Seed quality standards enable seed users to achieve their objectives in the establishment of uniform seedlings to a high and reliable level for a range of agricultural and horticultural crops, growing systems and market outlets. Quality standards of commercial seed lots are determined by their positions on the seed survival curves and the shape of their germination progress curves. Although comparative descriptions of germination curves can be achieved by the calculation of the mean germination time (MGT; delay to radicle emergence), single early counts of radicle emergence provide a convenient means of predicting MGT and differences between seed lots. Evidence is presented for an ageing and metabolic repair hypothesis as the overall physiological basis to explain the principles behind the standard germination and vigour tests (ageing, electrolyte leakage, cold test, germination rate and seedling size). The work of the International Seed Testing Association (ISTA) in developing convenient, inexpensive and internationally repeatable tests is illustrated.

Changes in tomato (Lycopersicon esculentumMill.) seed quality were monitored during seed development and maturation in glasshouse experiments in 2 years. The end of the seedfilling period (mass maturity) occurred 35–41 d after anthesis (differing among trusses) in 1989 and 42 d after anthesis in 1990. Seed moisture contents at this developmental stage were 53–72% (wet basis), while the onset of ability to germinate (during 21-d tests at 20°/30°C) and the onset of tolerance to rapid enforced desiccation occurred just before (1990) or just after (1989) mass maturity. In 1989, seed quality was assessed primarily by seedling size in a glasshouse experiment; maximum mean seedling dry weight 25 d after sowing was not achieved until 24–40 d after mass maturity. In 1990, seed quality was assessed primarily by germination following storage; maximum normal germination after 35 d in storage at 40 °C with 14 ± 0.5% moisture content was attained 23 d after mass maturity, but with little difference among seed lots harvested 10 d earlier or up to 30 d later. The results contradict the hypothesis that maximum seed quality is attained at the end of the seed-filling period and that seed viability and vigour begin to decline immediately thereafter.

The high emergence and uniform seedling size required for glasshouse production of modular transplants of peppers is not always achieved due to vigour differences among commercial seed lots. The mean germination time (MGT) at 18 and 25°C was determined in laboratory germination tests for 11 lots of the cultivar Demre and found to be related to seedling size (root and hypocotyl length) and variation. The longer the MGT (germination slower and more spread in time) the smaller and more variable the seedlings. MGT at both temperatures was also related to mean emergence time (MET) in transplant modules in two experimental runs. In turn, MET was related to mean seedling weight (R²=0.72, R²=0.75, p<0.001 for fresh weight and R²=0.83, p<0.001; R²=0.68, p<0.01 for dry weight) in both runs. Slow germinating lots (high MGT) were slower to emerge in modules (high MET) and produced smaller seedlings. The MGT at 25°C of five further lots of Demre was related to MET in modules (R²=0.84, p<0.05). MGT and MET were both inversely related to the variation in fresh weight of individual seedlings (MGT: R²=0.79, p<0.05; MET: R²=0.96, p<0.01) and variation in dry weights (MGT: R²=0.74, NS; MET: R²=0.89, p<0.05). Germination after controlled deterioration (CD) for the five lots was inversely related (R²=0.93, p<0.01) to MGT indicating that seed ageing was a cause of low vigour and high MGT. The need for repair of deterioration is discussed as a possible explanation of differences in MGT and performance in modules.

A wide range of seedling emergence in commercial seed lots of watermelon (10 lots), melon (10 lots) and cucumber (9 lots), all with standard germinations above 98%, was seen in low temperature emergence (LTE), high temperature (HTE) and an 8 cm deep sowing (MSE) in the field and in salt stress conditions (SSE) in trays at 20°C. Final emergence was closely related to both the rate of emergence, measured as mean emergence time (MET; the reciprocal of the rate of emergence), and to the mean germination time (MGT; the reciprocal of the rate of germination) for physiological germination (2 mm radicle) in the laboratory at 25°C. Slower germinating and emerging lots, so-called low vigour lots, had lower levels of emergence in all sowings. Single early counts of physiological germination identified low vigour lots for all three species and are suggested as a quick routine test. The physiological age of the seed lots, determined using accelerated ageing (45°C in 100% relative humidity) and controlled deterioration (45°C and 20 or 24% moisture content), was significantly related to MGT which was higher (i.e. germination was slower) in physiologically older seed. Previous work suggests that cucurbit seeds appear to retain germination capacity over several years although ageing is reflected in a slower rate of germination (high MGT). MGT can also be described as the length of the lag period from the start of imbibition to radicle protrusion. We propose that this period is needed for the repair of the effects of ageing and is therefore longer in aged seeds.

Germination percentage, seedling fresh weight and sensitivity index of the pepper (Capsicum annuum L. cv. Sera Demre) seed lots harvested 50, 60 and 70 days after the anthesis (daa) in 2001 and 2002 were determined under the salt (NaCl) and osmotic (PEG) stresses at the same water potentials of -0.3, -0.6 and -0.9 MPa. The objective was to study whether the germination and seedling growth were inhibited by the salt toxicity or osmotic effect during the development. The higher the salt and osmotic stress concentrations the lower was the germination percentage and seedling fresh weight. The seed germination was higher and sensitivity index were lower in NaCl than in PEG at the same water potential and harvest in both the years. They were able to germinate at all the concentrations of NaCl but at -0.9 MPa of PEG, none of the seeds of any harvest germinated in both the years. The seeds harvested 70 daa showed the highest germination and seedling weight in all the NaCl and PEG concentrations in both the years. Results showed that the inhibition of the germination at the same water potential of NaCl and PEG resulted from the osmotic effect rather than the salt toxicity. Moreover, the seeds harvested 70 daa appeared to be more tolerant to the salt and osmotic water stress conditions than the other two lots