A high level of resistance to the bean common mosaic virus strains NL3 and NL4 when inoculated separately or together was confirmed in the cultivars Turkish Brown, Valja and 1750–73. Following crosses between the susceptible cv. The Prince and all three resistant cultivars, inoculation of F2 and F3 populations revealed that the cvs Turkish Brown and Valja each differed from The Prince in being homozygous for a major recessive gene conferring resistance to both NL3 and NL4. Homology tests indicated that the same gene was present in both Turkish Brown and Valja. Polygenes in Turkish Brown and Valja also appeared to confer some resistance to NL3, or environmental variation led to continuous distribution patterns in the F2's of resistant parents crossed with The Prince. Although a major recessive gene controlled resistance to NL3 in cv. 1750–73, it differed from that in the two other resistant cultivars. In addition, cv. 1750–73 carried a dominant gene determining reaction to the virus; probably the I gene originally found in Corbett Refugee. An attempt is made to relate these results to Drijfhout's (1978) gene-for-gene model. Using Drijfhout's gene nomenclature all the cultivars tested appear to carry the strain nonspecific gene bc-u. Further genetical tests will be necessary to determine with certainty which, if any, of Drijfhout's strain-specific resistant bc-genes are present in the three resistant cultivars studied here.

This study was carried out to investigate the effect of crossing the subtropical fat-tailed Ossimi (O) sheep with the Hampshire (H) on ewe and lamb performance. Data used involved 457 ewe records of Ossimi, Hampshire and four crosses, and 404 lamb records of Ossimi and five crosses.

Hampshire ewes performed less well than the local Ossimi ewes in various reproduction traits. They weaned 0·26 lamb/ewe run with the rams compared with 0·82 from the local ewes mated to Hampshire rams. The Hampshire ewes seemed to be anoestrous during the first part of the normal breeding season of the local ewes (May–July). Different Hampshire–Ossimi cross-bred groups showed better ewe reproduction performance than the purebred Hampshire ewes, but were inferior to the Ossimi. The first cross ewes were, generally, the best among all the cross-bred ewes and the reproduction performance declined with increasing percentage of Hampshire genes. When the first cross was interbred, ewe performance declined clearly in the F2. All cross-bred groups of ewes gave significantly heavier annual greasy-fleece weight than Ossimi ewes.

The only lamb performance trait that was improved by up-grading the Ossiroi sheep with the Hampshire breed was the first greasy-fleece weight, while lamb survival and weaning weight were clearly decreased with the advance of up-grading.

The recombined cross-bred groups ( and ⅝ Hampshire) proved to be the best cross-bred and showed considerable improvement in lamb performance traits over the local Ossimi sheep, except for lamb survival.

It is concluded that crossing Ossimi sheep with the Hampshire improved only fleece weight but not lamb production.

Ewes in body condition scores of 2·4 (thin) or 3·2 (fat) on a 5-point scale and suckling twin lambs were grazed at two stocking rates for the first 16 weeks of lactation. Paddocks were grazed for periods of 2 weeks at densities of 80 and 160 ewes/ha in weeks 1–8 and then 70 and 140 ewes/ha in weeks 9/16 of lactation.

Intakes of herbage by ewes were not significantly affected by body condition. Estimation of milk yield by weekly measurement of secretion rates over 4 h failed to demonstrate significant differences due to body condition except in weeks 9, 11 and 12, although there was a tendency throughout for fat ewes to produce more milk. However, the daily growth rates of the lambs during the first 8 weeks and the overall live-weight gains were significantly higher for lambs suckled by fat ewes than for those suckled by thin ewes. Intake of herbage by lambs was not affected by the body condition of the ewes.

Herbage intakes, milk yields and lamb growth rates were all significantly higher at the low stocking density than at the high stocking density.

