Rising from the shadows: Selective foraging in model shoot parasitic plants.

Despite being sessile, plants nonetheless forage for resources by modulating their growth. Adaptative foraging in response to changes in resource availability and presence of neighbours has strong implications for performance and fitness. It is an even more pressing issue for parasitic plants, which draw resources directly from other plants. Indeed, parasitic plants were demonstrated over the years to direct their growth towards preferred hosts and invest resources in parasitism relative to host quality. In contrast to root parasites that rely mostly on chemical cues, some shoot parasites seem to profit from the ability to integrate different types of abiotic and biotic cues. While significant progress in this field has been made recently, there are still many open questions regarding the molecular perception and the integration of diverse signalling pathways under different ecological contexts. Addressing how different cues are integrated in parasitic plants will be important when unravelling variations in plant interaction pathways, and essential to predict the spread of parasites in natural and agricultural environments. In this review, we discuss this with a focus on Cuscuta species as an emerging parasitic model, and provide research perspectives based on the recent advances in the topic and plant-plant interactions in general.

Potential Plant-To-Plant Transmission: Shared Endophytic Bacterial Community Between Ziziphus lotus and Its Parasite Cuscuta epithymum.

Microbiota associated with host-parasite relationships offer an opportunity to explore interactions among plants, parasites, and microbes, thereby contributing to the overall complexity of community structures. The dynamics of ecological interactions between parasitic plants and their hosts in arid environments remain largely understudied, especially in Africa. This study aimed to examine the bacterial communities of Cuscuta epithymum L. (clover dodder), an epiphytic parasitic plant, and its host, Ziziphus lotus L. (jujuba), in an arid environment. Our goal was to uncover the ecological complexities of microbial communities within the framework of plant-plant interactions. We conducted a comprehensive analysis of the bacterial composition and diversity within populations of the C. epithymum parasite, the infected- and non-infected jujuba host, and their interface at the shoots of the host. This involved amplicon sequencing, targeting the V5-V6 regions of the 16S rRNA gene. A total of 5680 amplicon sequence variants (ASVs) were identified, with Pseudomonadota, Bacillota, and Actinobacteriota being prevalent phyla. Among the bacterial communities, three genera were dominant: Cutibacterium, Staphylococcus, and Acinetobacter. Interestingly, analyses of alpha-diversity (p = 0.3 for Shannon index and p = 0.5 for Simplon index) and beta-diversity (PERMANOVA, with p-values of 0.6 and 0.3) revealed no significant differences between Cuscuta-infected and non-infected jujube shrubs, suggesting a shared shoot endophytic bacteriome. This finding advances our comprehension of microbial communities linked to plant-parasite interactions in the arid environments of Africa. Further research on various hosts is required to confirm plant-to-plant bacterial transmission through Cuscuta infection. Additionally, studies on functional diversity, cytology, ecophysiology and the mechanisms by which bacterial communities transferred between host and parasite are necessary.

Heinz-resistant tomato cultivars exhibit a lignin-based resistance to field dodder (Cuscuta campestris) parasitism.

Cuscuta species (dodders) are agriculturally destructive, parasitic angiosperms. These parasitic plants use haustoria as physiological bridges to extract nutrients and water from hosts. Cuscuta campestris has a broad host range and wide geographical distribution. While some wild tomato relatives are resistant, cultivated tomatoes are generally susceptible to C. campestris infestations. However, some specific Heinz tomato (Solanum lycopersicum) hybrid cultivars exhibit resistance to dodders in the field, but their defense mechanism was previously unknown. Here, we discovered that the stem cortex in these resistant lines responds with local lignification upon C. campestris attachment, preventing parasite entry into the host. Lignin Induction Factor 1 (LIF1, an AP2-like transcription factor), SlMYB55, and Cuscuta R-gene for Lignin-based Resistance 1, a CC-NBS-LRR (CuRLR1) are identified as factors that confer host resistance by regulating lignification. SlWRKY16 is upregulated upon C. campestris infestation and potentially negatively regulates LIF1 function. Intriguingly, CuRLR1 may play a role in signaling or function as an intracellular receptor for receiving Cuscuta signals or effectors, thereby regulating lignification-based resistance. In summary, these four regulators control the lignin-based resistance response in specific Heinz tomato cultivars, preventing C. campestris from parasitizing resistant tomatoes. This discovery provides a foundation for investigating multilayer resistance against Cuscuta species and has potential for application in other essential crops attacked by parasitic plants.

