Biology, distribution and impacts of silverleaf nightshade (Solanum elaeagnifolium Cav.)

The Invasion of Alien Populations of Solanum elaeagnifolium in Two Mediterranean Habitats Modifies the Soil Communities in Different Ways

We aimed to explore how the invasion of the alien plant Solanum elaeagnifolium affects soil microbial and nematode communities in Mediterranean pines (Pinus brutia) and maquis (Quercus coccifera). In each habitat, we studied soil communities from the undisturbed core of both formations and from their disturbed peripheral areas that were either invaded or not by S. elaeagnifolium. Most studied variables were affected by habitat type, while the effect of S. elaeagnifolium was different in each habitat. Compared to maquis, the soil in pines had higher silt content and lower sand content and higher water content and organic content, supporting a much larger microbial biomass (PLFA) and an abundance of microbivorous nematodes. The invasion of S. elaeagnifolium in pines had a negative effect on organic content and microbial biomass, which was reflected in most bacterivorous and fungivorous nematode genera. Herbivores were not affected. In contrast, in maquis, organic content and microbial biomass responded positively to invasion, raising the few genera of enrichment opportunists and the Enrichment Index. Most microbivores were not affected, while herbivores, mostly Paratylenchus, increased. The plants colonizing the peripheral areas in maquis probably offered a qualitative food source to microbes and root herbivores, which in pines was not sufficient to affect the much larger microbial biomass.

The relationship between Invasive Alien Solanum elaeagnifolium Cav. characters and impacts in different habitats

Invasive alien plants are one of the most serious threats to agriculture. The growth traits of Solanum elaeagnifolium Cav. in crops and their demographics in invaded vs non-invaded communities were examined. The majority of S. elaeagnifolium germination was observed in the spring compared to the summer. Five stages were distinguished, which started with a short time of seedling and juvenile stages, extended flowering, and fruiting stages, and seed dispersion in the winter season. An increase in shoots/roots ratio, leaf area ratio and leaf mass fraction during growth with the varied rate was proved. The accumulation coefficient of dry mass exceeded 0.93 and was significant (P > 0.001) with great variability within plant parts, and stage intervals. While the high growth rate is influenced by the stages and habitats. The recipient communities are affected negatively by S. elaeagnifolium invasion which is associated with lower diversity, richness, and evenness vs non-invaded communities. High similarities were found in the invaded area and communities. Finally, high and varied growth and plasticity of S. elaeagnifolium characterized their invasion behavior via different habitats. There were suitable determinants indices of diversity that can be used in the comparison between invaded and non-invaded communities. This knowledge may be useful for use in agro-environment protection and to improve the management methods of invasive alien species.

Early detection, herbicide resistance screening, and integrated management of invasive plant species: a review

Invasive plant species (IPS) are often considered weeds that cause high yield losses in crops, negatively affect the environment, and disrupt certain ecosystem services. The negative impact of IPS on biodiversity is increasing and disturbing native vegetation. The management of plant invasions can be divided in two phases (before and after invasion). Prior to introduction it is crucial to develop the knowledge base (biology, ecology, distribution, impact, management) on IPS, prevention measures and risk assessment. After introduction if eradication fails, the monitoring and the integrated management of IPS are imperative to prevent the naturalization and further dispersal. This review uses two major invasive weed species (Amaranthus palmeri S. Wats. and Solanum elaeagnifolium Cav.) as case studies to propose a framework for early detection, rapid herbicide resistance screening, and integrated management. The holistic framework that is presented exploits recent: (i) novel detection tools, (ii) rapid tests and assays for herbicide resistance, and (iii) biology, ecology, distribution traits, and management tools for the IPS. Farmers, advisors, researchers, and policymakers need briefing on IPS growth dynamics, adaptability rates, and response to conventional and novel treatments to prevent new invasions, eradicate isolated stands, and mitigate the impact of invasive weed species in the long term. © 2022 Society of Chemical Industry.

