Genetic diversity of Solanum elaeagnifolium,an invasive problematic weed in Jordan

Solanum elaeagnifolium (silverleaf nightshade) is a problematic weed that is common in Jordan and difficult to control. The weed exhibits distinct morphological variations in growth habit, leaf shape, leaf margins, flower colour and presence or absence of spines between individuals among and within populations suggesting genetic differences. Genetic variations among 61 samples of S. elaeagnifolium collected from heavily infested sites in the central Jordan Valley were investigated using six simple sequence repeat (SSR) markers and eight amplified fragment length polymorphism (AFLP) primer combinations. Results showed that 111 out of 675 AFLP bands were polymorphic generating polymorphism information content (PIC) of 38.0%, while 23 SSR polymorphic alleles were detected generating a PIC of 30.8%. Phylogenetic analysis using RaxML software identified four major clades with a clear clustering of the samples with their collection sites. Genetic analysis using both techniques revealed high level of genetic diversity among S. elaeagnifolium samples collected from a small geographical area indicating that a range of genetic diversity may be detected in weed populations across the country that may complicate its management.     

Genetic diversity within and between sulfonylurea‐resistant and susceptible populations of Schoenoplectus juncoides in Japan

To reveal the effects of herbicide selection on genetic diversity in the outcrossing weed species Schoenoplectus juncoides, six sulfonylurea‐resistant (SU‐R) and eight sulfonylurea‐susceptible (SU‐S) populations were analysed using 40 polymorphic inter‐simple sequence repeat loci. The plants were collected from three widely separated regions: the Tohoku, Kanto and Kyushu districts of Japan. Genetic diversity values (Nei's gene diversity, h) within each SU‐S population ranged from h = 0.125 to h = 0.235. The average genetic diversity within the SU‐S populations was H_S = 0.161, and the total genetic diversity was H_T = 0.271. Although the H_S of the SU‐R populations (0.051) was lower than that of the SU‐S populations, the H_T of the SU‐R populations (0.202) was comparable with that of the SU‐S populations. Most of the genetic variation was found within the region for both the SU‐S and SU‐R populations (88% of the genetic variation respectively). Two of the SU‐R populations showed relatively high genetic diversity (h = 0.117 and 0.161), which were comparable with those of the SU‐S populations. In contrast, the genetic diversity within four SU‐R populations was much lower (from h = 0 to 0.018) than in the SU‐S populations. The results suggest that selection by sulfonylurea herbicides has decreased genetic diversity within some SU‐R populations of S. juncoides. The different level of genetic diversity in the SU‐R populations is most likely due to different levels of inbreeding in the populations.     

Genetic diversity of the weed species,Stellera chamaejasme,in China inferred from amplified fragment length polymorphism analysis

Stellera chamaejasme is a perennial weed with a wide geographic range that is found from the Altai of eastern Russia, northern China and Mongolia southwards as far as the western Himalayas of the Qinghai–Tibet and Yungui Plateaus. The genetic diversity and population structure of 17 populations of S. chamaejasme, represented by 349 individuals, were assessed by using amplified fragment length polymorphism markers. The results showed a relatively high level of genetic variation at the species level. The proportion of total diversity among populations was 0.4370, suggesting significant genetic differentiation and a low gene flow among the populations of this species. The Mantel test indicated that genetic differentiation among populations was significantly correlated with geographic distance. Genetic drift through range expansion and a low gene flow among populations might result in a lower diversity in peripheral populations, compared to central populations. A Bayesian analysis revealed two potential gene pools in S. chamaejasme, which was confirmed by neighbor‐joining clustering and principal coordinate analysis. These results demonstrate that it is necessary to develop suitable biocontrol agents for populations with different gene pools.     

Genetic diversity of Orobanche cumana populations from Spain assessed using SSR markers

Orobanche cumana (sunflower broomrape) is found in Spain as an allochthonous species parasitising exclusively sunflower. For many years, it was distributed in the Guadalquivir Valley and Cuenca province, but in recent years, it has spread to new areas. The objective of this research was to study genetic diversity of O. cumana populations from Spain using robust co‐dominant molecular markers. Cluster analysis on a set of 50 populations using 15 microsatellite markers revealed the existence of two distant gene pools, one in Cuenca province and another one in the Guadalquivir Valley. Within each gene pool, both inter‐ and intrapopulation variability were extremely low. This population structure probably reflects a founder effect, with the two genetically distant gene pools deriving from separate introduction events. Different races occurred within the same gene pool, suggesting that current races might have evolved through mutation from a common genetic background. Most of the populations from new areas were identical to the populations from the Guadalquivir Valley. Only a few populations showed larger intrapopulation variation. In these cases, our results suggested the co‐existence of both gene pools within the same population, as well as the occurrence of genetic recombination between them. Genetic recombination between distant gene pools is an important mechanism for creating new variation, which might also have an effect on race evolution. These results will contribute to the establishment of improved crop breeding and management strategies for O. cumana control.     

