBD (P ≤0.05), but only for bluebunch wheatgrass. The main root axis IBD was positively related to the number and length of roots, estimated exploitation efficiency of second-order roots, and specific root length, and was negatively related to estimated exploitation potential of first-order roots. Conversely, crested wheatgrass and cheatgrass, which rely mainly on root proliferation responses, exhibited fewer allometric relationships. Thus, the results suggested that species such as bluebunch wheatgrass, which display slow root growth and architectural root plasticity rather than opportunistic root proliferation and rapid growth, exhibit correlative allometry between the main axis IBD and morphological, allocation, and functional traits of roots.

Genotypic variation for root traits of maize ( Zea mays L.) from the Purhepecha Plateau under contrasting phosphorus availability

Phosphorus (P) deficiency is a major constraint for maize production in many low-input agroecosystems. This study was conducted to evaluate genotypic variation in both root (root architecture and morphology, including root hairs) and plant growth traits associated with the adaptation of maize landraces to a P-deficient Andisol in two locations in the Central Mexican highlands. Two hundred and forty-two accessions from the Purhepecha Plateau, Michoacan were grown in Ponzomaran with low (23 kg P 2O 5 ha −1) and high (97 kg P 2O 5 ha −1) P fertilization under rain-fed field conditions, and subsequently a subset of 50 contrasting accessions were planted in the succeeding crop cycle in Bonilla. Accessions differed greatly in plant growth, root morphology and P efficiency defined as growth with suboptimal P availability. The accessions were divided into 3 categories of P efficiency using principal component and cluster analyses, and 4 categories according to the retained principal component and their relative weight for each genotype in combination with growth or yield potential. The distribution of accessions among three phosphorus efficiency classes was stable across locations. Phosphorus-efficient accessions had greater biomass, root to shoot ratio, nodal rooting, nodal root laterals, and nodal root hair density and length of nodal root main axis, and first-order laterals under P deficiency. Biomass allocation to roots, as quantified by the allometric partitioning coefficient ( K) was not altered by P availability in the efficient accessions, but inefficient accessions had a lower K under low P conditions. Accessions with enhanced nodal rooting and laterals had greater growth under low P. Dense root hairs on nodal root main axes and first-order laterals conferred a marked benefit under low P, as evidenced by increased plant biomass. Late maturity improved growth and yield under low P. These results indicate that landraces of the Central Mexican highlands exhibit variation for several root traits that may be useful for genetic improvement of P efficiency in maize.

Remarks on the Permian dasycladalean alga Sinoporella leei Yabe, 1949

Sinoporella leei was first described and illustrated by Yabe in 1949 as a new species and was ascribed to a new subgenus of the genus Triploporella (Steinmann). This alga was not illustrated again until Mu published 25-years later a photomicrograph of a longitudinal-tangential section. The recent finding of new specimens in Permian strata of the Guangxi region (South China) allows us to better illustrate this alga, and to improve our understanding of its morphology to the extent that we find it necessary to emend the current diagnosis. The new observations focus mainly on the morphology of the second-order laterals, on their relationship to the first-order laterals, and the connection of the first-order laterals to the main stem. These data suggest that Sinoporella represents a self-standing, discrete genus that differs from Triploporella. We also consider the lack of cystophores (cyst containers sensu De Castro) and the possible occurrence of individual cysts in the first order laterals as characteristics that do not accord with Barttolo's emended diagnosis of Triploporella.

Root anatomy of Pinus taeda L.: seasonal and environmental effects on development in seedlings

