Invasive Weed Ageratina Adenophora Research Articles

Toxicological assessment of invasive Ageratina adenophora on germination and growth efficiency of native tree and crop species of Kumaun Himalaya.

The present study was designed to assess the allelopathic potential of invasive weed Ageratina adenophora leaf extracts on seed germination and seedling development efficiency of native tree [viz. Quercus leucotrichophora A. Camus (Oak) and Pinus roxburghii Sarg. (Pine)] and crop [(Triticum aestivum L. (Wheat) and Lens culinaris Medik. (Lentil)] species of Kumaun Himalaya. Pot experiments were conducted in the glasshouse of the Botany Department, D.S.B. Campus, Kumaun University Nainital, following a Completely Randomized Block Design (CRBD) with three treatments (C1-25%, C2-50%, and C3-100% of aqueous leaf extract) and one control, each with five replicates. The experiment lasted one year for tree species and continued until the seed maturation phase for crop species. Parameters such as seed germination proportion, root and shoot measurements, biomass, and crop productivity traits were recorded accordingly. Our bioassay results indicated that the inhibitory effect of leaf extracts on the measured traits of the selected native species was proportional to the applied extract concentrations of A. adenophora. Overall, lentil among crops and oak among tree species exhibited more inhibition compared to wheat and pine, respectively. At the highest concentration, reductions of 44%, 34%, 36%, and 24% in biomass production capacity were recorded for wheat, lentil, pine, and oak, respectively, while wheat and lentil productivity decreased by up to 33% and 45%, respectively. These results suggest that water-soluble allelochemicals produced by A. adenophora may impede the establishment of selected crop and tree species in agroecosystems and forest ecosystems invaded by this weed species. However, further studies on the characterization of phytochemicals and their specific role in seed germination and growth are warranted. Furthermore, the allelopathic potential of A. adenophora can be explored for the preparation of biopesticides and nature-friendly option to improve soil health, crop productivity, and reduce environmental pollution and management of this invasive weed.

Screening plant growth-promoting bacteria from the rhizosphere of invasive weed Ageratina adenophora for crop growth.

Plant-growth promoting rhizobacteria (PGPR) play a vital role in soil fertility and crop production. The rhizosphere of many crop plants has been well documented by screening PGPR for their plant-growth promoting (PGP) mechanisms. However, the rhizosphere of grass species that may act as potential habitats for novel PGPR remains relatively unexplored. Ageratina adenophora is a noxious weed that has invaded more than 40 tropical and subtropical countries in Asia, Oceania, Africa, and Europe. Its presence has led to changes in plant species composition, reducing their biodiversity and destroying ecosystem function. In this study, we screened 1,200 bacterial strains isolated from the rhizosphere soil of A. adenophora in three floristic regions in Yunnan Province, China. Samples were screened for their in vitro ability for N-fixation, production of the plant growth regulator indole-3-acetic acid (IAA), and the synthesis of 1-amino-cyclopropane-1-carboxylate (ACC) deaminase, which controls the levels of ethylene in developing plant roots. We found that 144 strains showed at least one of these PGP attributes. 16S rRNA gene sequencing showed that most (62.5%) of the samples were bacteria closely related to members of the genera Pseudomonas (27 strains), Providencia (20 strains), Chryseobacterium (14 strains), Ensifer (12 strains), Enterobacter (nine strains), and Hafnia (eight strains). Their abundance and biodiversity in the soil of individual floristic regions correlate positively with the invasion history of A. adenophora. From these PGP bacterial strains, KM_A34 (Pantoea agglomerans), KM_C04 (Enterobacter asburiae), and KM_A57 (Pseudomonas putida), which had the greatest in vitro ability of N-fixation, and IAA and ACC deaminase production, respectively, were selected. The strains were evaluated for their effect on the seed germination and growth of soybean, faba bean, pea, wheat, and Chinese cabbage other than A. adenophora. Chamber experiments showed these strains significantly (P < 0.05) increased (14.2-43.4% over the controls) germination rates of the soybean, faba bean, pea, and/or Chinese cabbage seeds. They also reduced relative seed germination times (20.8-48.8% over the controls) of soy bean, faba bean and/or wheat seeds. Greenhouse pot experiments showed that they significantly (P < 0.05) promoted the aboveground and belowground height of plant foliage (12.1-23.1% and 11.5-31.4% over the controls, respectively) and/or the dry weights (16.1-33.5% and 10.6-23.4% over the controls, respectively) of the soy bean, faba bean, pea, wheat and/or Chinese cabbage. These data indicate that the rhizosphere microbiota of A. adenophora contain a PGPR pool that may be used as bioinoculants to improve the growth and productivity of these crops.

