The rate of development of resistance to Du-Ter in Spodoptera littoralis (Boisd.) has been determined. The results show that true resistance to Du-Ter could not be induced throughout 33 successive generations. Also, it was found that the rate of development of resistance to DDT in the DDT + Du-Ter strain after being selected with DDT + Du-Ter pressure for 17 successive generations was 11·5- and 43-fold that in the DDT strain. It is concluded that the application of DDT and Du-Ter mixture, having dissimilar modes of action, considerably controls the development of resistance to DDT.

An attempt has been made to produce barley lines in accordance with an ideotype designed in 1968. Current lines are early maturing, uniculm, six-row barleys, of medium height, high harvest index, and moderate resistance to lodging. However, they have lax leaves of medium length, in contrast to the short, erect leaves of the ideotype. When sown in narrow rows at a rate three times that of tillered lines, they have given grain yields greater than the two- and six-row tillered controls, especially in favourable seasons, but less so in dry years. The quality of the grain has not been examined. In the absence of plasticity in number of tillers, uniculm lines show increased plasticity in number of grains per ear and weight per grain. It is possible that the uniculm habit, apart from effects on morphology and maturity, may permit more exacting selection of high-yielding plants than is possible among plants each comprising many mutually competing culms.

The carcasses of 20 Landrace, 20 Hampshire and 20 Duroc Jersey barrows were dissected in order to study the influence of the breed on tissue weight distribution.

After weaning, at 56 days of age, the animals were allocated to individual pens and fed a standard diet containing 18% crude protein and 13 MJ ME/kg, until they reached their designated slaughter weight.

The Landrace and Hampshire pigs were slaughtered between 60 and 115 kg and the Duroc Jersey ones between 40 and 115 kg live weight. The right half carcasses were completely dissected using strictly anatomical criteria. Individual muscles were classified into eight anatomical groups (Carden & Goenaga, 1977).

The results were examined by covariance analyses utilizing the allometric equation. Carcass tissue composition was studied using the weight of the dissected side as covariate. When muscle: bone ratio was examined, the weight of total side muscle was used as the independent variable. The growth of different parts of a tissue relative to the corresponding whole tissue was studied.

Concerning carcass composition, there were significant breed differences in muscle and fat contents and in the muscle:bone ratio.

Breed differences were found in muscle distribution. The 6 values of muscle groups 1 (proximal hind limb), 2 (distal hind limb), 6 (distal forelimb) and 7 (muscles connecting forelimb to thorax) were statistically different as were the adjusted means of groups 3 (spinal column), 5 (proximal forelimb) and 8 (muscles connecting forelimb to neck and intrinsic muscles of neck and thorax).

Significant differences were also found in bone weight distribution. Slope values of the tarsals, os coxae, scapula and sternum were statistically different. Adjusted means of tibia-fibula, sacrum, spinal column, radius-ulna, carpals and ribs were also significantly different.

Finally, there were breed effects in the distribution of fat, the relative weight of subcutaneous and of intermuscular fat being statistically different.

The phosphorus status of five Nigerian coastal plain sands was evaluated by determining the relative abundance of the various P forms and the P adsorption capacities of the soils. Total P ranged from 4460 to 1129 mg/kg. Organic P had a range of 23–232 mg/kg and formed below 30% of total P in four of the profiles but above 50% in the hydromorphic Otegbo profile. The relative distribution of the various inorganic forms was in the increasing order of residual P, active P and occluded P, except in the Onne profile in which the residual P was relatively the least abundant. The relative distribution of the active P forms was in the decreasing order of Fe-P, Al-P and Ca-P.

The adsorption capacity varied widely among the soils. The amount adsorbed from the addition of 150 mg/100 g of soil ranged from 40–2 to 86–2 mg/100 g and was related to the clay content. The adsorption at 0–3 mg/1 P in equilibrium solution ranged from 19 to 265 mg/kg. The subsoils generally adsorbed more P than the surface soils. The P requirements of the soils estimated from the sorption capacities were in the low and medium ranges.