The environmental and seasonal effects on anatomical traits of Pinus taeda L. seedling roots were studied in the laboratory in three contrasting root growth media and also in typical outdoor nursery culture. Growth media with lower water regimen and high penetration resistance caused a reduction in lengths of the white and condensed tannin (CT) zones and acceleration of development of suberin lamellae in the endodermis. As a possible counter to this reduction in zone lengths, second-order laterals were produced closer to the tips of first-order laterals. This suggested there may be an advantage to producing more shorter roots under stressful conditions. Under outdoor nursery conditions (June to mid-December) the white zone was always a rather small part of the root system surface area (4.5% in December), but it dominated as a provider of cortical plasmalemma surface area (CPSA) in contact with modified soil solution (65% in December) because of its live cortex and capacity to increase nearly three fold the amount of CPSA per unit root length. The CT zone always provided most of the total root surface area (80% in December). Although it had no live cortex, a few cells of the CT zone endodermis remained non-suberized passage cells, perhaps giving this major part of the root system some capacity for ion and water absorption. A late summer increase in CPSA was due largely to the rapid production of mycorrhizae. Root systems were capable of very rapid replacement of roots lost due to undercutting and lateral root pruning. The great variation in CPSA per unit root length contained in the white, mycorrhizal and CT zones suggested a capacity to adapt rapidly to changing conditions.

Effects of decreasing soil water content on seminal lateral roots of young maize plants

AbstractSoil micropores that contain water at or below field capacity cannot be invaded by seminal or first‐order lateral roots of maize plants because their root diameters are larger than 10 μm. Hence, at soil‐water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40 cm wide, 50 cm high, and approximately 0.7 cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1–4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal‐root length and SWC in soil layers 0–10, 10–20, 20–30, 30–40, and 40–50 cm were measured at intervals of 2–3 d on scanner images by image analysis. At 15 d after planting, for treatments 1–4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal‐root elongation rate was at maximum above a SWC of 0.17 cm3 cm–3, corresponding to a matric potential of –30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05 cm3 cm–3. After destructive harvest for treatment 1–4, number of (root‐) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26 cm3 cm–3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first‐order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions.

Spatio-temporal Variations in Axial Conductance of Primary and First-order Lateral Roots of a Maize Crop as Predicted by a Model of the Hydraulic Architecture of Root Systems

Rates at which water can be transported along plant roots (axial pathway) vary through time, in part depending on xylem maturation. Because of experimental constraints, the dynamics of root functional heterogeneity under field conditions remains mostly uncharted territory. Recent advances in mechanistic modelling offer opportunities to bypass such experimental limitations. This paper examines the dynamics of local variations in axial conductance of primary and first-order lateral roots of a maize crop using the architecture-based modelling approach developed by Doussan et al. (Annals of Botany: 81, 213–223, 1998). Specifically, we hypothesised that points of major resistance to long distance water transfers could arise from discrepancies between the hydraulic maturity (or water carrying capacity) of main axes and branch roots. To test this assumption, spatial distributions of root axial conductance were tested after 30, 60 and 100 days at soil depths of 10, 50 and 100 cm under a maize (Zea mays L.) crop sown at a density of 8 plants m−2. As the crop developed, the corresponding root populations encompassed ever increasing amounts of hydraulically mature first-order laterals (branch roots): after a 100-day growth period, the vast majority of laterals had reached their maximum axial conductance at all soil depths down to 100 cm. In contrast, the axial conductance of a large proportion of main axes (primary roots) remained low, even at shallow soil depths and after 100 days of growth. The imbalance between the hydraulic maturity of primary and lateral roots was most conspicuous at soil depths of 100 cm, where ~10% only of the former compared to ~80% of the latter, had reached their maximum axial conductance after a 100-day growth period.

Apical diameter and branching density affect lateral root elongation rates in banana

Thick roots elongate faster than thinner ones. However, within one species, the growth achieved by roots of a given diameter can be very variable, and root diameter can only be considered as a determinant of root potential elongation rate. As root elongation is highly correlated to carbon availability, it can be hypothesized that local competition for resources, expressed as the number of lateral roots per unit length (i.e. the branching density), modulates root elongation. Using novel methods in field conditions, we have estimated apical diameters, elongation rates and growth durations of nearly 3500 banana lateral roots, in a field experiment with high radiations and a shaded glasshouse experiment with low radiations. Apical diameters and branching densities were lower in the experiment with low radiation, but elongation rates were higher. In both experiments, mean elongation rates of first-order laterals and thick second-order laterals were negatively correlated with bearing root branching densities. It is hypothesized that, even though apical diameters were lower, low branching densities in the shaded glasshouse allowed enhanced lateral root elongation. In both experiments, second-order laterals elongated more slowly than first-order laterals of similar diameter. A specific effect of root order, independent of branching density and apical diameter, contributed to explain these slow second-order lateral elongation rates. Most lateral roots elongated between 9 and 21 days and growth duration was mainly correlated with root diameter.