Two Novel Species of Mesophoma gen. nov. from China.

During an investigation of the fungal pathogens associated with the invasive weed Ageratina adenophora from China, some interesting isolates were obtained from healthy leaf, leaf spot, and roots of this weed. Among them, a novel genus Mesophoma, containing two novel species M. speciosa and M. ageratinae, was found. Phylogenetic analysis of the combined, the internal transcribed spacer (ITS), large nuclear subunit ribosomal DNA (LSU), the RNA polymerase II second largest subunit (rpb2), and the partial β-tubulin (tub2) sequences, showed that M. speciosa and M. ageratinae formed a distinct clade far from all genera previously described in the family Didymellaceae. Combined distinctive morphological characters, including smaller and aseptate conidia when comparing with nearby genera Stagonosporopsis, Boeremia, and Heterphoma, allowed us to describe them as novel species belonging to a novel genus Mesophoma. The full descriptions, illustrations, and a phylogenetic tree showing the position of both M. speciosa and M. ageratinae are provided in this paper. Moreover, the potential for two strains belonging to these two species to be developed into a biocontrol for the spread of the invasive weed Ag. adenophora is also discussed.

Effect of arbuscular mycorrhizal fungi on the responses of Ageratina adenophora to Aphis gossypii herbivory.

The invasive weed Ageratina adenophora can form a positive symbiotic relationship with native arbuscular mycorrhizal fungi (AMF) to promote its invasion ability. However, the function of AMF during the feeding of Aphis gossypii in A. adenophora was poorly understand. This study aimed to investigate the effects of two dominant AMF (Claroideoglomus etunicatum and Septoglomus constrictum) on A. adenophora in response to the feeding of the generalist herbivore A. gossypii. The results showed that A. gossypii infestation could significantly reduce the biomass, nutrient and proline contents of A. adenophora, and increase the antioxidant enzyme activities, defense hormone and secondary metabolite contents of the weed. Compared with the A. gossypii infested A. adenophora, inoculation C. etunicatum and S. constrictum could significantly promote the growth ability and enhanced the resistance of A. adenophora to A. gossypii infestation, and the aboveground biomass of A. adenophora increased by 317.21% and 114.73%, the root biomass increased by 347.33% and 120.58%, the polyphenol oxidase activity heightened by 57.85% and 12.62%, the jasmonic acid content raised by 13.49% and 4.92%, the flavonoid content increased by 27.29% and 11.92%, respectively. The survival rate of A. gossypii and density of nymphs were significantly inhibited by AMF inoculation, and the effect of C. etunicatum was significantly greater than that of S. constrictum. This study provides clarified evidence that AMF in the rhizosphere of A. adenophora are effective in the development of tolerance and chemical defense under the feeding pressure of insect herbivory, and offer references for the management of the A. adenophora from the perspective of soil microorganisms.

