Salix Sericea Research Articles

Comparison of native woody species for use as live stakes in streambank stabilization in the southeastern United States

Live stakes are cuttings taken from dormant woody plant species used to establish riparian vegetation. Although many species may be suitable, black willow (Salix nigra) is the species of choice in streambank stabilization projects in the southeastern United States. Studies were conducted on four species native to the southeastern United States that have potential for success as live stakes. Black willow, silky willow (Salix sericea), silky dogwood (Cornus amomum), and Virginia sweetspire (Itea virginica) were evaluated for biomass differences among species, effect of soaking stakes in tap water for 48 hours prior to installation, and differences in survival attributed to season of harvest. The experiment was conducted at the Paterson Horticulture Greenhouse Complex, Auburn University, Alabama. Each species was established from live stakes and had 100% survival when harvested during the dormant season. Total biomass of soaked and nonsoaked live stakes of silky dogwood was greater than soaked and nonsoaked black willow live stakes at nine months. This was driven by below-ground biomass. At nine months, silky dogwood belowground biomass for nonsoaked stakes was greater than belowground biomass for black willow, silky willow, and Virginia sweetspire. Belowground biomass of soaked silky dogwood stakes was similar to belowground biomass of silky willow and greater than belowground biomass of black willow. Soaking live stakes collected in the dormant season for 48 hours resulted in only one significant total biomass difference between soaked and nonsoaked in the species silky dogwood at six months. After nine months of growth, there were no differences between soaked and nonsoaked live stake biomass. Virginia sweetspire, a shrub, consistently had less biomass, diameter, and height than the other species. However, the nine month root:shoot ratio of Virginia sweetspire was greater than both willow species and similar to silky dogwood. There was 0% survival of black willow, silky willow, and silky dogwood after six months when live stakes were harvested during the growing season irrespective of soaking treatment. Live stakes of Virginia sweetspire harvested in the growing season had a survival rate of 80% for soaked stakes and 67% for nonsoaked stakes. The four native species evaluated in this study became established and survived as live stakes. These species are candidates for use in riparian enhancement and restoration projects, which will assist with increasing riparian plant diversity.

Effects of Stream Restoration on Woody Riparian Vegetation of Southern Appalachian Mountain Streams, North Carolina, U.S.A

Riparian revegetation, such as planting woody seedlings or live stakes, is a nearly ubiquitous component of stream restoration projects in the United States. Though evaluations of restoration success usually focus on in‐stream ecosystems, in order to understand the full impacts of restoration the effects on riparian ecosystems themselves must be considered. We examined the effects of stream restoration revegetation measures on riparian ecosystems of headwater mountain streams in forested watersheds by comparing riparian vegetation structure and composition at reference, restored, and degraded sites on nine streams. According to mixed model analysis of variance (ANOVA), there was a significant effect of site treatment on riparian species richness, basal area, and canopy cover, but no effect on stem density. Vegetation characteristics at restored sites differed from those of reference sites according to all metrics (i.e. basal area, canopy cover, and species composition) except species richness and stem density. Restored and degraded sites were structurally similar, with some overlap in species composition. Restored sites were dominated by Salix sericea and Cornus amomum (species commonly planted for revegetation) and a suite of disturbance‐adapted species also dominant at degraded sites. Differences between reference and restored sites might be due to the young age of restored sites (average 4 years since restoration), to reassembly of degraded site species composition at restored sites, or to the creation of a novel anthropogenic ecosystem on these headwater streams. Additional research is needed to determine if this anthropogenic riparian community type persists as a resilient novel ecosystem and provides valued riparian functions.

Do exotic generalist predators alter host plant preference of a native willow beetle?

