Abstract:
Seed of two cultivars namely Floradade (fresh produce cultivar) and Roma VF (canning cultivar) was used in this study. Experiments were undertaken to standardise the optimal water and substratum requirements for the germination of the seed. Two choices, representing three different substrata, are currently prescribed by the International Seed Testing Association (ISTA Rules, 1985) for the germination test on tomatoes. Best results were obtained with the roll paper method., described by ISTA as a "between paper" substratum. The water application for this germination substratum was standardised at 50 cm3 for four 383 x 254 mm sheets of "Anchor" germination paper containing 100 seeds. In investigations on methods for adjusting the moisture content of tomato seed prior to controlled deterioration treatments, seed imbibition in liquid water was found to be unsuitable. The seed coat is hairy and water is rapidly adsorbed. The consequent increase in mass of the seed is not necessarily the result of water absorbed through the seed coat. Full hydration and subsequent dehydration to the desired water content is therefore necessary. Controlled deterioration tests comparing moisture adjustment by means of imbibition from liquid water with moisture adjustment by means of equilibration in a relatively humid atmosphere, yielded dissimilar results. The latter method was used in subsequent studies on artificial ageing, since it is a more reliable simulation of seed moisture adjustment during storage. A modified version of the controlled deterioration test was applied as an accelerated ageing technique over a maximum short term period of eight days, while seed storage was applied over a longer period of 12 months. The purpose of this investigation was to compare the physiological and ultrastructural changes in the seed caused by the different ageing methods. The conclusions drawn from these investigations support the school of thought that the physiological and ultrastructural consequences of artificial ageing differ from those resulting from natural ageing over time. Rapid ageing techniques are therefore not recommended for the assessment of effects of seed treatments during seed storage. Investigations on the effects of a hot-water treatment of tomato seed, in interaction with ageing treatments, led to the conclusion that a hot-water treatment comprising 54°C for 25 minutes does not affect the viability of tomato seed during a storage period of at least one year, provided that the seed moisture content is maintained at a relatively low level (±7%).
