Invasive Alien Weed Research Articles

Effect of water trophic level on the impact of the water hyacinth moth Niphograpta albiguttalis on Eichhornia crassipes

Eutrophication contributes to the proliferation of alien invasive weed species such as water hyacinth Eichhornia crassipes. Although the South American moth Niphograpta albiguttalis was released in South Africa in 1990 as a biological control agent against water hyacinth, no post-release evaluations have yet been conducted here. The impact of N. albiguttalis on water hyacinth growth was quantified under low-, medium- and high-nutrient concentrations in a greenhouse experiment. Niphograpta albiguttalis was damaging to water hyacinth in all three nutrient treatments, but significant damage in most plant parameters was found only under high-nutrient treatments. However, E. crassipes plants grown in high-nutrient water were healthier, and presumably had higher fitness, than plants not exposed to herbivory at lower-nutrient levels. Niphograpta albiguttalis is likely to be most damaging to water hyacinth in eutrophic water systems, but the damage will not result in acceptable levels of control because of the plant's high productivity under these conditions. Niphograpta albiguttalis is a suitable agent for controlling water hyacinth infestations in eutrophic water systems, but should be used in combination with other biological control agents and included in an integrated management plan also involving herbicidal control and water quality management.

Prioritisation of potential agents for the biological control of the invasive alien weed, Pereskia aculeata (Cactaceae), in South Africa

Pereskia aculeata Miller (Cactaceae) is an invasive alien species in South Africa that is native in Central and South America. In South Africa, P. aculeata outcompetes native plant species leading to a reduction in biodiversity at infested sites. Herbicidal and mechanical control of the plant is ineffective and unsustainable, so biological control is considered the only potential solution. Climatic matching and genotype matching indicated that the most appropriate regions in which to collect biological control agents were Santa Catarina and Rio de Janeiro provinces in Southern Brazil. Surveys throughout the native distribution resulted in 15 natural enemy species that were associated with the plant. Field host range data, as well as previous host plant records, were used to prioritise which of the species were most likely to be suitably host specific for release in South Africa. The mode of damage was used to determine which species were most likely to be damaging and effective if released. The most promising species prioritised for further study, including host specificity and impact studies, were the stem-wilter Catorhintha schaffneri Brailovsky & Garcia (Coreidae); the stem boring species Acanthodoxus machacalis Martins & Monné (Cerambycidae), Cryptorhynchus sp. (Curculionidae) and Maracayia chlorisalis (Walker) (Crambidae) and the fruit galler Asphondylia sp. (Cecidomyiidae). By prioritising the potential biological control agents that are most likely to be host-specific and damaging, the risk of conducting host specificity testing on unsuitable or ineffective biological control agents is reduced.

Pseudocercospora lonicerigena a leaf spot fungus on the invasive weed Lonicera japonica in Brazil

Lonicera japonica (Japanese honeysuckle), a plant of Asian origin introduced as an ornamental into many countries, has become an invasive weed in some exotic situations, such as in southern Brazil. Classical biological control (CBC) with natural enemies collected in the centre of origin is considered to be the best alternative for sustainable management of L. japonica. In the context of this strategy, previous knowledge of the natural enemies already present in the target area is of great importance in order to avoid un-necessary introductions of CBC agents from the weed’s native range. Recently, examination of populations of L. japonica in localities in the Brazilian states of Rio de Janeiro and Parana revealed the presence of leaf spots consistently associated with a cercosporoid hyphomycete. A molecular and morphological study of this fungus led to its recognition as Pseudocercospora lonicerigena. There were few differences when the Brazilian isolate was compared with a strain found in North America. This is the first report of this fungus in Brazil. The fungus was isolated in pure culture and inoculation of healthy leaves of L. japonica eventually led to leaf yellowing and necrosis, indicating that P. lonicerigena is not highly pathogenic, as evidenced by the continuing advance of this weed in southern Brazil. Therefore, the introduction of additional co-evolved natural enemies collected in Asia, perhaps piggy-backing on an ongoing project already underway in New Zealand, will be necessary to control this invasive alien weed in Brazil.

