Parasitized Plants Research Articles

Parasitism by Cuscuta gronovii mediated soil legacy effects and the competitive ability of invasive and native plant species by changing soil abiotic and biotic properties

Parasitic plants can mediate soil conditioning by invasive and native host plant species, but how this may affect the competitive ability of these plants when they later grow in the conditioned soil has never been tested. This study tested whether soil conditioned by three invasive and three native plant species, either parasitized by a holoparasitic plant Cuscuta gronovii or non-parasitized, would differentially affect the competitive ability of those species. In the first phase, field soil was conditioned using individuals of the six host plant species, either parasitized or non-parasitized. The second phase tested the competitive ability of individuals of those invasive and native plants by growing them alone or in competition with Trifolium repens in either live or sterilized conditioned soil. In the soil conditioning phase, parasitism significantly increased soil NH4+-N concentration by 17 %, decreased soil organic carbon by 18 %, and marginally decreased microbial biomass carbon concentration by 21 %. In the soil feedback phase, native plant species generally had higher competitive ability in soil that was conditioned by parasitized plants than in soil that was conditioned by non-parasitized plants. In contrast, soil conditioned by parasitized plants had only a marginal effect on the competitve ability of invasive plants, compared to growth in soil conditioned by non-parasitized plants. Native plants had greater competitive ability in soil with lower soil organic carbon, while invasive plants had greater competitive ability in soil with higher microbial biomass carbon and lower NH4+-N. These findings demonstrate that parasitism by C. gronovii mediated different soil legacy effects of invasive and native plant species through changes in soil organic carbon, soil NH4+-N, and microbial biomass carbon levels. Broadly, these results suggest that parasitic plants may limit invasions by alien plant species and promote the co-existence of the invaders with native plant species through soil-mediated legacy effects.

A neotropical mistletoe influences herbivory of its host plant by driving changes in the associated insect community.

Parasitic plants are important sources of stress and can strongly impact their host plants through direct and indirect associations with other herbivores and their associated organisms. In the tropics, mistletoes are frequent parasitic plants, influencing different trophic levels involved with the host plant. Here, we investigated the direct and indirect influences of multiple partners involved in interactions between the mistletoe Psittachantus robustus and its host tree, Vochysia thyrsoidea. More specifically, we assessed if the presence of the mistletoe modified herbivory levels of its host by altering the diversity of associated insects. We found that insect feeding guild modulated mistletoe influence on insect community, and there were fewer species and individuals of leaf-chewing insects in parasitized than non-parasitized trees. Despite this decrease in leaf-chewing insects, there were increased levels of herbivory in parasitized plants. Mistletoes' presence did not influence the hemipteran sap-sucking insects, but this herbivore guild directly responded to the abundance of their associated ants. Overall, our study found empirical support for the crucial role of mistletoes on their host-associated organisms, ultimately shaping the herbivory levels of their tree hosts. By exposing the distinct effects of the different partners involved, our results shed light on the intricated interactions mediated by parasitic plants, opening the path for new investigations.

The mistletoe Struthanthus flexicaulis reduces dominance and increases diversity of plants in campo rupestre

The interaction between hemiparasites and their host plants is an important structuring mechanism for plant communities. The mistletoe Struthanthus flexicaulis (Loranthaceae) is widely distributed in the campo rupestre ecosystem and likely has an important role in structuring the communities of which its hosts are part. The main goals of this study were to investigate the effects of parasitism by S. flexicaulis on host plants in a degraded area of campo rupestre and to determine how parasitism affects characteristics of the structure of this plant community over time. We found that parasitized plants had smaller crowns and branch growth, and suffered higher mortality compared to non-parasitized plants. Parasitism by S. flexicaulis decreased dominance and increased the diversity and evenness of plants in the community over time. Parasitism leads to competition with the host for water and nutrients, which may decrease the performance of the host and, consequently, leading to host death. The high mortality of the most abundant plant species led to a restructured woody plant community. These results reinforce the importance of parasitic plants that frequently play a key role in maintaining species diversity in plant communities.