The results are reported for an experiment in which nitrogen rates from 0 to 672 kg/ ha and potassium rates from 0 to 558 kg/ha were applied annually on an S. 24 perennial ryegrass sward. At each of the five crops cut annually the yields of herbage dry matter and crude protein, and the potassium content of the herbage dry matter were determined. The potassium content of the soil was also measured annually. Models relating each of these variates to the nitrogen and potassium rates were derived, and their validity is demonstrated with reference to the results from earlier experiments. The problems associated with determining the correct rate of potassium fertilizer to apply on swards receiving given rates of nitrogen fertilizer are discussed using the models to predict the effects of different nitrogen-potassium combinations. In order to relate the implications of this discussion more closely to practical grassland management, economic as well as biological criteria are taken into account by incorporating cost factors in the models.

Groups of weaner pigs, and single animals, were observed in a temperature-controlled room isolated from external noise and light for periods of up to 4 weeks. Continuous records were made of motor activity, food intake and water consumption.

In the presence of a cycle of 12 h light and 12 h dark at 25 °C groups of pigs were most active in the light and took most of their food towards the end of the light period. Single pigs also tended to be more active in the light, but the rhythms were less marked, and one animal was most active during the dark period.

In continuous light, rhythms of activity and ingestion tended to collapse after only a few days, particularly in pigs which were kept by themselves. When the ambient temperature was increased to 35 °C during 12 h light and decreased to 25 °C during 12 h dark, a group of pigs was most active in the dark.

Experiments were made over a 3-year period in order to evolve a production package for yam that would eliminate the laborious operations of hand weeding and staking. First, nine herbicides were applied to yam plots before or after yam emergence. On the basis of weed control effectiveness and low phytotoxicity to yam plants, ametryne (2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-S-triazine) was chosen for subsequent experimentation. Next, ametryne at 2, 4 or 6 kg/ha was applied to yam plots either immediately after planting, or with 1 kg/ha paraqviat (l, 1'-dimethyl-4,4'- bipyridinium ion) 3 weeks after planting. The delayed applications gave more effective weed control and higher yields than the early applications. For the delayed application, 4 and 6 kg ametryne/ha did not give significantly different yields, but yielded significantly more than 2 kg/ha. When a combination of ametryne at 4 kg/ha and paraquat at 1 kg/ha was applied 3, 6 or 9 weeks after planting, the weed control effectiveness was greatest at 6 weeks after planting while the 3- and 6-week applications did not give significantly different yields. Herbicide applied 9 weeks after planting gave the poorest weed control and the lowest yields.

Finally comparisons were made between the conventional staked, hand-weeded yam production, and a new production package in which the yams were not staked and weeds were controlled with ametryne (4 kg/ha) + paraquat (1kg/ha) applied at or just before emergence. When small (150g) setts were used, yields from the new package were not significantly lower than those from the conventional system, even though the new package was considerably less laborious. Cultivation with large setts, however, resulted in a decrease in yield when the plants were not staked. Strategies that could further enhance the attractiveness of the new production

A model study of light absorption by rectangular hedgerows with different row orientations was made.

The effect of row orientation on daily light absorption is greatest around 25° latitude. North–south orientation gives highest absorption for most of the year near the equator. At higher latitudes, up to 55°, absorption is highest with N–S orientation during the summer months and with E–W orientations for the rest of the year, but the magnitude of the difference between orientations decreases with increasing latitude. From 65° upwards, E–W orientation gives highest absorption all the year round, but the difference among orientations is minor. The effect of orientation will be smaller as cloudiness is greater.

The results of this study are wholly consistent with yield differences due to different orientations, reported in the literature.

An analysis of development of Golden Promise and Maris Mink spring barley grown in England and in Scotland was made in 1976 and 1977. In both seasons the differences between varieties at a site were small. Rates of leaf emergence and primordium production and the number of primordia formed and the number which died were almost the same at both sites in 1976. In 1977 both leaf emergence and ear initiation started later in Scotland and the rates of leaf emergence and spikelet initiation were slower. Fewer spikelet primordia were formed in Scotland than in England in 1977 but a higher proportion survived to produce potentially fertile florets. Tillers emerged at the same leaf stage of the main shoot and the frequency of tillering differed at some tiller positions between England and Scotland, but the number of tillers produced was similar at both sites.