Germinating seedlings and mature shoots of Cuscuta campestris respond differently to light stimuli during parasitism but not during circumnutation.

Seedlings of the parasitic plant genus Cuscuta (dodder) locate hosts by circumnutation, coil around the host near soil level and form a haustorium, establishing a primary parasitism beneath the canopy. Mature shoots elongating from the parasitic region parasitize other hosts on the upper surfaces of their canopy. Although parasitism by dodder is stimulated by blue and far-red light, and inhibited by red light, the responses to light signals during the developmental stages are not comprehensively understood. Therefore, we compared the effects of different types of light on both circumnutation and parasitism by germinating seedlings and mature shoots of Cuscuta campestris. Seedlings established parasitism under blue and far-red light, but not under red light, as has been reported repeatedly. By contrast, mature shoots exhibited coiling around the host and haustoria formation even under a red light as well as under blue and far-red light. These findings indicate that C. campestris modified its response to red light during the transition from young seedlings to mature shoots, facilitating parasitism. Light quality did not affect the circumnutation of either seedlings or mature shoots, indicating that circumnutation and the coiling movement that leads to parasitism were regulated by different environmental signals.

Cuscuta australis (dodder) parasite eavesdrops on the host plants' FT signals to flower.

Many plants use environmental cues, including seasonal changes of day length (photoperiod), to control their flowering time. Under inductive conditions, FLOWERING LOCUS T (FT) protein is synthesized in leaves, and FT protein is a mobile signal, which is able to travel to the shoot apex to induce flowering. Dodders (Cuscuta, Convolvulaceae) are root- and leafless plants that parasitize a large number of autotrophic plant species with varying flowering time. Remarkably, some dodder species, e.g., Cuscuta australis, are able to synchronize their flowering with the flowering of their hosts. Detailed sequence inspection and expression analysis indicated that the FT gene in dodder C. australis very likely does not function in activating flowering. Using soybean host plants cultivated under inductive and noninductive photoperiod conditions and soybean and tobacco host plants, in which FT was overexpressed and knocked out, respectively, we show that FT-induced flowering of the host is likely required for both host and parasite flowering. Biochemical analysis revealed that host-synthesized FT signals are able to move into dodder stems, where they physically interact with a dodder FD transcription factor to activate dodder flowering. This study demonstrates that FTs can function as an important interplant flowering signal in host-dodder interactions. The unique means of flowering regulation of dodder illustrates how regressive evolution, commonly found in parasites, may facilitate the physiological synchronization of parasite and host, here allowing the C. australis parasite to time reproduction exactly with that of their hosts, likely optimizing parasite fitness.

Parasite dodder enables transfer of bidirectional systemic nitrogen signals between host plants.