Microsatellite variability of sulfonylurea‐resistant and susceptible populations of Schoenoplectus juncoides (Cyperaceae) in Kinki,Japan

Schoenoplectus juncoides is one of the most harmful weeds found in East Asian paddy fields. Recent emergence of biotypes that are resistant to the herbicide sulfonylurea (SU) has made weed control difficult. To examine the effect of the evolution of this herbicide resistance on genetic diversity within local populations, we investigated microsatellite variability within and among paddy field populations of S. juncoides in Kinki, Japan. In vivo assay of acetolactate synthase activity and root elongation assay in the presence of SU revealed that of 21 populations, five were sulfonylurea‐susceptible (SU‐S) and eight were completely sulfonylurea‐resistant (SU‐R). The remaining eight populations were a mixture of SU‐S and SU‐R individuals. The average gene diversity for SU‐R populations (H_S = 0.168) was lower than those for SU‐S (H_S = 0.256) and mixed (H_S = 0.209) populations, but the difference was not significant. This indicates that positive selection for SU‐R phenotype did not cause a genome‐wide reduction in genetic diversity. Genetic differentiation among S. juncoides populations was higher than that observed for most weed species studied previously. Although populations in neighbouring paddy fields showed a high level of differentiation, Bayesian clustering analyses suggested that some level of gene flow occurs among them and that the genetic exchange or colonisation between neighbouring populations could contribute to the geographical expansion of the resistant allele.     

Morphological variation of Solanum elaeagnifolium in south‐eastern Australia

Solanum elaeagnifolium (silverleaf nightshade) is an invasive perennial weed in Australia, with aerial growth commencing in spring from either the perennial root system or the soil seedbank, with senescence occurring in autumn. A total of 642 S. elaeagnifolium individuals were collected at flowering from 92 locations in south‐eastern Australia to study morphological variation and its implications for management. Large morphological variation was found between individuals from different locations. Leaf length, width and area ranged from 1.44 to 10.6 cm, 0.39 to 4.09 cm and 0.41 to 25.8 cm² respectively. Plants from higher rainfall regions were significantly taller and had larger leaves, suggesting a possible correlation between rainfall and morphology. Scanning electron microscopy comparison of leaf surfaces showed lower trichome and stomatal densities on the adaxial surface (67.0 ± 3.3 trichomes mm^?2 and 603.4 ± 29.2 stomata mm^?2 respectively) than on the abaxial surface (131.9 ± 7.2 trichomes mm^?2 and 813.7 ± 30.5 stomata mm^?2 respectively). The morphological plasticity of S. elaeagnifolium highlighted in this study could probably contribute to its adaptability and partly explain its establishment and continuing expansion in Australia.     

Genetic diversity of the declining arable plant Centaurea cyanus: population fragmentation within an agricultural landscape is not associated with enhanced spatial genetic structure

Agricultural intensification has recently resulted in the decrease in frequency and abundance of arable weed species. This includes the previously widespread Centaurea cyanus, whose populations are now fragmented and infrequent in western Europe. The consequences of habitat modification and fragmentation in terms of genetic diversity of the remaining populations have not yet been addressed. We used ten microsatellite markers to assess the genetic diversity and genetic structure of populations contained in an agricultural landscape in north‐eastern France. The ten microsatellites were all highly polymorphic. Centaurea cyanus appears to be a genetically variable species, with high levels of genetic diversity within each cultivated field. Genetic structure was investigated using a Bayesian method. The partitioning of the genetic variation into three clusters was not associated with sampling locations, and most individuals were admixed. These results suggest that the cornflower populations investigated may have multiple origins in the past and that genetic variation has been reshuffled by human transportation of seeds. Thus, anthropogenic dispersal associated with farming activities is probably a major factor driving the structure of genetic diversity in arable land plants. Despite low levels of genetic differentiation between populations, fine‐scale spatial genetic structure was observed within populations, suggesting limited local dispersal. We conclude that in areas where C. cyanus has become rare, the recent fragmentation of populations may in the future cause a loss of genetic diversity and even extinction.     

