Seed germination ecology of Conyza sumatrensis populations stemming from different habitats and implications for management.

Conyza sumatrensis (Retz.) E. H. Walker is an obnoxious weed, emerging as an invasive species globally. Seed germination biology of four populations of the species stemming from arid, semi-arid, temperate, and humid regions was determined in this study. Seed germination was recorded under six different environmental cues (i.e., light/dark periods, constant and alternating day and night temperatures, pH, salinity, and osmotic potential levels) in separate experiment for each cue. Populations were main factor, whereas levels of each environmental cue were considered as sub-factor. The impact of seed burial depths on seedling emergence was inferred in a greenhouse pot experiment. Seed germination was recorded daily and four germination indices, i.e., seed germination percentage, mean germination time, time to reach 50% germination, and mean daily germination were computed. Tested populations and levels of different environmental cues had significant impact on various seed germination indices. Overall, seeds stemming from arid and semi-arid regions had higher seed germination potential under stressful and benign environmental conditions compared to temperate and humid populations. Seed of all populations required a definite light period for germination and 12 hours alternating light and dark period resulted in the highest seed germination. Seed germination of all populations occurred under 5-30°C constant and all tested alternate day and night temperatures. However, the highest seed germination was recorded under 20°C. Seeds of arid and semi-arid populations exhibited higher germination under increased temperature, salinity and osmotic potential levels indicating that maternal environment strongly affected germination traits of the tested populations. The highest seed germination of the tested populations was noted under neutral pH, while higher and lower pH than neutral had negative impact on seed germination. Arid and semi-arid populations exhibited higher seed germination under increased pH compared to temperate and humid populations. Seed burial depth had a significant effect on the seedling emergence of all tested populations. An initial increase was noted in seedling emergence percentage with increasing soil depth. However, a steep decline was recorded after 2 cm seed burial depth. These results indicate that maternal environment strongly mediates germination traits of different populations. Lower emergence from >4 cm seed burial depth warrants that deep burial of seeds and subsequent zero or minimum soil disturbance could aid the management of the species in agricultural habitats. However, management strategies should be developed for other habitats to halt the spread of the species.

Garlic (Allium sativum) based interplanting alters the heavy metals absorption and bacterial diversity in neighboring plants.

Heavy metals are naturally occurring elements that have a high atomic weight and let out in the environment by agriculture, industry, mining and therapeutic expertise and thrilling amassing of these elements pollutes the environment. In this study we have investigated the potential of garlic interplanting in promoting hyper accumulation and absorption of heavy metals to provide a basis for phytoremediation of polluted land. Monoculture and inter-plantation of garlic were conducted to investigate the absorption of cadmium and lead contamination in the land. A group of experiments with single planting (monoculture) of Lolium perenne, Conyza canadensis and Pteris vittata as accumulators were used. The results have shown that garlic has a potential as a hyper accumulate and absorb heavy metals. It was found that the accumulation of Cd and Pb was much higher with inter-planting. Garlic boosts up the absorption of heavy metals in Lolium perenne of Cd 66% and Pb 44% respectively. The Inter-planting of garlic with Pteris vittata promotes the Cd 26% and Pb 15%. While the maximum accumulation of Lead 87% and Cadmium 77% occurred in Conyza canadensis herb plant. The bacterial diversity in the soil was analyzed for each experimental soil and was found that the Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, and Planctomycetes were commonly abundant in both single planting (monoculture) of ryegrass and interplanting ryegrass with garlic habitats. Variances were observed in the bacterial floral composition of single (monoculture) and intercropping (interplant) soils. Relative abundance of bacterial taxa revealed that the proportion of Proteobacteria, Acidobacteria, and Actinobacteria in the inter-planting group was slightly higher, while Firmicutes and Planctomycetes were low. This study provides the evidence to control the heavy metals contaminated soils with weed species. Growth promotion and heavy metal uptake of neighboring plants proved the specific plant-plant and plant-microbial associations with garlic plants. This inter-planting strategy can be used to improve heavy metal absorption.

