The aim of this study was to identify a fluorescence parameter whose estimate could be used reliably for a drought tolerance test in durum wheat (Triticum durum). Twenty-five cultivars were grown in a glasshouse over two seasons (1987/88 and 1988/89) at Foggia, Southern Italy. Photochemical and non-photochemical quenching (qQ and qE), the half time of fluorescence decay (tP½) and the initial slope of fluorescence decay (ISPS) were measured on control and dehydrated pre-darkened excised leaves; qQ and qE were measured twice: first at 14 s after actinic illumination and second at the steady state.

No great difference in qQ and qE was apparent between control and dehydrated leaves at the steady state; however, at 14 s after illumination there was a decrease in qQ and in ISPS and an increase in tP½ in dehydrated leaves. The predictive capability of fluorescence parameters was assessed by comparison with a yield-based drought susceptibility index (DSI). The percentage decrease in qQ at 14 s showed the highest correlation with DSI (r = 0·75, significant at P < 0·001), so it may be considered a good indicator of drought tolerance in durum wheat. Results obtained at different developmental stages with different fluorescence levels (Fo, P and Fm) and parameters (qQ, qE and tP½) indicated that for maximum reliability the test must be applied at the vegetative phase.

Effects of rhizobial inoculation and applied nitrogen on the utilization efficiency of N, P and K were studied in relation to the yield advantage in additive maize/mungbean intercrops at Los Baños, Philippines in 1988. Inoculation increased grain yield of both maize (Zea mays L.) and mungbean (Vigna radiata (L.) Wilczek). Yield of maize increased by 60% in the sole crop and 71% in the intercrop as the N application rate was increased from 0 to 90 kg/ha, with a corresponding decrease of 29–35% in the yield of the associated mungbean. Intercropping reduced mungbean yield by 35–57%; maize was less affected. Inoculation also improved the land equivalent ratio (LER). The highest LER (1·49) was obtained at 30 kg N/ha with inoculation.

Nutrient absorption by both maize and mungbean was reduced due to intercropping, mungbean being more affected than maize. The reductions in the N absorption efficiency of maize ranged from 4 to 37% and those of mungbean from 37 to 58%. Increases in N rate increased N absorption of maize but caused greater reductions in N absorption of mungbean. Reductions in P absorption by intercropped maize declined with increases in applied N and with inoculation. Inoculation, however, had a lesser effect on K absorption efficiency.

Land equivalent ratio analysis in terms of N, P and K utilization efficiency showed that the increase in LER over unity was due largely to a higher total uptake of nutrients by the component crops in the mixture than by the sole crops. The greater efficiency of intercrops than of the sole crops in converting absorbed nutrients to grains also contributed to the yield advantage.

A field experiment was conducted in 1990 and 1991 under intermediate deepwater conditions (15–50 cm) at Cuttack, India with two rice cultivars - Banaprabha, a semi-tall (130 cm), short duration (95 days), upland cultivar and Gayatri, a photosensitive, semi-dwarf (100 cm), lowland cultivar of long duration (170 days). The cultivars were direct-sown either in pure stands using 400 seeds/m2 at 20 cm row spacing or in mixed stands composed of alternate rows sown with 200, 300 or 400 seeds/m2 each at 10, 15 or 20 cm inter-row spacing. Mixed-row cropping of Banaprabha and Gayatri produced 17–21% higher grain yield than a pure crop of Gayatri. Panicles/m2 increased with higher seed rate and decreased with wider row spacing but a reverse trend was observed in panicle weight. Maximum grain yield was obtained at a row spacing of 15 cm but the effect of varying seed rates at each row spacing was non-significant. Gayatri produced up to 82% of its pure crop yield and contributed up to 70% of the total yield in the mixed crop system. Therefore, the yield advantage under mixed cropping was due to the late maturing cultivar benefitting from the increased area available after the harvest of the early cultivar. A crop stand using 200–300 seeds/m2 of each cultivar at a 15 cm row spacing was found to achieve the optimum productivity from the mixed cropping system.

