The effect of the nutritional status of grapevine 'Crimson Seedless' on growth, fruit set and quality was studied in two growing periods. The vines were treated with three nitrogen rates (24, 36, 48 kg/ha.) combined with three potassium levels (240, 285, 330 kg/ha). Increasing N supply enhanced N-concentrations in the petioles. N-fertilization also increased K concentrations in the petioles. The K-fertilization variants themselves did not alter the K content of the petioles. High Nfertilization improved vegetative growth (leaf area, cane diameter) and reduced bud burst, bud fertility and fruitfulness. Excessive N-supply negatively affected yield per vine by reducing the number of fruit clusters. Cluster size, however, was improved with increasing N-nutrition whereas the number of berries per cluster and the cluster compactness remained unchanged. The single berries were bigger (size, weight) and their shape remained typically for the cv. The amount of juice per berry increased and fruit firmness decreased in the high N-variants. The only effect of high K fertilization was an increase of total soluble solids and a decrease of acid concentration. Anthocyanin contents generally showed a high variability in the experiment. Therefore, the color of berries might be more regulated by the ripening process than by the fertilizer treatments.
This research aims to evaluate the effects of biotic factors on the population density of the sugar cane soft scale P. tenuivalvata. Population estimation was performed in different sites of the sugar cane field, i.e, east, north, south, west and field center. Results show that, scales proportionally increased from May to December in all field sites and the scales wereintensively through September, October and November. Plants located in the west site intensively harbored the highest population of scales, followed by north site. The number of scales on plant in west and south sites was approximately similar. The field center harbored the lowest scale population. These results reveal that the west direction followed by north are preferred by this insect in its various stages . This could be attributed to the direction of the wind which always blows from north to west carrying crawlers to these directions where it may aggregate for feeding and growth. During the two successive seasons of the study, data also revealed the incidence of the Aphelinidae parasite Coccophagus scutellaris (Aphelinidae: Hymenoptera) parasitizing the different immature stages (except 1 st instar) and mature stage (adult females). The influence of such parasite on the insect was significant in both seasons. In conclusion, there are many biotic factors that can affect the population density of the sugar cane soft scale P. tenuivalvata. This can assist to avoid the difficult application of the insecticide and minimize the population of the environment. natural enemies (parasites).
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