Aspects of improving cold hardiness of tomato (Lycopersicon esculentum) var. Rossol.
Ghebretinsae, Amanuel Ghebrehiwet.
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Tomatoes, particularly those of the determinate type, are one of the most popular vegetables in the East African country Eritrea. The crop is a source of income to small farm operators as well as commercial growers, and plays an important role in the nutritional supply of the population. Nonetheless, tomato production is limited during the cool season resulting - on the one hand - in a reduced nutritional supply during this period and - on the other hand - in an increased economic potential of the crop. Although performance of tomato plants under low temperature conditions is genetically influenced, prevailing temperatures as well as management practices also affect growth and development. In order to understand the long-term effects of a cold spell on tomato plants, experiments were carried out to determine the effect of a cold spell on plant vegetative and reproductive characteristics of determinate type ''Rossol'' tomatoes. Plants were moved for two to five subsequent nights from a tunnel to a cold room (4°C). The fruit set stage of "Rossol" tomatoes was found to be most sensitive to cold temperature, followed by the flowering stage. The juvenile stage was, of all the developmental stages examined, the least sensitive to cold. Furthermore, subjecting tomato plants for five subsequent nights (cumulative 60hrs) to 4°C resulted in a significant retardation of growth and development and in yield reduction. However, tomatoes exposed to a two-night cold spell during either the vegetative or the flowering stage recovered quickly and, ultimately, performed well. Furthermore, trials were carried out under tunnel and field conditions to investigate the impact of potassium application as well as mulching on cold tolerance of "Rossol" tomatoes. Under low temperature conditions, increasing the level of potassium to up to 150% of the recommended level (157.5kg*ha-1 ) resulted in quicker ontogenetic development and increased yields significantly. On the other hand, supplying tomato plants with 50% and 200% of the recommended potassium level reduced growth, delayed development and decreased yield and yield attributes. Using black plastic mulch also increased plant growth and speeded up plant development. Maize stover mulch, however, retarded plant growth and development so that certain stages ofthe phenological cycle were reached later than by non-mulched plants. However, yield and yield attributes increased significantly using stover mulch. Therefore, the management practises potassium fertilization and mulching provide excellent tools to increase the tolerance of tomato plants to low temperature conditions. Furthermore, organic mulches can be used to delay crop development and time maturity to achieve high retail process of the commodity in the cool winter months.