Ecophysiological attributes of Mikania micrantha, an exotic invasive weed, at two different elevations in the tropical forest regions of the Western Ghats, South India

Mikania micrantha H.B.K. is a fast‐growing, perennial vine and one of the world's worst alien invasive weeds. It is a major threat to agro‐ecosystems, plantation crops and agro‐forestry systems. An attempt was made to understand the physiological adaptation and ecological amplitude of M. micrantha at two different altitudes and seasons in the Western Ghats of south India. The relationships between the net photosynthetic rate (PN) and other physiological parameters, like stomatal conductance (gs), transpiration rate, intercellular CO2 concentration, vapor pressure deficit and water use efficiency, and environmental factors, like photosynthetically active radiation (PAR), leaf temperature and air temperature, were analyzed in order to understand their physiological adaptabilities. The PN exhibited a peak at 10.00 hours and declined gradually at both elevations; however, the populations at the lower elevation had a significantly greater PN than the populations at the higher elevation in November. The PN and gs were positively correlated with the PAR. Under significantly different PAR levels, the difference in the average PN was not significant for summer but was significant for winter between the two elevations. It suggested that the photosynthetic ability of M. micrantha is not affected by a difference in altitude (451 m and 912 m), as the differences in the environmental parameters were inconspicuous between the two elevations. These results indicated that this weed possesses great phenotypic plasticity and thrives better at lower elevations.

Biološke invazije - na primeru korovskih biljaka

In the past two decades, ecologists have focused mainly on two basic aspects of biological invasions: firstly, the particular characteristics of species that determine their invasiveness, and secondly, on the properties of communities that determine their resistance to invasion. Depending on the period when it was unaccidental or accidental introduction of alien plant species, they are divided into four categories: archaeophytes, paleophytes, neophytes and neotophytes. In relation to the status after the introduction and the level of sustainability, alien plant species are grouped into: ephemeral, naturalized and invasive. In relation to the total invasive alien weed flora of the Republic of Serbia attribute most aggressive, in terms of crop production, can be assigned to species: Abutilon theophrasti Medic., Amaranthus retroflexus L., Ambrosia atremisiifolia L., Cuscuta campestris Yunk., Erigeron canadensis L., Galinsoga parviflora Cav., Iva xanthifolia Nutt., Polygonum aviculare L., Portulaca oleraceae L., Sorghum halepense (L.) Pers., Stenactis annua (L.) Ness. and Xanthium strumarium L. On the other hand, in the category of invasive alien weed species, which for now does not occur in a high abundance in the crop field, but that can be expected in the near future in the crop field if we do not take control measures, that’s are: Amaranthus deflexus L., Asclepias syriaca L., Ambrosia trifida L., Eleusine indica L., Solidago canadensis L., Kochia scoparia (L.) Schrad., Iva xanthifolia Nutt., Fallopia japonica Houtt., Xanthium spinosum L., etc.

Suppressive fodder plants as part of an integrated management program for Parthenium hysterophorus L.

Parthenium hysterophorus L. is an alien invasive weed in both Australia and Pakistan infesting rangelands, reducing fodder biomass and causing significant livestock production losses. Previous studies have identified a number of introduced and native fodder species that can suppress the growth of P. hysterophorus in glasshouse trials. These species can also provide an adequate fodder biomass for livestock production. In this study 11 of these fodder species were sown at the recommended rates into P. hysterophorus infested field sites at Injune and Monto, Australia while an additional five species were sown into similar infested field sites at Islamabad and Mardan, in northern Pakistan. Measurements taken on dry shoot biomass production of the fodder species were used to determine their P. hysterophorus growth suppressing ability and fodder biomass production. In Australia, all of the fodder species suppressed the growth of P. hysterophorus, with Setaria incrassata, Cenchrus ciliaris, Clitoria ternatea, Themeda triandra and Astrebla squarrosa (Injune field site), and Chloris gayana, C. ciliaris, Dichanthium sericeum, Clitoria ternatea and Bothriochloa insculpta (Monto field site) all suppressing growth by >62% and producing at least 329gm−2 of dry fodder biomass. In Pakistan, all of the fodder species suppressed the growth of P. hysterophorus, with Sorghum almum, C. ciliaris and C. gayana suppressing growth by >73% and producing at least 622gm−2 of dry fodder biomass. Some species such as S. incrassata performed well at just one field site, while others (C. ciliaris and C. gayana) performed well at all the four field sites, indicating that such plants could be considered as part of a new integrated weed management system for P. hysterophorus in both Australia and Pakistan.