Effects of elevation and habitat on leaf and reproductive traits of Ageratina adenophora (Sprengel) King & Robinson

Elevational gradients as well as habitat variability provide variation in environmental conditions enabling plants to alter their functional traits with respect to their surroundings on the way to sustain and better perform. Phenotypic plasticity has been suggested as one of the foremost mechanisms that invasive species implement to endure and invade wide geographical areas. The present study was performed to understand the leaf functioning and reproductive approaches adopted by the invasive weed Ageratina adenophora in response to different habitats of Kumaun Himalaya along elevational ranges. ANOVA showed significant effects of elevational ranges, habitats and their interactions on most of the investigated traits. A wide range in leaf area (367–1278 cm2/plant) and seed number (2803–12,240 seeds/plant) across the elevational zones indicated high plastic responses. Linear regression analysis revealed that the specific leaf area (r = -0.279; p < 0.05) and leaf area ratio (r = -0.255; p < 0.05) decreased significantly with increasing elevation. Reproductive traits like seed number (r = -0.284; p < 0.05) and reproductive index (r = -0.416; p < 0.05) also decreased significantly with increasing elevation. The results revealed that this species responds to heterogeneous environments via altering its leaf traits and reproductive performance. The large differences in trait values between habitats and elevations suggested a high degree of plasticity, which is leading to the successful encroachment and establishment of A. adenophora across an elevational gradient without undergoing adaptive evolution.

Predicting the Current and Future Distribution of the Invasive Weed Ageratina adenophora in the Chitwan–Annapurna Landscape, Nepal

With increasing globalization, trade, and human movement, the rate of alien species introduction has increased all around the globe. In addition, climate change is thought to exacerbate the situation by allowing range expansion of invasive species into new areas. Predicting the distribution of invasive species under conditions of climate change is important for identifying susceptible areas of invasion and developing strategies for limiting their expansion. We used Maxent modeling to predict the distribution of one of the world's most aggressive invasive weeds, Ageratina adenophora (Sprengel) R. King and H. Robinson, in the Chitwan–Annapurna Landscape (CHAL) of Nepal under current conditions and 3 future climate change trajectories based on 3 representative concentration pathways (RCPs 2.6, 4.5, and 8.5) in 2 different time periods (2050 and 2070) using species occurrence data, and bioclimatic and topographic variables. Minimum temperature in the coldest month was the most important variable affecting the distribution of A. adenophora. About 38% (12,215 km2) of the CHAL area is climatically suitable for A. adenophora, with the Middle Mountain physiographic region being the most suitable one. A predicted increase in current suitable areas ranges from 1 to 2% under future climate scenarios (RCP 2.6 and RCP 8.5). All protected areas and 3 physiographic regions (Siwaliks, High Mountain, High Himalaya) are likely to gain climatically suitable areas in future climate scenarios. The upper elevational distribution limit of the weed is expected to expand by 31–48 m in future climate scenarios, suggesting that the weed will colonize additional areas at higher elevations in the future. In conclusion, our results showed that a vast area of CHAL is climatically suitable for A. adenophora. Expected further range expansion and upslope migration in the future make it essential to initiate effective management measures to prevent further negative impacts of this invasive plant.

Remotididymella ageratinae sp. nov. and Remotididymella anemophila sp. nov., two novel species isolated from the invasive weed Ageratina adenophora in PR China.

