Genetic variation in a population of tetraploid potatoes: Response to the potato leafhopper and the potato flea beetle

Progenies from a group of tetraploid parental clones from the USDA potato breeding program were used to investigate variation in resistance to the potato leafhopper,Empoasca fabae (Harris), and the potato flea beetle,Epitrix cucumeris (Harris). The study utilized two mating designs: i) selfing and testing both the parents and the S₁ progeny; and ii) nine clones, used as males, were each crossed to three different clones, and progenies from the resulting families were tested. Statistically significant differences between families were measured in each test for both insects. Non-additive genetic variance was larger than additive genetic variance in progeny reaction to leafhopper infestation and hopperburin, but was smaller in progeny reaction to flea beetles. Environmental variation contributed heavily to the total variation of plant reaction to both insect species. Selecting individuals was indicated to be slightly more effective than selecting males on half-sib progeny performance but not as effective as selecting clones on S₁ progeny performance. Because of the large environmental variance and small additive variance for both the leafhopper and flea beetle, slow progress in increasing the level of resistance to these two species in this sample population was predicted. Resistance to leafhopper infestation was genetically quite highly correlated (positive) with resistance to hopperburn, but phenotypically the correlation was considerably smaller. Negative genotypic, phenotypic, and environmental correlations between leafhopper infestation and flea beetle infestation suggest that selecting for resistance to one of these species, in the population sampled for these tests, would tend to increase susceptibility to the other.     

Reaction of some wild and cultivated potato varieties to charcoal rot

With a view to select potato varieties possessing resistance to charcoal rot, laboratory tests were carried out at the Central Potato Research Institute, Simla (India). Five hundred and twenty six clones comprising tuber-bearing species ofSolanum and varieties and hybrids of potato were screened for their reaction toMacrophomina phaseoli (Maubl.) Ashby. A high degree of resistance was observed in six clones ofSolanum chacoense and four hybrids withS. chacoense germ plasm, while moderate susceptibility was observed in another six clones ofS. chacoense, three clones ofSolanum tuberosum ssp.andigena and nineteen hybrids produced at the Institute.     

On the parafollicular cells in the thyroid gland of the bovine foetus

The thyroids of 117 bovine foetuses were studied by some histochemical and selective staining methods with respect to the occurrence of parafollicular cells. Furthermore, 7 foetuses were studied by electron microscopy. The length of the foetuses varied from 6 to 72 cm corresponding to an estimated age of about 2 to 9 months. Parafollicular cells were observed in the thyroids of all foetuses examined. The ultrastructure of the parafollicular cells in the foetuses differed very little from that described in adult animals. Histochemically, Luxol fast blue positive phospholipids and α-glycerophosphate dehydrogenase activity could be observed in the cells. The Solcia-Sampietro method gave positive results in most of the foetuses examined. The reactions observed at light microscopic level were rather faint in the youngest foetuses. The functional aspects of the results are discussed.     

THE ISOLATION OF MYCOPLASMA HYOSYNOVIAE AND EXPOSURE OF PIGS TO EXPERIMENTAL INFECTION

Arginine-utilising mycoplasmas isolated from the pneumonic lungs of 4 pigs were identified as M. hyosynoviae by their growth characteristics, biochemical activity and serological similarity to each other and to 2 type strains of M. hyosynoviae in growth inhibition tests. A purified culture of one M. hyosynoviae isolate was inoculated intravenously into 3 pigs which were killed 9 days later. Although arthritis was not observed clinically, M. hyosynoviae was isolated from 8 of 9 joints cultured, the tonsils and retropharyngeal lymph nodes of all 3 pigs and the lungs of 2 pigs. No histopathological changes were observed in synovial membranes of the joints cultured or lungs but severe depletion of lymphocytes in the cortex of lymphoid follicles in lymph nodes and tonsils was observed.