Assessment of Allelopathic Potential of <i>Wedelia trilobata</i> on the Germination, Seedling Growth and Chlorophyll Content of Rape

Wedelia trilobata(L.) Hitche is a widespread alien invasive weed in south China and has been reported to show allelopathic potential causing biological suppression on some plants. In this study, the allelopathic effects of aqueous extracts from the leaves ofW. trilobatawere tested on the seed germination, shoot growth and total chlorophyll content of rape (Brassica campestrisL.) using Petri dish bioassay. The results showed that the aqueous extracts at the concentration from 25% to 100% caused a significant reduction in the germination percentage, shoot length and total chlorophyll content of rape. This inhibitory effect was concentration-dependent. These results suggested there was a strong potential phytotoxic effect ofW. trilobataon rape andthis effect might reduce the production of some crop species.

Report of Bruchidius tuberculatus (Hochhut 1847) (Chrysomelidae: Bruchinae) from biodiversity hotspot region of Kashmir Himalaya - a promising biocontrol agent against invasive alien weed Centurea iberica Trev. ex Spreng.

Invasion by alien species threaten native biodiversity, alter the functioning of ecosystems, and cause substantial economic impacts. Biological control of these invasive species using co-evolved natural enemies has long been considered a safe, cost effective, and environmentally benign tool for pest management. Here, we for the first time report the Mediterranean endophagous seed beetle Bruchidius tuberculatus (Hochhut 1847) as a potential biocontrol agent of a noxious medicinal weed ‘Iberian starthistle’ Centurea iberica Trev. ex Spreng. This is also the first report of this bruichid from the Indian subcontinent, which accidentally got introduced into Kashmir Himalaya, perhaps as a seed contaminant. Adults of the species were bred from the flower heads of the invasive alien weed species. Grubs of the beetle were found to be efficient predispersal specialist seed feeders, exerting a substantial control on total viable seed output at natural population levels. As the narrower host range of endophagous species is a preferable weed control strategy, this Mediterranean bruchid seems to be a promising host specific biological control agent of the noxious weed. Key words: Centaurea iberica, Bruchidius tuberculatus, Biocontrol, Invasion.

A plant‐traits approach to assessing the success of alien weed species in irrigated Mediterranean orchards

AbstractIn addition to their impact on natural habitats, invasive alien plants can have a significant negative effect on agricultural systems and cause economic losses. Flood‐irrigated orchards in the Mediterranean Basin are vulnerable to the invasion of alien weeds, primarily because of the traditional management practices used in the orchards, which are characterized by high soil moisture during the dry summer period, nutrient availability and high levels of disturbance. This study sought to determine whether their biological traits can explain the success of alien weed species. To answer this question, 408 floristic relevés were conducted in 136 flood‐irrigated orchards on the Plains of Lleida (Catalonia, NE of Spain). Richness and cover of native and alien weeds were compared. Furthermore, a set of biological traits were compared between successful and non‐successful weeds for the whole data and separately between native and alien weeds using logistic regression and classification trees. In flood‐irrigated orchards, alien species covered most of their area, even though the richness of alien species was lower than that of the native species. The most important species wereC4species with seeds dispersed by water, and on the other hand, rosulate and caespitose‐reptant hemicryptophytes with long flowering period. Most of these traits fitted with those of the invasive alien weeds, which were mostlyC4species with seeds dispersed by water. Perennial life form characterized successful native weeds. In this study, we discuss how the traditional management of flood irrigation in fruit‐tree orchards favours invasive alien weeds that have specific traits, acting as a reservoir for the spread of alien weeds into other crops and surrounding riparian habitats. We also propose changing management practices in order to avoid the selection of alien weeds and to promote native species.

Field release of a prospective biological control agent of weeds, Ceratapion basicorne, to evaluate potential risk to a nontarget crop

Ceratapion basicorne is a prospective biological control agent of yellow starthistle (Centaurea solstitialis), which is an invasive alien weed in the USA. Although the weevil has a strong preference for yellow starthistle, it has been reported to develop sometimes on safflower in larval transfer and no-choice experiments. Although safflower was not attacked by this insect in previous field experiments, a release permit was denied because of concern for risk to safflower. Adult C. basicorne were released in a field experiment in which two varieties of safflower were grown in solid blocks on either side of a small number of yellow starthistle plants. Plants were dissected at the time of weevil pupation. Immature insects were reared to adult stage on artificial diet or were preserved in acetone to identify by molecular genetic analysis. C. basicorne infested 54% of the yellow starthistle plants and 0% of 1021 safflower plants. A different weevil, Ceratapion orientale, infested 1.5% of the safflower plants. These results corroborate two other published field studies in which C. basicorne was not reared from safflower. The combined results of nine experiments provide a point estimate that the probability of attack is less than 0.00059, with 99.9% confidence that it is less than 0.0045. The consistency of results from field experiments in three countries and the absence of any report of this insect being reared from safflower in the field in the weevil’s native range support the conclusion that this insect poses no significant risk to safflower.

