I. Demir

Changes in seed quality during seed development and maturation in tomato

Changes in tomato ( Lycopersicon esculentum Mill.) 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.

Effect of salt and osmotic stresses on the germination of pepper seeds of different maturation stages

ABSTRACT 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. Key words : Capsicum annuum , salinity, water stress, germination

Evaluation of seed quality: from physiology to international standardization

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 germination and potential longevity of watermelon (Citrullus lanatus) seeds during development

Abstract Changes in germination and potential seed longevity (Ki of the viability equation) were monitored during the development of watermelon (Citrullus lanatus) seeds grown in warm (minimum and maximum temperatures were 16.8 and 40.1°C) and cool (9.8 and 35.1°C) sites in 2002. Maximum seed weight (mass maturity, end of seed filling phase) was attained 25 days after anthesis (DAA) under both growing conditions. However, maximum germination was observed at 30 DAA in both sites. Potential seed longevity was achieved at 45 and 40 DAA, which were 20 and 15 days after mass maturity (the time of maximum seed dry weight) in warm and cool sites, respectively. When the maximum quality was achieved, fruit flesh was pale red, red, and 98–100% of the seeds were brown coloured. Seed dry mass and maximum potential longevity were consistently greater in cool than in warm growing sites. Dried seeds had higher germination percentages than those of fresh ones until mass maturity (25 DAA) at both sites.

The effect of controlled hydration treatment on germination and seedling emergence of unaged and aged pepper seeds during development

Pepper (Capsicum annuum L.) seeds were harvested 50, 60, 70, and 80 days after anthesis (daa) and 50, 55, 60, 65, 70, 75, and 80 daa in 2000 and 2001, respectively. After drying, a proportion of each sample was aged at 20% moisture content, 45 °C for 24 h. Both unaged (UA) and aged (A) seeds were hydrated in aerated water at 25 °C for 48 h (controlled hydration, CH). Seed quality was then assessed by counting germination after 3 days, normal germination percentage after 14 days, seedling emergence, and fresh and dry weight. Maximum seed quality of unaged seeds occurred 70 daa in 2000, and between 65 and 75 daa in 2001. CH treatment improved seed quality in both unaged (UA) and aged (A) seed lots. The maximum benefit was observed in seed lots harvested 60 and 70 daa in 2000, and 65, 70, and 75 daa in 2001. There was less improvement in the less mature (50-55 daa) and overmatured (80 daa) seed samples. It was concluded that CH treatment could be used to improve seed quality in seed lots harvested in once-over mechanical practices that contain immature and overmature seed proportions together.

Controlled deterioration for vigour assessment and predicting seedling growth of winter squash (Cucurbita maxima) seed lots under salt stress

Abstract The controlled deterioration (CD) test (45°C and 24% moisture content) was used to assess the seed vigour of three winter squash (Cucurbita maxima) seed lots. Germination after CD was correlated with seedling growth parameters under salt stress conditions (50, 100, and 150 mM NaCl) in an unheated glasshouse emergence test. Germinations after CD for 24, 48, and 72 h were all 94% or greater, and these treatments were not successful in ranking the lots. However, germination of squash seeds after CD for 96 h ranged from 25% to 75% for the three lots. Seedling emergence was >90% at both 50 and 100 mM NaCI and did not differ among lots. However, at 150 mM NaCI, emergence did differ among the lots, and the CD 96‐h germinations were positively and significantly related to mean seedling emergence time, seedling fresh and dry weight, hypocotyl length, and cotyledon width. The CD test can be used to predict seedling performance of winter squash seed lots under salt stress. However, the method should be further verified by using a larger number of seed lots.

Seed development and maturation in edible dry bean (Phaseolus vulgaris L.) cv. Teebus

A study of seed development and maturation in edible dry bean cv. Teebus was conducted on field-grown plants. Mass maturity (maximum seed dry mass) occured 43 days after flowering (DAF) when seed moisture content was 52%. Harvest maturity (at a seed moisture content of 12.7%) was reached 15 days after mass maturity (58 DAF). Fresh seeds produced 90.5% normal seedlings at 30 DAF (13 days before mass maturity), when they had acquired only 48% of their maximum dry mass. Only 3% of rapidly dried seeds produced normal seedlings at this stage. Maximum seed quality (as determined by normal germination and conductivity of steep water), as well as maximum desiccation tolerance, were attained 5 days after mass maturity when seed moisture content was 34%. Respiration initially increased sharply, followed by a relatively constant high level for several days, after which it diminished to near zero levels when moisture content was 16.8% (5 days before harvest maturity). ATP content followed much the same pattern, but t...

THE EFFECT OF HEAT TREATMENT OF WATERMELON SEED ON GERMINATION, HYPOCOTYL EMERGENCE AND ABSCISIC ACID CONTENT

Seeds of watermelon (Citrullus lanatus) with a moisture content of 7.2% were heat treated at 60 °C for 15 or 20 h, and their performances compared with that of untreated seeds. Radicle emergence of treated seeds was only slightly lower than that of the control when germinated at 25 °C. To ascertain the effect of the treatments on hypocotyl growth (emergence) per se, radicle emergence was synchronized in all treatments and emergence from deep plantings in sand determined. Small differences in emergence were observed when seeds were germinated at 25 °C, but seed treatment resulted in large reductions in emergence at 15 °C. This demonstrates that the hypocotyls developing from heat-treated, germinated seeds are less able to withstand low germination temperatures, which could be an important factor in emergence failure. Levels of free abscisic acid (ABA) were higher at 15 °C than at 25 °C, with hypocotyls of treated seeds containing more free ABA and its breakdown products than the control at the lower temperature.

Effect of controlled hydration treatments on storage longevity of aubergine seeds during development

The effects of controlled hydration treatments on seed storage longevity of aubergine (Solanum melongena L.) seeds harvested 45, 50, 55, and 60 days after anthesis (daa) in 1999 and 2000, were studied. Treated and control seeds were stored at 30 oC with 12% moisture content and sampled monthly for up to 180 days. Longevity was assessed by changes in P50 (half-viability period) and regression coefficients of the survival curves following probit analysis. The treatments extended P50 values between 19 and 65 days longer than the control, depending on the seed lot. Controlled hydration also substantially decreased life span of seeds in time (regression coefficient). The maximum advantage was obtained in 45 and 60 daa in 1999 and 2000 during development, respectively. Results showed that controlled hydration treatment could be used to prolong the storage longevity of aubergine seed lots from different stages of development.