Expansion of a holoparasitic plant, Orobanche lutea (Orobanchaceae), in post-industrial areas - a possible Zn effect

Industrial waste sites, although extremely difficult to revegetate, may be suitable for rare plants such as Orobanche lutea that are condemned to extinction due to their low ability to compete in their natural habitats. The presence of potentially toxic metals seems to facilitate the expansion of O. lutea (parasitizing Medicago falcata) and was found in hundreds of exemplars per m2 in south Poland and potentially could spread to other localities, causing yield loss in agricultural plants. The main aim of this research was to characterize the interaction between the host, the parasitic plant and symbiotic microbes under different metal concentration in the substratum. The parasite was more common on more polluted soil and when the parasite was connected to the host, potentially toxic metals (Zn, Cd and Pb) were shared by both plants; thus, the content and concentration of these potentially toxic metals in the host were lower than those in plants without parasites. While the performance index (PIABS) of photosynthesis was lower in parasitized plants on control soil, on metal-rich industrial waste soil, PIABS was higher in the parasitized plants than in cases where M. falcata grew alone. This result suggests a role of this parasite in toxicity attenuation, although the biomass of parasitized plants and those growing on polluted sites was lower than that in control sites. In the described case, mycorrhizal colonization and arbuscular richness in M. falcata were even more highly developed on polluted sites than in control ones. The data presented support the hypothesis that the expansion of O. lutea is most likely supported by the increased concentrations of Zn and Cd in areas connected with industrial waste. Although, on industrial wastes the host yield was decreased in the parasite presence, its photosynthetic capacity was even increased.

Fluorescence Imaging in the Red and Far-Red Region during Growth of Sunflower Plantlets. Diagnosis of the Early Infection by the Parasite Orobanche cumana.

Broomrape, caused by the root holoparasite Orobanche cumana, is the main biotic constraint to sunflower oil production worldwide. By the time broomrape emerges, most of the metabolic imbalance has been produced by O. cumana to sunflower plants. UV-induced multicolor fluorescence imaging (MCFI) provides information on the fluorescence emitted by chlorophyll (Chl) a of plants in the spectral bands with peaks near 680 nm (red, F680) and 740 nm (far-red, F740). In this work MCFI was extensively applied to sunflowers, either healthy or parasitized plants, for the first time. The distribution of red and far-red fluorescence was analyzed in healthy sunflower grown in pots under greenhouse conditions. Fluorescence patterns were analyzed across the leaf surface and throughout the plant by comparing the first four leaf pairs (LPs) between the second and fifth week of growth. Similar fluorescence patterns, with a delay of 3 or 4 days between them, were obtained for LPs of healthy sunflower, showing that red and far-red fluorescence varied with the developmental stage of the leaf. The use of F680 and F740 as indicators of sunflower infection by O. cumana during underground development stages of the parasite was also evaluated under similar experimental conditions. Early increases in F680 and F740 as well as decreases in F680/F740 were detected upon infection by O. cumana. Significant differences between inoculated and control plants depended on the LP that was considered at any time. Measurements of Chl contents and final total Chl content supported the results of MCFI, but they were less sensitive in differentiating healthy from inoculated plants. Sunflower infection was confirmed by the presence of broomrape nodules in the roots at the end of the experiment. The potential of MCFI in the red and far-red region for an early detection of O. cumana infection in sunflower was revealed. This technique might have a particular interest for early phenotyping in sunflower breeding programs. To our knowledge, this is the first work where the effect of a parasitic plant in its host is analyzed by means of fluorescence imaging in the red and far-red spectral regions.