Pharmacological and Antagonistic Potentials of Mikania micrantha

The antimicrobial, chemical and allelopathical properties of invasive alien weed Mikania micrantha Kunth ex H.B.K were analyzed. The extraction was performed in different solvents by soxhlet extraction technique. Some bacteria (Acinetobacter sp. and Bacillus subtilis) were found to be highly inhibited, whereas the extract was found effective against Fusarium species (F. eridiforme) among the fungi. Of all the solvents used for extraction, methanolic hot extract showed good antimicrobial properties against tested pathogenic strains. The preliminary qualitative phytochemical assay divulged the presence of glycosides and quinones in the test plant. Germination rate was higher for all crops with control treatment. The germination rate decreased with the increase in the extract concentration and was found to be lowest at 5% concentration of extract. Generally, the radicle length of all bioassayed species decreased with increasing concentrations of Mikania, with Barley and Paddy being the most susceptible to the plant extract at full strength. The broad spectrum of activity of the extract indicated possibilities for wide use of M. micrantha for controlling the human pathogenic bacteria and phytopathogenic fungus that have been widely destroying crops.DOI: http://dx.doi.org/10.3126/njst.v12i0.6483 Nepal Journal of Science and Technology 12 (2011) 75-84

Effects of phosphorus and light intensity on the growth and competition of the two weed species, Veronica persica and Chorispora tenella

Veronica persica Poir. (Persian speedwell) is an invasive alien weed species in the upland soils throughout China. Its dominance in weed flora could be alleviated by Chorispora tenella (Pall.) (tender chorispora) in P‐poor soils and in an intense light environment. Here, three experiments in growth chambers were carried out in order to explore the effect of P and light intensity on the growth and competition of V. persica and C. tenella, the pH value in their rhizospheres, and the kinetic parameters (Km and Vmax) of the H2PO4‐ uptake by the two weed species. The ANOVA results showed that the light intensity and P level in the soil obviously influenced the growth of the two weed species. However, the effect of the P level in the soil was greater for V. persica and the effect of the light intensity was greater for C. tenella. The restriction of the growth of V. persica by a low P level in the soil was much more than that of C. tenella, but it was reversed in the two species in relation to a low light intensity. In addition, the pH was lower in the rhizosphere of C. tenella after the P‐deficient treatment and there was a lower Km in the uptake of H2PO4‐ than for V. persica, suggesting that C. tenella could adapt to a low‐P environment more easily. In conclusion, C. tenella growing together with V. persica had a competitive advantage under high‐light‐intensity and low‐P‐level conditions, but it lost its advantage with an increase in P fertilization and a decrease in light intensity.

The infection process of Puccinia xanthii f. sp. ambrosiae-trifidae on Ambrosia trifida

Puccinia xanthii Schwein. f. sp. ambrosiae-trifidae S.W.T. Batra is an obligate parasitic rust fungus of Ambrosia trifida Linn. Field investigations in Liaoning Province, China, showed that it is an effective biocontrol agent of this alien invasive weed. Its infection of the plant was observed by light microscopy combined with Coomassie Brilliant Blue R-250 staining. We report the infection process, including teliospore germination and basidiospore formation on the host leaf surface, penetration of host tissue, and development of fungal hyphae within the host tissue. Fresh teliospores began to germinate from the germ pore within 1 h under suitable conditions and soon produced basidiospores or secondary basidiospores. Basidiospores falling on host leaves germinated from the end of the basidiospore opposite to the apiculus. Appressoria of germ tubes tended to orient along leaf epidermis cell ridges or at junctions near stomata rather than fixing randomly on the leaf surface. These germ tubes grew for short or longer distances before forming appressoria. The rust fungus directly penetrated the host epidermis by infectious pegs rather than through stomata. Within host tissues, the rust fungus formed intraepidermal vesicles, primary hyphae, intracellular hyphae, and M-haustoria. The intricate infectious structures formed by P. xanthii f. sp. ambrosiae-trifidae on or in host tissues suggest that the rust fungus is a suitable organism for researching the interaction between the pathogen and host plant.