Abstract1 Selection can favour herbivores that choose host plants benefitting their offspring either by enhancing growth rates or by increasing larval defences against native predators. For exotic predator species that feed on herbivores, their success with invading new habitats may depend upon overcoming defences used by native prey. Whether exotic predators can alter herbivore host choice has remained unexamined. Therefore, we compared the efficacy of larval defence by Chrysomela knabi (a native beetle species) that had fed on two native willow hosts: Salix sericea (a phenolic glycoside (PG)‐rich species) and Salix eriocephala (a PG‐poor species), when attacked by exotic generalist predators. In addition, the preference and performance of C. knabi on S. sericea and S. eriocephala was examined.2 Chrysomela knabi preferred and performed better on S. sericea. In a common garden, adult C. knabi were nine‐fold more common and oviposited five‐fold more frequently on S. sericea than on S. eriocephala. In the laboratory, adult feeding preference on leaf discs and survival rates of larvae were both greater on S. sericea, and time to pupation was shorter.3 Chrysomela knabi larvae produced significantly more salicylaldehyde when fed S. sericea leaves than when fed S. eriocephala leaves. Additionally, those larvae with greater salicylaldehyde had reduced predation by two exotic generalist predators, Harmonia axyridis larvae and juvenile Tenodera aridifolia sinensis.4 The results obtained in the present study suggest that selection favoured the preference of C. knabi for PG‐rich willow plants because larvae grew and survived better and that selection by common exotic generalist predators would reinforce this preference.

Ozone Sensitivity of 28 Plant Selections Exposed to Ozone Under Controlled Conditions

Ambient, ground-level ozone is the most important air pollutant affecting vegetation in the US. However, ozone-sensitive bioindicators need to be identified for use in field surveys to detect ozone-induced symptoms. To identify such bioindicators, 28 plant selections were exposed to ozone within greenhouse chambers during 2003 and 2004. Plants most sensitive to ozone included Asclepias incarnata (swamp milkweed), Asclepias syriaca (common milkweed), Cephalanthus occidentalis (buttonbush), Platanus occidentalis (American sycamore), Salix × cotteti (Bankers dwarf willow), Salix lucida (shining willow), Salix nigra (black willow), Salix sericea (silky willow), and Symphoricarpos albus (snowberry). Plants moderately sensitive included Aster novaeangliae (New England aster), Monarda didyma (bee-balm), Rhus aromatica (aromatic sumac), Salix discolor (pussy willow), Salix exigua (sandbar willow), Salix purpurea (basket willow), Sambucus ebulus (European dwarf elderberry), and Symphoricarpos spp. (mixture of “snowberries”). Plants more tolerant to ozone included Aster macrophyllus (bigleaf aster), Aster novibelgii (New York aster), Cercis canadensis (redbud), Populus maximowizii × trichocarpa (hybrid poplar), Rudbeckia laciniata (cutleaf, or tall green-headed coneflower), Salix amygdaloides (peach-leaved willow), Salix eriocephala (diamond willow), Sambucus canadensis (American elder), Sambucus nigra (European elder), Symphoricarpos orbiculatus (coralberry), and Viburnum trilobum (highbush-cranberry). The incidence and severity of ozone-induced symptoms varied with species, ozone concentration, and length of exposure. Pigmented adaxial leaf surface stipple, bifacial necrosis, and premature defoliation were common foliar symptoms induced by ozone; leaf reddening, bronzing, and chlorosis occurred less frequently. Species that produced classic ozone-induced stipple in this study may serve as useful bioindicators in field surveys to confirm that ozone injury occurs in many parts of the country. Such findings may have a positive impact on establishing more stringent air-quality standards to protect vegetation and the environment.

Testing the growth–differentiation balance hypothesis: dynamic responses of willows to nutrient availability

Here, the growth-differentiation balance hypothesis (GDBH) was tested by quantifying temporal variation in the relative growth rate (RGR), net assimilation rate (NAR), and phenylpropanoid concentrations of two willow species (Salix sericea and Salix eriocephala) across five fertility levels. Initially, RGR increased and total phenylpropanoids declined (although every individual phenolic did not) as fertility increased, but NAR was unaffected. Subsequently, NAR and phenylpropanoids declined in the low fertility treatment, generating a quadratic response of secondary metabolism across the nutrient gradient. As above- and below-ground growth rates equilibrated, NAR and phenylpropanoids increased in the low fertility treatment, re-establishing a negative linear effect of fertility on secondary metabolism. A transient quadratic response of secondary metabolism is predicted when GDBH is integrated with models of optimal phenotypic plasticity, occurring when low NAR imposes carbon constraints on secondary metabolism in low nutrient environments. Once plants acclimate to nutrient limitation, the equilibrium allocation state is predicted to be a negative correlation between growth and secondary metabolism. Although both willow species generally responded according to GDBH, the complexity observed suggests that prediction of the effects of nutrient availability on secondary metabolism (and other plastic responses) in specific cases requires a priori knowledge of the physiological status of the plant and soil nutrient availability.

