Susceptibility of eliteAcacia mearnsii families to Ceratocystis wilt in south Africa

Ceratocystis albofundus is a recently described pathogen infectingAcacia mearnsii in South Africa, and it causes a disease known as Ceratocystis wilt. Symptoms of the disease include die-back, gummosis and wilting of infected trees. In order to select trees tolerant to this fungus, susceptibility tests were conducted on trees representing fourteen families ofA. mearnsii. A virulent isolate ofC. albofundus was selected and inoculated into the stems of twelve-month-old plants in a plantation. Lesion lengths, in the bark, and disease development were assessed after 6 weeks. All fourteen families ofA. mearnsii were susceptible to infection byC. albofundus. Considerable variation was, however, noticed between individual trees within the same family and the incorporation of disease tolerant trees into breeding programmes is proposed.     

Aerobic stability of sugar-cane silage inoculated with tropical strains of lactic acid bacteria

Aerobic stability is an important feature in the evaluation of silages. The aims were to investigate the chemical and microbiological changes that occur in sugar-cane (Saccharum spp.) silage after aerobic exposure, to identify the major species of yeasts associated with the aerobic deterioration process and to select lactic acid bacteria (LAB) strains that can improve the aerobic stability of this silage. Fourteen wild LAB strains belonging to Lactobacillus plantarum, L. brevis and L. hilgardii were evaluated using experimental silos. Silage samples were collected at 0, 96 and 216 h after aerobic exposure to determinate the DM, WSC, pH, products of fermentation, to evaluate the silage temperatures and to identify yeast species associated with the aerobic deterioration of silage. The strains tested were able to modify the fermentative and chemical parameters and the diversity of yeasts species of silage after aerobic exposure. There was no association between the facultative or obligatory heterofermentative fermentation patterns and the increased aerobic stability of silage. Aerobic stability of sugar-cane silages was associated with high acetic acid and 1,2-propanediol concentrations. L. hilgardii UFLA SIL51 and UFLA SIL52 strains promoted an increase in aerobic stability of silage.     

Comparative study of Kenaf varieties and growing conditions and their effect on kraft pulp quality

Kenaf (Hibiscus cannabinus L.) is an annual plant which produces a very high fiber yield per hectare and has demonstrated to be a suitable material for pulping. The crop conditions influence fiber production, but there is no information about their effect on pulp quality. The aim of this work was to study the effect of kenaf varieties and crop conditions (watering dose and harvesting time) on sulfate pulp quality. The study has been made on bast fiber sulfate pulps due to their high added value. The quality criteria were fiber dimensions, chemical composition and pulp quality. Kenaf variety or crop conditions have significant effect on fiber dimensions, holocellulose content, kappa number and breaking strength. To obtain high fiber yield and good delignified pulps it is recommended to grow the Salvador variety and to employ advance harvesting. Received: 20 January 1999     

Selective sparing of a class of striatal neurons in Huntington's disease

A distinct subpopulation of striatal aspiny neurons, containing the enzyme nicotinamide adenine dinucleotide phosphate diaphorase, is preserved in the caudate nucleus in Huntington's disease. Biochemical assays confirmed a significant increase in the activity of this enzyme in both the caudate nucleus and putamen in postmortem brain tissue from patients with this disease. The resistance of these neurons suggests that the gene defect in Huntington's disease may be modifiable by the local biochemical environment. This finding may provide insight into the nature of the genetically programmed cell death that is a characteristic of the disease.