Occurrence of Glyphosate-Resistant Horseweed (Conyza canadensis) Population in China

Horseweed （Conyza canadensis）, an invasive alien weed, is one of the main weeds in orchards in China. Although glyphosate has been used for control of horseweed and many other weeds in orchards for more than 25 years in China, a case of glyphosate-resistant horseweed has not been identified in orchard in China so far despite glyphosate-resistant horseweed cases have been reported in some other countries. Seeds of 25 horseweed populations were collected from different orchards with different glyphosate application history. Potted seedlings with 11-13-leaf growth stage were treated with glyphosate at 0.035, 0.07, 0.14, 0.28, 0.56, 1.12, 2.24, 4.48, and 8.96 kg a.i. ha-1. The dosage dependence response curve of each population was constructed with Log-logistic dose response regression equations. The ED50 value of each population was calculated and compared with the susceptible population from China. Different populations had different relative glyphosate-resistant levels which increased with the number of years of glyphosate application. Two populations with the highest resistance levels, 8.28 and 7.95 times, were found in Ningbo, Zhejiang Province, China, where glyphosate was used for weed control in orchards twice each year for 15 yr. The two resistant populations accumulated approximately two to four times less shikimic acid than the two susceptible populations 48 h after glyphosate application.

A new derivative of triterpene with anti-melanoma B16 activity from Conyza canadensis

A new derivative of triterpene named Erigeronol 1 was isolated from the EtOH extract of the aerial part of Conyza canadensis together with 15 known compounds for the first time from this plant.The structure of Erigeronol 1 was elucidated as 3-O-（hydroxyacetyl） -23,28-dihydroxy-β-amyrin by hydrolysis and spectroscopic analysis.Erigeronol 1 showed potent cytotoxic activity with IC_（50） value of 7.77±0.47μg/mL against melanoma B16 determined by the 3-（4,5-dimethylthiazo-2-yl）-2,5-diphenyltetrazolium bromide（MTT） method.

A cross-city molecular biogeographic investigation of arbuscular mycorrhizas in Conyza canadensis rhizosphere across native and non-native regions

Introduction:The ecological processes underlying the suppressive impacts of invasive species on native species diversity,both above-and below-ground,in non-native regions are not well understood.We therefore aimed to investigate the cross-city biogeographic patterns of arbuscular mycorrhizal(AM)diversity in Conyza canadensis rhizosphere in native(North American)and non-native(Kashmir Himalayan)regions.Methods:We recovered AMF spores from rhizospheric soils of Conyza in native and non-native ranges,besides doing so from the uninvaded sites in the introduced region.DNA extracted from AMF spores was processed for cloning and PCR-RFLP of SSU rRNA gene to yield the restriction groups(RGs)followed by their sequence analysis to determine the sequence groups(SGs).Results:The results indicated greater diversity of RGs and SGs in Conyza rhizosphere in native than in non-native sites.In the introduced region,however,the AMF diversity was more in uninvaded than in invaded sites.The species composition of AMF varied significantly between native and non-native regions and so also between invaded and uninvaded habitats.Conclusions:Though difference in AMF diversity between Conyza invaded and uninvaded sites may be attributed to invasion,the role of other evolutionary factors seems likely for differences between the native and non-native regions.We suggest that the ecological processes underlying these evolutionary differences in two biogeographic regions,besides the intensity of urbanization,might play some role in these differences.

Pyromeconic acid derivatives from Conyza canadnsis(L.) Cronq

A new pyromeconic acid derivative,pyromeconic acid-3-O-β-D-glucopyranoside-3′-（O-β-D-glucopyranoside）-6′-（O-4″-hydroxybenzoate） （1）,along with two known ones,were isolated from the whole plants of Conyza canadensis.Their structures were elucidated based on the analysis of their spectroscopic data.The in vitro antibacterial testing results showed that all of these three compounds were inactive towards two bacterial strains,Escherichia coli and Staphyloccocus aureus.

Enhanced fitness due to higher fecundity,increased defence against a specialist and tolerance towards a generalist herbivore in an invasive annual plant

Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction.To assess the importance of the different mechanisms governing the success of Conyza canadensis,a globally successful invader,we simultaneously tested several recent hypotheses potentially explaining the factors leading to biological invasion.Methods We tested(i)whether plants from the non-native range showed a higher fitness than plants from the native North American range,(ii)whether they differed in resistance against an invasive generalist herbivore,the slug Arion lusitanicus and against a recently established specialist aphid herbivore,Uroleucon erigeronense and(iii)experimentally assessed whether C.canadensis releases allelopathic chemicals that have harmful effects on competing species in the nonnative range.We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.Important Findings The invasion success of C.canadensis in Europe cannot be attributed to a single trait,but to a combination of factors.Invasive plants benefited from increased growth and above all,increased reproduction(a key trait in an annual plant)and were less attacked by a co-migrated specialist enemy.The observed loss of defence against generalist slugs did not translate into a decreased fitness as invasive C.canadensis plants showed a high re-growth potential.In contrast to earlier in vitro studies,we detected no allelopathic effects on the competing flora in the non-native range.The latitudinal cline in vegetative biomass production in the non-native range observed in our common garden study indicates a high adaptive potential.However,only further genetic studies will provide conclusive evidence whether the differentiation in the non-native range is caused by pre-adaptation and sorting-out processes of putatively repeatedly introduced populations of this composite,long-distance disperser with highly volatile seeds or evolved de novo as a rapid response to new selection pressures in the nonnative range.