Membrane Damage During Seed Deterioration And Its Measurement And Control In Forage Species

Studies of physiological response to seed deterioration, seed vigor tests and seed priming are essential for quality assessment of forage species and development of grassland production. A series of experiments were carried out under laboratory, glasshouse, and field conditions; using seeds of 3 forage legume and 2 forage grass species, namely, lucerne (Medicago saliva), vetch (Vicia benghalensis), milkvetch (Astragalus adsurgens), sudangrass (Sorghum sudanense), and wheat grass (Elymus sibiricus). Seed membrane damage and the contents leaked out during seed deterioration were studied. Sequences of seed deterioration were measured by electrical conductivity tests and the differences in mechanisms between forage legume and grass species were determined. The relationship between ethylene production during germination and disease resistance in the process of seed deterioration was detected. Vigour test techniques for assessing seed deterioration were evaluated and the seed priming method was developed for forage crops.The results showed that the membrane of deteriorated seed was damaged, and its permeability increased as indicated by increase in leakage. However, the responses were different between legumes and grasses. For all legume species tested, electrical conductivity of seed leakage was significantly correlated with seed viability (P < 0.01). The relationships could be expressed by the following regression equations: y = -1.866x + 288.56 (r = -0.982) for lucerne; y = -1.099x + 194.20 (r = -0.902 ) for vetch; and y = -1.889 x + 308.22 (r = -0.983) for milkvetch, where y is electrical conductivity and x is seed viability. However, this relationship did not exist for the two grass species, and the electrical conductivity values of grass species were very low.The contents of calcium, potassium, and 17 amino acids, both in total and in individuals, that leaked from aged lucerne and vetch seeds were significantly higher (P < 0.05) than that from control seeds; however, a non-significant difference (P > 0.05) existed between aged and control seed of two grass species for these leakage components. This study presents the first explanation, from the aspect of seed solute leachate, as to why different responses toseed electrical conductivity vigour tests resulted between forage legume and forage grass seed in previous studies. The results demonstrated that the electrical conductivity test is not suitable for vigour evaluation for some grass seeds.A laboratory experiment was conducted on sudangrass to study seed coat permeability and its relationship to electrical conductivity (EC) of seed leachate. The result confirmed that the seed coat of sudangrass, although it does not prevent seeds quickly absorbing water and germinating, it prevents tetrazolium salts penetrating into the seed, and restricts certain seed leachates leaking out. Therefore, seed lot quality is not detectable by the EC test. In addition, the result indicated that this seed coat semi-permeability was gradually formed during seed maturation. As the seed matured, the EC value and imbibition rate gradually decreased. In conclusion, the EC test is not able to detect seed lot deterioration, but it can reflect the degree of seed maturation.The study also indicated that the amino acid content changed after seed ageing, and the changes varied between species. For lucerne, contents of all 17 amino acids except cystine in aged seeds were higher, and of tyrosine, glysine, phenylalanine and proline, significantly higher (P < 0.05), than those in control seeds. For sudangrass, only the contents of glysine, threonine and alanine were significantly higher (P < 0.05) in aged seed than those in the control, but contents of the other 14 amino acids did not show significant difference (P > 0.05) between aged and control seeds.The effect of aging treatments on ethylene production of seed during germination, and their relationship to seed viability in lucerne, vetch, wheat grass and sudangrass were studied. The results showed that ethylene production decreased an...