Dodder (Cuscuta spp., Convolvulaceae) is a genus of parasitic plants with worldwide distribution. Dodders are able to simultaneously parasitize two or more adjacent hosts, forming dodder-connected plant clusters. Nitrogen (N) deficiency is a common challenge to plants. To date, it has been unclear whether dodder transfers N-systemic signals between hosts grown in N-heterogeneous soil. Transcriptome and methylome analyses were carried out to investigate whether dodder (Cuscuta campestris) transfers N-systemic signals between N-replete and N-depleted cucumber (Cucumis sativus) hosts, and it was found that N-systemic signals from the N-deficient cucumber plants were rapidly translocated through C. campestris to the N-replete cucumber plants. Unexpectedly, certain systemic signals were also transferred from the N-replete to N-depleted cucumber hosts. We demonstrate that these systemic signals are able to regulate large transcriptome and DNA methylome changes in the recipient hosts. Importantly, N stress also induced many long-distance mobile mRNA transfers between C. campestris and hosts, and the bilateral N-systemic signaling between N-replete and N-depleted hosts had a strong impact on the inter-plant mobile mRNAs. Our 15N labeling experiment indicated that under N-heterogeneous conditions, N-systemic signals from the N-deficient cucumber hosts did not obviously change the N-uptake activity of the N-replete cucumber hosts; however, in plant clusters comprising C. campestris-connected cucumber and soybean (Glycine max) plants, if the soybean plants were N-starved, the cucumber plants exhibited increased N-uptake activity. This study reveals that C. campestris facilitates plant-plant communications under N-stress conditions by enabling extensive bilateral N-systemic signaling between different hosts.

Physiological and ecological warnings that dodders pose an exigent threat to farmlands in Eastern Africa.

Invasive holoparasitic plants of the genus Cuscuta (dodder) threaten African ecosystems due to their rapid spread and attack on various host plant species. Most Cuscuta species cannot photosynthesize and hence rely on host plants for nourishment. After attachment through a peg-like organ called a haustorium, the parasites deprive hosts of water and nutrients, which negatively affects host growth and development. Despite their rapid spread in Africa, dodders have attracted limited research attention, although data on their taxonomy, host range, and epidemiology are critical for their management. Here, we combine taxonomy and phylogenetics to reveal the presence of field dodder (Cuscuta campestris) and C. kilimanjari (both either naturalized or endemic to East Africa), in addition to the introduction of the giant dodder (C. reflexa), a south Asian species, in continental Africa. These parasites have a wide host range, parasitizing species across 13 angiosperm orders. We evaluated the possibility of C. reflexa to expand this host range to tea (Camelia sinensis), coffee (Coffea arabica), and mango (Mangifera indica), crops of economic importance to Africa, for which haustorial formation and vascular-bundle connections in all three crops revealed successful parasitism. However, only mango mounted a successful postattachment resistance response. Furthermore, species distribution models predicted high habitat suitability for Cuscuta spp. across major tea- and coffee-growing regions of Eastern Africa, suggesting an imminent risk to these crops. Our findings provide relevant insights into a poorly understood threat to biodiversity and economic wellbeing in Eastern Africa, and provide critical information to guide development of management strategies to avert Cuscuta spp. spread.

Host-produced ethylene is required for marked cell expansion and endoreduplication in dodder search hyphae.

The genus Cuscuta comprises stem holoparasitic plant species with wide geographic distribution. Cuscuta spp. obtain water, nutrients, proteins, and mRNA from their host plants via a parasitic organ called the haustorium. As the haustorium penetrates into the host tissue, search hyphae elongate within the host tissue and finally connect with the host's vascular system. Invasion by Cuscuta spp. evokes various reactions within the host plant's tissues. Here, we show that, when Arabidopsis (Arabidopsis thaliana) is invaded by Cuscuta campestris, ethylene biosynthesis by the host plant promotes elongation of the parasite's search hyphae. The expression of genes encoding 1-aminocylclopropane-1-carboxylic acid (ACC) synthases, ACC SYNTHASE2 (AtACS2) and ACC SYNTHASE6 (AtACS6), was activated in the stem of Arabidopsis plants upon invasion by C. campestris. When the ethylene-deficient Arabidopsis acs octuple mutant was invaded by C. campestris, cell elongation and endoreduplication of the search hyphae were significantly reduced, and the inhibition of search hyphae growth was complemented by exogenous application of ACC. In contrast, in the C. campestris-infected Arabidopsis ethylene-insensitive mutant etr1-3, no growth inhibition of search hyphae was observed, indicating that ETHYLENE RESPONSE1-mediated ethylene signaling in the host plant is not essential for parasitism by C. campestris. Overall, our results suggest that C. campestris recognizes host-produced ethylene as a stimulatory signal for successful invasion.

