Willow Genotypes Research Articles

Clonal Variation in Survival and Growth of Hybrid Poplar and Willow in an IN SITU Trial on Soils Heavily Contaminated with Petroleum Hydrocarbons

Species and hybrids between species belonging to the genera Populus (poplar) and Salix (willow) have been used successfully for phytoremediation of contaminated soils. Our objectives were to: 1) evaluate the potential for establishing genotypes of poplar and willow on soils heavily contaminated with petroleum hydrocarbons and 2) identify promising genotypes for potential use in future systems. We evaluated height, diameter, and volume after first year budset by testing 20 poplar clones and two willow clones. Unrooted cuttings, 20 cm long, were planted in randomized complete blocks at 0.91- × 0.91-m spacing at Gary, IN, USA (41.5°N, 87.3°W). Four commercial poplar clones (NM6, DN5, DN34, and DN182) were planted as 20- and 60-cm cuttings. Sixty-cm cuttings exhibited greater height and diameter than 20-cm cuttings; however, we recommend continued use and testing of different combinations of genotype and cutting length. We identified promising genotypes for potential use in future systems and we recommend allocating the majority of resources into commercial poplar clones, given their generalist growth performance. However, further utilization and selection of experimental clones is needed. Specific clones rather than genomic groups should be selected based on the geographic location and soil conditions of the site.

Genotypic variation in drought response of willows grown under ambient and enhanced UV-B radiation

The response of growth of willows to combinations of UV-B radiation and drought stress was studied in a 4-week greenhouse experiment. Eleven hybrid ( Salix myrsinites L. × Salix myrsinifolia Salisb.) clones and four S. myrsinifolia clones were subjected to two UV-B (ambient; enhanced) and two water treatments (well-watered; drought-stressed). According to our results, enhanced UV-B radiation (twice the ambient level) or drought stress (50% less water than well-watered) decreased the growth of hybrid and S. myrsinifolia plantlets, but fast-growing S. myrsinifolia plantlets were more susceptible to drought stress than slower-growing hybrids were. Our results also suggest that enhanced UV-B radiation and drought stress have an additive negative effect on growth of willows. Within hybrid and S. myrsinifolia plantlets, the variation in growth between different clones and families was significant. Drought stress produced family- and clone-specific reactions, whereas the response of studied willow genotypes to enhanced UV-B and UV-B × drought was mostly similar.

Willow genotype, but not drought treatment, affects foliar phenolic concentrations and leaf‐beetle resistance

AbstractIn a greenhouse experiment we examined the effect of willow genotype and irrigation regime (moderate drought and well‐watered) on plant growth parameters, foliar nitrogen, and phenolic concentrations, as well as on the preference and performance of the blue leaf beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae). The 10 vegetatively propagated willow genotypes in the experiments were F2 full‐sibling hybrids, originated from a cross between Salix viminalis (L.) (Salicaceae) (high in condensed tannins) and Salix dasyclados (L.) (Salicaceae) (rich in phenolic glycosides). Insect bioassays were conducted on detached leaves in Petri dishes as well as with free‐living insects on intact potted plants. The 10‐week long irrigation treatments caused statistically significant phenotypic differences in the potted willow saplings. Total biomass was somewhat higher in the well‐watered treatment. The root to total biomass ratio was higher in the drought‐treatment plants. There was significant genotypic variation in foliar nitrogen concentrations, and they were higher in the drought‐treatment plants. There was also a strong genotypic variation in each of the phenolic substances analyzed. Condensed tannins, which accounted for the greatest proportion of total phenolic mass, were higher in the well‐watered treatment. There was, however, no difference in levels of the other phenolics (salicylates, cinnamic acid, flavonoids, and chlorogenic acid) between irrigation treatments. The sum of these phenolics was higher in the well‐watered treatment. There was a strong variation in P. vulgatissima larval development on different willow genotypes, and larval performance was negatively correlated with levels of salicylates and cinnamic acid. There was, however, no effect of irrigation treatment on larval performance. Phratora vulgatissima preferred to feed on well‐watered plants, and we found a preference for oviposition there, but neither feeding nor oviposition site preference was affected by willow genotype. Adult feeding and oviposition preferences were not correlated with larval performance.

Geographic variation in phenotypic traits in Phratora spp. and the effects of conditioning on feeding preference

AbstractThe leaf beetle genus Phratora (L.) (Coleoptera: Chrysomelidae) includes important pests of cultivated willows and poplars. The feeding preference of P. vulgatissima and P. vitellinae collected from different geographical locations was studied under laboratory conditions. There were geographic differences in the amount consumed of different willow host genotypes by each beetle species. Correlation analysis showed that, regardless of these individual differences between willow genotypes and locations, the ranking of preferred host genotypes was significantly related between locations. There were differences in the preference of host genotypes by P. vulgatissima adults and larvae after being confined to a specific willow genotype for a month, suggesting the possibility of a conditioning effect on food preference. This study also permitted the assessment of possible geographic differentiation in morphological traits. Both beetle species generally showed an increase in body size, width, and percentage fat of dry body weight with a more northerly location. These results are discussed in relation to using varietal mixtures as a pest management strategy.

