DNA-based molecular markers may provide information about introduced weedy species that would be useful in biological weed control efforts. Chloroplast DNA restriction fragment length polymorphisms (cpDNA RFLP) and random amplified polymorphic DNA (RAPD) analysis are two DNA-based marker techniques that can provide estimates of genetic variation in native and introduced populations of weedy species. Profiles provided by these techniques could furnish the necessary information to determine the geographic origins of introduced species and provide evidence for multiple introductions. Although DNA-based markers would not necessarily identify the genetic basis for host-pest compatibility, they would enable identification of specific host genotypes. Current criteria for selecting a weedy species as a target for biological control are primarily political and economic. The importance of genetic diversity and population structure in determining the vulnerability of plant populations to insects or diseases has not been fully appreciated. Estimates of genetic diversity based on DNA marker analysis could be used as one criteria for determining which plants are targeted for biological control. The success of biological weed control efforts has been limited by the high levels of genetic diversity occurring in target weed specks and the lack of biocontrol agent and target weed compatibilities. DNA-based markers may be used to increase our understanding of these factors and contribute to the success of biological weed control by helping to target the most vulnerable species and provide more realistic expectations of the potential for success given available resources.

Eight taxa have recently been proposed as being encompassed by the genus Trichinella on the basis of allozyme and biological data. In this paper we show that an analogous 8 taxon structure for this genus results from the random amplified polymorphic DNAs (RAPDs). Five 10-mer or 20-mer primers were used under different polymerase chain reaction (PCR) conditions to produce multiband RAPD fingerprints from muscle larvae of 40 isolates of Trichinella spp. The resulting RAPD data were analysed following the numerical taxonomic approach, and the resulting classification was compared to that derived from allozyme data. The agreement found between allozymes and RAPDs, while supporting the polyspecific structure of the genus Trichinella, confirms the potential of RAPDs as a tool for the detection of cryptic species. The selected primers were tested on individual muscle larvae in an attempt to standardize a RAPD assay for the routine identification of the 8 taxa of Trichinella. Only 1 of the 5 primers yielded reproducible fingerprints from the single larvae. Using this primer, the 5 species and the 3 other taxa of the genus Trichinella can be identified in a single assay without the need for massive in vivo parasite production.

Random amplified polymorphic DNA (RAPD) offers a potential basis for the development of a diagnostic assay to differentiate the potato cyst nematode species Globodera rostochiensis and G. pallida. Nine decamer primers have been tested for their ability to amplify species-specific DNA sequences. Primer OPG-05 produced 2 discrete DNA fragments, which were consistently present in 5 G. rostochiensis populations and absent in 5 G. pallida populations. These fragments were detectable in single females as well as in single 2nd-stage juveniles. Their amplification is extremely efficient, and reproducible over a wide range of template concentrations. One-fifth of a single juvenile is sufficient to generate reproducible RAPD markers. The amplification from single juveniles requires no DNA isolation. The use of a crude homogenate does not impair the polymerase chain reaction.

The technique of Random Amplified Polymorphic DNA (RAPD) PCR has been used to detect DNA polymorphisms among Toxoplasma gondii strains. Seven arbitrary oligonucleotides (10-mer) were used as primers to amplify total genomic DNAs and significant genetic heterogeneity was detected among 11 T gondii strains with different virulence for mice. The polymorphisms observed allowed relationship dendrograms of T. gondii strains to be constructed by PHYLIP and PAUP analyses. The genetic relationships of the T. gondii strains generated by 2 analyses using completely different assumptions were similar. Both analyses revealed 2 groups of T. gondii strains, one formed by the 6 virulent strains and the other formed by the 5 avirulent strains. This suggests that the genus Toxoplasma may actually contain 2 groups, correlated with their virulence, which have probably evolved independently following their initial separation. Significant polymorphisms were also detected between 2 different laboratory stocks of the T. gondii RH strain.

This study analyses the different populations of Trypanosoma brucei spp. which may coexist within the midgut of wild tsetse flies (Stevens et al. 1994). Cloned trypanosome populations characterized by multilocus enzyme electrophoresis (MLEE) were further analysed by the random amplified polymorphic DNA (RAPD) technique, allowing detection of genetic variation at a finer level than that possible by MLEE. Genetic distance matrices derived from the results of each of the two biochemical methods were calculated and compared using a computer program based on the method of Mantel (1967). The observed correlation was used to investigate the degree of linkage disequilibrium (LD) in the data, association between unrelated polymorphic markers providing a measure of the departure from panmixia. The potential of each biochemical method to detect linkage was evaluated by an extended Mantel test. The MLEE/RAPD correlation test evidenced significant LD within the population, suggesting a predominantly clonal method of reproduction for these West African trypanosomes. Analysis of RAPD data by the extended Mantel test also showed significant LD, while the results with MLEE data were less conclusive, providing an indication of the relative potential of the two techniques to detect fine genetic variation.

The random amplified polymorphic DNA (RAPD) technique was successfully used to produce genetic fingerprints distinguishing between Trichinella spiralis and Trichinella britovi. The same patterns were obtained from purified and crude DNA preparations of pooled and single muscle larvae. RAPD fingerprinting was applied to muscle larvae preserved under different conditions and recovered from different hosts. Larvae recovered from fresh and frozen meat and stored at – 20 °C for a long time or under 70% ethyl alcohol at room temperature for 30 d gave good and reproducible results. Single larvae recovered from a naturally infected wild boar and from a human biopsy gave fingerprints congruent to those obtained from T. britovi reference strains. The results prove that RAPD analysis is a quick method to distinguish between the autochthonous Trichinella species of Central-Southern Europe in less than 1 d after the detection of the infection. If necessary, the biological material can be frozen or stored under 70% ethyl alcohol at room temperature and sent to laboratories able to perform the RAPD analysis. The RAPD technique requires no prior knowledge of the molecular biology of the organism to be investigated and therefore appears to be a promising tool in parasitology for the identification of sibling species.

In order to protect and develop valuable snappers (Lutjanus spp.), genetic diversity and molecular markers of five species (Lutjanus vitta, L. fulvus, L. fulviflamma, L. sebae and L. stellatus) were detected and analysed using random amplified polymorphic DNA (RAPD) and simple sequence repeats (SSR) techniques. The polymorphic loci ratio (P) (86.00–92.11%), the mean intraspecies genetic distances (D) (0.1775–0.3431) and the intraspecies genetic diversity indexes (Hi) (0.1022–0.1634) were calculated using the RAPD technique. The genetic diversities of L. fulviflamma and L. vitta were richest in terms of P, and D and Hi, respectively. The results of SSR showed that low effective numbers of alleles (1.7893–3.6591), medium average heterozygosities (0.332–0.676) and medium polymorphism information contents (PIC) (0.302–0.641) occurred in five species of snappers, indicating comparatively rich genetic diversity among these fish. Nine molecular markers in the products amplified by primers OPA8 and OPP10, and six molecular markers in 11 microsatellite loci were found to be useful as specific markers to identify five species of snappers. Two neighbour-joining (NJ) dendrograms based on the results of RAPD and SSR suggested that L. stellatus and L. sebae are closely related and clustered in one branch, with L. vitta, L. fulviflamma and L. fulvus in the other.