Does the differential seedling mortality caused by slugs alter the foliar traits and subsequent susceptibility of hybrid willows to a generalist herbivore?

Abstract1. Many Salicaceae species naturally form hybrid swarms with parental and hybrid taxa that differ in secondary chemical profile and in resistance to herbivores. Theoretically, the differential mortality in the seedling stage can lead to changes in trait expression and alter subsequent interactions between plants and herbivores. This study examines whether herbivory by the generalist slugArion subfuscus, which causes extensive mortality in young willow seedlings, causes shifts in (a) the foliar chemistry of F2 willow hybrids (Salix sericeaandSalix eriocephala), and (b) the subsequent susceptibility to Japanese Beetles,Popillia japonica.2. In 2001, two populations of F2 seedlings were generated: those that survived slug herbivory (80–90% of seedlings placed in the field were killed by the slugs) were designated as S‐plants, whereas C‐plants (controls) experienced no mortality.3. Common garden experiments with cuttings from these populations, in 2001 and 2002, revealed extensive variation in the phenolic chemistry of F2 hybrids, but revealed no significant difference between S‐ and C‐plants, although the levels of foliar nutrients, proteins and nitrogen tended to be higher in S‐plants.4. Concentrations of salicortin and 2′‐cinnamoylsalicortin explained 55 and 38% of the the variation in leaf damage caused by Japanese beetles, and secondary chemistry was highly correlated within replicate clones (salicortinR2= 0.85, 2‐cinnamoylsalicortinR2= 0.77, condensed tanninsR2= 0.68).5. Interestingly, Japanese beetle damage and condensed tannins were positively correlated within the S‐plants, but not in the C‐plants, suggesting that slugs had selected for plants with a positive relationship between tannins andP. japonicadamage. This is unlikely to be a consequence of a preference for tannins, but is suggested to be related to the elevated nutrient levels in the S‐plants, perhaps in combination with the complex‐binding properties of tannins.6. The damage was highly correlated within replicate clones and a model choice analysis suggested that Japanese beetle damage may be explained by four factors: concentrations of salicortin, condensed tannins, and nitrogen, as well as the specific leaf area (thick leaves were damaged less).

Specificity of Phenolic Glycoside Induction in Willow Seedlings (Salix sericea) in Response to Herbivory

Salix sericea (Marsh.) (Salicaceae) seedlings were used to investigate phytochemical induction of phenolic glycosides following beetle herbivory. Seven-week-old full-sibling seedlings were subjected to one of three damage treatments: Plagiodera versicolora adults, P. versicolora larvae, or Calligrapha multipunctata bigsbyana adults. Salicylate concentrations were measured locally (within damaged leaves) and systemically (above and below damaged leaves) 4 d later. Herbivory caused differential salicylate induction; 2'-cinnamoylsalicortin was induced, whereas salicortin was not. The induction of 2'-cinnamoylsalicortin was not specific with regard to the species or developmental stage of beetle tested but did vary with leaf age: induction occurred in the younger undamaged leaves but not in the damaged leaves or in the older undamaged leaves. The amount of leaf area consumed had no detectable effect on induction, indicating an "all-or-none" response triggered by even small amounts of herbivory. Locally, herbivory caused a decrease in salicortin concentrations, probably because of degradation within the damaged leaves. These results suggest a specific but generalized induced response to these leaf-feeding beetles.