Herbicide performance in the control of Conyza spp. where three plant heights

Intensive use of the herbicide glyphosate has led to herbicide resistant Conyza spp. populations. Thus, there is a need to indicate alternative herbicides and the appropriate developmental stage for controlling these populations. This study identifies alternatives for controlling glyphosate-resistant horseweed, with treatment applications at different plant heights. For this purpose, field experiments were conducted in the 2016/17 and 2017/18 crop years. The evaluated treatments were: glyphosate (540 g ae ha-1), glyphosate (1080 g ae ha-1), glyphosate (2160 g ae ha-1), glyphosate (3240 g ae ha-1), glyphosate + 2.4-D (1080 + 1005 g ae ha-1), glyphosate + saflufenacil (1080 + 49 g ae/ai ha-1), paraquat (400 g ai ha-1), diquat (400 g ai ha-1), ammonium glufosinate (600 g ai ha-1), and control (without application). These treatments were applied to plants with a maximum of 5 cm; plants between 6 and 15 cm; and plants between 16 and 25 cm. The results showed that glyphosate did not control weeds, regardless of rate. With the exception of 2,4-D, which needs complementation with sequential application of another contact herbicide, all alternatives were viable for the control of Conyza spp. plants with a maximum height of 5 cm.

Seed germination ecology of Conyza stricta Willd. and implications for management.

Numerous cropping systems of the world are experiencing the emergence of new weed species in response to conservation agriculture. Conyza stricta Willd. is being a newly emerging weed of barley-based cropping systems in response to conservational tillage practices. Seed germination ecology of four populations (irrigated, rainfed, abandoned and ruderal habitats) was studied in laboratory and greenhouse experiments. The presence/absence of seed dormancy was inferred first, which indicated seeds were non-dormant. Seed germination was then recorded under various photoperiods, constant and alternating day/night temperatures, and pH, salinity and osmotic potential levels. Seedling emergence was observed from various seed burial depths. Seeds of all populations proved photoblastic and required 12-hour light/dark period for germination. Seeds of all populations germinated under 5-30°C constant temperature; however, peak germination was recorded under 17.22-18.11°C. Nonetheless, the highest germination was noted under 20/15°C alternating day/night temperature. Ruderal and irrigated populations better tolerated salinity and germinated under 0-500 mM salinity. Similarly, rainfed population proved more tolerant to osmotic potential than other populations. Seeds of all populations required neutral pH for the highest germination, whereas decline was noted in germination under basic and alkaline pH. Seedling emergence was retarded for seeds buried >2 cm depth and no emergence was recorded from >4 cm depth. These results add valuable information towards our understanding of seed germination ecology of C. stricta. Seed germination ability of different populations under diverse environmental conditions suspects that the species can present severe challenges in future if not managed. Deep seed burial along with effective management of the emerging seedlings seems a pragmatic option to manage the species in cultivated fields. However, immediate management strategies are needed for rest of the habitats.

Physiological response of Conyza Canadensis to cadmium stress monitored by Fourier transform infrared spectroscopy and cadmium accumulation.

The cadmium(Cd) pollution of soil causes serious environmental problems. Cd is a high toxic and high water soluble element without biological function, and it is easily taken in by plants owing to its high bioavailability. Thus it easily entered the food chain and threaten people's health. Here，different concentrations of Cd solutions were used to study the physiological response and Cd accumulation characteristics of Conyza Canadensis (L.) Cronq. The physiological response was characterized by Fourier Transform Infrared (FTIR) spectroscopy, and Cd accumulation in plant and distribution were tested by Atomic absorption spectroscopy (AAS) under different concentrations Cd stress. When Cd concentrations toxicity <3 mg·L-1, the C. Canadensis (L.) Cronq. could grow normally without any symptoms, and the Cd concentrations increased to 7 mg·L-1, the C. Canadensis (L.) Cronq. had a little lower biomass, but there was no significant difference in the biomass among treatment concentrations. The peak shape of each component remained unchanged before and after Cd treatment. Only the absorption peak of some functional groups involved in Cd adsorption shifted with different degrees, such as hydroxy groups (3417-3429 cm-1), carboxyl groups (1380-1386 cm-1), and acid amide groups (1631-1637 cm -1). The characteristic peak absorption intensity of root, stem and leaf was different with the increase of heavy metal concentration. The absorbance of the roots with high Cd concentration was higher than that with medium-low Cd concentration. This shows that high concentration of Cd could induce C. Canadensis (L.) Cronq. seedlings to produce a large number of protein, amino acid and other substances, and through osmotic regulation to enhance stress resistance, provide nitrogen source, reduce heavy metal toxicity, and stabilize the internal environment. After Cd treatment, the characteristic peaks of stem and leaf were higher than or close to the control. This is due to the high tolerance of C. Canadensis (L.) Cronq. seedlings to heavy metals. The Cd accumulation in the shoots (stems and leaves) of C. Canadensis (L.) Cronq. was obviously lower than that in roots and the Cd content in the shoots usually increased with increasing Cd concentration. The maximum accumulation of Cd in shoots was 1898.07 mg·kg-1 after 11 days grown in the water spiked with 7 mg·L-1 Cd concentration. The study suggests that C. Canadensis (L.) Cronq. has some remediation effect and endurance ability against heavy metal polluted contaminated soil and has potential utilization value in the technical field of phytoremediation of Cd polluted soil.