Changes in root morphology accompanying mycorrhizal alleviation of phosphorus deficiency in micropropagated Annona cherimola Mill. plants

The effect of the mycorrhizal inoculation on survival rate, growth, nutrient uptake and root morphology during the acclimatization period and plant establishment of micropropagated juvenile or adult cherimoya plants ( Annona cherimola Mill.) was determined. Although mycorrhizal colonization did not improve the survival rate of plants, which was already high in non-inoculated plants, it had a positive effect on plant development (shoot length, leaf number, leaf area and fresh and dry weights). Mycorrhizal juvenile plants tripled the macronutrients and increased by four the micronutrient uptake, and mycorrhizal adult plants increased by two phosphorus and all micronutrients, with copper uptake increased five times. Moreover, mycorrhizal colonization changed the root morphology of adult plants increasing three-fold the total number of roots, doubling the number of first-order laterals and increasing second-order laterals by four. Total root length was also increased three-fold, adventitious root length was almost doubled, first-order laterals tripled and second-order roots length increased four-fold. The effect of mycorrhizal colonization seems to be stronger or different in juvenile than in adult plants, suggesting that ontogenic stage is an important factor determining mycorrhizal effect and the plant performance during the acclimatization period.

Struvea thoracica sp. nov. (Cladophorophyceae), a new deep-water chlorophyte from the Great Barrier Reef and New Caledonia

G.T. Kraft and A.J.K. Millar. 2005. Struvea thoracica sp. nov. (Cladophorophyceae), a new deep-water chlorophyte from the Great Barrier Reef and New Caledonia. Phycologia 44: 305–311.Struvea thoracica Kraft & Millar, sp. nov., is described from deep-water habitats along the mid-north to southern Great Barrier Reef and in New Caledonia. Plants reach 26 cm in length and at maturity consist of coarse fibrous blades to 2 mm in thickness, 18 cm in length, and 12 cm in width borne on simple to ramified stalks 8–18 cm in length and 2.5 mm in diameter. Organization of the blades is dorsiventral, with first-order laterals arising oppositely on axial bearing cells, the laterals in turn producing a further order of branches that are strongly curved ‘ventrally’. This results in a ‘dorsal’ surface on which the primary laterals are evenly spaced, coarse, and prominently exposed, imparting the ‘ribcaged’ appearance for which the alga is named. Cell division in all branch orders is segregative, as evidenced by the rounded cytoplasts that form distally within the walls of axial cells as they undergo their first cell divisions, as well as by the gaps left between the end walls of daughter cells and the lateral walls of the parent cells following cell divisions in higher branch orders, a feature also of the tenacula that occasionally form apically on second- and higher-order laterals. The new species is distinguished from the other two members of the genus (the type, S. plumosa Sonder, and S. elegans Børgesen) by its greater blade thickness, dorsiventrality of blade construction, and relatively few tenacular cells.

Rapid predictions of cold tolerance in Douglas-fir seedlings using chlorophyll fluorescence after freezing

Chlorophyll fluorescence measurements were performed on the foliage of 3-year-old (11/2+11/2) nursery-grown Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings after exposure to controlled freezing temperatures, in the laboratory, to assess low temperature tolerance. The seedlings were propagated in an Irish nursery and lifted at monthly intervals overwinter 1999 and 1999–2000. Excised shoots from first-order laterals were frozen, in the dark. After freezing, needles were immediately assessed using chlorophyll fluorescence. The excised shoots were then maintained under controlled conditions for 14 days and visually assessed for needle damage. The chlorophyll fluorescence parameter, F v/F m, accurately predicted cold hardiness and was linearly related to visual needle damage and short-term survival. An equation was constructed using F v/F m data for determining the LT50, that is, the freeze temperature causing 50% seedling damage. The predictions of F.LT50 (fluorescence-based empirical determination of LT50) have been tested over two seasons (i.e., against a second independent data set) with variability between 0 and 1.8 °C of visual estimates, though predictions were often ≤ 1.1 °C of the visual assessment. This approach provided a simple, rapid and accurate prediction of cold tolerance, under climatic conditions where in situ measurements are unreliable. The method can be used to predict if Douglas-fir seedlings have developed sufficient tolerance for lifting to the cold-store, or for planting.