Pathotypic and genetic diversity in the population of Rhizoctonia solani AG1‐IA causing rice sheath blight in China

Sheath blight, caused by Rhizoctonia solani AG1‐IA, is one of the most serious diseases of rice. In this study, a total of 175 isolates of R. solani AG1‐IA were collected from five rice‐growing regions in China. Pathogenicity tests revealed that all isolates were virulent to five cultivars with different levels of resistance at the rice seedling stage in the greenhouse. There was considerable variation in aggressiveness, and the isolates were classified into three pathotypes based on disease severity, with moderately virulent isolates prevalent in the population. Forty‐three haplotypes were identified based on ITS sequencing, and 39 haplotypes were distinct among isolates. There were high levels of haplotype diversity and nucleotide diversity within the populations of R. solani AG1‐IA. High gene flow (Nm = 1·63–5·22) was detected, consistent with relatively low differentiation between pairs of populations. Five populations were divided into two distinct clusters by the unweighted pair group method with arithmetic mean (UPGMA), and no spatial population differentiation was discernible. The majority (97·8%) of genetic diversity was distributed among isolates within populations, with only 2·2% of the genetic diversity attributed to differences among populations. The star‐like shape of the haplotype network provided evidence of signatures of population expansion in recent history. No significant relationships were found between the genetic diversity and aggressiveness or geographic origin among populations of R. solani AG1‐IA. These results highlight that the population characteristics of R. solani AG1‐IA should be taken into account in evaluating the germplasm resistance of rice cultivars to sheath blight.     

Genetic diversity of East and West African Striga hermonthica populations and virulence effects on a contrasting set of sorghum cultivars

The root hemiparasite Striga hermonthica causes very significant yield loss in its dryland staple cereal host, Sorghum bicolor. Striga‐resistant sorghum cultivars could be an important part of integrated S. hermonthica control. For effective resistance breeding, knowledge about the diversity of the parasite is essential. This study aimed (i) to determine the genetic diversity within and between seven S. hermonthica populations from East and West Africa using 15 microsatellite markers and (ii) to assess the virulence and host–parasite interactions of these Striga populations grown on 16 diverse sorghum genotypes in a glasshouse trial. Most of the genetic variance (91%) assessed with microsatellite markers occurred within S. hermonthica populations. Only a small portion (8%) occurred between regions of origin of the populations. A positive correlation (R² = 0.14) between pairwise geographic and genetic distances reflected the slightly increasing differentiation of S. hermonthica populations with increasing geographic distance. East African S. hermonthica populations, especially those from Sudan, had significantly greater average infestation success across all sorghum genotypes than West African populations. Some specific host–parasite interaction effects were observed. The high genetic variation among individuals of each S. hermonthica population underlines the high potential adaptability to different hosts and changing environments. This points to the need to manage sorghum resistance alleles in space and time and to employ resistant varieties as part of integrated S. hermonthica control, so as to hinder the parasite overcoming resistance.     

Genotypic diversity and migration of clonal lineages of Botrytis cinerea from chickpea fields of Bangladesh inferred by microsatellite markers

An analysis of allelic diversity at nine microsatellite loci provided an insight into the population structure of Botrytis cinerea from four fields (sampled in 2003 and 2004) that represented important regional locations for chickpea production in Bangladesh. Although three populations were limited by sample size after clone‐correction, a total of 51 alleles were amplified among 146 B. cinerea isolates from Bangladesh, which revealed a high amount of within‐population and overall genetic diversity (H_S = 0·48 and H_T = 0·54, respectively). The percentage of maximal genotypic diversity (G) ranged between populations (G = 23–40), with a total of 69 haplotypes detected (G = 25). Bayesian cluster analysis depicted two major clusters distributed among the four Bangladesh populations, indicating population admixture from two origins that have spread throughout these regions. Genotype flow between regions was detected and indicated the spread of clonal lineages, consistent with relatively low differentiation among the four populations (mean G_ST = 0·1, P < 0·05). These results highlighted the potential threat of host resistance breakdown as a result of considerable genetic diversity, genotype flow and the evolutionary potential of B. cinerea.     

