Genetic variation of morphological and phenological characters of yellow nutsedge (Cyperus esculentus L.) from California was investigated and compared with isozyme data from the same populations. The importance of collection location, individual genotype, and isozyme genotype to phenotypic characteristics was evaluated. Analyses were conducted on 20 individuals collected from each of 10 widely separated populations in California. Replicate plants were started by tubers, grown in pots buried outdoors, and measured during the period from planting through flowering. Results showed that yellow nutsedge is variable across its range in California in all measured traits, including days to sprouting and flowering, height, rachis number and length, aboveground biomass, tuber weight, number of rays, ray length, number of spikelets per ray, as well as spikelet length and width. Population (collection location) was a larger variance component than genotype (individuals over all locations). As found in isozyme analysis, relatively more variation was found among than within populations, typical of clonally reproducing species. Overall, more variation was found in quantitative traits than in isozymes. The level of variation, based on coefficients of variation for each character and population, was similar within populations and not clearly related to cropping history or climate at each site. The two most common isozyme genotypes in the collection differed in four characters: date of emergence, weight of 10 tubers, rachis number, and mean ray length, which may represent different adaptive responses to cultural practices. These results indicate that isozymes do not reflect the high level of genetic and adaptive diversity of yellow nutsedge. Factors that are likely to determine the patterns of variation in this species include breeding system (vegetative reproduction), founder effects, polyploidy, and homogeneity of the agricultural environmental.

Witchweed, [Striga asiatica (L.) Kuntze5 STRLU], an important parasitic weed throughout much of the old world, occurs as a recent (30 yr) introduction in a limited region in North and South Carolina. Reproduction in this population has been shown to occur primarily through self-pollination of flowers. Genetic diversity in two populations from this region was assessed, utilizing starch gel electrophoresis and staining of enzymes. An average of 64 individuals was observed to be monomorphic at an estimated minimum of 32 genetic loci coding 18 enzyme systems. This lack of polymorphism is attributable to the probable founding of the population by one or a few individuals coupled with the predominantly autogamous breeding system.

A high level of genetic purity in crop varieties must be achieved and maintained for agronomic performance as well as to encourage investment and innovation in plant breeding and to ensure that the improvements in productivity and quality imparted by breeders are delivered to the farmer and, ultimately, to the consumer. Traditionally, morphological comparisons have formed the basis for genetic purity evaluations. However, replicated field observations are time-consuming, expensive and unreliable. Morphology cannot provide information on the purity of specific genetic attributes that relate to grain quality or to pest or herbicide resistance bred into varieties. Biochemical assays, including isozymes, can distinguish varieties within several species. Isozymes have been routinely used in checking seed-lot purity in maize (Zea mays L.) for the past 20 years. Newer DNA-based technologies such as restriction fragment length polymorphisms and more recently developed methods that use the polymerase chain reaction can allow even more discriminative and faster identification of varieties. However, none of the DNA methods have replaced biochemical methods for seed purity assays, other than in a relatively select group of crops with very high seed value, due to their high datapoint cost. It will require further miniaturization, automation and enhanced capabilities to process numerous samples simultaneously before newly developed methods supplant biochemical methods for routine usage in purity testing. New varieties that have major genes for herbicide or insect resistance incorporated within them require purity assays during product development and following seed production of the commercial variety. Immunological or DNA sequence assays can be developed and automated systems are required to process hundreds of thousands of individuals. Ultra-high, micro-array technologies and single-molecule detection systems are now under development. These technologies offer the promise that adequate distinction and high sample throughput will be combined. New methods may eclipse the capabilities of biochemical methodologies, thereby potentially raising genetic purity standards and enabling farmers and consumers better to utilize and benefit from increasingly productive varieties that are bred from a more diverse base of genetic resources.

The isozymes of 10 enzymes connected with energy metabolism in Tegillarca granosa were analysed by vertical polyacrylamide gel electrophoresis. Esterase and α-amylase are enzymes related to energy intake, their activities were high in the digestive gland. Malate dehydrogenase, malic enzyme, isocitrate dehydrogenase, succinate dehydrogenase, alcohol dehydrogenase, lactate dehydrogenase, 6-phosphogluconate dehydrogenase (G-6-PDH) and adenosine triphosphatase (ATPase) are enzymes related to energy metabolism. The main energy supply of T. granosa comes from aerobic respiration; anaerobic metabolism and the pentose phosphate pathway take an auxiliary role in energy metabolism. The high activity of G-6-PDH in T. granosa might mean a considerable proportion of carbohydrates metabolized through this pathway. This reaction could provide abundant NADP for metabolism in T. granosa. Compared with other shellfish, T. granosa had lower activity of ATPase, which might have some relationship with the amnicolous life and low motility of this animal.