Effects of soil bulk density on seminal and lateral roots of young maize plants (Zea mays L.)

AbstractIt is well established that increasing soil bulk density (SBD) above some threshold value reduces plant root growth and thus may reduce water and nutrient acquisition. However, formation and elongation of maize seminal roots and first order lateral (FOL) roots in various soil layers under the influence of SBD has not been documented. Two studies were conducted on a loamy sand soil at SBD ranging from 1.25 g cm–3 to 1.66 g cm–3. Rhizotrons with a soil layer 7 mm thick were used and pre‐germinated plants were grown for 15 days. Over the range of SBD tested, the shoot growth was not influenced whereas total root length was reduced by 30 % with increasing SBD. Absolute growth rate of seminal roots was highest in the top soil layer and decreased with increasing distance from the surface. Increasing SBD amplified this effect by 20 % and 50 % for the top soil layer and lower soil layers, respectively. At the end of the experiment, total seminal roots attributed to approximately 15 % of the total plant root length. Increasing SBD reduced seminal root growth in the lowest soil layer only, whereas FOL root length decreased with SBD in all but the uppermost soil layer. For FOL, there was a positive interaction of SBD with distance from the soil surface. Both, increasing SBD and soil depth reduced root length by a reduction of number of FOL roots formed while the length of individual FOL roots was not influenced. Hence, increasing SBD may reduce spatial access to nutrients and water by (i) reducing seminal root development in deeper soil layers, aggravated by (ii) the reduction of the number of FOL roots that originate from these seminal roots.

The morphological changes of wheat genotypes as affected by the levels of localized phosphate supply

Effects of localized phosphate supply on the seedling growth of wheat (Triticum aestivum L.) genotypes 81(85)5-3-3-3 (P-efficient) and NC37 (P-inefficient) were studied using a device which allowed only 3 cm length of root segment to be exposed to phosphate treatment. Localized supply of 0 mmol P L−1 and the rest of root supplied with 0.1 mmol P L−1 (HLH), increased the shoot height, leaf area, root/shoot ratio for 81(85)5-3-3-3, length of root and root axis for NC37, and root axis length and density of first-laterals for both the genotypes, compared to plants with the whole root system in P-sufficient solution (HHH). This suggested that above- and below-ground morphological parameters of wheat were promoted by a localized P-deficiency, presumably via a P deficiency signal. There was a significant difference in the number of first-order laterals between the two wheat genotypes when most of the roots were grown without P and only 3 cm length of root was supplied with 0.3 mmol P L−1. The relationship between the number and density of 2nd-order lateral roots and level of local P supply was quadratic. Maximum number and density of 2nd-order lateral roots were obtained with a localized P supply of 0.70 mmol L−1.

Hormone physiology of pea mutants prevented from flowering by mutations gi or veg1.

The veg1 (vegetative) mutant in pea (Pisum sativum L.) does not flower under any circumstances and gi (gigas) mutants remain vegetative under certain conditions. gi plants are deficient in production of floral stimulus, whereas veg1 plants lack a response to floral stimulus. During long days in particular, these non-flowering mutant plants eventually enter a stable compact phase characterised by a large reduction in internode length, small leaves and growth of lateral shoots from the upper-stem (aerial) nodes. The first-order laterals in turn produce second-order laterals and so on in a reiterative pattern. The apical bud is reduced in size but continues active growth. Endogenous hormone measurements and gibberellin application studies with gi-1, gi-2 and veg1 plants indicate that a reduction in gibberellin and perhaps indole-3-acetic acid level may account, at least partially, for the compact aerial shoot phenotype. In the gi-1 mutant, the compact phenotype is rescued by transfer from a 24- to an 8-h photoperiod. We propose that in plants where flowering is prevented by a lack of floral stimulus or an inability to respond, the large reduction in photoperiod gene activity during long days may lead to a reduction in apical sink strength that is manifest in an altered hormone profile and weak apical dominance.