Spatial genetic structure and dispersal of the cacao pathogen Moniliophthora perniciosa in the Brazilian Amazon

Moniliophthora perniciosa is the causal agent of witches’ broom in Theobroma cacao (cacao). Three biotypes of M. perniciosa are recognized, differing in host specificity, with two causing symptoms on cacao or Solanaceae species (C‐ and S‐biotypes), and the third found growing endophytically on lianas (L‐biotype). The objectives of this study were to clarify the genetic relationship between the three biotypes, and to identify those regions in the Brazilian Amazon with the greatest genetic diversity for the C‐biotype. Phylogenetic reconstruction based on the rRNA ITS regions showed that the C‐ and S‐biotypes formed a well‐supported clade separated from the L‐biotype. Analysis of 131 isolates genotyped at 11 microsatellite loci found that S‐ and especially L‐biotypes showed a higher genetic diversity. A significant spatial genetic structure was detected for the C‐biotype populations in Amazonia for up to 137 km, suggesting ‘isolation by distance’ mode of dispersal. However, in regions containing extensive cacao plantings, C‐biotype populations were essentially ‘clonal’, as evidenced by high frequency of repeated multilocus genotypes. Among the Amazonian C‐biotype populations, Acre and West Amazon displayed the largest genotypic diversity and might be part of the centre of diversity of the fungus. The pathogen dispersal may have followed the direction of river flow downstream from Acre, Rondônia and West Amazon eastward to the rest of the Amazon valley, where cacao is not endemic. The Bahia population exhibited the lowest genotypic diversity, but high allele richness, suggesting multiple invasions, with origin assigned to Rondônia and West Amazon, possibly through isolates from the Lower Amazon population.     

Virulence and Molecular Diversity within Colletotrichum lindemuthianum Isolates from Andean and Mesoamerican bean Varieties and Regions

Virulence on a standard set of 12 common bean differential varieties, DNA sequence of repetitive-elements (Rep-PCR) and random amplified microsatellites (RAMS) were used to assess the genetic variability of 200 Colletotrichum lindemuthianum isolates collected from Andean and Mesoamerican bean varieties and regions. High levels of pathotypic (90 pathotypes) and genetic diversity (0.97) were identified among 200 isolates, revealing that C. lindemuthianum is a highly diverse pathogen. Although a significant number of pathotypes were common to Andean and Mesoamerican regions, many more were only found in the Mesoamerican region. Cluster analysis of virulence and molecular data did not separate isolates into groups that were structured with common bean gene pools. No genetic differentiation (G _ST=0.03) was apparent between Andean and Mesoamerican isolates of C. lindemuthianum. The diversity exhibited by C. lindemuthianum does not appear to cluster according to common bean gene pools, and the high diversity found in the Mesoamerican region seems to indicate that C. lindemuthianum originated and was disseminated from this region. Due to the high genetic variation exhibited by C. lindemuthianum, stacking major resistance genes appears to be the best option for developing cultivars with durable anthracnose resistance.     

Genetic structure of the fungal grapevine pathogen Eutypa lata from four continents

The generalist ascomycete fungus Eutypa lata causes Eutypa dieback of grapevine (Vitis vinifera) worldwide. To decipher the cosmopolitan distribution of this fungus, the population genetic structure of 17 geographic samples was investigated from four continental regions (Australia, California, Europe and South Africa), based on analysis of 293 isolates genotyped with nine microsatellite markers. High levels of haplotypic richness (R = 0·91–1) and absence of multilocus linkage disequilibrium among loci supported the preponderance of sexual reproduction in all regions examined. Nonetheless, the identification of identical multilocus haplotypes with identical vegetative compatibility groups, in some vineyards in California and South Africa, suggests that asexual dispersal of the fungus among neighbouring plants could be a rare means of disease spread. The greatest levels of allelic richness (A = 4·89–4·97) and gene diversity (H = 0·66–0·69) were found in Europe among geographic samples from coastal areas surrounding the Mediterranean Sea, whereas the lowest genetic diversity was found in South Africa and Australia (A = 2·78–3·74; H = 0·49–0·57). Samples from California, Australia and South Africa, which had lower genetic diversity than those of Europe, were also characterized by demographic disequilibrium and, thus, may represent founding populations of the pathogen. Low but significant levels of genetic differentiation among all samples (D_EST = 0·12, P = 0·001; F_ST = 0·03, P = 0·001) are consistent with historical gene flow preventing differentiation at continental scales. These findings suggest that global, human‐mediated spread of the fungus may have resulted in its current global distribution.     