The pattern of leaf growth and death was followed in stands of cowpea grown in the field at Ibadan, Nigeria. Temperature affected this pattern. Leaf area index increased quicker and leaf death started sooner during warm seasons. Individual leaves died while pods at the same node were filling. The rate of leaf appearance increased with temperature and the duration of expansion of individual leaves decreased so that a constant number of leaves were expanding at one time. The mean rate of expansion of individual leaves increased with temperature proportionately more than the duration decreased, hence final leaf size increased with temperature. Base temperatures for leaf appearance and leaf expansion were 16 and 20 °C respectively.

The pattern of dry weight accumulation and partition of cowpea crops grown in Nigeria is described. For the first 50 days, increase in dry matter was proportional to intercepted radiation. Differences in dry weight between crops were due equally to variations in incident solar radiation, the fraction of this radiation intercepted, and the efficiency with which it was used. The variation in total pod weight from 206 to 312 g/ma resulted from differences in number of pods, mean pod weight being constant. The pod weight ratio was relatively constant and there was a strong relationship between final number of pods and total plant dry weight.

Twenty-seven British Friesian heifer calves were housed as a group but fed individually barley-lucerne pellets according to a scale related to body weight. At 16 weeks and again at 31 weeks of age nine calves were implanted subcutaneously at the base of the ear with 300 mg trenbolone acetate (group T), nine calves were similarly implanted with 140 mg trenbolone acetate and 20 mg oestradiol-17/? (group TE) and the remaining nine calves were sham implanted (group C).

As a result of increased feed conversion ratios, body-weight gains were significantly greater in group T (0–80 kg/day) and group TE (0–87 kg/day) than in group C (0–72 kg/ day) during the 15 weeks following the second implant, but there was no significant difference between groups following the first implant.

Following both implants in groups T and TE the mean concentrations of urea and albumin in serum decreased, and that of globulin increased. The mean urea: creatinine ratio in the urine of animals in groups T and TE relative to that in group C also decreased.

The heifers were served by an Aberdeen Angus bull at the first and, when they occurred, subsequent oestruses. Following calving the mean milk yields in the first lactation in group T (641 kg in 96 days) and group TE (1993 in 212 days) was considerably lower than in group C (3636 kg in 293 days). The udder size in both groups of animals treated with the anabolic steroids was markedly reduced. It is concluded that despite an improvement in feed conversion ratios and body-weight gains, trenbolone acetate should not be administered to prepuberal heifers which will be retained for breeding and milk production.

Origins of the monogerm character are described and a programme to produce a wide range of monogerm fully fertile lines is discussed. Back crossing to multigerms and hybridization among accessions of monogerm lines with relatively poor performance, together with selections from monogerm commercial varieties, provided sources from which improved lines were derived by recombination and selection. In the fifth year, experimental multiline varieties were synthesized which gave promising performance when evaluated in Institute trials at several locations in 2 years.

Dissection data for 1006 pig carcasses taken from the first 2 years of the Meat and Livestock Commission's (MLC) Commercial Pig Evaluation (CPE) were used to examine the relationships between carcass components and carcass weight over the growth period from 46 to 92 kg carcass weight. Alternative models were tested and parameters examined for different genotypes (pigs from different companies in CPE), sexes (barrows and gilts), feeding regimens (ad libitumand restricted feeding) and years.

Generally, linear allometry provided an acceptable description of carcass development, although some curvilinearity was indicated for the head, kidneys, rump back joint, M. psoas and total dissected lean. Growth coefficients conformed to the generally accepted pattern of carcass development in pigs. Using linear allometry, proportional weight increases were comparable for all genotypes and sexes, but dissected fat increased relatively faster on the restricted feeding regimen.

At a constant carcass weight of 66·5 kg, all tissue weights and the weights of primary components and most joints differed by genotype. The ratio of carcass lean weights for the two extreme genotypes was 1·04; comparable ratios for carcass fat weights were 1·13 (restricted-fed pigs) and 1·07 (ad libitum-fed pigs).

Significant differences were recorded between sexes and between feeding regimens, largely reflecting differences in fatness. Some important year differences were also found.