Comparative studies of ectomycorrhiza formation in Alnus glutinosa and Pinus resinosa with Paxillus involutus

Mycorrhiza ontogeny and details of Hartig net and mantle structure were compared in ectomycorrhizas synthesized in growth pouches between the broad host range fungus Paxillus involutus and the tree species European black alder (Alnus glutinosa) and red pine (Pinus resinosa). In Alnus glutinosa, a paraepidermal Hartig net was restricted to the proximal (basal) portion of first-order laterals; the hypodermal layer appeared to be a barrier to fungal penetration. Phi-thickenings were present in some cortical cells but these were not related to lack of fungal ingress into the cortex. The mantle was often present close to the root apex but in many roots it was loosely organized and patchy. In several instances, the mantle formed around the root apex was only temporary; renewed root growth occurred without the formation of a mantle. In Pinus resinosa, the Hartig net developed between cortical cell layers of monopodial and dichotomously branched first–order laterals. Fungal hyphae in the Hartig net exhibited a complex labyrinthine mode of growth. The mantle had a pseudoparenchymatous structure and covered the root, including apices of dichotomously branched roots. The Paxillus–Pinus resinosa interaction had all the characteristics of a compatible ectomycorrhizal association. The Paxillus–Alnus glutinosa interaction, however, showed only aspects of superficial ectomycorrhizas, including the presence of a minimal (sometimes absent) and mostly proximal Hartig net and variable mantle development. Sclerotia were produced in the extraradical mycelium of Paxillus involutus when associated with either Alnus glutinosa or Pinus resinosa.

Propagation of Magnolia virginiana ‘Santa Rosa’ by Semi-Hardwood Cuttings

Abstract Terminal, semi-hardwood cuttings (tips of first-order laterals) of Magnolia virginiana L. ‘Santa Rosa’ (‘Santa Rosa’ sweetbay) were collected on November 13, 1997, and treated with 0, 6, 12 or 25 mM (0.0, 0.13, 0.25 or 0.5%) indolebutyric acid (IBA) in factorial combination with equivalent mM concentrations of naphthaleneacetic acid (NAA) (0.0, 0.11, 0.23 or 0.46%). Rooting was maximized (83%) for cuttings treated with 25 mM (0.5%) IBA alone. Percent rooting for treatments of NAA alone or in combination with IBA never exceeded that of IBA alone at 12 or 25 mM (0.25% or 0.5%). Root number and root length were unaffected by any treatment with means of 2.4 roots and 10 cm (4 in), respectively.

Propagation of Thuja x ‘Green Giant’ by Stem Cuttings: Effects of Growth Stage, Type of Cutting, and IBA Treatment

Abstract Stem cuttings of Thuja L. x ‘Green Giant’ (‘Green Giant’ arborvitae), consisting of 22 cm (8.6 in) terminals (tips of first-order laterals) or 20 cm (7.8 in) laterals (side shoots removed from those portions of terminal cuttings inserted into the rooting medium), were collected on three dates associated with specific stock plant growth stages (softwood, semi-hardwood, and hardwood) and treated with indolebutyric acid (IBA) in 50% isopropanol ranging from 0 to 9000 ppm (0.9%). Regardless of cutting type or auxin treatment, cuttings rooted in high percentages at each growth stage. Overall rooting for softwood, semi-hardwood, and hardwood, cuttings was 85%, 86%, and 96%, respectively. Semi-hardwood cuttings were the only cuttings in which percent rooting was affected by IBA treatment or cutting type, with lateral cuttings rooting in higher percentages than terminal cuttings (92% vs. 79%, respectively), while IBA concentrations of 3000 (0.3%) or 6000 ppm (0.6%) proved optimal for both cutting types. Mean root number and mean root length varied by growth stage, cutting type, and IBA concentration. In general, rooting percentages and root length were optimized at the hardwood stage with either cutting type treated with 3000, 6000 or 9000 ppm (0.3%, 0.6% or 0.9%) IBA, resulting in >10 roots per cutting.