A plant parasite uses light cues to detect differences in host-plant proximity and architecture.

Sunlight filtered by green plant tissue becomes diminished in its ratio of red to far-red wavelengths (R:FR). Some parasitic plants exploit this change by growing towards regions of low R:FR to locate host plants. In principle, variation in R:FR can also convey ecologically relevant information about host proximity or architecture. Here, we demonstrate that the parasitic vine Cuscuta epilinum Weihe (Convolvulaceae) can distinguish fine-scale differences in R:FR associated with differences in the proximity and shape of potential host plants. We conducted dual-choice experiments by placing parasite seedlings between targets, including low R:FR fields manipulated via LED lighting and pairs of model plants exhibiting realistic R and FR reflectance but differing in proximity or shape. Seedlings consistently distinguished between low-R:FR fields of differing intensity. Furthermore, they exhibited preferences for nearer plant models versus identical models placed 4 cm further away and between same-sized models exhibiting shape differences. Our results indicate that parasites can discriminate minute differences in R:FR signatures corresponding to host factors (proximity and shape) that impact seedling survival. This keen sensory ability underpins the parasite's sophisticated foraging behaviour and highlights the broader importance of light cues in plant ecology.

Responses of Rhizospheric Microbial Communities of Native and Alien Plant Species to Cuscuta Parasitism.

Parasitic plants have major impacts on host fitness. In the case of species of the holoparasitic Cuscuta genus, these impacts were shown to be particularly strong in some invasive alien plants, which has raised interest in the underlying mechanism. We hypothesized that Cuscuta parasitization may exert strong influence in shaping the diversity patterns in the host rhizosphere microbiome and that this may vary between native (coevolved) and alien (non-coevolved) plants. Here, we report on a field study exploring the effect of parasitization by Cuscuta australis on the rhizosphere microbiota (16S and ITS rDNA) of four plant species sharing and three plant species not sharing the parasite's native range. Despite a predominant role of the host species in shaping the rhizosphere microbiota, the role of host origin and of parasitization still appeared important in structuring microbial communities and their associated functions. Bacterial communities were more strongly influenced than fungi by the native range of the host plant, while fungi were slightly more affected than bacteria by parasitization. About 7% of bacterial phylotypes and 11% of fungal phylotypes were sensitive to Cuscuta parasitization. Parasitization also reduced the abundance of arbuscular mycorrhizal fungi by ca. 18% and of several genes related to plant growth promoting functions (e.g., nitrogen metabolism and quorum sensing). Both fungi and bacteria differentially responded to host parasitization depending on host origin, and the extent of these shifts suggests that they may have more dramatic consequences for alien than for native plants.

Stem parasitic plant Cuscuta australis (dodder) transfers herbivory-induced signals among plants.

Cuscuta spp. (i.e., dodders) are stem parasites that naturally graft to their host plants to extract water and nutrients; multiple adjacent hosts are often parasitized by one or more Cuscuta plants simultaneously, forming connected plant clusters. Metabolites, proteins, and mRNAs are known to be transferred from hosts to Cuscuta, and Cuscuta bridges even facilitate host-to-host virus movement. Whether Cuscuta bridges transmit ecologically meaningful signals remains unknown. Here we show that, when host plants are connected by Cuscuta bridges, systemic herbivory signals are transmitted from attacked plants to unattacked plants, as revealed by the large transcriptomic changes in the attacked local leaves, undamaged systemic leaves of the attacked plants, and leaves of unattacked but connected hosts. The interplant signaling is largely dependent on the jasmonic acid pathway of the damaged local plants, and can be found among conspecific or heterospecific hosts of different families. Importantly, herbivore attack of one host plant elevates defensive metabolites in the other systemic Cuscuta bridge-connected hosts, resulting in enhanced resistance against insects even in several consecutively Cuscuta-connected host plants over long distances (> 100 cm). By facilitating plant-to-plant signaling, Cuscuta provides an information-based means of countering the resource-based fitness costs to their hosts.

