Alison A. Powell

Comparison of the seed germination and early seedling growth of soybean in saline conditions

Germination and seedling growth of soybean ( Glycine max L.) cv. Williams were examined on paper towels pre-moistened with a range of saline solutions (germination: 0–500 mMolal NaCl; seedling growth: 0–330 mMolal NaCl). The Na + , K + and Ca 2+ concentrations in the embryonic axis immediately before germination and in the seedling 3.5 d after germination were measured. Germination decreased at NaCl concentrations of 330 mMolal (81% germination) and above. At 420 mMolal NaCl, only 40% of seeds germinated, and at 500 mMolal NaCl there was no germination. Seedling growth rate decreased drastically with increasing salinity. At 220 mMolal NaCl, seedling growth rate had declined to 5% of the control, whereas at 330 mMolal NaCl seedling growth was almost zero 3–4 d after germination. Thus, soybean seeds were more tolerant of salinity in the germination than in the seedling phase. The results suggest that the greater tolerance of salinity during the germination phase might, in part, be the result of a lower sensitivity to high tissue Na + concentrations. Germination (40%) was possible at a tissue Na + concentration in the embryonic axis of 9.3 mg g FW -1 , whereas seedling growth was completely inhibited at a tissue Na + concentration of 6.1 mg g FW -1 . Germination at higher tissue Na + concentrations was associated with higher K + and Ca 2+ concentrations in the embryo axis, compared with growing seedlings, suggesting that these ions may protect the seeds in the pre-germination phase against salinity.

Vigour differences in brassica seed and their significance to emergence and seedling variability

Seeds of the Brussels sprout cultivar Asmer Aries having low vigour as a result of ageing emerged more slowly when sown in module trays and had slightly lower final emergences than seeds which had not undergone ageing and were of high vigour. Low seed vigour also resulted in the production of seedlings which were shorter and more variable in height at the first-leaf stage. Once the seedlings reached the transplanting stage there was greater variability in the fresh and dry weights of seedlings produced from seeds having low vigour, although the mean seedling weights differed little from those produced by high-vigour seeds. Similar observations were made for samples of commercial seed of cauliflower, Brussels sprouts, Dutch cabbage, red cabbage and calabrese provided by vegetable transplant propagators and in use in 1988. Low-vigour seeds again emerged more slowly with low final emergence and produced smaller and more-variable seedlings. The implications of these observations for the production of vegetable seedlings for transplanting are discussed.

Seed vigour in cultivars of dwarf French bean ( Phaseolus vulgaris ) in relation to the colour of the testa

Differences in the field emergence of 30 commercial seed lots of dwarf French beans were associated with the colour of the testa, the 11 lots with a white testa having a lower mean field emergence of 67% compared with 91% for lots with black (11 lots) or brown (8 lots) testae. The white-seeded lots also had higher leachate conductivities (mean 42 μ S/cm/g) and imbibed more rapidly (an average 43% weight increase after 6 h imbibition) than black- or brown-seeded lots (average 25 μS/cm/g; 30% weight increase). The extent of damage to the testa which was slight in all lots was not related to differences in either the field emergence or rate of imbibition of the lots. In two successive imbibition cycles seeds of Provider (brown testae) took up water far more rapidly in the second imbibition (78% weight increase after 3 h) than the first (25% weight increase). The coloured testae normally adhere very tightly to the cotyledons but were loosened following the first imbibition leading to a more rapid uptake of water. The rapid imbibition of Tenderette (white testae) which has a loose fitting testa even in the dry seed was increased only slightly by a second imbibition. When seeds were imbibed from one end only from which the testa was removed Tenderette imbibed rapidly (90% weight increase after 12 h) whereas in Provider the tightly adhering testa limited the rate of water uptake (42% weight increase after 12 h) despite the ready access of water to the seed. It is suggested that the degree of adherence of the testa to the cotyledons is the major factor influencing the rate of imbibition of cultivars of dwarf French beans differing in testa colour and its role in determining seed vigour is discussed.

Association of differences in seed vigour in long bean ( Vigna sesquipedalis ) with testa colour and imbibition damage

Field emergence of 11 seed lots from six cultivars of long bean, all having laboratory germination of > 80%, ranged from 0 to 83%, indicating differences in seed vigour. Vigour differences occurred within and between cultivars, seed lots from cultivars with white or partly white testas having particularly poor emergence (0–21%) compared with those with brown or black testas (41–83% field emergence). The significant ranked correlations between field emergence and (i) solute leakage, measured by the electrical conductivity of seed soak water ( r = –0·864), (ii) the percentage of cotyledons made up of completely living tissue, revealed by vital staining ( r = 0·895), and (iii) the proportion of hard seeds ( r = 0·916) indicated that lots with low vigour and potentially poor field emergence could be identified before sowing. Seed lots having low vigour imbibed water rapidly; the improved vital staining when seeds imbibed slowly indicated that damage occurred during imbibition and was a cause of low seed vigour. Rapid water uptake by low-vigour seed lots was partly explained by the incidence of seeds with cracked testas, but other factors could not be eliminated. The significance of differences in water uptake between cultivars differing in testa colour is discussed in relation to breeding for improved emergence.

Scottish wildflower seeds: Production and use

Summary In this brief review, the use of wild flower seeds is described as a contribution to the enhancement of biodiversity and as a way of improving grassland and other plant communities. Ecological concerns about sowing seeds in locations that are climatically contrasted to the countries from which the seed is sourced are discussed. Characteristics that aid the spread and survival of normally uncultivated species create difficulties in seed production and use. Establishment of a crop for seed production and subsequent weed control can be troublesome and procedures to achieve these have been developed based on experience. Harvesting methods are selected and modified to suit the maturity and dispersal characteristics of different species. Drying and processing, to ensure the removal of a large proportion of the unwanted material, such as appendages that aid wind dispersal, insect parts and weed seeds, can consist of as many as 10stages for some species. As the final stage in production, seed quality control of wild flower seeds through germination testing has not been routine in the past. Our research has identified appropriate dormancy breaking treatments for a range of species, so that we currently can test the quality of seeds both from different harvest years and periods of storage.

Morphological and physiological characteristics of seeds and their capacity to germinate and survive.

The past few years have seen a marked increase in the number of papers on seed science that are received for publication in Annals of Botany, from under ten per year to over 40, resulting in 44 papers on seeds published in the last two years. The topics range from aspects of ecology, through physiology to molecular biology. The topic of dormancy has received considerable attention, including papers that have examined the morphological features that regulate dormancy and germination, and the influence of dormancy on survival in a range of environments. The first four of the papers in this Highlight fall into this category

Seedling vigour and susceptibility to diseases and pests

The emergence and early seedling growth of pea, faba bean (field and broad bean), chickpea and lentil can be reduced by both seed- and soil-borne fungi. The susceptibility to soil fungi in pea is largely due to areas of dead tissue on the cotyledons, caused by both ageing and rapid imbibition, resulting in the leakage of solutes into soil. The influence of dead tissue and leakage on fungal growth is discussed, as is the evidence for similar phenomena in the other crops. The significance of seedling vigour in relation to pests is considered and exemplified by the effects of leaf weevil (Sitona lineatus) on pea and faba bean.