Molecular and Historical Aspects of Corn Belt Dent Diversity

Tens-of-thousands of open-pollinated cultivars of corn (Zea mays L.) are being maintained in germplasm banks. Knowledge of the amount and distribution of genetic variation within and among accessions can aid end users in choosing among them. We estimated molecular genetic variation and looked for influences of pedigree, adaptation, and migration in the genetic makeup of conserved Corn-Belt Dent-related germplasm. Plants sampled from 57 accessions representing Corn-Belt Dents, Northern Flints, Southern Dents, plus 12 public inbreds, were genotyped at 20 simple sequence repeat (SSR) loci. For 47 of the accessions, between 5 and 23 plants per accession were genotyped (mean = 9.3). Mean number of alleles per locus was 6.5 overall, 3.17 within accessions, and 3.20 within pooled inbreds. Mean gene diversity was 0.53 within accessions and 0.61 within pooled inbreds. Open-pollinated accessions showed a tendency toward inbreeding (FIS = 0.09), and 85% of genetic variation was shared among them. A Fitch-Margoliash tree strongly supported the distinctiveness of flint from dent germplasm but did not otherwise reveal evidence of genetic structure. Mantel tests revealed significant correlations between genetic distance and geographical (r = 0.54, P= 0.04) or maturity zone (r = 0.33, P = 0.03) distance only if flint germplasm was included in the analyses. A significant correlation (r = 0.76, P \u3c 0.01) was found between days to pollen shed and maturity zone of accession origin. Pedigree, rather than migration or selection, has most influenced the genetic structure of the extant representatives of the open-pollinated cultivars at these SSR loci

Meningo-encephalitis accompanying retinochoroiditis in a murine model of congenital toxoplasmosis

A histopathological study of the brains of adult mice infected in utero with Toxoplasma gondii and presenting manifestations of ocular toxoplasmosis is reported. All brains contained Toxoplasma tissue cysts. A sub-acute/chronic meningo-encephalitis was the main feature of the inflammatory response in the brain. Microscopical features suggest that autoimmune processes may play a part in the disease. We suggest that our mouse model will provide a simple and inexpensive tool for the investigation of histopathological processes in the CNS resulting from congenital Toxoplasma infection

The effect of congenital and adult-acquired toxoplasma infections on activity and responsiveness to novel stimulation in mice

Activity and responsiveness to novel stimulation were assessed in three groups of mice infected with Toxoplasma . One group was infected when adult; two groups were infected congenitally, one born to dams infected during gestation, the other to dams chronically infected prior to mating. Each mouse was tested in a box, the floor of which was marked off into 16 equal squares, and its activity was measured over ten minutes by counting the number of times the mouse entered each square. Infected mice were more active. In addition, infected mice showed a smaller relative preference for the more novel central area of the box, especially towards the end of the observation period. These differences were independent of emotionality (as measured by defecation counts), general health (as measured by subjective health ratings and body weight) and the number of Toxoplasma tissue cysts in specified brain regions. The authors suggest that differences arise from pathological changes caused by proliferating toxoplasms in the brains of the infected mice; an immunopathological reaction due to the presence of tissue cysts in the brain may also be involved. Other possible factors contributing to observed deficits in behaviour are also discussed. The authors suggest that such deficits may render Toxoplasma -infected mice more susceptible to predation by the domestic cat, the definitive host of Toxoplasma

Encephalitis and retinochoroiditis in a murine model of congenital toxoplasmosis

Paper presented as part proceedings of the 67th meeting of the British Neuropathological society held at the university of Sheffield on the 12th and 13th July 198