Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. A STUDY OF THE RELATIONSHIP BETWEEN SEED VIGOUR AND SEED PERFORMANCE IN TRIFOLIUM PRATENSE L. CV. GRASSLANDS PA WERA A thesis presented in partial fulfilment of the requirement for the Degree of Master of Agricultural Science in Seed Technology at Massey University Palmerston North New Zealand Yan Rong Wang 1989 ABSTRACT Significant differences in seed vigour within lots of red clover cv. Pawera, white clover cv. Huia and lucerne cv. Wairau were recorded in a preliminary experiment. Subsequently, 7 high viability Pawera seed lots were used to explore the relationship between seed vigour, as measured in the laboratory, and seed performance, both in the field and in storage. Four vigour testing techniques i.e. conductivity, accelerated aging (AA), controlled deterioration (CD) and speed of germination were employed. Results for standard germination (SG) and each of the vigour tests were related to seed performance by correlation analysis. Field performance was monitored for 6 seed lots, sown at 8 dates through spring and autumn. Seed storability was determined by measuring the viability of 4 seed lots under 5 storage conditions ( including ambient open storage and simulated temperate controlled storage :20 °c, 45% to 90% RH ) over a total of 11 months. The effects of mechanical damage, thousand seed weight, imbibition rate and storage fungi on seed viability and vigour were also investigated and seed quality changes during storage were monitored. The vigour rankings found in the laboratory were consistent with those for field emergence, emergence rate over the 8 sowings and performance during storage. Low vigour lots also showed a significant reduction in seedling dry weight for the autumn sowings when soil temperatures were very low. Each of the four vigour techniques were able to provide more accurate parameters for predicting seed performances than the SG test. For predicting seed field emergence over all the sowings, the best result was provided by the CD test at either 16% or 18% seed moisture content (r = 0.933 and 0.911 resp. ), followed by AA (2-day AA of surface sterilized seed) (r = 0.840) and conductivity (r = -0.602). For predicting seed storability, the best result was obtained from the CD test (at either 18% or 20% seed moisture content) for ambient storage conditions, and from both CD (either 18% or 20% seed moisture content) and AA (3-day aging) under controlled storage conditions. Correlation coefficients for vigour tests and storage performance tended to vary between storage periods. ii Seeds which imbibed water rapidly (within 4h) were low in viability and vigour, but this was generally related to the extent of mechanical damage to the seed coat. Seed weight was not related to seed vigour. Seed deterioration during storage was associated with increasing conductivity, abnormal seedlings and dead seed content, and decreasing germination rate, normal seedlings, and field emergence. Vigour was lost before viability. The deterioration rate was quicker at high RH (75 and 90% RH), since the seeds were quickly invaded by storage fungi. The present experimental results strongly suggest that standard germination was a poor predictor of seed performance, both in the field and during storage. Both accelerated aging and cormolle 0.30, i.e. r > 0.548) to field emergence at least at 6 of the 8 sowings 6-11 Correlation coefficients between initial quality of 4 Pawera seed lots and germination after storage for different periods at 20 °C-45% RH 6-12 Correlation coefficients between initial quality of 4 Pawera 85 85 86 87 90 91 93 94 95 96 99 Xlll seed lots and germination after storage for different periods at 20 °C-60% RH 6-13 Correlation coefficient for initial quality of 4 Pawera seed lots and germination after storage for different periods at ambient conditions 6-14 Correlation coefficient between initial quality of 4 Pawera seed lots and germination after storage for different periods at 20 °C-75% RH and 20 °C-90% RH 6-15 Summary of best vigour tests for predicting seed storability at ambient conditions 100 101 102 103 XIV LIST OF FIGURES FIGURE 4- 1 Standard germination after different periods of accelerated aging of 4 lucerne seed lots. 4-2 Standard germination after different periods of accelerated aging in red clover (J\), and white clover (D). 4-3 Imbibition (rate per 2h) of 7 red clover cv. Pawera seed lots. 4-4 Conductivity of 7 red clover cv. Pawern seed lots after different periods of soaking. 5-1 Moisture content of Pawera seed lots after storage at different relative humidities (RI 1) 5-2 Storage fungi content of Pawera seed lots after storage at different relative humidities (RI I) 5-3 Standard gerniination of 4 Pawcra seed lots stored under conditions of 20 °C-45% RI I (A), 20 °C-60% Rll (I3), and ambient (C). 5-4 Standard germination of 4 Pawera seed lots stored under conditions of 20 °C-75% RH (A), 20 °C-90% RH (B). 5-5 Pour-day count of standard gennination of 4 Pawera seed lots stored under conditions of 20 °C-45% Rll (A), 20 °C-60% RH (13), and ambient (C). 5-6 Four-day count of standard germination of 4 Pawera seed lots PAGE 51 52 55 57 65 65 69 70 73 xv stored under conditions of 20 °C-75% RH (A), 20 °C-90% RH (B). 5-7 Conductivity of 4 Pawera seed lots stored at 20 °C-45% RH. 5-8 Conductivity of 4 Pawera seed lots stored at 20 °C-60% RH (A), and ambient (13). 5-9 Conductivity of 4 Pawera seed lots stored at 20 °c-7 5% RH. 6-1 Relationship between AA.2(1), AASS2 (2), CD16 (3), and CD18 (4), and field emergence averaged across the 8 sewings. 6-2 Relationship between conductivity and seed storability at ambient conditions for 7 months (1), and 11 months (2). 6-3 Relationship between AA3 and seed storability at ambient conditions for 7 months (1), and 11 months (2). G-4 Relationship between CD 18 and seed storability at ambient conditions for 7 months (1), and 11 months (2). 6-5 Relationship between CD20 and seed storability at ambient conditions for 7 months (1), and 11 months (2). 74 80 81 82 97 104 104 105 105 XVI LIST OF PLATES PLATE 1. Standard germination ( 4-day count) for seed lots 3 and 4 2. Germination (4-day count) following controlled deterioration at 18 % seed moisture content 3. Seed infected with a Aspergillus glaucus following storage at 20 °C-75% RH for 5 months 4. Seed infected with a Penicillium sp. following storage at 20 °C-90% RH for 2 months 5. Gem1ination (4-day count) after storage under ambient conditions and at 20 °C-45% RH for 3 months 6. Field emergence of a low vigour (lot 3) and high vigour (lot 4) seed lot 7. Seedling size for a low vigour (lot 3) and high vigour (lot 4) seed lot , 5 weeks after sowing in autumn PAGE 61 61 67 67 75 88 88 xvii LIST OF APPENDICES APPENDICES 1. Seed moisture content (%) of 4 Pawera seed lots stored for 11 months at different relative humidities 2. Storage fungi content of 4 Pawera seed lots stored for 11 months at different relative humidities PAGE 141 142 xviii