Community structure of insect herbivores in a hybrid system: examining the effects of browsing damage and plant genetic variation

Abstract. 1. Using three genetic classes of willows,Salix eriocephala,Salix sericea, and their interspecific F1 hybrid, the influence of browsing damage and the importance of genetic class on insect community structure were evaluated.2. Three‐year‐old plants grown from seeds generated from controlled crosses were placed in a common garden after a damage treatment was imposed on them (plants were either left undamaged during the previous winter or they had 50% of the previous year's growth removed). Clipping damage caused large increases in mean shoot length for plants.3. The abundance of eight species of insect herbivores was determined for every plant to evaluate community structure for three genetic classes across the two damage levels. Based onmanova, damage treatment had a modest effect on the relative abundance of herbivores (i.e. their proportional representation). In contrast, dramatic differences were detected among genetic classes for relative abundance; in cases where damage treatment influenced relative abundance of herbivores, the importance of genetic class was at least 20‐fold greater than that of damage treatment. No interaction between genetic class and browsing treatment was detected for community structure.4. The weak response of the herbivore community to clipping damage, contrasted to the large response to genetic class, was very surprising because mean shoot length was greatly altered by damage treatment. These findings, coupled together with previous research, suggest that plant genetic differences can act as the primary basis for herbivore community structure, while the effects of browsing may not be as common.

Preference and performance of a willow-feeding leaf beetle: soil nutrient and flooding effects on host quality.

The distribution and abundance of herbivores on plants growing under different environmental conditions may depend upon preference and/or performance. Soil nutrients and water availability are key determinants of herbivore distribution, as both influence plant growth and tissue quality. However, the effects of water on plant quality may depend upon the availability of nutrients and vice versa. Surprisingly few studies have examined the interactions between the two. We investigated the effects of soil nutrient and water availability on (1) the growth and chemistry of the silky willow (Salix sericea Marshall), and (2) the preference and performance of the imported willow leaf beetle (Plagiodera versicolora Laichartig). We conducted two common garden experiments using a similar 2x2 fully factorial design with two levels of soil nutrients (low, high) and two levels of water availability (field capacity, flooded). In the first experiment (larval performance), larval development time and pupal weight were not influenced by nutrient or water availability to the plant. This occurred despite the fact that plants in the high nutrient treatments had higher protein concentration and lower foliar concentrations of the phenolic glycoside 2'-cinnamoylsalicortin. In the second experiment (adult preference), we caged four plants (one from each treatment) and released beetles into cages. We found that plant growth and leaf protein depended upon the interaction between nutrient and water availability. Plant growth was greatest in the high nutrient-field capacity treatment and leaf protein was greatest in the high nutrient-flooded treatment. In contrast, adults settled and oviposited preferentially on the high nutrient treatment under flooded conditions, but we found no evidence of interactions between nutrients and water on preference. Thus, at least under flooded conditions nutrients affect adult preference. We also found that foliar protein was correlated positively with adult oviposition preference and per capita egg production. Our results, then, suggest that soil nutrients can influence adult preference, and that adults choose high-quality hosts (high protein) that promote egg production.

Soil nutrients and water availability interact to influence willow growth and chemistry but not leaf beetle performance

AbstractWe investigated the effects of soil nutrient and water availability on the growth and chemistry of the silky willow (Salix sericea Marshall), and on the performance of the imported willow leaf beetle (Plagiodera versicolora Laichartig). Our major aims were to determine whether there are nutrient–water interactions on plant traits and whether this leads to parallel interactions for herbivore performance. We used a 2 × 3 fully factorial design, which consisted of high and low nutrient treatments crossed with dry, field capacity, and flooded water treatments. We found that nutrient additions increased plant growth, but only in field capacity and flooded conditions (nutrient–water interaction). Leaf nitrogen content also depended on the interaction between soil nutrients and water: nutrient addition resulted in a larger increase in foliar nitrogen in the field capacity treatment than in the flooded and dry treatments. Of the two phenolic glycosides measured, salicortin and 2′‐cinnamoylsalicortin, only one was affected by the treatments. 2′‐cinnamoylsalicortin concentration was lower in the high nutrient–dry treatment compared with the other treatments. In contrast to plant responses, there were no interactions found for larval or pupal weight or development time. Nutrient addition led to an increase in female pupal weight, and foliar N was positively correlated with female pupal weight and negatively correlated with female development time. In addition, leaf water was positively correlated with female development time. The lack of interactions for insect performance may stem from the small absolute differences in foliar nitrogen content associated with the interaction between the nutrients and water. Taken together, our results suggest that nutrient–water interactions influence plant traits that are potentially important for insect performance (leaf nitrogen and water), but these interactions do not produce parallel interactions in beetle performance.