Salicylic acid mediates resistance in the willow Salix viminalis against the gall midge Dasineura marginemtorquens.

Resistant willow (Salix viminalis L.) genotypes react with a rapid hypersensitive response (HR) when attacked by the gall midge Dasineura marginemtorquens Bremi. In general, infected plant genotypes or species that react hypersensitively to pathogens accumulate salicylic acid (SA) locally and systemically. Thus, pathogen-induced HRs are strongly associated with accumulation of SA. In this study, we tested the hypothesis that SA mediates resistance in S. viminalis against D. marginemtorquens. By means of HPLC, we found accumulation of SA in a resistant S. viminalis genotype, but not in a susceptible genotype one to two days after D. marginemtorquens egg hatch. To test whether this correlation between accumulation of SA and resistance is causal, we treated a normally susceptible S. viminalis genotype exogenously with SA and found a decreased larval survival frequency on treated shoots. Thus, the hypothesis that SA mediates resistance in the S. viminalis/D. marginemtorquens system was strongly supported. Interestingly, great similarity seems to exist between the biochemical signaling associated with pathogen-induced HRs and this gall-inducer induced HR.

Effect of plantation design on stem‐infecting form of rust in willow biomass coppice

Planting of genotype mixtures is a major strategy for the non‐chemical control of willow rust in short‐rotation coppice willows grown for biomass. In 1997 and 1998, the relative severity and spatiotemporal distribution of stem canker damage by Melampsora spp. on Salix viminalis `Bowles Hybrid' in a field trial containing monocultures and two design mixtures (random or regular) of three or five genotypes were assessed. Sphaerellopsis filum, a hyperparasite of Melampsora spp. was detected in all plots during the summer (1998) between the time of the two canker assessments. The percentage of rust pustules with this hyperparasite was initially greater in monoculture plantings than in mixtures in June, but by July, more than 92% of pustules were parasitized, irrespective of plantation design. The stem rust assessments showed that, in general, there were fewer cankers per stool in plots containing mixtures of willow genotypes compared with monoculture plantings. The distribution of rust cankers was different between monocultures and willow mixture designs, with differences between years for monocultures.

A rapid hypersensitive response associated with resistance in the willow Salix viminalis against the gall midge Dasineura marginemtorquens

AbstractGreat genotypic variation in resistance against the gall midge Dasineura marginemtorquens Bremi (Diptera: Cecidomyiidae) exists within its willow host Salix viminalis L. (Salicaceae). In some resistant genotypes larvae die within 40 h after attempting to initiate galls. The present study tested the hypothesis that the hypersensitive response (HR) is involved in incompatible interactions between D. marginemtorquens and S. viminalis. By means of UV/blue light and visible light microscopy, we verified a rapidly (within 12 h after egg hatch) spreading cell death of an HR‐type due to larval attack in resistant willow genotypes. Twelve h after egg hatch, the cell death had spread up to six cell layers in resistant S. viminalis genotypes whereas in susceptible genotypes only up to two cell layers were affected. In the groups of dead cells on the resistant genotypes accumulation of phenolics was observed within 24 h after egg hatch. The rapidity of the cell death induction, the early local accumulation of phenolic compounds, and the strong association of the cell death with larval mortality suggest that the formation of dead cells in resistant willow genotypes should be interpreted as a true HR.

Does host genotype diversity affect the distribution of insect and disease damage in willow cropping systems?

Summary Planting of willow genotype mixtures for biomass production has been suggested as a non‐chemical strategy for pest management. Basic information on spatial dynamics of important insects and pathogens is necessary for the effective deployment of host genotypes in a plantation. In 1998 and 1999 the degree and spatial distribution of damage by Melampsora spp. and Phratora vulgatissima were studied concurrently in a field trial containing monocultures of willow Salix genotypes with different willow rust and beetle susceptibilities, and two design mixtures (random or regular) of three or five genotypes. For both years, there was more rust and beetle damage on plants in monocultures than in mixtures. There were significant differences in the vertical distribution of beetle damage along stems between plantation designs for the 2 years, yet only in 1999 for rust. Rust severity along stems was significantly correlated between leaves, indicating localized spread of disease. In contrast, beetle damage severity along stems was weakly correlated between alternate leaves and leaves farther apart, suggesting beetle movement from tree to tree. In 1998, spatial distribution of rust was aggregated in 67% of plots studied and in 40% for beetles. There was no significant difference in the distribution of beetle damage between planting design, but rust was aggregated in 75% of mixtures and 33% of monocultures. While beetle damage distribution was similar between years, rust was aggregated in all monoculture plots but in only 8% of mixtures in 1999. The difference between years and design for rust was probably because of the later stage of rust development in 1999 and the delaying effect of mixtures on this development. In 1998, there were significant negative correlations between the extent of rust and beetle damage on individual trees. However, only 20% of plots showed a significant spatial dissociation between these two types of damage. There were fewer discernible interactions in 1999. Plantation design provides the basis for integrated control of rust and beetle damage within willow cropping systems by delaying the spread and development of both organisms. Both pest and disease can be assessed successfully simultaneously under field conditions, a major saving in human resources. Initial selection of willow mixture configuration should primarily take into account the effects of spatial design on rust development.

