Clonal individuals from 16 hemp dogbane populations with phenotypic variation were analyzed using isozyme and randomly amplified polymorphic DNA (RAPD) analysis. Plants originated from populations in Michigan and Illinois. Three known Apocynum species, spreading dogbane, hemp dogbane, and prairie dogbane, were evaluated. Genetic distance among populations was more pronounced with isozyme analysis compared to RAPD analysis. The combined isozyme and RAPD analysis data separated spreading dogbane from all other plants analyzed. Genetic variation was present among the 16 hemp dogbane populations, but was less than expected based on the phenotypic variation present among the collections. The short genetic distance between the 16 hemp dogbane collections and the three Apocynum species suggests that variation among populations of hemp dogbane may be from outcrossing with other closely related Apocynum species. Isozyme and RAPD analyses were also conducted on plants from two populations in Michigan to determine the level of genetic variation among plants within the same population. Genetic analysis revealed that one population was entirely clonal, while the other population was a mixture of clonal and segregating plants.

The identities of two novel perennial nutsedge biotypes collected near Bakersfield, CA, were assessed using isozyme and random-amplified polymorphic deoxyribonucleic acid markers in conjunction with morphological analysis. The two biotypes, designated as CK (Cyperus rotundus cv. ‘Kempeni’) and CR (Cyperus esculentus cv. ‘Robusta’), morphologically resemble purple nutsedge and yellow nutsedge, respectively. Plants from both biotypes exhibited more prolific growth than the typical forms and possessed some traits that are not characteristic of the species they resemble. The morphological study was conducted on a total of 15 purple nutsedge, yellow nutsedge, CK, and CR populations collected in the first year and on 20 additional nutsedge populations were collected in the second year. The genetic analysis was performed on populations from the first year only. In general, there was agreement among the results obtained from the morphometric, isozymatic, and deoxyribonucleic acid studies. Populations of CR clustered with yellow nutsedge populations, indicating that CR is within the normal range of variation of this species and may represent a new introduction. Populations of CK, however, were distinct from both purple nutsedge and yellow nutsedge populations. Considering the low level of genetic variation reported in purple nutsedge and its strict vegetative mode of reproduction, CK might represent a sexually reproducing ecotype of purple nutsedge or a hybrid with yellow nutsedge.

Genetic diversity and genetic variation of 240 adult plants of four tea populations in Hunan – Camellia sinensis var. sinensis, C. sinensis var. assamica cv. Duntsa, C. ptilophylla and C. sinensis var. assamica cv. Jianghua – were studied by rapid amplification of polymorphic DNA (RAPD) markers. The results showed 226 loci using 21 random primers (10 bp), of which 201 (88.9%) were polymorphic. The genetic diversity analysis indicated that Shannon's index was 0.43; 74.7% of which was within-population genetic diversity while 25.3% was among-population variation. The gene diversity indexes of total populations (HT), within populations (HS) and among populations (HST) were, respectively, 0.37, 0.28 and 0.09. The coefficient of gene differentiation (GST) among populations was 0.23, indicating a 76.7% variation within populations and 23.3% among populations. These results displayed a rich within-population genetic variation, as in Shannon's diversity index. Interpopulation gene flow (Nm) was 0.74, which indicates the limited genetic exchange between populations.

Neospora caninum is a protozoan parasite that causes bovine abortion. The epidemiology of N.caninum is poorly understood and little is known about the genetic diversity of the parasite, or whether individual isolates differ in virulence. Such diversity may, among other factors, underlie the range of pathologies seen in cattle. In this study we analysed biological and genetic variation in 6 isolates of N. caninum originating from canine and bovine hosts by measurement of growth rate in vitro, Western blotting and random amplification of polymorphic DNA (RAPD). This comparative analysis of intra-species diversity demonstrated that heterogeneity exists within the species. The relative growth rate in vitro, as assessed by 3[H]uracil uptake, showed significant variation between isolates. However, no significant differences were detected between the antigenic profiles of each isolate by Western blotting. RAPD-PCR was performed on DNA from the 6 Neospora isolates; 3 strains of Toxoplasma gondii, Sarcocystis sp. and Cryptosporidium parvum were also analysed. Twenty-six RAPD primers gave rise to 434 markers of which 222 were conserved between all the Neospora isolates and distinguished them from the other Apicomplexa. An additional 54 markers were unique for Neospora but were polymorphic within the species and able to differentiate between the individual isolates. The RAPD data were subjected to pair-wise similarity and cluster analysis and showed that the Neospora isolates clustered together as a group, with T. gondii as their nearest neighbour. N. caninum isolates showed no clustering with respect either to host or geographical origin. The genetic similarity between Neospora isolates from cattle and dogs suggests that these hosts may be epidemiologically related, although further analysis of bovine and canine field samples are required. The genetic and biological diversity observed in this study may have important implications for our understanding of the pathology and epidemiology of neosporosis.

The Leishmania donovani complex is considered to be composed of 3 species; L. donovani, L. infantum and L. chagasi, although this classification has been challenged. Genotypic relationships within the complex were evaluated at different levels by: binding of the probe Lmet9, specific for L. chagasi and Old World Leishmania spp.; partial sequencing of a constitutive major surface protease single gene (mspC) and random amplification of polymorphic DNA (RAPD). The Old World Leishmania spp. and the L. donovani complex have a monophyletic origin. Leishmania chagasi clearly belongs to the L. donovani complex but it is indistinguishable from L. infantum, which suggests introduction of L. chagasi into the New World in recent history. Leishmania infantum/L. chagasi was identified as a monophyletic group within the L. donovani complex but L. donovani may be paraphyletic. Diversity within L. donovani is substantial and phylogeographical patterns of association were found.