From sensitivity to resistance - factors affecting the response of Conyza spp. to glyphosate.

BACKGROUND: Conyza bonariensis and C. canadensis are troublesome weeds, particularly in fields with minimum tillage, on roadsides and in perennial crops. The distribution of these difficult-to-control species is further increased by the spread of glyphosate-resistant populations. A preliminary investigation has demonstrated the existence of various degrees of glyphosate tolerance/resistance in these populations, underscoring the need to examine the relationship between glyphosate efficacy and plant growth conditions. RESULTS: In populations exposed to glyphosate at different temperatures, glyphosate tolerance increased linearly as the temperature was increased, whereas when grown under the same temperatures, they largely responded similarly to the herbicide. Furthermore, the sensitivity of plants to glyphosate decreased significantly with plant age and increased following temporal exposure to shading. Dose-response studies confirmed the glyphosate resistance of four C. bonariensis populations that were 8-30 times more resistant to glyphosate than the most glyphosate-sensitive population. These populations retained their characteristic glyphosate resistance even under unfavourable growth conditions. CONCLUSION: These findings indicate that the effect of glyphosate on both Conyza species is strongly linked to growing conditions. This has great importance for our understanding of glyphosate resistance and for control of these weeds in agricultural systems. © 2015 Society of Chemical Industry.

Identification of a Cd accumulator Conyza canadensis.

One of key steps of phytoremediating heavy metal contaminated soils is still the identification of hyperaccumulator and accumulator. In a former published article, Conyza canadensis L. Cronq. expressed some basic properties of Cd-hyperaccumulators. In this study, concentration gradient experiment and two sample-analyzing experiments were used to identify whether this plant is a Cd-hyperaccumulator. When grown on soil spiked with Cd at the rate of 10 and 25 mg kg(-1) in concentration gradient experiment, C. canadensis had both Cd enrichment factor (EF) and Cd translocation factor (TF) greater than 1, while the shoot biomass did not differ significantly as compared to the control. On the other hand, with Cd-spiking rates of 10 and 25 mg kg(-1), the Cd concentration in the shoot did not exceed 100 mg kg(-1), which is considered as the minimum shoot Cd concentration to qualify as a hyperaccumulator. In the sample-analysis experiments from a Pb-Zn mine area and wastewater irrigation region, C. canadensis also showed Cd-accumulator characteristics. Based on the results accomplished, we propose C. canadensis as a Cd-accumulator.

The effect of several adjuvants on glufosinate effectiveness in Conyza species.

The effect of several adjuvants on the effectiveness of glufosinate and the role of adherence and contact angle modifications due to the presence of these adjuvants in the spraying solution on the increase in efficacy observed on the broadleaved weeds Conyza albida and Conyza bonariensis has been determined under laboratory controlled conditions. The adjuvants used on the experiment were a mixture of methyl oleate and palmitate (MO/MP), a dodecylbenzene ammonium sulphonate (DBAS), a paraffinic oil (PO), an alkylglycol ester (AGE), and a lecithin + propionic acid + non ionic surfactant based product (LI-700). Dose-response experiments showed that C. albida displayed higher susceptibility to glufosinate than C. bonariensis, no matter the adjuvant tested. However, none of the mixtures increased the herbicide effectiveness on C. atlbida, with LI 700 and PO showing an antagonistic effect on the herbicide efficacy. On C. bonariensis, MO/MP and DBAS showed significant better results than non-amended glufosinate controls, with LI 700 showing again an antagonistic effect. Both adherence and contact angle studies were inconclusive, since adjuvants with best adherence and contact angle values were not the most effective ones. Therefore, other unknown parameters putatively modified by adjuvants such as herbicide penetration should be questioned.

Tissue culture and transient transformation of Marestail (Conyza canadensis (L.) Cronquist).