The effects of plant genetic variation and soil nutrients on secondary chemistry and growth in a shrubby willow, Salix sericea: patterns and constraints on the evolution of resistance traits

Investigators often examine the factors—genetic or environmental—that determine the concentrations of secondary chemicals and growth, but few have examined both simultaneously. We used a factorial genetic design and manipulated nutrient availability to Salix sericea (Salicaceae) in order to quantify: (1) genetic variation, plasticity, and genetic variation in plasticity for growth rate and the concentrations of two phenolic glycosides (salicortin and 2′-cinnamoylsalicortin), and (2) tradeoffs between secondary chemistry and growth rate, and between the two phenolic glycosides. We found genetic variation and genetic variation in plasticity for both chemicals but not for growth rate. Nutrient fertilization enhanced growth and decreased salicortin concentration. More importantly, nutrient environment affected the expression of genetic variation. Heritability was significant only in the medium (both phenolic glycosides) and in the high (2′-cinnamoylsalicortin only) fertilizer treatments, and there was significant genetic variation in plasticity. There was no evidence suggesting that selection for increased chemical concentration would occur at the expense of growth rate. Finally, it appears that selection in favor of one chemical would result in positive correlational selection for the other. Overall, the evolution of these traits might be constrained by a lack of genetic variation in some environments, but not by negative genetic correlations between the different traits.

Seedling herbivory by slugs in a willow hybrid system: developmental changes in damage, chemical defense, and plant performance.

We evaluated feeding preference and damage by the slug, Arion subfuscus, on seedlings of two willow species, Salix sericea and S. eriocephala, and their F1 interspecific hybrids. Trays of seedlings were placed in the field and excised leaves were presented to slugs in choice tests. Slugs preferred feeding on and caused the most damage to S. eriocephala seedlings. S. sericea seedlings were least preferred and least damaged. F1 hybrid seedlings were intermediate in preference and damage. Slug preference of and damage to these seedlings decreased over time, suggesting developmental changes in resistance. Seedlings were sampled for phenolic glycoside and tannin chemistry weekly to coincide with the field and laboratory experiments. Concentrations of phenolic glycosides and tannins increased linearly with seedling age, coincident with changes in slug preference and damage, indicating a developmental change in defense. Slug deterrence was not detected at low concentrations of salicortin when painted on leaves or discs, but both salicortin and condensed tannins deterred slug feeding at concentrations between 50 and 100mg/g, levels found in adult willows. Seedling performance was related to damage inflicted by slugs. Due to lower levels of damage when exposed to slugs in the field, S. sericea plants had significantly greater biomass than S. eriocephala plants. Biomass of F1 hybrids was equal to S. sericea when damaged. However, undamaged S. eriocephala and F1 hybrid plants had the greatest biomass. Because F1 hybrid seedlings performed as well as the most fit parent in all cases, slugs could be an important selective factor favoring introgression of defensive traits between these willow species.

Phenolic glycosides and condensed tannins in Salix sericea, S. eriocephala and their F1 hybrids: not all hybrids are created equal.

The performance of hybrids depends upon the inheritance and expression of resistance traits. Secondary chemicals are one such resistance trait. In this study, we measured the concentrations of phenolic glycosides and condensed tannins in parental and F1 hybrid willows to examine the sources of chemical variation among hybrids. S. sericea produces phenolic glycosides, salicortin and 2'-cinnamoylsalicortin, and low concentrations of condensed tannin in its leaves. In contrast, S. eriocephala produces no phenolic glycosides but high concentrations of condensed tannins in its leaves. These traits are inherited quantitatively in hybrids. On average, F1 hybrids are intermediate for condensed tannins, suggesting predominantly additive inheritance or balanced ambidirectional dominance of this defensive chemical from the parental species. In contrast, the concentration of phenolic glycosides is lower than the parental midpoint, indicating directional dominance. However, there is extensive variation among F1 hybrids. The concentration of tannin and phenolic glycosides in F1 hybrid families is either (1) lower than the midpoint, (2) higher than the midpoint, or (3) indistinguishable from the midpoint of the two parental taxa. It appears that the production of the phenolic glycosides, especially 2'-cinnamoylsalicortin, is controlled by one or more recessive alleles. We also observed a two-fold or greater difference in concentration between some hybrid families. We discuss how chemical variation may effect the relative susceptibility of hybrid willows to herbivores.