Dissection data for 1006 carcasses taken from the first 2 years of the Meat and Livestock Commission's (MLC) Commercial Pig Evaluation (CPE) were used to examine the growth of tissue weights in joints relative to the corresponding total tissue weight in carcass, and the growth of fat depots relative to total fat over the carcass weight range, 46–92 kg. Growth relationships were examined using a linear allometric model. Differences in tissue weight distribution between genotypes (pigs from different companies in CPE), sexes (barrows and gilts) and feeding regimens (restricted and ad libitum feeding) were examined at constant lean, bone or fat weight as appropriate, common allometric regression slopes being assumed.

Lean and bone showed the same pattern of development. Relative growth was lowest in the proximal limb joints (ham and hand) increasing inwards to the joints of the back. With minor differences, the same pattern was found for subcutaneous fat and intermuscular fat. Fat depots differed considerably in their growth relative to total fat: intermuscular fat grew more slowly (allometric growth coefficient, b = 0·87), subcutaneous fat at the same rate and perinephric and retroperitoneal fat (flare fat) more rapidly (b = 1·24).

Significant differences were recorded between genotypes in lean distribution and in the distribution of fat depots. However, the differences were small and of little commercial importance. There were also differences in fat partition between genotypes, flare fat being the most variable depot.

Sex and feeding regimen also influenced tissue distribution and fat partition.

The results are discussed in relation to the robustness of regression equations for predicting overall carcass composition from subcutaneous fat measurements and sample joint dissections.

The time of parturition was recorded for 522 Friesian cows. Calvings were evenly distributed throughout the 24 hours with no bias towards day or night calving. Cows about to enter their third or subsequent lactation, but not younger cows, showed a significantly lower incidence of calving during the hours when milking was occurring. Possible mechanisms which would account for this rinding are discussed.

Growth and nitrogen fixation of three cultivars of Phaseolus vulgaris L., inoculated with strain CIAT 161 of R. phaseoli, were compared at day-night temperatures of 36–25, 30–20 and 26–15 °C.

Temperature affected the duration and magnitude of N2 (C2H2) fixation. Maximum fixation increased from 33·8 μmol C2H4 produced/plant/h at 35–25 °C to 73·0 μmol C2H4 produced/plant/h at 25–15 °C, but the peak in fixation was increasingly delayed as growth temperature was reduced. In the 25–15 °C treatment this delay in the onset of fixation led to decreasing leaf nitrogen concentrations and visible N-deficiency symptoms at the 28 day harvest.

Varietal differences in response to temperature were not marked, though one cultivar achieved greater nodule development at 35–25 °C than the others. This earlyflowering cultivar again appeared weak in N2 (C2H2) fixation with low specific nodule activity at all temperatures studied.

Results are related to bean production in Latin America, and to the possible need for ‘starter’ nitrogen in the cooler bean-producing regions.

Two field experiments with cotton were conducted over two growing seasons on calcareous, heavy to medium textured, alluvial soils, to study the influence of N and P fertilizer rates, the method of fertilizer placement and the time of N fertilizer application on cotton yield, product quality and fertilizer utilization.

Nitrogen application up to 50 kg/ha in the first experiment and up to 120 kg/ha in the second experiment increased seed cotton yield; higher nitrogen rates in the first experiment had an adverse effect on seed production due to abnormal rainfall which caused an intense vegetative growth and delayed the time of maturity.

Split application of N at sowing and at early flowering was slightly superior to a single application at sowing or to split applications at sowing, early flowering and initiation of fruiting. Addition of nitrogen during the flowering stage failed to influence cotton production significantly.

Banding P and N fertilizers increased plant height significantly, compared with the broadcasting method; placement methods, however, did not significantly affect seed yield.

Increasing amounts of N and P fertilizers had essentially no effect on lint quality.

The phosphate concentrations in the tops derived from fertilizer phosphate, were low ranging from 1–2 to 2–4 % of the P concentration in the tops and it was not affected by the different treatments.

The utilization coefficients of the nitrogen fertilizer sources by cotton were high, nitrate N being utilized much more efficiently than ammonium N.