Glyphosate resistant crops are useful to agriculture by facilitating the use of nonselective herbicides, such as RoundUp, that have low human and environmental toxicity. The occurrence of glyphosate resistant weeds, however, has raised concern about the future utility of these crops. Conyza canadensis (L.) Cronquist (marestail or horseweed) is one such glyphosate resistant weed that has yet to be fully analyzed or established in tissue culture. Tissue culture enables the examination of physiological characteristics of a plant in an aseptic and controlled environment. For the present study, mairstail was cultured on a Murashige and Skoog based medium supplemented with 6-benzylaminopurine, and alpha-naphthaleneacetic acid. Plant regeneration was achieved on the same basal medium supplemented with only gibberellic acid. Glyphosate resistance could be demonstrated in the cultured tissues. The cultures could also be transformed with Agrobacterium tumefaciens without chemically inducing virulence using phenolics or glucose and resulting in a transformation frequency (transgenic events per total number of explants used) of about 13%. The tissue culture growth, preliminary glyphosate resistance data and genetic transformation data gathered in this project provide the means to further evaluate the mode of glyphosate resistance expressed by marestail.

[Responses of Conyza canadensis to different concentrations of copper in soil].

Through pot experiment and physiological-biochemical analysis, the study showed that the electric conductivities of Conyza canadensis collected from heavy Cu pollution (I), light Cu pollution (II) and control (III) sites were enhanced, while the chlorophyll (a + b) contents were reduced with increasing Cu concentration. The protein and proline contents in I were increased at first and then reduced, but those in II and III were reduced with increasing Cu concentration. The activities of SOD, POD and CAT were intensified under Cu stresses. When the Cu concentration was 1 200 mg x kg(-1), their activities in I, II and III were increased 194.1%, 206.2% and 118.6%, 170.1%, 182.9% and 111.3%, and 115.1%, 155.4% and 107.3%, respectively, in comparing with the control, which illustrated that the tolerance of Conyza canadensis was in order of heavy Cu pollution site > light Cu pollution site > control site, and the three ecotypes showed distinct differences in tolerance.

Studies on the diversity of arbuscular mycorrhizal fungi and the efficacy of two native isolates in a highly alkaline anthropogenic sediment.

A field survey of the arbuscular mycorrhizal status of herbaceous plant species was conducted in a highly alkaline anthropogenic sediment resulting from the disposal of waste from an acetylene and polyvinyl chloride factory. Most plant species found at the site were mycorrhizal and the dominant mycotrophic plant species was Conyza bilbaoana. Fungal species richness was assessed by identification of spores extracted from the sediment and from continuously propagated trap pot cultures. All of the six species of arbuscular mycorrhizal fungi (AMF) found were from the genus Glomus. Glomus intraradices and G. mosseae were found in field-collected sediment samples and also occurred most frequently in trap cultures. To test the symbiotic effectiveness of these two fungi, seedlings of C. bilbaoana were inoculated with either native G. intraradices BEG163 or G. mosseae BEG198 and non-native G. intraradices BEG75 or G. mosseae BEG25 isolates in sterile and non-sterile sediment collected from the study site. All four isolates were able to colonise C. bilbaoana. However, AMF native to the target sediments were generally more effective than the non-native fungi in promoting plant establishment and growth under highly alkaline conditions. The non-native G. intraradices was, however, more effective than the non-native G. mosseae. The results of this study suggest the use of adapted AMF as inoculants for phytorestoration of alkaline anthropogenic-stressed sediments.

Potential of weed species applied to remediation of soils contaminated with heavy metals.

To screen out a series of ideal plants that can effectively remedy contaminated soils by heavy metals is the main groundwork of phytoremediation engineering and the first step of its commercial application on a large scale. In this study, accumulation and endurance of 45 weed species in 16 families from an agricultural site were in situ examined by using the pot-culture field experiment, and the remediation potential of some weed species with high accumulation of heavy metals was assayed. The results showed that Solanum nigrum and Conyza canadensis can not only accumulate high concentration of Cd, but also strongly endure to single Cd and Cd-Pb-Cu-Zn combined pollution. Thus 2 weed species can be regarded as good hyperaccumulators for the remediation of Cd-contaminated soils. Although there were high Cd-accumulation in Artemigia selengensis, Znula britannica and Cephalanoplos setosum, their biomass was adversely affected due to action of heavy metals in the soils. If the problem of low endurance to heavy metals can be solved by a reinforcer, 3 weed species can be perhaps applied commercially.