These results show that in Scotland the effect of longer photoperiod which enhances the rate of leaf emergence and primordium production compensates for the lower temperature which slows down these processes. The lower temperature in Scotland particularly in 1977 during the period of spikelet primordium death increased the proportion of spikelets that survived.

Two semi-dwarf and two conventional height European spring wheat varieties were grown at different sowing dates and sowing rates in two dry years. Yield component analysis showed the varieties to fall into three groups. The conventional height varieties were dependent for grain yield on either a high number of ears or a large number of spikelets per ear whereas the semi-dwarfs were dependent on high spikelet fertility.

The semi-dwarfs were consistently higher yielding over a range of environmental conditions than the conventional height varieties. Maintenance of high yield was associated with high spikelet fertility and 1000-grain weight, characters determined late in development. It is suggested that the change to the semi-dwarf plant type has resulted in high yields with greater consistency over a range of environmental conditions particularly when dry.

In St Vincent, West Indies, the yellow passionfruit (known as Passiflora edulisf. flavicarpa Degener, but probably specifically distinct from P. edulis Sims) is grown commercially and is pollinated by the indigenous bee Xylocopa mordax Smith. The diel patterns of anthesis and nectar availability are described and related to the timing of bee visits and pollination. Flower-bagging experiments confirmed that the setting of fruit depended on cross-pollination, was prevented by exclusion of flower visitors, and was sometimes limited in the field by inadequate pollination.

Bees collected Passiflora nectar, and evaporated it on their tongues from 45–50 % to 62–63 % sugar before storing it. But the Passiflora pollen deposited on the bee's dorsum was groomed off and rejected; only Gliriddia pollen was used for bee bread. Thus the bees treated ‘acceptable’ (Gliriddia) pollen and ‘unacceptable’ (Passiflora) pollen differently, and since pollen unacceptability improves the pollen's chance of reaching a stigma, it may be a widespread adaptation.

The yellow passionfruit flower shows many features characteristic of tropical Xylocopa flowers. Here, as elsewhere, this introduced crop depends for its pollination on indigenous bees which, though suitable morphologically and behaviourally, are not abundant enough to cause a high proportion of flowers to set fruit. The setting of fruit might be improved by increasing bee populations through provision of more timber for nestsites, and suitable flowers to supply pollen and nectar throughout the year.

Yields of two spring barley varieties, Golden Promise and Maris Mink, were greater at the Scottish Plant Breeding Station (SPBS) than at the Plant Breeding Institute (PBI) in both 1976 and 1977. In both seasons more ears per plant were produced and the number of grains per ear was greater at the SPBS. Weight per grain was greater at the Scottish Plant Breeding Station in both 1976 and 1977, but the distribution of grain size along the ears differed between seasons. Grain at the tip of the ears of plants grown at SPBS in 1976 was lighter than the corresponding grain on the Cambridge-grown plants. In 1977 the SPBS-grown plants had heavier grains at all the main shoot spikelet positions. At the SPBS the relative difference between main shoot and tillers 1 and 2 was smaller than at the PBI.

These results are taken to indicate that the combination of climatic factors in Scotland affects plant development in such a way that intraplant competition is reduced and more spikelet primordia survive to form grains and more tillers produce fertile ears.

Three ewes were intraduodenally infused with yeast RNA (15, 20 and 30 g/day) or control solutions for 3 days and the net changes in urinary allantoin excretion determined. Four mature wethers fitted with a re-entrant cannula in the proximal duodenum were fed two levels (0·66 and 1 × maintenance) of pelleted lucerne hay. Allantoin excretion was compared with total nucleic acid (NA) flow in the small intestine.

