ALBERT

Notes: The effects of different spring defoliation managements on potential harvestable seed yield and seed yield components of three contrasting white clover cultivars were assessed. The small-leaved cv. S184 produced more but smaller inflorescences than the large-leaved cv. Olwen and Menna, a medium-leaved cultivar. Cultivar Olwen, however, produced more ripe and brown (nearly ripe) inflorescences with more florets, seeds per floret and a higher seed yield per ten inflorescences than the other cultivars. Potential harvestable seed yield and individual seed yield components were only influenced by defoliation after bud emergence, as defoliation before bud emergence had no effect on seed yield components. Defoliation after bud emergence had a similar effect on all cultivars: the number of ripe inflorescences was unaffected by defoliation but the number of brown and therefore harvestable (ripe + brown) inflorescences was highest following defoliation three weeks after bud emergence. Florets per inflorescence, seed per floret, 1000 seed weight, seed yield per ten inflorescences and potential harvestable seed yield were not influenced by defoliation after bud emergence. Season had a significant effect on seed yield components and influenced the effect of defoliation treatments, emphasizing the importance of climate in white clover seed production. The results are discussed in relation to the spring defoliation of white clover seed crops, harvesting techniques and the provision of guidelines for optimizing seed yield.

Notes: Three white clover cultivars, S184 (small-leaved), Menna (medium-leaved) and Olwen (large-leaved), were sown at a seed rate of 3 kg ha-1 under spring wheat cv. Tonic. In the spring of the two following years, there were three pre-bud emergence mechanical defoliation treatments on which were superimposed four post-bud emergence treatments giving a total of twelve cutting treatments. Pre-bud emergence, plots were either cut twice (at approximately two weeks before bud emergence and at bud emergence), cut once at bud emergence or not cut. To each treatment were applied four post-bud emergence treatments: plots were not cut or cut once (one, two or three weeks after bud emergence). Counts of the total number of inflorescences and of the proportions in various ripeness categories were made throughout the period of seed crop development to determine the pattern of inflorescence development and optimum harvest date. Overall, inflorescence numbers were greatest in cv. S184and least in cv. Olwen. Defoliation before bud emergence had no effect on inflorescence production; however, it was significantly influenced by defoliation after bud emergence. Although delaying the initial development of the crop, inflorescence numbers of all cultivars were highest in both years following cuts two and three weeks after bud emergence. Optimum harvest date was not affected by defoliation or cultivar, numbers of ripe inflorescences in both years reaching a peak at the end of August. The number of brown inflorescences, which may also contribute to seed yield, reached a peak in both years in late July. Seasonal differences in inflorescence production were again observed, emphasizing the difference between first and second year crops and importance of climate in while clover seed production. The implications of these differences in numbers and proportions of inflorescences in various ripeness categories under different defoliation regimes are discussed in relation to seed crop management in the UK.

Notes: Introgression of reproductive traits from the annual, profuse flowering, ball clover (Trifolium nigrescens Viv.) into white clover (Trifolium repens L.) is one breeding strategy to improve seed yields of T. repens that must be achieved without sacrificing agronomic performance and persistency under grazing. The yield and persistency of hybrids between white clover and T. nigrescens were compared under rotational sheep grazing over three harvest years. The hybrids included the backcross (BC) 2 and 3 generations produced using white clover as the recurrent parent. The large-leaved T. repens variety Olwen, medium-leaved varieties AberDai and Menna and the small-leaved variety S184 were sown as controls. Hybrids and control varieties were sown with a perennial ryegrass companion; between April and the end of October in each harvest year the plots were rotationally grazed with sheep with clover and perennial ryegrass (DM) yield and the proportion of clover present measured over the growing season. The clover and total DM yields of the BC2 and BC3 were generally comparable with the small- and medium-leaved varieties within the experiment and significantly greater than the yields of the large-leaved variety Olwen. Throughout the 3 years of the experiment the BC2 maintained a clover content above 0·30 and comparable with the small-leaved varieties, while the clover content of the BC3 was comparable with the small- and medium-leaved varieties in the first and third harvest years. No significant difference in perennial ryegrass production was observed when grown with the backcrosses or the control varieties. Differences in stolon and growing-point density were observed at the end of the experiment with the density of the BC2 and BC3 less than the small-leaved variety S184 but, in common with the medium-leaved varieties, greater than the large-leaved variety Olwen. The implication of these results for the use of this material in future experiments and in the white clover breeding programme is discussed.