Indirect positive effects of a parasitic plant on host pollination and seed dispersal

Parasitic plants often have a strong fitness‐impact on their plant hosts through increased host mortality and reduced or complete suppression of reproduction. Tristerix corymbosus (Loranthaceae) is a hemiparasitic mistletoe that infects a wide range of host species along its distribution range. Among such species, Rhaphithamnus spinosus (Verbenaceae) is a frequent host with a flowering and fruiting season partially synchronized with mistletoe reproductive phenology. As parasitized hosts have, in principle, a larger flower display and fruit crop size than non‐parasitized hosts, we examined whether host and parasite reproductive synchrony make infected hosts more attractive for pollinators and seed dispersers than uninfected hosts. Our results showed that pollinator visit rates did not differ between parasitized and non‐parasitized hosts. Conversely, seed rain was higher in parasitized than non‐parasitized individuals. The number of seeds fallen under non‐parasitized plants was spatially associated with crop size, while parasitized plants did not show such association. Finally, the number of seedlings of R. spinosus was significantly larger near parasitized than non‐parasitized hosts. Our results suggest that the presence of the mistletoe might be responsible of the higher reproductive success showed by the parasitized fraction of R. spinosus. This effect, however, seems to be related to seed dispersal processes rather than pollination effects.

Effect of Branched Broomrape (Orobanche ramosa) Infection on the Growth and Photosynthesis of Tomato

The influence of the holoparasite branched broomrape on the vegetative growth, leaf chlorophyll content, photosynthetic rate, and chlorophyll fluorescence of tomato was studied over two growing seasons on plants grown in a commercial greenhouse. The presence of the parasite strongly reduced the aerial biomass by acting as a competing sink for assimilate, but more importantly, by compromising the efficiency of carbon assimilation via a reduction in leaf chlorophyll content and photosynthetic rate. The chlorophyll fluorescence parameters F0, Fm, Fv, and Fv/Fm were all altered in parasitized plants, indicating that branched broomrape–infected plants are more susceptible to photoinhibition. The degree of damage to the host was not dependent on either the number or the biomass of parasitic plants per host plant. We suggest that the ability to maintain a high photosynthetic rate, leaf chlorophyll content, or both and the ability to minimize photoinhibition can be developed as indirect assays for improved tolerance to branched broomrape.

Parasitism by Cuscuta pentagona attenuates host plant defenses against insect herbivores.

Considerable research has examined plant responses to concurrent attack by herbivores and pathogens, but the effects of attack by parasitic plants, another important class of plant-feeding organisms, on plant defenses against other enemies has not been explored. We investigated how attack by the parasitic plant Cuscuta pentagona impacted tomato (Solanum lycopersicum) defenses against the chewing insect beet armyworm (Spodoptera exigua; BAW). In response to insect feeding, C. pentagona-infested (parasitized) tomato plants produced only one-third of the antiherbivore phytohormone jasmonic acid (JA) produced by unparasitized plants. Similarly, parasitized tomato, in contrast to unparasitized plants, failed to emit herbivore-induced volatiles after 3 d of BAW feeding. Although parasitism impaired antiherbivore defenses, BAW growth was slower on parasitized tomato leaves. Vines of C. pentagona did not translocate JA from BAW-infested plants: amounts of JA in parasite vines grown on caterpillar-fed and control plants were similar. Parasitized plants generally contained more salicylic acid (SA), which can inhibit JA in some systems. Parasitized mutant (NahG) tomato plants deficient in SA produced more JA in response to insect feeding than parasitized wild-type plants, further suggesting cross talk between the SA and JA defense signaling pathways. However, JA induction by BAW was still reduced in parasitized compared to unparasitized NahG, implying that other factors must be involved. We found that parasitized plants were capable of producing induced volatiles when experimentally treated with JA, indicating that resource depletion by the parasite does not fully explain the observed attenuation of volatile response to herbivore feeding. Collectively, these findings show that parasitic plants can have important consequences for host plant defense against herbivores.