Genetic Structure of Mycosphaerella graminicola Populations from Iran, Argentina and Australia

Restriction fragment length polymorphism (RFLP) markers were used to assess the genetic structure of populations of Mycosphaerella graminicola collected from wheat fields. A total of 585 isolates representing 10 field populations were sampled from Iran, Argentina and Australia. The genetic structure of M. graminicola populations from Iran and Argentina is described for the first time. Results were compared to previously investigated populations from Israel, Uruguay and Australia. Populations from Iran exhibited high clonality and low gene diversity, suggesting an inoculation event. Populations from uninoculated fields in Argentina had gene and genotype diversities similar to previously described European and North American populations. Genotype diversity was high for populations from Australia and tests for multilocus associations were consistent with sexual recombination in these populations. Gene diversity was low and fixed alleles were found for several loci. These findings are consistent with a relatively small founding population for Australia. These 10 new populations were integrated into a genetic distance comparison with 13 global populations that were characterized earlier.     

Genetic structure of Verticillium dahliae isolates infecting olive trees in Tunisia using AFLP,pathogenicity and PCR markers

Since 2006, verticillium wilt of olive induced by Verticillium dahliae has caused considerable economic losses in olive orchards in Tunisia. The genetic structure of V. dahliae isolates collected from different olive growing regions was investigated using virulence tests, vegetative compatibility grouping (VCG) and amplified fragment length polymorphism (AFLP) analyses. In total, 42 isolates of V. dahliae from diseased olive trees were tested. Cluster analysis and principal coordinate analysis revealed that geographic origin was the main factor determining the genetic structure of V. dahliae populations and both methods indicated a genetic separation between the central and coastal isolates. Isolates were divided into two major groups: the AFLP‐I group included all isolates from Sidi Bouzid, Kairouan, Kasserine and Sfax (centre of the country) and the AFLP‐II group included isolates from Monastir, Zaghouane, Sousse, Mahdia (coastal region), and two isolates from Sfax. Analysis of the molecular variance (amova ) indicated a significant level of genetic differentiation among (76%) and within (23%) the two populations. Analyses of both the defoliating (D) and non‐defoliating (ND) pathotypes and VCG markers indicated that most of the isolates belong to VCG 2A and 4B/ND pathotype. The disease severity was highly variable among the isolates tested (P < 0·05) with no evidence of association between aggressiveness and geographical origin of the isolates. Overall, results of this study revealed a clear association between the genetic diversity of the isolates and their geographic origin, but not between genetic diversity and virulence patterns.     

Identification of Neofabraea species causing bull's eye rot of apple in Poland and their direct detection in apple fruit using multiplex PCR

Based on partial sequence analysis of the β‐tubulin gene, 19 isolates of fungi causing bull's eye rot on apple in Poland were classified into species: Neofabraea alba, N. perennans and N. kienholzii. To the authors’ knowledge, the detection of N. kienholzii is the second in Europe and the first in Poland. Species affiliation of these fungi was confirmed by a new species‐specific multiplex PCR assay developed on the basis of previously published methods. The new protocol allowed for the specific identification of bull's eye rot‐causing species, both from pure cultures and directly from the skin of diseased or apparently healthy apples. In 550 samples of diseased fruits collected from nine cold storage rooms located in three regions of Poland, in 2011 and 2012, N. alba was detected as the predominant species causing bull's eye rot, occurring on average in 94% of the tested samples. Neofabraea perennans was found in a minority of apple samples, N. kienholzii was found only in two apple samples, while N. malicorticis was not detected in any sample tested. In tests on 120 apparently healthy fruits, only N. perennans was detected in a single sample. The results of genetic diversity analyses of bull's eye rot‐causing fungi based on the β‐tubulin gene sequence and an ISSR (inter‐simple sequence repeat) PCR assay with two primers were consistent, showing the expected segregation of tested isolates with respect to their species boundaries. However, the genetic distance between N. perennans and N. malicorticis was very low, as reported previously.     

Evaluation of Galium species and populations using morphological characters and molecular markers

Three Galium species are believed to be present across western Canada: Galium aparine, Galium spurium and Galium boreale. Galium spurium and G. aparine are very difficult to distinguish morphologically, which is problematic for crop consultants and weed surveyors, and could have implications for control measures. Molecular techniques could potentially make identification easier and more rapid than using chromosome counts, as is currently done. The objective of this study was to identify morphological traits and/or genetic polymorphisms capable of species differentiation. To this end, Galium seed of unknown speciation were collected from nine field populations across western Canada and, along with two reference samples of G. spurium and G. aparine, were characterised for both morphological traits and their ribosomal ITS1‐5.8S‐ITS2 genomic sequence. In addition, single nucleotide polymorphism variation within the highly conserved 5.8S ribosomal RNA gene was identified that could consistently differentiate Galium species. Sequence analysis of the ITS1‐5.8S‐ITS2 region of field collections from western Canada indicated that all samples were G. spurium and all were highly related to each other. These results were supported by a distinct lack of variation in morphological traits, as nearly all plant traits measured did not differ between populations. This suggests that all sampled populations, and perhaps most of the Galium populations across western Canada, are derived from a single species, G. spurium.     