Notes: Greenhouse and field experiments were carried out to study the seed development and seed yield potential of three populations of Italian ryegrass (Lolium multiflorum Lam.). These included an ecotype (Bb 1276) collected in the Lombardy Plain region of northern Italy, cv. Tribune, which was derived from this ecotype, and cv. Lemtal, a widely used cultivar from Belgium. Artificial seed shedding techniques in the green-house study showed that Bb 1276 began shedding seed at a higher moisture content than cv. Tribune which in turn was higher than cv. Lemtal. The pattern and rate of shedding was similar for all three populations and generally Bb 1276 and cv. Tribune gave a greater proportion of shed seed than cv. Lemtal. Although the pattern of decline in seed moisture content was similar for all three populations, generally cv. Lemtal had a higher moisture content than cv. Tribune with Bb 1276 the lowest. Cultivar Lemtal had the highest mean 1000 seed weight, and Bb 1276 the lowest, with cv. Tribune intermediate. The field study involving cv. Tribune and cv. Lemtal showed that with the exception of 1000 seed weight, which for cv. Tribune was some 6% lower than that of cv. Lemtal, all the seed yield components were similar. Seed yields taken every 3 days after the standing crop had reached 50% moisture content showed that both cultivars increased in yield until harvest 3. After this date the seed yield of cv. Lemtal remained stable up to harvest 5 while that of cv. Tribune declined. The maximum seed yield of cv. Tribune was achieved at a seed moisture content of 42·9% while that of cv. Lemtal remained stable from 42·3% to 37·5%. The seed moisture content of the two cultivars again showed a similar pattern of decline but it was not possible to show consistent differences between cv. Lemtal and cv. Tribune. The 1000 seed weight of cv. Tribune was lower than that of cv. Lemtal, and the maximum seed weight of cv. Tribune appeared to be achieved earlier. Germination counts taken after harvest showed both populations exhibiting a high level of post harvest dormancy. Later counts taken 3 months after harvest were significantly higher than those taken earlier and there were no differences between cultivars or harvests.The results are discussed in relation to the potential for selecting for improved seed yield potential in Lolium multiflorum Lam. Populations from northern Italy and suggestions are made for maximizing the harvested seed yield of cv. Tribune.

Notes: Three white clover cultivars, S184 (small-leaved), Menna (medium-leaved) and Olwen (large-leaved), were broadcast or sown in 15, 30 or 60 cm drills at a seed rate of 3 kg ha-1. The three cultivars were either sown without a cover-crop or sown under a cover-crop of spring barley (cv. Crescent) or peas (cv. Countess). The effects of these methods of establishment on the stolon growth and components of seed yield were subsequently measured.Stolon growth and development was influenced by row spacing, cultivar and season. The overall plant response at all but the widest row spacing (60 cm) was to increase stolon growth such that inflorescence production, the number and proportion of ripe inflorescences and the other seed yield components were unaffected by row spacing. Cultivars differed in their response to row spacing. Cultivar Olwen produced most inflorescences and more ripe inflorescences when broadcast, cv. S184 when sown at 60 cm row spacing and cv. Menna at 15 or 30 cm row spacing. Cultivars also differed in their response to cover-crop, with cvs Menna and S184 producing more inflorescences and more ripe inflorescences when sown under barley and peas than when pure sown. The inflorescence production of cv. Olwen was not influenced by cover-crop.The relationship between vegetative and reproductive growth is discussed in relation to establishment, cultivar and climate and the possible implications for the establishment of white clover seed crops in the UK.

Notes: The roles of composition and oxygen pressure in in situ growth of superconducting YBaCuO films have been studied. Anomalous results are observed at low oxygen pressure. Off-stoichiometric, Ba-deficient films have superior superconducting properties and more bulk-like crystal structure compared to films made on the 1:2:3 stoichiometry. Films made at low pressure have an expanded c axis compared to the bulk value, although their Tc's are only slightly depressed. Tc and c-axis lattice parameters are reported as a function of the deposition conditions.

Notes: Selective growth of GexSi1−x on Si is demonstrated for the first time using a pulsed laser induced epitaxy technique, combined with either standard oxide or liftoff patterning processes. Two different dimensions of Ge0.12Si0.88/Si lateral wells are formed, 3.5 μm wide by 1700 A(ring) deep, and 6 μm wide by 1300 A(ring) deep. High-resolution transmission electron microscopy, combined with energy-dispersive x-ray imaging, reveals a well-defined two-dimensional (2D) Ge redistribution profile with no significant line or surface defects observed. The 2D Ge well distribution profiles, governed by heat and mass transport during the laser processing, are discussed.