Antioxidant Activity of Some Carduus Species Growing in Bulgaria

Background: Species of genus Carduus are traditionally used in Bulgarian folk medicine as diuretic, cardiotonic and antihemorroidal remedies. C. candicans ssp. globifer and C. kerneri ssp. austro-orientalis are Balkan endemic, whereas C. acanthoides, C. nutans, C. thoermeri C. are invasive alien weeds in the Americas, Australia and New Zealand, and causes major economic losses. The aim of the present study was to screen some Carduus spesies growing in Bulgaria for radical scavenging and inhibitition of lipid peroxidation in order to discover new natural sources of antioxidants for further investigation. Methods: Antioxidant activity of Carduus species were investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2´-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) di-ammonium salt (ABTS) free radicals; ferric reducing antioxidant power (FRAP) assay and inhibition of lipid peroxidation in linoleic acid system by the ferric thiocyanate method (FTC). Butylated hydroxytoluene (BHT) and ascorbic acid were used as positive controls. In addition, the quantification of total water soluble polyphenols and flavanoids were determinate by Folin-Chiocalteu reagent and AlCl3, respectively. Results: The highest concentrations of total water soluble polyphenols and flavonoids were found in C. thoermeri (2.06 ± 0.03 g /100 g dw and 3.31 ± 0.12 g /100 g dw, respectively), followed by C. nutans (1.88 ± 0.01 g/100 g dw; 2.60 ± 0.09 g /100 g dw, respectively) and C. candicans ssp. globifer (1.85 ± 0.04 g/100 g dw). Conclusions: All tested extracts demonstrate significant antioxidant activity moreover C. thoermeri, C. nutans and C. candicans ssp. globifer were found to be the most potent and can be a good new source of natural antioxidants.

The Potential of Chromolaena Odorata (L) to Decontaminate Used Engine Oil Impacted Soil Under Greenhouse Conditions

This study reports on the use of Chromolaena odorata (L) R.M. King and H. Robinson, an Asteraceae (compositae) and an invasive alien weed in Africa for the remediation of soil contaminated with used engine oil. Used engine oil from a motor service garage was used to artificially contaminate soil taken from a garden to give total petroleum hydrocarbon (TPH) of between 1 and 40 g kg−1. Chromolaena odorata (L), propagated by stem cuttings were transplanted into the contaminated soil and watered just enough to keep the soil at about 70% water holding capacity for 90 day. A set of control experiments containing 40 g kg−1 used engine oil but without plants was set up. All experiments were set up in triplicates. Although the plants in the experiments containing higher than 30 g kg−1 used engine oil showed relatively slower growth (fewer branches and leaves, and shorter in height) compared to those containing lower concentrations, the plants in all the experiments continued to grow until the end of the 90 day period. Residual TPH after 90 days showed that between 21 and 100% of oil was lost from the planted soil while only 11.5% was lost in the control, which did not contain plants during the same period. Analysis of plant tissues showed that both shoot and root tissues contained detectable levels of TPH and selected PAHs were also detectable. Biomass accumulation by Chromolaena odorata was affected adversely by concentrations of oil higher than 20g kg−1. Results of germination rates and germination energy measurements showed that Chromolaena odorata was able to reduce the toxicity of the contaminated soil after 90 days as compared to soils containing freshly contaminated soil.

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 ED 50 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.

Risk to nontarget plants from Ophraella communa (Coleoptera: Chrysomelidae), a potential biological control agent of alien invasive weed Ambrosia artemisiifolia (Asteraceae) in China

Ophraella communa LeSage is an oligophagous insect that shows promise for controlling the alien invasive weed Ambrosia artemisiifolia L. in China. This study was performed to evaluate the risk of O. communa on the basis of host-specificity testing of larval development under no-choice conditions and of oviposition preferences under choice conditions in greenhouses and in the open field. Under no-choice conditions, O. communa larvae experienced much higher mortality rates on the nontarget plants than on the target weed, but a small proportion of larvae completed development on the nontarget plants examined, including Xanthium sibiricum Patrin ex Widder, Helianthus tuberosus L., and H. annuus L. Multiple-choice tests indicated that O. communa showed a strong oviposition preference for the target weed over the nontarget plants and laid few eggs on the economically important Helianthus crops tested. In paired-choice trials, O. communa adults showed an obvious preference for the target weed over X. sibiricum but preferred X. sibiricum to H. annuus. The results suggest that X.sibiricum might be used as a lower-ranked host plant next to the target weed by O. communa, and that Helianthus crops would not be at risk of being used for oviposition in the field.