Morphological and molecular evidence for hybridization and introgression in a willow (Salix) hybrid zone.

Hybrid zones provide biologists with the opportunity to examine genetic and ecological interactions between differentiated populations. Accurate identification of hybrid genealogies is considered a necessary prerequisite to understanding observed patterns of hybridization-related phenomena. We analysed molecular and morphological data from individuals in a hybrid zone between two species of willows (Salix sericea Marshall and S. eriocephala Michaux) and report the use of randomly amplified polymorphic DNA (RAPD), chloroplast DNA (cpDNA), and ribosomal DNA (rDNA) markers, as well as vegetative morphology and foliar chemistry data to identify individuals in terms of hybrid genealogy and to infer the direction and extent of backcrossing and introgression within the hybrid zone. A novel version of a maximum likelihood estimate approach (developed for this study) was used to calculate hybrid index scores from RAPD marker data; this method produced results similar to those obtained using traditional arithmetic methods. Distribution of rDNA, cpDNA, and chemistry data were examined within the graphical context of RAPD-based hybrid index score histograms and principal component analyses (PCA) on RAPD and morphology data. Seven of the 21 plants classified as S. eriocephala in the field were possible introgressants. Another plant presented an unequivocal example of backcrossed S. sericea chemistry and RAPD markers. Inter- and intraspecific chloroplast diversity found within the hybrid zone suggests both historic introgression (perhaps in a glacial refugium), and contemporary hybridization. Patterns of inheritance and expression within the hybrid zone suggest that morphological characters are often not expressed in a simple additive fashion, and problems associated with both morphological and molecular data are considered.

Water availability alters the relative performance ofSalix sericea,Sralix eriocephala, and their F1hybrids

Seedlings of Salix eriocephala Michx., Salix sericea Marsh., and their F1hybrids were tested for their growth under contrasting water conditions. One-year old seedlings were grown in pots and subjected to one of two experiments, a scheduled-watering experiment (watered every 1, 4, 8, or 12 days) or a dry-down experiment (no watering after an initial period without water limitation). In the scheduled-watering experiment, short-term growth of hybrids was suppressed relative to the parents. However, subsequent watering allowed hybrids to recover. By the end of the 48-day experiments, hybrids exhibited heterosis across all treatments. In the dry-down experiment, hybrids again were highly susceptible to the onset of drought conditions. From these results, we hypothesize that temporal and spatial variability in water availability could determine the survivorship of hybrids and the frequency of introgression; high water availability may enhance the relative performance of hybrids, while low water availability may limit hybrids.Key words: Salicaceae, willows, hybridization, water relations, performance, heterosis.

Genetic Variation in Resistance of Hybrid Willows to Herbivores

We measured herbivore abundance on two species of willows (Salix sericea and S. eriocephala) and their interspecific hybrids in two common garden experiments to test alternative hypotheses concerning the genetic effects of hybridization on plant resistance. The first experiment used potted clones of naturally occurring parental and hybrid plants. Purity of parental plants was determined using 20 RAPD markers (pure S. eriocephala had a score of 1.0 and pure S. sericea had a score of 0). The cloned hybrid plants had hybrid scores between 0.40 and 0.60, indicating they were intermediate hybrids and probably had recombinant (F 2 -type) genotypes. The second experiment used potted one-year-old interspecific F 1 progeny and intraspecific progeny from crosses between genetically pure parents. We counted numbers of herbivores on plants after exposure to attack for about 2 months. Herbivore abundance data were analyzed with ANOVA and a priori contrasts were used to test fit of the data to 5 hypotheses (No Difference, Additive, Dominance, Hybrid Susceptibility, or Hybrid Resistance). We found genetic effects of hybridization on susceptibility to some herbivores in both experiments, with the additive, dominance, and hybrid susceptibility hypotheses supported by different herbivore species. There was also significant genetic variation among clones and genotypes within hybrid and parental taxa for herbivore resistance. For several herbivore species we found no difference in the susceptibility among hybrids and parents, which indicates genetic effects of hybridization on resistance were absent for these species. Differences between the hypotheses supported from this study and data from four years of prior field studies suggest that environmental variation is an important factor affecting relative hybrid and parental susceptibility in the field.