The host jasmonic acid pathway regulates the transcriptomic changes of dodder and host plant under the scenario of caterpillar feeding on dodder.

BACKGROUND: Dodder (Cuscuta spp., Convolvulaceae) species are obligate leaf- and rootless parasites that totally depend on hosts to survive. Dodders naturally graft themselves to host stems to form vascular fusion, from which they obtain nutrients and water. In addition, dodders and their hosts also exchange various other molecules, including proteins, mRNAs, and small RNAs. It is very likely that vascular fusion also allows inter-plant translocation of systemic signals between dodders and host plants and these systemic signals may have profound impacts on the physiology of dodder and host plants. Herbivory is a common biotic stress for plants. When a dodder parasite is attacked by lepidopteran insects, how dodder responds to caterpillar feeding and whether there are inter-plant communications between the host plants and the parasites is still poorly understood. RESULTS: Here, wild-type (WT) tobacco and a tobacco line in which jasmonic acid (JA) biosynthesis was silenced (AOC-RNAi) were used as the hosts, and the responses of dodders and their host plants to herbivory by Spodoptera litura caterpillars on the dodders were investigated. It was found that after caterpillar attack, dodders grown on AOC-RNAi tobacco showed much a smaller number of differentially expressed genes, although the genotypes of the tobacco plants did not have an effect on the simulated S. litura feeding-induced JA accumulation in dodders. We further show that S. litura herbivory on dodder also led to large changes in transcriptome and defensive metabolites in the host tobacco, leading to enhanced resistance to S. litura, and the JA pathway of tobacco host is critical for these systemic responses. CONCLUSIONS: Our findings indicate that during caterpillar attack on dodder, the JA pathway of host plant is required for the proper transcriptomic responses of both dodder and host plants. This study highlights the importance of the host JA pathway in regulating the inter-plant systemic signaling between dodder and hosts.

Cuscuta Species Identification Based on the Morphology of Reproductive Organs and Complete Chloroplast Genome Sequences.

The genus Cuscuta (Convolvulaceae) comprises well-known parasitic plants. Cuscuta species are scientifically valuable, as their life style causes extensive crop damage. Furthermore, dried seeds of C. chinensis are used as a Korean traditional herbal medicine. Despite the importance of Cuscuta species, it is difficult to distinguish these plants by the naked eye. Moreover, plastid sequence information available for Cuscuta species is limited. In this study, we distinguished between C. chinensis and C. japonica using morphological characterisation of reproductive organs and molecular characterisation of chloroplast genomes. The differences in morphological characteristics of reproductive organs such as style, stigma, infrastaminal scale, seed shape and testa ornamentation were useful for distinguishing between C. japonica and C. chinensis. Analysis of chloroplast genomes revealed drastic differences in chloroplast genome length and gene order between the two species. Although both species showed numerous gene losses and genomic rearrangements, chloroplast genomes showed highly similar structure within subgenera. Phylogenetic analysis of Cuscuta chloroplast genomes revealed paraphyletic groups within subgenera Monogynella and Grammica, which is consistent with the APG IV system of classification. Our results provide useful information for the taxonomic, phylogenetic and evolutionary analysis of Cuscuta and accurate identification of herbal medicine.

Identification of tomato introgression lines with enhanced susceptibility or resistance to infection by parasitic giant dodder (Cuscuta reflexa).