Effects of Broomrape Parasitism on Sunflower Plants: Growth, Development, and Mineral Nutrition

ABSTRACT Sunflower broomrape (Orobanche cumana Wallr.) is a parasitic plant that infects sunflower (Helianthus annuus L.) plants. In this work, sunflower plants were grown under greenhouse conditions in pots with the substrate infested or non-infested with broomrape seeds. At different numbers of days after sowing, plant height, internode lengths, number of leaves, head diameter, mineral composition of leaves, and potassium (K) concentration in stem were measured. The negative effects of broomrape parasitism were assessed from 57 d after sowing, when broomrape started to emerge. Parasitized plants exhibited lower shoot dry weight, height, and head diameter than control plants. The reduction in internode lengths was associated with a decrease in the gradient of K concentration from basal to apical stem. The mineral composition of leaves was also affected in parasitized plants. The concentrations of calcium (Ca), magnesium (Mg), manganese (Mn), and zinc (Zn) in leaves of parasitized plants were lower than those of the control plants, while there were few differences for K, phosphorus (P), iron (Fe), and copper (Cu). The effects of parasitism are discussed in relation to their competition for resources and to perturbations of the host physiology such as hormonal and water balance.

HOST–PARASITE–HERBIVORE INTERACTIONS: IMPLICATIONS OF HOST CYANOGENESIS

To examine the mediation of host-predator interaction by a.parasite, we studied the three-level interactions among a host plant, a root hemiparasitic plant, and their common predator, a generalist snail herbivore. The host species, Trifolium repens, is able to synthesize cyanogenic glucosides that have a significant role in plant herbivore resistance. Some T. repens populations are polymorphic with respect to cyanogenesis. Our second aim was to examine whether the mediation of the host plant-herbivore interaction by the parasitic plant could affect the maintenance of the cyanogenic polymorphism. The parasitic plant (Rhinanthus serotinus) was equally harmful to cyanogenic and acyan- ogenic hosts and grew equally well on both host types. In a no-choice experiment, both cyanogenesis and root hemiparasitism of the host plant reduced the growth of the herbivore (Arianta arbustorum). The herbivores consumed less leaf area of the parasitized plants than of unparasitized plants, but only when the host plant was acyanogenic. In a multiple-choice experiment, the snails were similarly affected by cyanogenesis but not by parasitic infection of the host. Thus, there was a discrepancy between food choice and performance of the herbivore. Our results suggest that the overall effects of the parasitic plant on the host plant were ameliorated through the indirect effects of the parasitic infection on herbivore per- formance and food consumption. This indirect effect of the parasitic infection seemed to be more beneficial for the acyanogenic plants: if parasitized, the leaf area of acyanogenic plants consumed by the herbivore was 45% higher than that of cyanogenic plants, whereas in unparasitized plants the corresponding figure was 114%. Thus, parasitism may decrease the advantage cyanogenic plants gain through decreased herbivory. Further, in mainly cy- anogenic T. repens populations, cyanogenesis might be a more important feeding deterrent than root parasitism; whereas in mainly acyanogenic populations root parasitism might be relevant to herbivore-T. repens interactions. We are the first to document the effects of a plant parasite on the performance of both the host plant and a host-feeding herbivore. Our results highlight the need to look beyond the direct effect of parasites on their hosts..

New Hosts of the Parasitic Flowering Plant, Alectra vogelii, in Malawi.