Solanum elaeagnifolium,a potential source of Potato virus Y (PVY) propagation*

In the context of an epidemiological study on Potato virus Y (PVY) in potato crops, Solanum elaeagnifolium Cav. was included in the weeds prospected. Surveys were carried out in four seed potato areas: Cap Bon, Manouba, Jendouba and Kairouan. S. elaeagnifolium was found in all areas, except Cap Bon. Virus‐like symptoms were observed on some S. elaeagnifolium plants in the field, i.e. leaf mottling and curling. Aphids were collected on these plants and were identified as Myzus persicae and Aphis fabae, both known to colonize potatoes and to transmit the standard PVY^N isolate with transmission efficiencies of 95% and 43%, respectively. Forty‐seven plant samples were tested with ELISA for the presence of PVY. Positive reactions were obtained from 2/6, 5/18, 8/23 samples collected in Manouba, Jendouba and Kairouan, respectively. Virus transmission was carried out using M. persicae as vector from two samples of each region onto plantlets of Nicotiana tabacum cv Xanthi. All inoculated plantlets displayed typical symptoms of the PVY^N strain group, confirmed by serological testing using specific antibodies. This is the first report of a PVY natural infection on S. elaeagnifolium in Tunisia. The abundance of this weed, its over‐wintering status and the high rate of PVY‐infected plants (31.9%) allow us to deduce that S. elaeagnifolium must be considered a reservoir species of PVY under natural conditions in Tunisia and probably in other Mediterranean countries. The presence of efficient aphid vectors of PVY on this weed in crops is additional evidence that S. elaeagnifolium may become a problem by acting as a source plant for PVY spread in potato crops.     

Genetic diversity and population structure of Striga hermonthica populations from Kenya and Nigeria

Striga hermonthica is a parasitic weed that poses a serious threat to the production of economically important cereals in sub‐Saharan Africa. The existence of genetic diversity within and between S. hermonthica populations presents a challenge to the successful development and deployment of effective control technologies against this parasitic weed. Understanding the extent of diversity between S. hermonthica populations will facilitate the design and deployment of effective control technologies against the parasite. In the present study, S. hermonthica plants collected from different locations and host crops in Kenya and Nigeria were genotyped using single nucleotide polymorphisms. Statistically significant genetic differentiation (F_ST = 0.15, P = 0.001) was uncovered between populations collected from the two countries. Also, the populations collected in Nigeria formed three distinct subgroups. Unique loci undergoing selection were observed between the Kenyan and Nigerian populations and among the three subgroups found in Nigeria. Striga hermonthica populations parasitising rice in Kenya appeared to be genetically distinct from those parasitising maize and sorghum. The presence of distinct populations in East and West Africa and in different regions in Nigeria highlights the importance of developing and testing Striga control technologies in multiple locations, including locations representing the geographic regions in Nigeria where genetically distinct subpopulations of the parasite were found. Efforts should also be made to develop relevant control technologies for areas infested with ‘rice‐specific’ Striga spp. populations in Kenya.     

Biology,distribution and impacts of silverleaf nightshade (Solanum elaeagnifolium Cav.)*

Silverleaf nightshade, Solanum elaeagnifolium, is listed as a noxious weed in its native range (Americas) and as an invasive alien plant in many countries across the world. Its local pattern of distribution in the EPPO region indicates that it is still in an establishment phase. S. elaeagnifolium invasiveness could be related to several biological traits: copious production of sexual and asexual propagules, its facility for long‐distance dispersion, its ability to endure considerable drought and to dominate shallow‐rooted vegetation, especially during summer dry periods, and its capacity to suppress more valuable species because it is unpalatable and toxic to cattle. Invasion of the Mediterranean semi‐arid region by S. elaeagnifolium was mainly facilitated by irrigation and animal production. Low moisture stress may favour this invasive species and sheep are an important pathway for its long‐distance dispersal. Once established, it is one of the most difficult weeds to eradicate because of its network of creeping horizontal and deep vertical roots. Its phenotypic plasticity enables it to adopt a rosette‐like growth pattern to escape control by repeated slashing. Thus, S. elaeagnifolium monitoring in the EPPO region is vital in order to contain established populations and prevent invasion.