The Rothamsted ley–arable experiments were on two fields with similar soils but with contrasting previous cropping: old grass on Highfield, old arable on Fosters field. Damage by take-all (Qaeumannomyces graminis var. tritici) occurred sooner in successive wheat crops grown after a lucerne ley and arable sequence (LU) than after a grass-clover ley and arable sequence (LC). On Highfield the difference was consistent and large, it occurred as soon as a second wheat crop was grown and resulted in wheat yielding 1 t/ha less after the LU than after the LC sequence. This difference did not persist in the next wheat crop where take-all was prevalent after both sequences. On Fosters field take-all developed more slowly and differences between sequences were mostly smaller.

Wheat seedling bio-assay of soil cores from the LU and LC sequences showed that little take-all fungus persisted through the leys and that soils were much infested after a first wheat crop in the LU sequence on Highfield, but not in the LC sequence on Highfield or in either sequence on Fosters field. Microscopic examination of roots from assay seedlings and from field plants showed that Phialophora radicicola var. graminicola (PRG) was most common in soils where take-all developed slowly, but our results did not show if this was a causal relationship. The occurrence of much PRG in the LU sequence on Fosters conflicts with previous reports which associate large populations of this fungus only with grassland soils.

Mouldboard ploughing, deep and shallow tined cultivation followed by conventional seed-bed preparation, and direct drilling were compared from 1972 to 1976 on a calcareous clay soil in two experiments, one on winter wheat and the other on spring barley.

At sowing the moisture content, bulk density and resistance to penetration in the surface layer of soil of uncultivated land were all greater than in soil that had been ploughed or cultivated deeply. Below 10 cm moisture content was less and root penetration was greater in the uncultivated soil. In all years winter wheat established and yielded well following direct drilling and shallow cultivation. In two dry autumns wheat establishment following ploughing was slower and less complete than with direct drilling, and in 1 year the yield was less. Spring barley established and yielded well without consistent differences in all years with all treatments.

The relationships between the number of stems per tuber and tuber characters measured before planting were studied using a wide range of tuber weights of the varieties Désirée and Maris Piper. The effects of the storage temperature of the seed tubers and the site of growth on these relationships were then investigated over 3 years.

Linear relationships between the numbers of stems per tuber and tuber weight accounted for more of the variation in numbers of stems than linear relationships established using tuber shape or sprout measurements. The linear relationships had positive slopes and intercepts, showing that small seed tubers produce more stems per unit weight than large seed tubers. There was little evidence of non-linear effects.

On average over all treatments, using ten plant samples, single linear relationships between above-ground stems and tuber weight accounted for 64 % of the variation in above-ground stems with D6sire'e and 58 % with Maris Piper. When separate regression lines were fitted for each treatment the best models in each variety accounted for about 86 % of the variation in above-ground stems. The best model with Désirée had parallel lines showing that the advantage, in terms of stem production, of small seed over large seed increases in environments favouring stem development. The relationships for each treatment are used to show how the stem density established can vary when planting tubers at the recommended spacing.

Seed tubers of comparable weight, planted at different sites, gave different numbers of stems suggesting that the optimum spacing may vary from one site to another.

It is suggested that breeding varieties for yield stability might be aided by selectingfor low variation in the relationship between the number of stems per tuber and tuber weight.

Varietal differences in resistance to non-aggressive chocolate spot infection were detected in the field, although complete resistance was not observed. Following artificial inoculation under growth-room conditions, a parent–offspring regression of disease scores for the heterogeneous stock Chivers was estimated as 0·51 ± 0·24, and although this cannot be regarded as a reliable heritability estimate, it demonstrates a degree of additive genetic control. An F2 diallel cross, under field conditions, indicated resistance to be controlled mainly by dominant alleles within a system of partial dominance. Detached-leaf tests indicated that within virtually complete dominance systems, dominant alleles facilitate fungal penetration and induce a hypersensitive response within the leaf. Control of further lesion development was indicated to be effected by a virtually complete additive system.