Rapid gall midge adaptation to a resistant willow genotype

Abstract 1 We conducted two experiments to investigate why a basket willow Salix viminalis L. genotype, known to be highly resistant to the leaf‐roller gall midge Dasineura marginemtorquens (Bremi), should support very high gall densities in a field plantation at Tälle, south Sweden.2 The first experiment was a field test of the hypothesis of fine‐scale host adaptation in the gall midge/willow system. Support for the hypothesis would be established if midges originating from resistant willows and those originating from nearby susceptible willows differed in their abilities to initiate galls and complete development on resistant plants.3 The objective of the second experiment was to explore whether there was a genetic basis to the trait for virulence in the midge population and to investigate any potential trade‐offs this trait may entail.4 Our results indicate that there was a fine‐scaled microgeographic genetic structure to the midge population at Tälle. Midges originating from resistant plants had a heritable trait that enabled them to establish galls on resistant plants.5 Midges able to initiate galls on the resistant genotype had longer developmental time on the susceptible genotype. This suggests that there is a physiological cost associated with being adapted to the resistant willow genotype.6 We suggest that driving forces behind the observed host adaptation are selection imposed on the midge population by very strong willow resistance and restricted gene flow in the midge populations due to the special life history features of D. marginemtorquens.

High oviposition rate of Dasineura marginemtorquens on Salix viminalis genotypes unsuitable for offspring survival

AbstractA short history of contact between Dasineura marginemtorquens and resistant genotypes of Salix viminalis has previously been suggested as an explanation for a poor correspondence between female oviposition preference and larval performance on certain host types. The discovery of resistant wild willows instigated a quest for an alternative hypothesis. This study presents data from laboratory and field experiments that were designed to detect variability in host preferences of individual members of the midge population. Field tests showed that the oviposition site choices of females followed the same random‐natured pattern as choices of females in laboratory situations. Ovipositing females did not distinguish between willow genotypes with very high or very low larval mortality. No differences in post‐alighting behavior of midges on the two willow types were discovered. Observations revealed that females usually remained and oviposited on the first plant with which they came into contact, regardless of genotype.

Gall initiation success and fecundity of Dasineura marginemtorquens on variable Salix viminalis host plants

AbstractGenotypic and environmentally determined differences in Salix viminalis L. suitability for Dasineura marginemtorquens (Bremi) (Diptera: Cecidomyiidae) growth and survival were investigated in laboratory and field experiments. Earlier studies have documented high neonate larval mortality on certain S. viminalis genotypes. Here we present results from laboratory experiments which show no difference in larval establishment behaviour on resistant and susceptible willow genotypes. These data indicate that larvae are not able to detect the plant characteristic responsible for resistance. In a field study insect performance was measured on willow shoots of dissimilar size. Adult body size was positively correlated to willow shoot length. In turn, body size was positively correlated to potential fecundity. These results are discussed in relation to observed high densities of D. marginemtorquens in vigorously growing willows cultivated for biomass production.

Variable Enemy Impact at Three Scales: Herbivore Species, Plant Species, and Plant Genotype

We tested predictions of the Enemy Impact and Tritrophic Level Hypotheses by examining survival and causes of mortality of two closely related, coexisting species of gall-forming sawflies, Phyllocolpa, among three species of willow that grow in the same habitat and among potted clones of one willow species. We hypothesized that: a) susceptibility of the Phyllocolpa species to shared natural enemies would vary among the three willow species, b) Phyllocolpa species would differ in susceptibility to their natural enemies on the same willow species, and c) willow genotype would influence the susceptibility of the Phyllocolpa species to their natural enemies. The sawfly species differ in their gall characteristics and oviposition sites. Phyllocolpa nigrita (species B) oviposits at the base of the leaf fold, and Phyllocolpa sp. nov. (species M) oviposits near the middle of the leaf fold

The Effect of Fire on Stimulating Willow Regrowth and Subsequent Attack by Grasshoppers and Elk

We performed two experimental burns of willow shrubs planted in common gardens so that we could quantify the changes in willow architecture and the response of herbivores following fire. The first burn, which,was conducted in May, showed no effect of fuel quantity on resprouting of willows. For the second burn, which was conducted in July, we used replicates of eight different willow genotypes from each of two different elevational sites. 73% of the willows resprouted from below ground parts following the May burn and 83% resprouted following the July burn. Plants began resprouting only ten days after the May burn compared to 21 days after the July burn (...)

Indole-3-acetic Acid Content in Buds of Five Willow Genotypes

Free IAA content in vegetative axillary buds from non-growing shoots of five willow genotypes was measured using RIA. The buds were analysed either immediately after removal of the bud scales or after several weeks culture in vitro with or without BA pre-treatment. Noncultured buds had lower IAA levels than buds cultured in vitro . Genotypic differences in the IAA level were found in buds cultured in vitro but not in non-cultured buds. BA pre-treatment resulted in decreased IAA levels in some clones but not in others. Specific morphogenic genotype differences could not be correlated to IAA levels.