The parasitic flowering plant genus Cuscuta (dodder) is a parasitic weed that infects many important crops. Once it winds around the shoots of potential host plants and initiates the development of penetration organs, called haustoria, only a few plant species have been shown to deploy effective defense mechanisms to ward off Cuscuta parasitization. However, a notable exception is Solanum lycopersicum (tomato), which exhibits a local hypersensitive reaction when attacked by giant dodder (Cuscuta reflexa). Interestingly, the closely related wild desert tomato, Solanum pennellii, is unable to stop the penetration of its tissue by the C. reflexa haustoria. In this study, we observed that grafting a S. pennellii scion onto the rootstock of the resistant S. lycopersicum did not change the susceptibility phenotype of S. pennellii. This suggests that hormones, or other mobile substances, produced by S. lycopersicum do not induce a defense reaction in the susceptible tissue. Screening of a population of introgression lines harboring chromosome fragments from S. pennellii in the genome of the recurrent parent S. lycopersicum, revealed that most lines exhibit the same defense reaction as shown by the S. lycopersicum parental line. However, several lines showed different responses and exhibited either susceptibility, or cell death that extended considerably beyond the infection site. These lines will be valuable for the future identification of key loci involved in the perception of, and resistance to, C. reflexa and for developing strategies to enhance resistance to infection in crop species.

Glucosinolates from Host Plants Influence Growth of the Parasitic Plant Cuscuta gronovii and Its Susceptibility to Aphid Feeding.

Parasitic plants acquire diverse secondary metabolites from their hosts, including defense compounds that target insect herbivores. However, the ecological implications of this phenomenon, including the potential enhancement of parasite defenses, remain largely unexplored. We studied the translocation of glucosinolates from the brassicaceous host plant Arabidopsis (Arabidopsis thaliana) into parasitic dodder vines (Convolvulaceae; Cuscuta gronovii) and its effects on the parasite itself and on dodder-aphid interactions. Aliphatic and indole glucosinolates reached concentrations in parasite tissues higher than those observed in corresponding host tissues. Dodder growth was enhanced on cyp79B2 cyp79B3 hosts (without indole glucosinolates) but inhibited on atr1D hosts (with elevated indole glucosinolates) relative to wild-type hosts, which responded to parasitism with localized elevation of indole and aliphatic glucosinolates. These findings implicate indole glucosinolates in defense against parasitic plants. Rates of settling and survival on dodder vines by pea aphids (Acyrthosiphon pisum) were reduced significantly when dodder parasitized glucosinolate-producing hosts (wild type and atr1D) compared with glucosinolate-free hosts (cyp79B2 cyp79B3 myb28 myb29). However, settling and survival of green peach aphids (Myzus persicae) were not affected. M. persicae population growth was actually reduced on dodder parasitizing glucosinolate-free hosts compared with wild-type or atr1D hosts, even though stems of the former contain less glucosinolates and more amino acids. Strikingly, this effect was reversed when the aphids fed directly upon Arabidopsis, which indicates an interactive effect of parasite and host genotype on M. persicae that stems from host effects on dodder. Thus, our findings indicate that glucosinolates may have both direct and indirect effects on dodder-feeding herbivores.

RNA mobility in parasitic plant - host interactions.

The parasitic plant Cuscuta exchanges mRNAs with its hosts. Systemic mobility of mRNAs within plants is well documented, and has gained increasing attention as studies using grafted plant systems have revealed new aspects of mobile mRNA regulation and function. But parasitic plants take this phenomenon to a new level by forming seamless connections to a wide range of host species, and raising questions about how mRNAs might function after transfer to a different species. Cuscuta and other parasitic plant species also take siRNAs from their hosts, indicating that multiple types of RNA are capable of trans-specific movement. Parasitic plants are intriguing systems for studying RNA mobility, in part because such exchange opens new possibilities for control of parasitic weeds, but also because they provide a fresh perspective into understanding roles of RNAs in inter-organismal communication.

Gypsy moth herbivory induced volatiles and reduced parasite attachment to cranberry hosts.

