CORESTA Meeting, Agronomy/Phytopathology, Montreux,1997, AP61
Vein to lamina ratio of South African tobacco
Tobacco and Cotton Research Institute, Rustenburg, South Africa
South African cigarette manufacturers demand a vein to lamina ratio of ± 20% in the cured tobacco. Currently very little of the tobacco produced fulfils this demand. The objective of this study was to test the hypothesis that the producer can manipulate this ratio to a higher extent by means of cultivation practices than by cultivar breeding. Before trials were set out all the production areas were extensively surveyed. Cultivar or genetic response was found to be the biggest contributor although seasonal variation also occurred. Little evidence was found to suggest that production practices can manipulate this characteristic. Trials were set out at Rustenburg and Loskop irrigation schemes over three seasons to test these findings. Four flue-cured cultivars were cultivated under four nitrogen levels ranging from 115 - 185 kg N ha-1 at a plant population of 16,666 plants ha-1. In a further trial at Rustenburg three air-cured cultivars were evaluated under two nitrogen levels of 200 and 300 kg N ha-1 and two plant populations of 15,300 and 30,600 plants ha-1. Leaves were sampled after curing and the vein to lamina ratio determined. Significant differences occured in both trials between the cultivars. Results showed that an increase in nitrogen fertilization caused a non-significant increase in the vein to lamina ratio. A very high plant population of 30,600 plants ha-1 with a narrow inter- row spacing of 65 cm caused a decrease in the vein to lamina ratio of about 2% on average over the three air-cured cultivars.