Examining the Role of Buzzing Time and Acoustics on Pollen Extraction of Solanum elaeagnifolium

Buzz pollination is a specialized pollination syndrome that requires vibrational energy to extract concealed pollen grains from poricidal anthers. Although a large body of work has examined the ecology of buzz pollination, whether acoustic properties of buzz pollinators affect pollen extraction is less understood, especially in weeds and invasive species. We examined the pollination biology of Silverleaf nightshade (Solanum elaeagnifolium), a worldwide invasive weed, in its native range in the Lower Rio Grande Valley (LRGV) in south Texas. Over two years, we documented the floral visitors on S. elaeagnifolium, their acoustic parameters (buzzing amplitude, frequency, and duration of buzzing) and estimated the effects of the latter two factors on pollen extraction. We found five major bee genera: Exomalopsis, Halictus, Megachile, Bombus, and Xylocopa, as the most common floral visitors on S. elaeagnifolium in the LRGV. Bee genera varied in their duration of total buzzing time, duration of each visit, and mass. While we did not find any significant differences in buzzing frequency among different genera, an artificial pollen collection experiment using an electric toothbrush showed that the amount of pollen extracted is significantly affected by the duration of buzzing. We conclude that regardless of buzzing frequency, buzzing duration is the most critical factor in pollen removal in this species.

Exploring the role of soil types on defense and fitness traits of silverleaf nightshade (Solanum elaeagnifolium), a worldwide invasive species through a field survey in the native range

Silverleaf nightshade (Solanum elaeagnifolium) is a highly successful invasive weed that has caused agricultural losses both in its home and invaded ranges. Surveying 50 sub-populations over 36,000 km² in its native range in South Texas, we investigated the interactions among soil type, population size, plant height, herbivory, and plant defenses in its home range with the expectation that populations growing in the plant's preferred sandier soils would host larger colonies of healthier and better defended plants. At each sampling location, on randomly selected plants, we measured height, insect herbivore damage, and presence, and density of internode spines. Soil type was determined using the NRCS Web Soil Survey and primarily grouped into sand, clay, or urban. Our results show a tradeoff between growth and defense with larger colonies and taller plants in clay soils, but smaller colonies of shorter, spinier plants in sandy soils. We also observed decreased herbivory in urban soils, further confirming the plant's ability to survive and even be strengthened by highly disturbed conditions. This study is a starting point for a better understanding of silverleaf nightshade's ecology in its home range and complicates the assumption that it thrives best in sandy soils.

Investigating the Invasion Pattern of the Alien Plant Solanum elaeagnifolium Cav. (Silverleaf Nightshade): Environmental and Human-Induced Drivers

Invasive alien plant species have impacts on nature conservation, ecosystem services and agricultural production. To identify environmental and human-related drivers of the invasion of Solanum elaeagnifolium (Solanaceae)—one of the worst alien invasive plants worldwide—we conducted an extensive drive-by survey across the Greek territory (presence/absence data; all national major multilane highways; 12–25% of the remaining road network; driven 3–5 times during 2000–2020). These data were linked in GIS with (i) physical environmental attributes (elevation, climate, soil properties) and (ii) type and intensity of human-related activities (land uses, settlements and road type). Compared to previous records, our survey showed that the range of S. elaeagnifolium increased by 1750% during the last decades, doubling its main distribution centers and reaching higher elevations. Our study revealed that the presence of S. elaeagnifolium is associated with (i) higher maximum temperatures and precipitation in summer and low precipitation in winter, as well as with (ii) soil disturbance related to agricultural activities, settlements and road networks, thus facilitating its spread mainly at low altitudes. Our study elucidates the current invasion pattern of S. elaeagnifolium and highlights the urgent need for its widespread monitoring, at least in the noninvaded areas in Greece that have been surveyed in this study. Preventative measures and integrative initiatives should be implemented quickly, and urgently incorporated into current agricultural, road network and conservation-management regimes.

Local adaptation to continuous mowing makes the noxious weed Solanum elaeagnifolium a superweed candidate by improving fitness and defense traits

The role of disturbance in accelerating weed growth is well understood. While most studies have focused on soil mediated disturbance, mowing can also impact weed traits. Using silverleaf nightshade (Solanum elaeagnifolium), a noxious and invasive weed, through a series of field, laboratory, and greenhouse experiments, we asked whether continuous mowing influences growth and plant defense traits, expressed via different avenues, and whether they cascade into offspring. We found that mowed plants produced significantly less number of fruits, and less number of total seeds per plant, but had higher seed mass, and germinated more and faster. When three herbivores were allowed to feed, tobacco hornworm (Manduca sexta) caterpillars, gained more mass on seedlings from unmowed plants, while cow pea aphid (Aphis craccivora), a generalist, established better on mowed seedlings; however, leaf trichome density was higher on unmowed seedlings, suggesting possible negative cross talk in defense traits. Texas potato beetle (Leptinotarsa texana), a co-evolved specialist on S. elaeagnifolium, did not show any differential feeding effects. We also found that specific root length, an indicator of nutrient acquisition, was significantly higher in first generation seedlings from mowed plants. Taken together, we show that mowing is a selective pressure that enhances some fitness and defense traits and can contribute to producing superweeds.