Interactions between species can have cascading effects that shape subsequent interactions. For example, herbivory can induce plant defenses that affect subsequent interactions with herbivores, pathogens, mycorrhizae, and pollinators. Parasitic plants are present in most ecosystems, and play important roles in structuring communities. However, the effects of host herbivory on parasitic plants, and the potential mechanisms underlying such effects, are not well known. We conducted a greenhouse study to ask whether gypsy moth (Lymantria dispar) damage, host cultivar, and their interaction affected preference of the stem parasite dodder (Cuscuta spp.) on cranberry hosts (Vaccinium macrocarpum). We then assessed the mechanisms that could underlie such effects by measuring induced changes in phytohormones and secondary compounds. We found that damage by gypsy moths delayed dodder attachment by approximately 0.3 days when dodder stems were added 2 days after damage, and reduced attachment by more than 50% when dodder stems were added 1 week after host plant damage. Gypsy moth damage significantly increased jasmonic acid (JA) levels, total volatile emissions, and the flavonol, quercetin aglycone, suggesting possible mechanisms underlying variation in dodder ability to locate or attach to hosts. Dodder preference also differed between cranberry cultivars, with the highest attachment on the cultivar that had significantly lower levels of total volatile emissions and total phenolic acids, suggesting that volatile composition and phenolics may mediate dodder preference. Our results indicate that herbivory can reduce subsequent attachment by a highly damaging parasitic plant, demonstrating the potential importance of early damage for shaping subsequent species interactions.

Waterfowl endozoochory: An overlooked long-distance dispersal mode for Cuscuta (dodder).

PREMISE OF THE STUDY: Dispersal of parasitic Cuscuta species (dodders) worldwide has been assumed to be largely anthropomorphic because their seeds do not match any previously known dispersal syndrome and no natural dispersal vectors have been reliably documented. However, the genus has a subcosmopolitan distribution and recent phylogeographic results have indicated that at least18 historical cases of long-distance dispersal (LDD) have occurred during its evolution. The objective of this study is to report the first LDD biological vector for Cuscuta seeds. METHODS: Twelve northern pintails (Anas acuta) were collected from Suisun Marsh, California and the contents of their lowest part of the large intestine (rectum) were extracted and analyzed. Seed identification was done both morphologically and using a molecular approach. Extracted seeds were tested for germination and compared to seeds not subjected to gut passage to determine the extent of structural changes caused to the seed coat by passing through the digestive tract. KEY RESULTS: Four hundred and twenty dodder seeds were found in the rectum of four northern pintails. From these, 411 seeds were identified as Cuscuta campestris and nine as most likely C. pacifica. The germination rate of C. campestris seeds after gut passage was 55%. Structural changes caused by the gut passage in both species were similar to those caused by an acid scarification. CONCLUSIONS: Endozoochory by waterbirds may explain the historical LDD cases in the evolution of Cuscuta. This also suggests that current border quarantine measures may be insufficient to stopping spreading of dodder pests along migratory flyways.

Cranberry Resistance to Dodder Parasitism: Induced Chemical Defenses and Behavior of a Parasitic Plant.

Parasitic plants are common in many ecosystems, where they can structure community interactions and cause major economic damage. For example, parasitic dodder (Cuscuta spp.) can cause up to 80-100 % yield loss in heavily infested cranberry (Vaccinium macrocarpon) patches. Despite their ecological and economic importance, remarkably little is known about how parasitic plants affect, or are affected by, host chemistry. To examine chemically-mediated interactions between dodder and its cranberry host, we conducted a greenhouse experiment asking whether: (1) dodder performance varies with cranberry cultivar; (2) cultivars differ in levels of phytohormones, volatiles, or phenolics, and whether such variation correlates with dodder parasitism; (3) dodder parasitism induced changes in phytohormones, volatiles, or phenolics, and whether the level of inducible response varied among cultivars. We used five cranberry cultivars to assess host attractiveness to dodder and dodder performance. Dodder performance did not differ across cultivars, but there were marginally significant differences in host attractiveness to dodder, with fewer dodder attaching to Early Black than to any other cultivar. Dodder parasitism induced higher levels of salicylic acid (SA) across cultivars. Cultivars differed in overall levels of flavonols and volatile profiles, but not phenolic acids or proanthocyanidins, and dodder attachment induced changes in several flavonols and volatiles. While cultivars differed slightly in resistance to dodder attachment, we did not find evidence of chemical defenses that mediate these interactions. However, induction of several defenses indicates that parasitism alters traits that could influence subsequent interactions with other species, thus shaping community dynamics.