To determine if Ageratina adenophora can accumulate diverse pathogens from surrounding native plants, we intensively sampled fungal communities, including endophytes, leaf spot pathogens and canopy air fungi, associated with Ag. adenophora as well as native plants in its invasive range. In total, we collected 4542 foliar fungal strains from 10 geographic sites, including 1340 from healthy leaves of Ag. adenophora, 2051 from leaf spots of Ag. adenophora and 1151 from leaf spots of 56 species of native plants and crops. Taxonomically, the common fungal genera included Colletotrichum, Diaporthe, Alternaria, Nemania, Xylaria, Neofusicoccum, Nigrospora, Epicoccum, Gibberella, Pestalotiopsis, Irpex, Schizophyllum and Clonostachys. We also isolated the cultivable fungi from 12 air samples collected from six areas in Yunnan Province, PR China. Among the total of 1255 air fungal isolates, the most common genera were Cladosporium, Trichoderma and Epicoccum. Among them, two new Remotididymella species, Remotididymella ageratinae from leaf spot of Ag. adenophora and Remotididymella anemophila from canopy air of Ag. adenophora were found. The two species showed both asexual and sexual reproductive structures. The conidia of R. ageratinae and R. anemophila are larger than those of R. anthropophila and R. destructiva. The size of ascospores of R. ageratinae and R. anemophila also differ from R. bauhiniae. Phylogenetic analysis of the combined ITS, LSU rRNA, rpb2 and tub2 sequences showed that R. ageratinae and R. anemophila each formed a distinct clade, separated from all species previously described in Remotididymella and confirmed them as new species belonging to Remotididymella. Full descriptions of R. ageratinae and R. anemophila are provided in this study.

Identification and preliminary characterization of chemosensory-related proteins in the gall fly, Procecidochares utilis by transcriptomic analysis

Chemoreception is critical for insect behaviors such as foraging, host searching and oviposition. The process of chemoreception is mediated by a series of proteins, including odorant-binding proteins (OBPs), gustatory receptors (GRs), odorant receptors (ORs), ionotropic receptors (IRs), chemosensory proteins (CSPs) and sensory neuron membrane proteins (SNMPs). The tephritid stem gall fly, Procecidochares utilis Stone, is a type of egg parasitic insect, which is an effective biological control agent for the invasive weed Ageratina adenophora in many countries. However, the study of molecular components related to the olfactory system of P. utilis has not been investigated. Here, we conducted the developmental transcriptome (egg, first-third instar larva, pupa, female and male adult) of P. utilis using next-generation sequencing technology and identified a total of 133 chemosensory genes, including 40 OBPs, 29 GRs, 24 ORs, 28 IRs, 6 CSPs, and 6 SNMPs. The sequences of these candidate chemosensory genes were confirmed by BLAST, and phylogenetic analysis was performed. Quantitative real-time PCR (qRT-PCR) confirmed that the expression levels of the candidate OBPs varied at the different developmental stages of P. utilis with most OBPs expressed mainly in the pupae, female and male adults but scarcely in eggs and larvae, which was consistent with the differentially expressed genes (DEGs) analysis using the fragments per kilobase per million fragments (FPKM) value. Our results provide a significant contribution towards the knowledge of the set of chemosensory proteins and help advance the use of P. utilis as biological control agents.

Stem galling of Ageratina adenophora (Asterales: Asteraceae) by a biocontrol agent Procecidochares utilis (Diptera: Tephritidae) is elevation dependent in central Nepal

ABSTRACT Gall inducers are widely used as biocontrol agents to suppress the vegetative and reproductive growth of invasive weeds. Procecidochares utilis Stone (Diptera: Tephritidae) is a gall forming fly that was released as a biocontrol agent against the noxious invasive weed Ageratina adenophora (Sprengel) R. King and H. Robinson (Asterales: Asteraceae). However, the effectiveness of P. utilis in controlling A. adenophora has been reported to vary according to geographic regions, with very low effectiveness in the Himalaya. In this study, we measured the abundance of P. utilis stem galling on A. adenophora along the elevation gradient (240–2965 m asl) in central Nepal. We found that elevation had a significant effect on gall abundance as well as gall size. Gall abundance and size peaked at mid-elevation (1940–2000 m asl). Stem galling by the fly reduced the stem diameter of the weed and all the three nutrients (N, P and K) in galls were significantly higher than in ungalled stems. Our study indicates that elevation is an important abiotic factor that strongly influences the P. utilis stem gall abundance, as well as gall size, and galls formed by P. utilis act as nutrient sinks. These findings provide insights in insect gall ecology, which may help the successful biocontrol of A. adenophora.

Characterization of the fungal community in the canopy air of the invasive plant Ageratina adenophora and its potential to cause plant diseases.