Determining insect parasitism rates is problematic due to the small size and lack of useful distinguishing morphological characters of many parasitoid taxa. To solve this problem, entomologists have employed one of four general methods to detect parasitoid protein or nucleic acid markers: serological assay; random amplified polymorphic DNA–polymerase chain reaction “RAPD-PCR” allozyme electrophoresis; or specific PCR. Serological methods, especially with monoclonal antibodies, are unrivalled for specificity, enabling discrimination at the stage as well as species level. However, they have not found favour with many workers, possibly due to complexity and expense. RAPD–PCR has been widely used, but can only be recommended for restricted applications because of its poor reproducibility. Allozyme electrophoresis provides reproducible detection and discrimination of closely related species. Specific-PCR is highly specific and reproducible, and also has the shortest latency for detection, usually 24 h or less after parasitization. The substantial existing literature on allozyme electrophoresis and specific PCR is used to support recommendations on what are apt to be fruitful enzyme systems or genomic regions for detecting and discriminating parasitoids in untried parasitoid–host assemblages.

Isozyme analysis (12 enzymes: 14 loci) was conducted on 99 isolates of Trypanosoma cruzi: 77 from Guatemala, 5 from Mexico and 17 from South American countries. Analyses of 4 population-genetic indices were undertaken to assess the possibility of genetic exchange occurring among Guatemalan isolates. The results provide evidence for a degree of genetic exchange occurring among isolates from this relatively small geographical area. Previous studies of population genetics on T. cruzi might have failed to detect this phenomenon because they tended to use isolates originating far from one another, rendering gene exchange unlikely for geographical reasons. Phylogenetic data, presented here, show considerable differences in genetic structure between Central and South American isolates, suggesting that different biological and clinical properties might be expected. For example, there are differences in clinical syndromes between Central and South America, a situation discussed further here.

The early development of indigenous and introduced Scots pine (Pinus sylvestris L.) ectomycorrhiza in natural forest humus was examined using molecular fingerprinting techniques. Non-mycorrhizal or mycorrhizal (Suillus bovinus (L. ex Fr.) O. Kuntze or Paxillus involutus (Batsch ex Fr.) Fr.) seedlings were placed in transparent two-dimensional microcosms on a thin layer of sieved humus to allow observation of ectomycorrhizal development and fungal growth. Twelve ectomycorrhizal morphotypes, mainly based on colour, gross morphology and outer mantle structure, were identified over a 3-month period. No successional trends in mycorrhiza formation were observed. For further characterization, individual ectomycorrhiza representing the different morphotypes were subjected to analyses of esterase (EST) isozyme profiles and RFLPs of the internal transcribed spacer (ITS) from fungal rRNA genes following amplification using PCR. All 10 morphotypes analysed displayed different esterase isozyme profiles, and the characteristic S. bovinus species diagnostic band (S. b. EST8) was detected in two white morphotypes. Ten Pink and Black ectomycorrhiza were all separated into one and three groups, respectively. A fast-running plant-specific polymorphic locus (Z) was also confirmed in most ectomycorrhizal morphotypes. Diagnostic species-specific (S. bovinus and Pink) EST bands were detected in intact external mycelium colonizing soil. Successful amplification of the ITS from individual ectomycorrhiza, of eight different morphotypes, was found to be mainly influenced by the DNA template concentration. Different RFLPs (Hinf I, Mbo I and Hha I) of the ITS placed the white morphotypes into two groups, one corresponding to S. bovinus, in agreement with the esterase fingerprinting. By contrast, Pink and Beige morphotypes displayed different EST profiles but nearly identical RFLP fingerprints. The ITS amplification success rate of standardized DNA template concentrations from 10 individual Pink and Black ectomycorrhiza was 90 and 50%, respectively. In all successful amplifications, the black morphotype yielded the smallest ITS fragment, similar to earlier reports for Cenococcum geophilum, that gave identical RFLPs. The ecological significance of the observed mycorrhizal diversity and combined application of these two identification methods is discussed.

Electrophoretic studies were carried out on isozymes of Glossina pallidipes to determine whether there are any genetic differences between natural populations from an area free of sleeping sickness (Nguruman) and an area where sleeping sickness is endemic (Lambwe Valley) in Kenya. Out of 12 enzymes examined, two enzymes, GPI and PGM, showed high polymorphism in the two populations, while the other 10 enzymes were all monomorphic. At the GPI locus, at least five alleles were detected, and two alleles were found at the PGM locus. There was a difference in the frequency of isozyme patterns between males and females, indicating that the PGM locus is on the sex-linked chromosome (X-chromosome). Nei's genetic distance (D) was 0.00154 between the two populations, which is the value within the range for local populations in different organisms examined so far. Some difference between the two populations was found in the level of average heterozygosity (H) and in allelic composition of the GPI locus, that is, the Lambwe Valley population is more heterogeneous than the Nguruman population.