Survival of off-host unfed Rhipicephalus (Boophilus) annulatus (Acari: Ixodidae) larvae in study arenas in relation to climatic factors and habitats in South Texas, USA

The cattle fever tick, Rhipicephalus annulatus (Say), is an economically destructive arthropod because of its ability to vector bovine babesiosis. Cattle fever ticks can spend more than 90% of their life cycle as questing larvae, but the effect of climatic factors on their off-host behavior and survival is unclear. The goal of this study was to measure the effects of specific ecological factors on off-host larvae in nature. The study was conducted in a south Texas pasture over a 20-mo period, during which time larval populations were surveyed and ambient weather variables - relative humidity and temperatures - were recorded. Oviposition success and larval survival varied between cattle fever tick cohorts and was affected by relative humidity and canopied (with tree cover) versus exposed habitat. The results show that relative humidity and the interaction of relative humidity and inhabiting canopied habitats play a key role in oviposition success. Additionally, canopied habitats have a positive influence on off-host larval survival in the spring and summer.

Population Dynamics of Off-Host Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) Larvae in Response to Habitat and Seasonality in South Texas

The cattle tick, Rhipicephalus microplus (Canestrini), is an economically destructive arthropod because of its ability to vector bovine babesiosis. It is known that cattle ticks can spend 80–90% of their lifecycle as questing larvae, yet the effect of climatic factors on their off-host behavior and survival is unclear. The goal of this study was to measure the effects of specific ecological factors on off-host questing larvae in nature. The study was conducted in a south Texas pasture over a two-year period, during which time larval populations were surveyed. Simultaneously, weather variables—precipitation, relative humidity, and ambient temperatures—were recorded. Larval survival rates varied among seasons, with the overall highest populations recorded in the spring and the lowest in the fall by a ratio of 20:1. In the winter, the larger numbers were collected from exposed habitats at a ratio of 6:1. Conversely, canopied habitats in the summer had 10-fold larger larval numbers. In the spring, exposed and canopied habitats showed no difference in tick larval survival rates. The results show that the interaction between season and habitat strongly influence off-host questing tick survival. Relative humidity was a key weather variable.

Intrusive trichome bases in the leaves of silverleaf nightshade (Solanum elaeagnifolium; Solanaceae) do not facilitate fluorescent tracer uptake

PREMISE OF THE STUDY

Solanum elaeagnifolium (silverleaf nightshade), having originated in the Americas, is now a serious summer-growing, perennial weed in many countries, including Australia. Most surfaces of the plants have a dense covering of trichomes, giving them a silvery-white appearance, hence the common name. We aimed to identify structural and functional properties of its leaves, especially the trichomes, that may affect the uptake of foliar-applied tracer dyes.

METHODS

The structure of leaves of Solanum elaeagnifolium was examined by light and scanning electron microscopy. The potential for transport of materials between trichomes and veins was studied with symplastic (carboxyfluorescein diacetate) and apoplastic (lucifer yellow) tracer dyes.

KEY RESULTS

Mature leaves had a dense covering of complex, stellate trichomes on both surfaces, particularly the abaxial. The basal cells of Solanum elaeagnifolium trichomes penetrated into the underlying palisade mesophyll layers. The innermost lobes of these basal cells sometimes contacted the bundle sheath of the veins, but were not observed to directly contact the xylem or phloem. We found that neither symplastic nor apoplastic dyes were transferred between the basal cells of the trichomes and the vascular tissues. The trichome layer repelled water-based tracer dyes, while one of four adjuvants tested facilitated entry of both symplastic and apoplastic dyes.

CONCLUSIONS

Our results did not support a transport function for the trichomes. The trichomes may protect the mesophytic leaves from invertebrate herbivory, while also probably decreasing radiation absorbed resulting in cooler leaves in this summer-growing species.