The ability to survive severe summer water stress determines the persistence, and therefore autumn yield, of temperate grasses in the Mediterranean environment. In the island of Corsica, sward survival and changes in carbohydrate content were investigated over 2 years, in two contrasting populations of cocksfoot (Dactylis glomerata L.): KM2, an early-flowering population of Mediterranean origin and Lutetia, a late-flowering cultivar bred in North West France.

In Expt 1 (1987/88) three spring defoliation intensities were imposed. In Expt 2 (1989/90) three levels of water deficit were imposed under a rain shelter.

In spring, dry matter (DM) yields and water-soluble carbohydrate (WSC) concentrations in leaf bases were similar (20–35% of DM) for both populations. From June to September, WSC reserves tended to decline in Lutetia, whereas accumulation of WSC was maintained until August (45% of DM) in KM2. Fructans formed the major component, and therefore followed the same seasonal pattern, as total WSC. Contents of trisaccharide and sucrose increased in late summer as drought progressed. Contents of glucose and fructose were lower but increased in August or in September according to treatment.

In both field experiments during summer, KM2 had 50% more live tillers/m2 than Lutetia, possibly because it remained in positive carbon balance for a longer period. WSC levels in summer and regrowth in autumn were reduced both by intense defoliation in spring and by severe water stress in summer. On average, autumn yields of KM2 were five times greater than those of Lutetia and the recovery yields were closely correlated with fructan contents of leaf bases in summer (r = 0·80; P < 0·001).

The role of fructans and low DP-sugars as solutes in osmotic adjustment and as substrates for regrowth are discussed, and the differences between populations are analysed.

The concentrations of water-soluble carbohydrate, N, nitrate-N, P, K, Ca, Mg and Na were determined in six plant species: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). Field crops of these species were grown at Aberystwyth in 1985,1986 and 1987. In 1985 and 1986 the rumen contents and faeces of lambs fed artificially dried diets of the different species were analysed for N, P, K, Ca, Mg and Na. The intake, apparent availability and, in 1986, retention of each element by the lambs on each diet were calculated.

The results illustrate the potential of dicotyledonous species to extend the range of concentration of some major elements beyond that normally found in temperate grasses. Chickweed was particularly high in P and K, dandelion in K and Mg, dock in Mg, ribwort in Ca and spurrey in Mg and Na. The apparent availability of the elements studied was as high in chickweed, dandelion and spurrey as in ryegrass. The apparent availability of N and P was lower in dock and ribwort than in ryegrass, possibly due to heat damage during drying. All five dicotyledonous species had a higher Mg concentration in herbage than ryegrass (c. 70% higher, on average) and all led to a higher Mg concentration in rumen contents than ryegrass (c. 70% higher, on average). Retention of Mg was three times as great, on average, in sheep fed dicotyledonous diets as in sheep fed ryegrass. The concentration of water-soluble carbohydrate was lower in the dicotyledonous species than in ryegrass. The concentration of nitrate-N was rather high in ribwort when harvested at a leafy stage in October. Dock was moderately low in nitrate-N, despite a rather high concentration of total N.

In a clay loam at Rothamsted, inoculated with lucerne stem nematode (Ditylenchus dipsaci) and a leaf nematode (Aphelenchoides ritzema-bosi), lucerne herbage yields were increased on average by 17 and 59% respectively, in the first and second years of a 4-year experiment (1988–91), by carbofuran granules applied around the seeds at sowing in spring 1988. In seven-row plots over the 4 years of the experiment, 1·65 kg a.i./ha increased total yield as much as did 3·3 kg a.i./ha (11 and 12%, respectively). In four-row plots over the same period, 1·9 kg a.i./ha increased total yield by 9%. The cultivars Euver and Vertus, which are partially resistant to D. dipsaci, yielded 44·3 and 48·5 t dry matter/ha, respectively, whereas Europe and Vela, which are susceptible to the nematode, yielded less (36·3 and 28·6 t/ha, respectively). When sown in summer 1990 in four-row plots, cultivars Europe and Euver yielded larger crops in 1991 in plots given 1·2 or 2·3 kg a.i. carbofuran/ha in 1990 (on average 34 and 48%, respectively) than in untreated plots. As little as 0·6 kg carbofuran/ha increased the yield of cv. Europe in infested soil.