Control of invasive alien weeds averts imminent plant extinction

Invasive alien species constitute a major threat to biodiversity and cases of extinction caused by invasive alien animals are abundant. However, while invasive alien plants also harm native biota there exists a lack of cases demonstrating their ability to cause extinction of native plant species. Different alien species (vertebrates, invertebrates, pathogens etc.) commonly deliver different simultaneous impacts like predation, disease or competition. In such situations, assessing the contribution of plant invasion in causing decline of a given plant population in its natural habitat can be difficult, yet is desirable to avoid or minimize wastage of managers’ resources. Using native angiosperms in lowland wet forests of Mauritius, we first compared native seedling diversity in forest areas that have been weeded of invasive alien plants about a decade previously, with adjacent similar but non-weeded areas. Then, using the weeded area, we compared results of native plant surveys carried out around the time that invasive alien plants were controlled, with the same community about a decade latter. Species richness and abundance of seedlings were higher in the weeded areas compared to the adjacent non weeded forest. We also found that several species that were presumed extinct or critically threatened with extinction had recovered dramatically as a consequence of the sole removal of invasive alien plants. This shows that the threat posed by invasive alien plants can be overwhelmingly important in driving native plant population declines in tropical forests and that imminent plant extinctions can be averted by timely control of alien plants.

Climatic analysis to determine where to collect and release Puccinia jaceae var. solstitialis for biological control of yellow starthistle

Puccinia jaceae var. solstitialis is an autoecious rust fungus that is native to areas of Afro-Eurasia with a Mediterranean climate. An isolate collected near Sivas, Turkey was released for classical biological control of yellow starthistle (YST), which is an invasive alien weed in California, USA. The fungus has been released throughout California, but long-term establishment rates are generally low, apparently because this ecotype is not well adapted to the climate where the weed is most invasive. Using a site with excellent establishment as a target, the Match Climates function in CLIMEX climate modeling software identified similar sites in and around the San Francisco Bay Area, east to the Central Valley and Sierra foothills, and along the coast of Southern California. Similar sites in other states include Walla Walla, Washington, Pendelton, Oregon and Salt Lake City, Utah. A Compare Locations model based primarily on experimentally measured temperature and humidity requirements of the rust produced similar results. Using Sacramento, California, which is in the center of YST distribution, as a target, the Match Climates function predicted that the best locations to search for rust accessions to use in California are near Tunis, Tunisia, Foggia, Italy, Khalkis, Greece, Kayseri, Turkey, and possibly Constantine, Algeria. This generally agrees with the prediction of a Compare Locations model based on the geographic distribution of YST in California. Climatic factors that limit the long-term establishment of the fungus are likely to be summer heat and/or dry stress and short dew periods.

Comparative study on morphological characteristics of "Huang-ying-hua", invasive alien weed Solidago canadensis L. and its relatives with the same genus.

"Huang-ying-hua" is a widely-used cut flower in florist currently,but it is similar to the invasive weed Solidago canadensis in morphological characteristics,so it has caused public concerns.Comparative studies on morphological characteristics of eight batches of "Huang-ying-hua" with 35 invasive populations of S.canadensis in our country,two populations of Solidago L.sampled from Canada and Solidago decurrens were conducted.The cluster analysis showed that seven batches of "Huang-ying-hua" samples were clustered together except the fifth batch,which was clustered with S.canadensis in one group,"Huang-ying-hua",S.canadensis,and the populations sampled in Canada were clustered into one group while S.decurrens was grouped into sole one.This showed "Huang-ying-hua" is similar to S.canadensis,not S.decurrens.The further comparative studies on morphological of S.gigantea and S.altissima showed that "Huang-ying-hua" and S.altissima were together and clustered with invasive populations,and the populations sampled from Canada were more similar to S.gigantea.S.canadensis,S.altissima and S.gigantea all belonged to S.canadensis complex.The length/width ratio of leaves,the length between triplinerved and leaf base,the number of epidermal hair on vein and the ratio of disc florets to ray florets were the important morphological characteristics of "Huang-ying-hua" and other species in genus of Solidago L.