Oak powdery mildew changes growth patterns in its host tree: host tolerance response and potential manipulation of host physiology by the parasite

Context

Parasites can induce strong effects on their host’s growth, not only as a result of host resource exploitation (growth loss) but also with a potential adaptive value for host (tolerance response) and themselves (increased transmission).

Aims

We assessed these three types of phenotypic changes in oak seedlings infected by powdery mildew.

Methods

A manipulative field experiment with three levels of parasite inoculum was designed in order to tease apart infection from genetic effects on oak growth. Seedlings were monitored during 3 years for height growth, phenology and infection.

Results

Powdery mildew infection induced both significant growth loss and qualitative changes in plant architecture. The most striking and unexpected change was increased growth polycyclism in infected seedlings. This benefitted both the host as a form of compensation for infection-caused height loss, and the pathogen, by increasing sporulation.

Conclusion

The study highlights the effect of parasites in the expression of plant phenotypic traits, such as phenology and ultimately tree architecture. Both host tolerance and parasitic manipulation may be involved in the observed changes in growth patterns. These results suggest a complex interplay between development and defence in trees and emphasize the need to better assess tolerance mechanisms when considering the defence strategies of trees against pathogens.     

Estimating coarse root biomass with ground penetrating radar in a tree-based intercropping system

Conventional measurements of tree root biomass in tree-based intercropping (TBI) systems can be inadequate in capturing the heterogeneity of rooting patterns or can be highly destructive and non-repeatable. In this study, we estimated coarse root biomass using ground penetrating radar (GPR) of 25-year-old trees inclusive of five species (Populus deltoides × nigra clone DN-177, Juglans nigra L., Quercus rubra L., Picea abies L. Karst, and Thuja occidentalis L.) at a TBI site in Southern Ontario, Canada. Subsurface images generated by GPR were collected in grids (4.5 × 4.5 m) centred on tree stems. The predictive relationship developed between GPR signal response and root biomass was corrected for species effects prior to tree-scale estimates of belowground biomass. Accuracy of the tree-scale estimates was assessed by comparing coarse root biomass measured from complete excavations of the corresponding tree. The mean coarse root biomass estimated from GPR analysis was 54.1 ± 8.7 kg tree^?1 (mean ± S.E.; n = 12), within 1 % of the mean coarse root biomass measured from excavation. Overall there was a root mean square error of 14.4 kg between measured and estimated biomass with no detectable bias despite variable conditions within the in-field and multi-species study. Root system C storage by species, calculated with species-specific root carbon concentrations, is estimated at 5.4 ± 0.7–34.8 ± 6.9 kg C tree^?1 at this site. GPR is an effective tool for non-destructively predicting coarse root biomass in multi-species environments such as temperate TBI systems.     

Characterization of black locust (Robinia pseudoacacia L.) heartwood extractives: identification of resveratrol and piceatannol

Robinia pseudoacacia L. heartwood is characterized by a very high natural durability. However, a significant difference was observed between the mature and juvenile heartwood, the latter presenting less durability against fungi decay, which could be attributed to lower extractive content. In order to elucidate this idea, extractives from mature and juvenile heartwoods of black locust trees were investigated. Results showed that extractive and phenolic contents were higher in mature than in juvenile heartwoods. The identification of phenolic compounds by UPLC–DAD–MS/MS revealed, for the first time, the presence of resveratrol and piceatannol. These two stilbenes as well as the flavonoid dihydrorobinetin were present at the highest level in mature heartwood, and as they are known antifungals, they could account for the great durability of mature heartwood. The stilbenes were detected in significant amounts particularly in mature heartwood where piceatannol reached a level tenfold higher than that reported for Japanese knotweed roots, the primary natural source of these stilbenes, whereas resveratrol level was comparable with reported values. As resveratrol and piceatannol receive increasing demand for nutraceutical, cosmetic and, possibly, pharmaceutical purposes, due to their beneficial health effects, this study underlines the use of R. pseudoacacia as a promising sustainable and economical source of resveratrol and piceatannol.     

Pheromone-based decision support tools for management of <Emphasis Type="Italic">Halyomorpha halys</Emphasis> in apple orchards: development of a trap-based treatment threshold

The invasive brown marmorated stink bug, Halyomorpha halys (Stål), has become a serious pest in mid-Atlantic apple orchards. Because no decision support tools exist for H. halys management, calendar-based insecticide applications have been the only successful technique for mitigating H. halys injury in orchards. Following the identification of the two-component aggregation pheromone of H. halys, we conducted a study to determine whether biological information generated by traps baited with this pheromone and pheromone synergist could be used to make management decisions. In this study, experimental apple orchards were treated with a H. halys-targeted insecticide only when a predetermined cumulative threshold of either 1, 10, or 20 adults per trap was reached. Once threshold was reached, two alternate row middle sprays 1 week apart were triggered and the threshold was reset. For comparison, some orchards were also subjected to a weekly alternate row middle spray or left untreated as controls. At harvest, significantly less fruit injury was observed when treated weekly or using a threshold of 1 or 10 H. halys adults per trap to trigger insecticide applications. Orchards treated using a cumulative threshold of 20 adults per trap or when left unsprayed had significantly higher fruit injury. In addition, insecticide applications were reduced by 40% using a threshold of 10 adults per trap. Our results suggest that baited pheromone traps can be used as decision support tools to trigger insecticide applications when needed to mitigate risk and effectively manage H. halys in apple orchards.     