Alectra vogelii Benth. (Family: Scrophulariaceae) is a vascular hemiparasite of various leguminous crops in Africa, including peanut (Arachis hypogaea), bambara groundnut (Vigna subterranea), cowpea (Vigna unguiculata), common bean (Phaseolus vulgaris), soybean (Glycine max), and mung bean (Vigna radiata) (1). It is a common parasite of peanut in Angola, Burkina Faso, Malawi, Mozambique, Nigeria, Swaziland, Zambia, and Zimbabwe (2). During April and May 2000, A. vogelii was observed parasitizing several wild Arachis species in a field at the Chitedze Agricultural Research Station near Lilongwe, Malawi. These species were part of a germ plasm enhancement program that included A. appressipila (ICRISAT Groundnut Accession number [ICG] 8127), A. batizocoi (ICG 8124), A. benensis (ICG 13215), A. cardenasii (ICG 13164 and 13166), A. correntina (ICG 8918), A. duranensis (ICG 13200), A. helodes (ICG 8955 and 14917), A. hoehnei (ICG 13228), A. magna (ICG 8960), A. pintoi (ICG 13222 and 14914), A. stenosperma (ICG 13172 and 13223), and A. valida (ICG 13230). In addition, A. vogelii was observed on four unidentified Arachis species (ICG 13231, 14875, 14888, and 14907). Parasitized plants were less vigorous and connections between A. vogelii and host plants could be observed by carefully removing the soil in the root zone. Mature A. vogelii plants were 0.3 to 0.5 m and had multiple stems branching at the base. Subsoil plant parts were a deep orange color. Flowers were prominent lemon yellow with horseshoe-shaped stigmata and leaves were light green. This is the first report of A. vogelii parasitizing wild Arachis species.

Influence of glyphosate on amino acid composition of Egyptian broomrape.

The parasitic plant broomrape is entirely dependent on its host for reduced carbon and nitrogen and is also susceptible to inhibition by glyphosate that is translocated to the parasite through a host. Studies were conducted to examine the effect of broomrape parasitism on amino acid concentrations of two hosts: common vetch that is tolerant of low levels of glyphosate and oilseed rape that has been genetically engineered for glyphosate resistance. The influence of glyphosate on the amino acid content of broomrape and the two hosts was also examined. Amino acid concentrations in leaves and roots of parasitized common vetch plants were generally similar to those of the corresponding tissues of nonparasitized plants. Amino acid concentrations in broomrape were lower than those of the parasitized common vetch root. For common vetch, glyphosate applied at rates that selectively inhibited broomrape growth did not alter individual amino acid concentrations in the leaves, but generally increased amino acid levels at 0.18 kg ha-1. Glyphosate application also increased the amino acid concentrations, with the exception of arginine, of broomrape growing on common vetch and did not generally influence concentrations in leaves or roots of common vetch. In oilseed rape, parasitization by broomrape generally led to higher amino acid concentrations in leaves but lower concentrations in roots of parasitized plants. Broomrape had higher amino acid concentrations than roots of the parasitized oilseed rape. Glyphosate applied at 0.25 and 0.5 kg ha-1 generally increased the amino acid concentrations in oilseed rape leaves, but the 0.75 kg ha-1 application caused the amino acid concentrations to decrease compared to those of untreated plants. In oilseed rape root the general trend was an increase in the concentration of amino acids at the two highest rates of glyphosate. Individual amino acid concentrations in broomrape attachments growing on oilseed rape were generally increased following glyphosate application of 0.25 kg ha-1. These results indicate that low rates of glyphosate alter amino acid profiles in both host and broomrape and raise questions about the regulation of amino acid metabolism in the parasite.

Influence of Parasitism by Pilostyles ingae (Rafflesiaceae) on its Host Plant, Mimosa naguirei (Leguminosae)

Mimosa naguirei (Leguminosae) is parasitized by Pilostyles ingae (Rafflesiaceae) in the Serra do Cipó, in southeastern Brazil. The study examined the influence of this parasite on various parameters of M. naguirei in an attempt to establish general patterns for future research. It was found that the percentage of parasitized plants varied along an altitudinal gradient of 500 m. The parasitic plant influenced the architecture of the host plant. The number of branches on parasitized plants was significantly greater than the number of branches on non-parasitized plants. Branches of parasitized plants were significantly shorter than branches on non-parasitized plants. The density of P. ingae flowers decreased from the stem base to apex. The number of fruits produced by parasitized plants was not greater than the number of fruits produced by non-parasitized plants, although parasitized plants produced smaller fruits and lighter seeds. Seed germination did not differ significantly between parasitized and healthy plants.