The average proportion of the recovery of the infused RNA-N dose as urinary allantoin–N amounted to 0·119 ± 0·0046. The values of the net increase of allantoin-N (Y, g/day) above control levels were highly significantly correlated (n = 12, r = 0·98) with amounts of RNA-N infused (X, g/day): y = 0·1185 (± 0·0086) X–0·004 (P < 0·001). The average ratio of urinary allantoin-N to NA-N passing the duodenum during 24 h was 0·173. A difference between the two conversion factors is discussed in relation to endogenous allantoin excretion and purine base composition of yeast and bacterial RNA.

In a field experiment in the north-west region of Tasmania, poppies (Papaver somniferum L.) were harvested at weekly intervals beginning 10 days after full bloom and continuing until 4 weeks after the dry commercial harvest stage. At each harvest the plants were cut off at ground level and partitioned into terminal capsules, lateral capsules, seed and the combined stem plus leaf component.

The dry-matter yield of total plant and of all the components except seed achieved maximum values 2–3 weeks after full bloom and then progressively declined. For the total plant this decrease between maximum dry weight and that at the time of commercial harvest (8 weeks after full bloom) amounted to 26% while for terminal capsules it was 37% for lateral capsules 15% and for stem plus leaves 39%. In contrast, the dry-matter yield of total seed rose to a maximum by 4 weeks after full bloom and then remained constant for the duration of the experiment.

The morphine concentration of both terminal and lateral capsules reached a maximum value of 1·1% 6 weeks after full bloom and then decreased by about 10% at the dry harvest stage. The morphine concentration of stem and leaves also reached a maximum of 0·1% about the same time as capsules but decreased rapidly and had halved by dry commercial harvest. The mutually compensating factors of decreasing dry-matter yield and increasing morphine concentration gave similar total plant morphine yields at any time of harvest from 2 to 7 weeks after full bloom. The morphine extracted from the whole plant at these times of harvest was about 50% greater than that derived from capsules alone at the time of dry commercial harvest.

Field trials were made in the rainy seasons of 1970–4 at the Indian Agricultural Research Institute, New Delhi, to evaluate several systems of intercropping maize and sorghum with soya beans. Maize yields were not affected by intercropping with soya beans but sorghum yields were reduced. Though the yield of soya beans when intercropped was less than that of a sole crop, the combined grain yield of the two crops in an intercrop was more than the individual components. Land equivalent ratio (LER) increased to a maximum of about 48 and 31% by intercropping maize and sorghum with soya beans compared with the cereal sole crops. Maize rows planted 120 cm apart and intercropped with two rows of soya beans or sorghum planted 90 cm apart intercropped with one row of soya beans proved to be the best intercropping pattern.

A closed-circuit respiration chamber was used to study (a) the effect of confinement in a chamber on the heat production of pigs already accustomed to restraint in a metabolism cage; (b) changes in daily heat production of pigs following a reduction in the energy intake; and (c) the effect of increasing or decreasing the environmental temperature.

An automatically recharged version of the oxygen burette used by Waring & Brown (1965) is described. During tests of the chamber and burette system the mean recoveries of carbon dioxide and oxygen were, respectively, 0·994 and 0·995.

It is concluded that measurements of heat production on the first day of confinement were within the normal range of variation and provided valid estimates of energy expenditure.

The minimum value for the respiratory quotient (RQ) occurred on the third day following a reduction in energy intake, and it is concluded that the direct effect of previously ingested nutrients was eliminated by the third day. However, there appeared to be a further decline in heat production until 6–7 days following the reduction in energy intake.

The heat production of singly caged pigs fed almost to appetite was similar at 22 and 29 °C. Heat production increased at 15 °C, indicating that this was below the lower critical temperature of fed 25 kg pigs. The response of heat production to the low temperature continued for at least 18 days. Variations in heat production between animals and litters were as high as 15% in three experiments.

Four genotypes of dry beans were compared at three planting dates during one season (April to June, 1976) and four planting dates during a second season (November 1976 to January 1977). Yield declined with delay in planting in both seasons but in the second season yields were lower at the first planting and declined less rapidly. Canadian Wonder was the most stable-yielding genotype and had highest mean yield though it may have been inferior to other genotypes at the two most favourable plantings. Its stability was attributed to drought escape and good field resistance to drought and disease. Mexican 142 was the least stable genotype. A black-seeded landrace yielded well in dry conditions in spite of its long duration.

