and there were no significant differences between cv. RvP and Bb 1277.The results are discussed in relation to the breeding potential of the high nutritive value of the Po valley ecotype Bb 1277 and the use ofthe DMD and FI determinations for selecting for improved herbage quality in Italian ryegrass.The influence of harvesting date on the nutritive value of the Italian ryegrass cv. RvP from Belgium and of Bb 1277, an introduced ecotype from the Po valley, was investigated.Ten clonally replicated genotypes of each population were grown as closely spaced plants and two ramets of each genotype harvested every 4 d for a period of 28 d after inflorescence emergence. Dry matter digestibility (DMD) was estimated and fibrosity index (FI) determined on both the leaf and stem fractions, and cellulose and lignin concentrations were determined on the stem fractions.The nutritive value of the leaf in terms of both DMD and FI, which was the same for both cv. RvP and Bb 1277 throughout the period of harvesting, was always higher and declined at a slower rate with increasing maturity than that of the stem. The stem of Bb 1277 declined in DMD and increased in FI and cellulose concentration at a significantly slower rate than cv. RvP. Significantly higher levels of DMD were detected in the stem of Bb 1277 for harvests 5 to 8 and significantly lower levels of FI and cellulose concentration from harvests 4 to 8. It was not, however, possible to detect any significant diflerences in stem lignin concentration. Dry matter yields increased throughout the period of harvesting

An experiment is described in which the effects of different spring managements on the potential seed yield and seed yield components of three white clover cultivars of contrasting leaf types were assessed. Cv. S184, the small-leaved variety, produced more but smaller inflorescences than CVS Olwen, a large-leaved variety, or Menna, a medium-leaved variety. However, cv. Olwen, produced inflorescences with more florets, seeds per inflorescence and a higher seed yield per ten inflorescences than the other cultivars. Both potential seed yield and the individual yield components were influenced by management. Cv. Olwen produced more inflorescences and a higher potential seed yield under a cutting system than under grazing systems, which reduced the number and size of the inflorescences. Cvs S184 and Menna were less influenced by management system and performed similarly under cutting and grazing. The highly significant relationship between the number of ripe inflorescences and potential seed yield showed clearly that high seed yields are only achieved if the crop is harvested when the number of ripe inflorescences is at a maximum. The relatively short duration of the period of maximum ripre inflorescences emphasized the importance of determining the correct harvesting date, although weather conditions Correspondence to: Dr P. A. Hollinglon, Institute for Grassland and Anima! Production, Welsh Plant Breeding Station, Aberyslwyth, Dyfed. SY23 3EB, U.K. also play an important part in deciding when to harvest. Florets per inflorescence, seed set and 1000 seed weight remained relatively constant over the harvest period, and were not influenced by harvest date. The results are discussed in relation to the management of white clover seed crops and the importance of climatic conditions during seed production.

Three contrasting white dover varieties, Olwen (large-leaved), Menna (medium-leaved) and SI 84 (small-leaved) were sown with and without a grass companion in 30 cm drills. Two grazing and one mechanical spring defoliation managements were imposed. Counts of the total number of inflorescences and of the percentage in various ripeness categories were made throughout the period of seed crop development to determine the pattern of inflorescence development and optimum harvest date. Inflorescence numbers were greatest in cv, SI 84 and least in cv, Olwen and, in general, varieties produced both more inflorescences and a greater proportion of ripe inflorescences when grown under spring defoliation managements similar to those for which they were bred. Thus, cv. Olwen produced more ripe inflorescences, and a lower proportion of brown inflorescences (semi-ripe), after mechanical defoliation while cv, Menna produced more ripe inflorescences following mechanical defoliation and rotational grazing. However, cv. S184 produced more ripe inflorescences under both grazing managements than under mechanical defoliation. Optimum harvest date was not affected by management or variety, total inflorescence number and maximum ripe inflorescences having reached a peak on 11 September. However, varieties Correspondence lo: Dr A. H. Marsiiiiii. Instiiuie for Crassland and Animal Produclion, Welsh Plant Breeding Station, Abcrysiwyih. Dyfed, SY23 3EB, U.K.differed in the proportion of ripe and brown (semi-ripe) inflorescences on this date, with cv. Menna and cv. S184 containing a significantly higher proportion of brown inflorescences than cv. Olwen, The implications of these differences in inflorescence development, the proportions of inflorescences in the various ripteness categories and their contribution to seed yield are discussed in relation to the management of white clover seed crops and harvesting method under UK climatic conditions. IntroduetionWhite clover seed production in the United Kingdom is limited because of the difliculty of obtaining consistent economic seed yields (Hides et ai, 1984) despite the higher seed yield potential of recently bred UK varieties (Evans and Davies, 1978; Evans ei al., 1986). This can be attributed partly to variable weather conditions during critical periods of crop growth (Hides et al.., 1984) and also to the lack of suitable seed crop management practices for optimising seed yield. Clearly, if UK seed production is to be increased then it is essential that management systems are developed which improve the reliability of seed yield of these varieties within the constraints of the variable UK climate, Deflning optimum seed crop management practices is also complicated by the fact that varieties have been bred for the demands of different agricultural systems and are classified into leaf size categories, each exhibiting different growth patterns and stolon morphologies. Smallleaved varieties, which have a dense mat of small, branched stolons, have been bred for persistency under continuous heav...

AbstraetNine varieties of Italian ryegrass were subjected to two generations of selection for cold tolerance using a controlled environment test. Selection led to a significant overall improvement in average tiller survival from 39-8 to 47-7%, even though the selection intensity achieved was not more than 20%. Although individual varieties varied in initial tolerance from 31-1 to 71 4%, the cold room tests were not sufficiently sensitive to attach significance to differences in response to selection which varied from 0-3 to 17-6%. Agronomic assessment of spaced plants indicated that the winter and spring growth potential of all nine varieties was unaffected by selection for cold tolerance. Although some of the selected populations showed a significant decline in their total yields and persistency, others showed no significant change in these characteristics. The plant breeding implications of these results are discussed.

Inoculation in the glasshouse revealed marked differences in resistance to both ryegrass mosaic virus (RMV) and crown rust (Puccinia coronata Corda) among eight unselected populations of Italian ryegrass (Lolium multiflorum Lam.). Two generations of selection for crown rust resistance led to a significant improvement in all eight populations, while one generation of selection for RMV gave a more variable response. Frequency distributions of individual genotype scores suggested that much of the resistance to crown rust was under the control of one or two genes with major effects, while resistance to RMV appeared to be controlled by a large number of genes each having a small effect. In the field, resistance to RMV meeisured after 20 months was strongly correlated with that obtained in the glasshouse. Natural infection by crown rust in the field was too low to reveal any differences between populations, although three populations from the Po Valley region of Northern Italy became heavily infected with Puccinia recondita. Selection for disease resistance significantly reduced the persistency of three populations, but that of four others was unaffected and one showed a significant improvement. Selection reduced water‐soluble carbohydrate (WSC) levels in spring slightly but significantly from 27.6 to 25.8% WSC overall. These results emphasize that agronomic performance must be monitored during selection for disease resistance.