The DTPA-extractable Zn in 28 Tarai soils was found to be significantly correlated with Bray's ‘percent yield’ values for rice and wheat. The critical limit of ‘available’ Zn, below which responses of both crops to applied Zn may be expected, was 0–53 mg Zn/kg soil. On the basis of this critical limit, it may be inferred that in the 16 Zn deficient soils, rice and wheat yields would respond markedly to zinc application. The magnitude of crop response in these soils was greater in rice (39–244%; mean value 117%) than in wheat (33–101%; mean value 60%).

Seven hundred and fifty purebred Angoni, Barotse and Boran cattle and their crosses sired by Friesian and Hereford bulls were compared for live-weight and carcass characters in Zambia. The cattle were born between September and December in three consecutive years and were reared on unimproved veld. In the first year all females and a random half of the males received supplementary feed in winter and the males were slaughtered at 2·5 years of age. The remaining males received the same total amount of winter supplementary feed prior to slaughter at 3·0 years of age. The males born in the second year were pen fed for a period prior to slaughter at 3·0 years of age. Males born in the third year were slaughtered at 3·5 years of age and received no supplementary feed.

Genotype differences were important at all live weights and there were year of birth x genotype interactions at the 0·5, 1·0 and 1·5 year weights and a genotype × feed treatment interaction at the 2×0 year weight. Boran purebreds were heavier than the Angoni and Barotse purebreds; at 3·0 years the differences were +42·3 kg ( + 12·9%) and + 25·2 kg (+ 7·7 %) respectively. Cross-breds had heavier live weights than their corresponding purebreds with Boran crosses consistently heavier than the Angoni and Barotse crosses. The Friesian and Hereford sired Boran cross-breds were + 51·0 kg (+13·5 %) and + 43·0 kg (+ 11·6 %) heavier respectively than the purebred Borans at 3·0 years of age.

There were large differences between the genotypes for all carcass characters with Borans having heavier carcasses than the Angonis and Barotses by + 20·3 kg (+ 10·6 %) and + 19·1 kg ( + 10·0%) respectively. The average carcass weight advantages of Friesian and Hereford crosses with the Angoni, Barotse and Boran breeds over the corresponding purebreds were + 40·3 kg ( + 19·0%), + 33·6 kg ( + 16·2%) and + 31·0 kg ( + 14·0%) respectively. There were few important carcass differences between the corresponding Friesian and Hereford crosses.

The mortality rate during the experiment was 8·2% with only small differences between genotypes.

The interactions found in the experiment indicated that breed comparisons should be conducted over a number of years and at various management levels. For growth and carcass production under the conditions of the experiment the use of exotic crossbreds is clearly advantageous.

Four experiments were carried out over a 2-year period to investigate the effect of plant density and spatial arrangement and the time of lifting on yield and root size of carrots. Plant arrangement was varied by growing the plants in 1-, 2-, 3-, 4-, 5- and 10-row systems in beds with rows 12–5 and 37–5 cm apart. With each row arrangement crops were grown at target densities of 108, 323 and 537 plants/ma. There were three times of harvest. Total root yield was not significantly affected by plant arrangement or, in three out of the four experiments, by plant density but yields progressively increased with later harvests at all density levels. Yields of canning-size roots (20–30 mm diameter) were influenced by plant density and time of harvest and there were highly significant interactions between these variables on canning root yields. Highest absolute yields were obtained from the latest harvests from the medium and high plant density treatments; with the lowest density treatments the highest yields of canners were obtained from the earliest harvests. Mean root weight was significantly affected by plant density and harvest time. Row system effects on mean root weight were shown to be largely accounted for by differences in percentage seedling emergence and hence the plant density obtained under the different row system treatments and a possible reason for this effect is discussed. The relationship between mean root weight and plant density was not affected by the pattern of plant arrangement in these experiments. Total root yields were shown to be related to cumulative potential evapotranspiration from sowing rather than to chronological time. It is concluded that with the range of row systems used in these experiments, row spacing had little effect on root yield but confirmed previous work that plant density and time of harvest were the most important variables controlling mean root size and hence the yield of roots of any particular size grade.