The most important components determining planting date effects on yield were numbers of pods per plant and seeds per pod. Canadian Wonder had markedly more stable numbers of pods than any other genotype.

Cooler temperatures in July and August retarded crop development in the first season. For one planting of the second season, flowering was retarded by 7–10 days in all genotypes and this was apparently an effect of water shortage. No effect of water was apparent on the time taken from flowering to maturity.

Three experiments, each consisting of a feeding trial plus a digestibility and nitrogen retention study, compared long barley straw with rolled barley as basal diets and oat hulls with maize starch as energy supplements for yearling dairy cattle. The protein ontent of the diets was varied by the addition of flshmeal.

Growth rates were reduced by the dietary combination of high fibre and low protein, so that diets rich in straw, or containing a supplement of oat hulls, gave a large response to a supplement of fishmeal compared with low straw or maize starch supplemented diets. The data suggest a crude protein concentration of 115 g/kg dry matter as a requirement for high fibre diets supplemented with fishmeal, when fed to yearling cattle. Retention of nitrogen reflected the pattern of live-weight gain. Molar proportions of VFA were affected by changes in the roughage: concentrates ratio, except where energy and protein intakes were both low.

Barley straw was of a higher nutritive value than oat hulls.

Trials were conducted on 21 farms to examine the influence of supplementary zinc on growth rate of 978 beef cattle maintained on winter rations typical of N.E. Scotland.

The concentration of zinc in the normal farm rations ranged from 13·3 to 32·1 mg/kg D.M. and half of the animals on trial on each farm received supplements providing an additional 60 mg Zn/kg D.M. Before supplementation, the farm mean plasma zinc concentrations varied from 0·73 to l·10mg Zn/l; these levels were not elevated by zinc supplementation.

The differences in mean daily weight gain between zinc-supplemented and control cattle on individual farms during 100–140 days on trial ranged from –0·14 to +0·22 kg/day and were not related to plasma zinc concentration before supplementation or to the zinc content of the basal rations. The mean daily weight gain of heifers receiving supplementary zinc was significantly greater (P < 0·02) than that of the controls by 0·05 kg/day during the first 60–80 days only. Bulls and steers showed no response to supplementary zinc.

Fishmeal, soya-bean meal and urea were compared as nitrogen sources in diets rich in fibre for yearling cattle, using feeding trials and digestibility and nitrogen retention studies. All animals were individually fed. Diets supplemented with fishmeal supported the highest rates of daily live-weight gain and nitrogen retention. There was no response in dry-matter intake and digestibility from extra nitrogen, either from fishmeal or urea, when the crude protein of the diet was 8·5% or over, and a small response in digestibility when soya-bean meal was used.

Molar proportions of VFA, rumen NH3-N concentrations and blood urea nitrogen concentrations were all affected by both amount and source of nitrogen supplementation. Multiple regression analysis showed the undegradable protein supply to be more critical with high than with low fibre diets.

In three pot experiments and one field trial, the apical portion of the main stem of two soya-bean varieties (cv. Hampton and cv. Bossier) were removed at 3 weeks or 5 weeks after sowing in order to evaluate the response of the plants to the loss of apical dominance.

The results showed that early loss of apical dominance in Hampton (an indeterminate variety) led to increased vegetative development but shorter plants, higher dry-matter accumulation and increased seed yield through the production of more and/or heavier pods. On the other hand, apical debudding of Bossier (a determinate variety) during the vegetative stage evoked no significant beneficial response and in the case of field debudding at 3 weeks after sowing, plant height was decreased and seed yield was significantly reduced.

The response of soya bean to the loss of apical dominance therefore seems to be a function of the stage of vegetative development when the loss occurs as well as the growth habit of the variety.