The stunting of lucerne plants, associated with D. dipsaci infestation, was greatly decreased by carbofuran, which prevented infestation of the first crop by D. dipsaci and A. ritzema-bosi. Stem nematode infestation of lucerne plots was adequately and quickly assessed by measuring the lengths of rows stunted by D. dipsaci. Other methods of assessment were laborious and no more reliable.

Progeny tests for resistance to potato leafroll virus using true seedlings in a glasshouse in Scotland ranked progenies by the percentages of seedlings showing primary symptoms, in accordance with the known phenotypes of their parents. Symptoms were more obvious in seedlings grown under sodium lamps than in those grown under fluorescent strip lights. These glasshouse seedling progeny tests were then evaluated by comparing them with field clonal trials. The progeny tests were found to identify effectively those progenies most resistant to potato leafroll virus but were not effective for identifying the most resistant clones within progenies.

Inoculation of Brassica napus cv. ISN–129 with Azotobacter chroococcum following the application of different amounts of nitrogen produced the greatest increase in seed yield and total dry matter when no external nitrogen had been applied. The yield increase in response to inoculation could be attributed to a greater number of primary branches and pods, associated with a higher leaf area index, particularly at the pod-filling stage, and a faster crop growth rate.

For the production of hybrid and synthetic varieties, high rates of cross-fertilization are needed. Two aspects of cross-fertilization in Vicia faba L. were studied at Wageningen in 1989 and 1990. The occurrence of cross-fertilization between pollen receptor lines in large-scale assays for crossfertilization was determined. Furthermore, the contribution of the genotype of the donor, of the receptor, and of their specific interactions in terms of cross-fertilization rate were studied.

Inter-receptor cross-fertilization may represent from 2 to 70% of the total cross-fertilization. Interreceptor cross-fertilization increases when donors and receptors do not match for flowering height.

The genotype of the receptor appeared to be of importance for the cross-fertilization rate. No differences in cross-fertilization rate due to genetic differences between pollen donors were noticed. Also no significant specific donor x receptor interaction effect on cross-fertilization rate could be observed.

Field experiments were carried out in which three different sowing techniques: sowing by hand, with a conventional seed drill and with a precision drill, were used to plant an indeterminate and a determinate cultivar of Vicia faba at two sowing dates and at three population densities in 1989 and 1990 in Southern Germany.

Delayed sowing reduced field emergence rates in both years. Hand sowing produced the poorest stands in some instances due to an insufficient sowing depth being achieved. Only at late sowing dates did precision drilling give greater field emergence rates than conventional drilling. During the early stages of growth, hand and precision sowing resulted in crops with the greatest light interception and dry matter production. However, these differences between sowing techniques decreased later on. Lodging was most severe in conventionally drilled crops, particularly at high population density. Thus, when lodging occurred, dry matter and grain yields decreased with increasing plant density in conventional sowings, although they tended to increase in hand-sown and precision-drilled crops. Overall, apart from this interaction, there was no significant effect of sowing technique on grain yield. Grain yields and dry matter production were generally higher in the indeterminate cultivar Herz Freya than in the determinate cultivar Ticol, but there were no differential effects of sowing technique.

To develop an effective breeding programme for rainfed production of the common bean (Phaseolus vulgaris L.), the inheritance of seed yield under such conditions should be understood, preferably considering the effects of environment to account for site or season specificity. Thus, heritability, expected and realized gain from selection, and combining ability were evaluated for a nine-parent diallel of common bean without reciprocals but including parents, at two locations each in Mexico and Colombia, using the F2 and F3 population bulks. Heritability estimated from regressions of F3 on F2 ranged from 0·09 ± 0·18 (S.E.) to 0·75±0·25 for seed yield, from 0·26±009 to 0·34±009 for days to maturity and from0·57±004 to 0·80±004 for 100-seed weight. Expected gain from selection in the F2 was estimated as a percentage of the population mean, selecting the upper 20% of the populations. Expected gain in seed yield ranged from 1·8 to 8·4% in Mexico and from 6·5 to 28·1% in Colombia. Realized gains in seed yield in the F3 were 0·4–7·4% in Mexico and 2·9–15·7% in Colombia. Realized gain values for days to maturity were < 2·2%, and for 100-seed weight > 13·4%. General combining ability (GCA) mean squares (estimated using Griffing's Method 2, Model 1) were significant (P <0·01) and larger than those for specific combining ability (SCA) for all traits at all locations. The parents from the Mexican highlands tended to have a positive GCA effect for yield in Mexico but negative values in Colombia, whereas parents adapted to mid-elevation tropical environments showed the opposite tendency. However, all significant GCA values of breeding line V8025 were positive in both countries.