Airborne fungi and their ecological functions have been largely ignored in plant invasions. In this study, high-throughput sequencing technology was used to characterize the airborne fungi in the canopy air of the invasive weed Ageratina adenophora. Then, representative phytopathogenic strains were isolated from A. adenophora leaf spots and their virulence to A.adenophora as well as common native plants in the invaded range was tested. The fungal alpha diversities were not different between the sampling sites or between the high/low part of the canopy air, but fungal co-occurrences were less common in the high than in the low part of the canopy air. Interestingly, we found that the phytopathogenic Didymellaceae fungi co-occurred more frequently with themselves than with other fungi. Disease experiments indicated that all 5 Didymellaceae strains could infect A. adenophora as well as the 16 tested native plants and that there was large variation in the virulence and host range. Our data suggested that the diverse pathogens in the canopy air might be a disease infection source that weakens the competition of invasive weeds, a novel phenomenon that remains to be explored in other invasive plants.

Biology and management of the invasive weed Ageratina adenophora (Asteraceae): current state of knowledge and future research needs

SummaryBiological invasion is increasing worldwide and the management of invasive species is becoming an important priority for vegetation managers. Success of invasive species management depends on a thorough understanding of the biology of the organism in question and the effectiveness of current management efforts, in order to identify the best practices for management improvement. In this review, we synthesised current biological knowledge of a noxious invasive weed Ageratina adenophora to identify knowledge gaps and assessed management efforts to identify best practices. Finally, we proposed some priority areas for future research to fill knowledge gaps and improve management. Our analysis showed that A. adenophora has already invaded 40 countries, mainly in Asia, Oceania, Africa and Europe. Phenotypic plasticity, allelopathic interference and invasion‐mediated changes in the soil microbial community are the proposed mechanisms that facilitate rapid spread of this weed. However, allelopathy as a mechanism of invasion success of this weed has not been supported by ecologically meaningful experiments. Though mechanical, chemical and biological control measures have been used, their success remains limited and the weed continues to spread in new regions. Among seven biological control agents examined to date, gall fly (Procecidochares utilis) and leaf spot fungus (Passalora ageratinae) have been effective in limited areas to suppress growth of this weed. Some perennial native grasses (e.g. Setaria sphacellata and Lolium perenne) have shown potential to competitively suppress A. adenophora. In conclusion, understanding the invasion mechanisms, exploring further to identify effective biological control agents, combined with approaches of ecological restoration, could help in the management of this weed.

Effect of aqueous extract and compost of invasive weed Ageratina adenophora on seed germination and seedling growth of some crops and weeds

A study was conducted to investigate the effects of invasive weed Ageratina adenophora on the seed germination and seedling growth of Triticum aestivum, Brassica campestris and on weeds Ageratum conyzoides, Bidens pilosa, Galinsoga parviflora and Cyperus rotundus. The aqueous extracts of Ageratina plant’s part root, stem and leaf; and compost extract of Ageratina on different concentrations (control, 1, 2.5, 5 and 10%) were used to determine its effect on the seed germination, shoot and root length of Triticum aestivum, Brassica campestris and some common weed seeds under laboratory condition. The compost of A. adenophora at different doses viz. 0, 10, 20, 40 and 50g compost/kg soil was also applied to study the effect on the seed germination and seedling growth of B. campestris and T. aestivum and some weed seeds. The aqueous and compost extracts of Ageratina caused significant reduction in the seed germination and seedling length (shoot and root) which increased progressively on increasing the concentration of invasive plant's extract. The stem and leaf extracts of A. adenophora have more inhibitory effect on the germination percentage of winter crops as compared to root extract on the test crop seeds under study. In the compost of A. adenophora, the weeds showed more reduction in comparison to the crop plants B. campestris and T. aestivum.&#x0D; J. Biodivers. Conserv. Bioresour. Manag. 2018, 4(2): 11-20