Effects of host plant hybridization on resistance to willow leaf rust caused by Melampsora sp.

SummaryPatterns of resistance to willow leaf rust caused by Melampsora sp. were measured on Salix eriocephala, Salix sericea, and their interspecific hybrids in natural field populations in 1991–94 and on potted plants in common garden experiments in 1994 and 1995. Testing was carried out to establish if the resistance of hybrids was intermediate between pure parental species (additive), equal to one of the parents (dominant), lower than both parents (susceptible), higher than both parents (resistant), or not different than either parent (null hypothesis). Support was generally found for hybrid susceptibility in the field and common garden experiments, with the null hypothesis of no difference having some support. The results from the common garden study suggest that the susceptibility of hybrids seen in the field is due to genetic differences. Hybridization between these species of willows results in increased susceptibility to this pathogen. The variation among years in the relative susceptibility of hybrid and parental willows may be due to environmental effects on the willows or to shifts in the abundance of Melampsora races.

Willow hybridization differentially affects preference and performance of herbivorous beetles

AbstractWe examined the preferences and performances of five beetle species (four chrysomelids and one scarab) on two species of willows (Salix sericea and S. eriocephala) and their interspecific hybrids. Beetle species differed markedly in their responses. In preference assays, two chrysomelid beetle species (Calligrapha multipunctata bigsbyana and Plagiodera versicolora) preferred hybrids, two chrysomelids (Chrysomela scripta and Ch. Knabi) preferred hybrids and S. sericea, and the scarab beetle (Popillia japonica) preferred S. eriocephala. Experiments with purified salicortin indicated that salicortin concentration may contribute to these preferences.The relative performance (growth rate, pupal/adult weight and survivorship) of these beetles on the three willow taxa did not correspond with their feeding preferences. Three species exhibited intermediate performance on hybrid willows (the two Chrysomela spp. and P. japonica); the Chrysomela spp. performed best on S. sericea, while P. japonica performed best on S. eriocephala. One species performed equally well on all three taxa (C. multipunctata bigsbyana). The performance of Pl. versicolora was not tested.Our results support the general pattern that willow taxa with phenolic glycosides are more acceptable to specialist willow herbivores while those taxa without phenolic glycosides are more acceptable to generalist herbivores. We also show that to predict the relative susceptibility of hybrid and parental plants to herbivores, consideration must be given to the inheritance of traits affecting both preference and performance.

The Genetic Basis for Variation in the Concentration of Phenolic Glycosides in Salix sericea: an Analysis of Heritability

The Genetic Basis for Variation in the Concentration of Phenolic Glycosides in Salix sericea: an Analysis of Heritability

The genetic basis for variation in the concentration of phenolic glycosides in Salix sericea: an analysis of heritability

Willows and many other members of the Salicaceae often produce phenolic glycosides, and the concentrations of these are known to vary among plants. We used progeny from a factorial half-sib quantitative genetics experiment with Salix sericea to determine whether the concentration of two phenolic glycosides, salicortin and 2′-cinnamoylsalicortin, show additive heritability. We found that the concentration of salicortin was much higher than 2′-cinnamoylsalicortin, and that both compounds showed additive genetic variation. However, the heritability of these two chemicals differed dramatically. We obtained heritability values of 0.20 for salicortin and 0.59 for 2′-cinnamoylsalicortin. Plant growth parameters were not strongly correlated with the concentrations of these phenolic glycosides.