Although direct selection for seed yield under water deficit can result in genetic gains in the common bean (Phaseolus vulgaris L.), progress could be enhanced through selection for additional traits that are related to underlying mechanisms of adaptation to water deficit. Carbon isotope discrimination (Δ) has received considerable attention as an indicator of water use efficiency and adaptation to water deficit. To test the utility of Δ as a selection criterion, Δ and other traits were measured in F2 and F3 generations of a nine-parent diallel grown under rainfed conditions at two locations in Colombia with contrasting soil types. An irrigated trial was also conducted at one location. Significant (P 0·05) differences among parents, F2 and F3 were found for carbon isotope discrimination (Δ), leaf optical density (OD), leaf nitrogen (N) and potassium (K) concentrations, relative duration of pod-filling period (RDPF), shoot dry weight (SDW) and harvest index (HI). Effect of location and water regime and their interactions with genotype were also frequently significant. Heritability estimates, determined by regressing the F3 on the F2, ranged from 0·11±011 (S.E.) to 0·33 ±0·10 for OD, 0·22 ± 0·07 to 0·44±0·09 for N, 0·04±0·05 to 0·29±0·08 for K, 0·40 ± 0·08 to 0·43 ± 0·15 for RDPF and 0·30±0·22 to 1·00±0·24 for SDW. All values for Δ and HI did not differ significantly from zero. Correlations between seed yield and OD and RDPF were negative, whereas those with N, K, SDW, and HI were positive. For all traits, mean square values for general combining ability (GCA) were usuall significant and larger than those for specific combining ability (SCA). All significant GCA effects for Δ for ‘Rio Tibagi’, ‘San Cristobal 83’ and ‘Apetito’ were negative, while those for ‘Bayo Rio Grande’, ‘Bayo Criollo del Llano’, ‘Durango 222’ and BAT1224 were positive. Although Δappears unsuitable as an indirect criterion for selection for yield under water deficit, further study of genotypes exhibiting contrasting values of A might reveal differences in mechanisms of adaptation to water deficits, thus leading to other selection criteria or identification of valuable parental lines.

Titan broiler chickens kept in batteries at the Universidad Agraria, Lima, were fed diets containing duckweed (Lemna gibba) in proportions of 0, 10, 15 and 25%. The weight gain of broilers fed 15% duckweed was similar to that of the controls; 25% duckweed in the diet resulted in a significant decrease in feed consumption and weight gain.

To determine if Titan and Arbor Acres broiler chickens could be maintained on duckweed diets under commercial conditions, birds were fed diets containing 0 and 5% duckweed. Female birds (Titan and Arbor Acres) fed diets containing 5 % duckweed showed increased final weights. The pigmentation of all birds receiving the diet containing duckweed was significantly increased.

Duckweed used at levels of up to 15 % in the diets of broiler chickens could represent an important protein source for poultry feed in developing countries where soyabean meal or fish-meal are not available.

Extensive grazing experiments were conducted over four summer breeding seasons in north-west Queensland between 1984 and 1989. Ewes in the last third of pregnancy were grazed on Mitchell grass (Astrebla spp.) pastures of varying forb (herbaceous plant other than a grass) content. Pastures of low forb content (F-) were attained by stocking paddocks heavily with wethers prior to the experiment, or by selecting paddocks which already contained pastures of low forb content. Pastures of high forb content (F+) were kept without animals prior to the experimental period. Pastures comprised a range of forb biomass (29–828 kg DM/ha) and percentage forbs in total biomass (3–49%). Lamb marking percentage was found to be dependent on the biomass of forbs and proportion of forbs in the pasture, in two experiments. Ewes which grazed F+ pastures had lower lamb marking percentages than those grazing F- pastures.