Understanding the naturalization of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> in Portugal: a comparison with Australian plantations

Despite the potential utility of a biogeographical approach to understanding the naturalization of exotic species, studies using this approach are scarce. Eucalyptus globulus is an economically important Australian tree species that has become naturalized in a number of countries where it was introduced. Portugal is an ideal territory to study the naturalization of E. globulus owing to: a long introduction history, the antipodal location compared to Australia and the large cultivated area. Wildling density was assessed in 116 E. globulus plantations in central Portugal through 213 transects established along plantation borders. Boosted regression trees were used to model the influence of plantation-scale variables. Results from this survey were compared with data obtained in plantations from seven Australian regions, where a similar sampling protocol had been used. In Portugal, wildlings were more abundant in plantations that were: located in moist aspects, coppiced, with older tree stems and corresponding to intermediate site growth indexes. The overall density (127 plants ha^?1) was 14.9 times higher than in the Australian estate, but this ratio was reduced to 3.1 in a more comparable subset of unburnt, first rotation plantations. A generalized linear model fitted using a dataset combining the two surveys showed that country influenced wildling density, together with plantation rotation and stem age. These results provide insights into the naturalization of a widely cultivated tree species, pointing to a fundamental role of the introduction history, possibly acting along with the biogeographical characteristics of the introduced range.     

Preliminary study on antifertility activity of Calotropis procera roots in female rats

The effect of ethanolic extract of the roots of Calotropis procera has been studied in albino rats to explore its antifertility and hormonal activities. A strong antiimplantation (inhibition 100%) and uterotropic activity was observed at the dose level of 250 mg/kg (1/4 of LD(50)). No antiestrogenic activity could be detected.     

Use of crop models to understand genotype by environment interactions for drought in real-world and simulated plant breeding trials

Crop simulation models of plant processes capture the biological interactions between the sensing of signals at an organ level (e.g. drought affecting roots), the response of the plant at a biochemical level (e.g. change in development rate) and the result at the organ (or crop) level (e.g. reduced growth). In dissecting the complex control of phenotypes like yield, simulation models have several roles. Models have been used to generate an index of the climatic environment (e.g. of drought stress) for breeding programme trials. In wheat and sorghum grown in northern Australia, this has shown that mid-season drought generates large genotype by environment interaction. By defining gene action to calculate the value of input trait parameters to crop models, simulated multi-environment trials estimate the yield of ‘synthetic’ sorghum cultivars grown in historical or artificial climates with current or potential management regimes. In this way, the biological interactions among traits constrain the crop yields to only those that are biologically possible in the given set of environments. This allows the construction of datasets that are more ‘realistic’ representations of gene by trait by environment interaction than is possible using only the statistical attributes (e.g. means, variances and correlations) of real-world trait datasets. This approach has an additional advantage in that ‘biological and experimental noise’ can be manipulated separately. These ‘testbeds’ for statistical techniques can be extended to the interpretation of a crossing and selection programme where the processes of chromosomal recombination are simulated using a quantitative genetics model and applied to the trait parameters. Statisticians are challenged to develop improved methods for the resulting simulated phenotype datasets, with the objective of revealing the (known) underlying genetic and environment structure that was input to the simulations. These improved methods can then be applied to existing plant breeding programmes.     

Screening techniques and sources of resistance to abiotic stresses in cool-season food legumes

Summary The adaptability and productivity of cool-season food legumes (chickpea, faba bean, lentil, pea) are limited by major abiotic stresses including drought, heat, frost, chilling, waterlogging, salinity and mineral toxicities. The severity of these stresses is unpredictable in field experiments, so field trials are increasingly supplemented with controlled-environment testing and physiological screening. For drought testing, irrigation is used in dry fields and rain-out shelters in damp ones. Carbon isotope discrimination (Δ¹³C) is a well-established screen for drought tolerance in C3 cereal crops which is now being validated for use in grain legumes, but it is relatively expensive per sample and more economical methods include stomatal conductance and canopy temperature. Chickpea lines ICC4958 and FLIP87-59C and faba bean line ILB938 have demonstrated good drought tolerance parameters in different experiments. For frost tolerance, an efficient controlled-environment procedure involves exposing hardened pot-grown plants to sub-zero temperatures. Faba beans Cote d’Or and BPL4628 as well as lentil ILL5865 have demonstrated good freezing tolerance in such tests. Chilling-tolerance tests are more commonly conducted in the field and lentil line ILL1878 as well as derivatives of interspecific crosses between chickpea and its wild relatives have repeatedly shown good results. The timing of chilling is particularly important as temperatures which are not lethal to the plant can greatly disrupt fertilization of flowers. Salinity response can be determined using hydroponic methods with a sand or gravel substrate and rapid, efficient scoring is based on leaf symptoms. Many lines of chickpea, faba bean and lentil have shown good salinity tolerance in a single article but none has become a benchmark. Waterlogging tolerance can be evaluated using paired hydroponic systems, one oxygenated and the other de-oxygenated. The development of lysigenous cavities or aerenchyma in roots, common in warm-season legumes, is reported in pea and lentil but is not well established in chickpea or faba bean. Many stresses are associated with oxidative damage leading to changes in chlorophyll fluorescence, membrane stability and peroxidase levels. An additional factor relevant to the legumes is the response of the symbiotic nitrogen-fixing bacteria to the stress.     

Genetic diversity of selected pigmented traditional rice (Oryza sativa L.) varieties from Mindanao,Philippines using agromorphological traits and simple sequence repeats markers

Journal of Crop Science and Biotechnology - Philippine pigmented traditional rice varieties (TRVs) offer potential novel genes for genetic improvement. In this study, forty-three pigmented...