Twenty pasture species collected during the experiments were analysed for the ratio of 13C: 12C and photosynthetic pathway was determined. Five forb and all three grass species had C4-dicarboxylic acid pathways, ten forbs had Calvin-C3 pathways and two forbs had crassulacean acid metabolism pathways.

Estimates of the proportion of C3 and C4 species in the diet were determined by analysing the ratio of 13C:12C in faeces. The apparent high proportion of Calvin-C3 pathway forbs in the diet of ewes compared to the proportion in the total pasture biomass indicated that ewes preferentially select C3 forbs in the diet, although there was no dependence of lambing percentage on the estimated proportion of C3 forbs in the diet. Management strategies that may improve lambing percentage in the Mitchell grass areas of north-west Queensland are discussed.

The objectives of this study were (i) to evaluate a new surgical procedure to catheterize hepatic vessels as well as the posterior aorta and vena cava, (ii) to test a modification of a downstream dilution technique in order to measure blood flows through splanchnic tissues and hindquarters in rapid succession, and (iii) to improve the reliability of splanchnic blood flow measurements using paraamino hippuric acid (PAH). Ten adult ewes were used. The transhepatic surgical approach used proved successful; it was relatively easy to set up and a good recovery of hepatic functions was obtained. The attempt to measure splanchnic and hindquarters blood flow in rapid succession by alternating the sites of PAH infusion was unsuccessful, probably because of transient modifications in infusion rates due to different blood pressures in veins and arteries. Indeed, arterial PAH concentrations changed with infusion site. Finally, a better reproducibility of splanchnic blood flow measurements was obtained in sheep, fed every 3 h, by infusing the required amount of PAH partly via the mesenteric vein and partly via a ruminal vein.

A surgical preparation was developed to measure uptake of amino acids from the small intestine into the cranial mesenteric vein (CMV) of lambs. Results from this preparation were compared with those from the traditional hepatic portal vein (PV) preparation in the same lambs. Necropsy revealed that, in contrast to the PV preparation which included all portal-drained viscera, the CMV preparation drained primarily small intestine (0·84–0·92 small intestinal mass). The CMV preparation contributed 0·238 of blood flow from and 0·307 of oxygen consumption by the PV preparation. Venous-arterial differences for alpha-amino nitrogen (AAN), phenylalanine (Phe) and tyrosine (Tyr) were three- to fourfold greater in the CMV than in the PV preparation, indicating that the CMV preparation is more sensitive for measuring amino acid uptake. The ratio CMV/PV for uptake of AAN was 0·61 (P< 0·001), but this ratio was much closer to unity (mean 0·84) for Phe and Tyr. Since the CMV preparation drains primarily the small intestine, through which all amino acid absorption occurs, it should prove to be extremely valuable for studying absorption from and metabolism within this organ using a combination of arteriovenous and isotopic tracer techniques.

A study was conducted on eight preparturient camels which were kept in individual stalls adjacent to the Cairo abattoir during 1989. Four novel phenomena are described in this paper: (i) a significant (P < O·05) prepartum decrease in plasma concentrations of progesterone evident over the 48 h preceding parturition; (ii) a remarkably consistent increase in total plasma unconjugated oestrogens, commencing 2–4 days prior to parturition and peaking in excess of 200 pg/ml for c. 2 h before delivery; (iii) a tenfold increase to 5·4±0·19 ng/ml (mean±S.E.) in plasma concentrations of 13, 14-dihydro-15-keto-prostaglandin F2α (PGFM) between days –10 and – 1, showing a sudden and large increase during the 5 h prior to delivery; and (iv) three peaks of total plasma corticosteroids during the 4 h preceding delivery, with the third peak showing the greatest magnitude (24·0±3·11 ng/ml). These results suggest that the dromedary camel is an example of a species in which luteal secretion of progesterone, especially 3α-dihydroprogesterone, is required throughout pregnancy and in which cessation of luteal function, associated with a rapid increase in the oestrogen: progesterone ratio and the secretion of prostaglandin F2α (PGF2α), is a requirement for parturition.