The Lolium-Festuca complex of related species provides a wide range of variation for the development of versatile grasses adapted to meet the changing requirements of livestock farming. Various approaches have been used in order to harness the full potential of this variation. Tetraploid hybrids between the two ryegrass species L. perenne and L. multiflorum have resulted in stable and successful commercial varieties. Hybrids between more distantly related ryegrass and fescue species have demonstrated useful combinations of traits from both parents. Chromosome doubling is necessary in these hybrids to restore fertility in synthetic amphiploids. However, genetic instability can still be a problem and research is in progress to obtain tighter control of chromosome pairing. An alternative approach is to introduce a few specific traits from fescues into ryegrasses, or vice versa, using introgressive breeding procedures. This review outlines the progress already achieved in exploiting the ryegrass–fescue complex by using these various approaches and assesses the potential of hybrid derivatives.

In experiments conducted between 1982/83 and 1984/85 on the winter barley cv. Igri, nitrogen, including slow release forms, applied at several growth stages in the autumn, increased vegetative growth, including vegetative tiller numbers, nitrogen content and greening, particularly in the early sown crops. By spring, these effects were less apparent and only very infrequently did autumn nitrogen applications result in an increase in fertile tiller number and yield, although the autumn nitrogen treatments had been tested in combination with several different sowing dates and spring nitrogen levels. Studies on leaf production over the winter showed that the additional leaf produced after nitrogen application was subsequently lost through leaf senescence (especially in the severe winter of 1984/85) and therefore the treated and untreated plots often recommenced growth in the spring with similar amounts of live leaf tissue. It is argued that the use of autumn nitrogen on winter cereals in the north of Scotland cannot be supported agronomically and may also be undesirable for environmental reasons.

Experiments in 1985 and 1986, at Woburn Experimental Farm in Bedfordshire, tested the effects of fungicides, applied in autumn, and a growth regulator, applied at GS3O–31 or GS32–33 in spring, on winter barley grown on two contrasting soil types in each year. Leaf diseases did not become severe in any of the experiments but take-all (Gaeumannomyces graminis var. tritici) was prevalent in 1985. Triadimenol (‘Baytan’) was more effective than flutriafol (‘Ferrax’) in decreasing the severity of takeall and its activity against the disease was related to earliness of sowing.

Mean responses in grain yield to the fungicide treatments were mostly small and not significant but did not conflict with the hypothesis that crops on lighter soils benefit more from autumn fungicides than those on heavier soils. Mean effects of the growth regulator sprays were also small but they interacted with both soil type and season. Over the 2 years the later spray applied to crops on the heavier soil gave the largest mean response. Sprays applied to crops on lighter soils were often detrimental to yield, especially in 1985.

Urea (supplying 15 kg N/ha) applied to winter wheat (Triticum aestivum) at flag leaf emergence and again at ear emergence improved grain yield in only two, but increased grain nitrogen (N) in four out of five experiments. The size of the improvements in yield and nitrogen content differed over varying sites and seasons but were not affected by cultivar or propiconazole (250 g a.i./ha) plus tridemorph (500 g a.i./ha) fungicide applied with the urea. Breadmaking quality was assessed on grain from one site in 1985 and in 1986. The beneficial effects on loaf quality of urea and fungicide applied separately were reduced when they were applied as a mixture. In 1986 this negative interaction was associated with effects on sodium dodecyl sulphate (SDS) sedimentation volume, flour sulphur content (S), N/S ratio and dough resistance. The effect of urea also interacted with cultivar on SDS sedimentation volume in 1985 and dough resistance in 1986.

Three experiments carried out at Bridget's Experimental Husbandry Farm, Hampshire between 1984 and 1987 on clay loam and silty clay loam soils over chalk investigated the response of winter wheat grown after grass to spring-applied fertilizer nitrogen. The influence of method of establishment and the use of a nitrification inhibitor were also studied. Yields were similar whether the crops were established by direct drilling or following ploughing. Crops required between 88 and 209 kg N/ha nitrogen fertilizer for optimum yield. There was no consistent difference in nitrogen requirement nor were there consistent differences in nitrogen offtake (which is the amount of N in kg/ha removed in harvested grain) or apparent fertilizer recovery following ploughing or direct drilling. The use of a nitrification inhibitor increased grain yield when applied in the autumn without fertilizer, but not when applied with fertilizer in the spring.

Spring barley and spring oats were strip-seeded into crops of the white clover cultivar Alice at Hereford in 1987 and cultivar S184 at Aberystwyth in 1988. Drilling was done with or without a band-spray of glyphosate, a moderate or low (1988 only) dose of paraquat or into plots where the clover had been killed by herbicide 2 months previously.

In the first experiment, initial cereal emergence was sparse; growth was suppressed in the unchecked (unsprayed) clover base but was vigorous in the clover-free plots; the cereals also became dominant in the swards sprayed with herbicide. Whole-crop yields in mid-August were 13, 3–4 and 8–10 t DM/ha in the plots in which clover was killed, unchecked or checked with herbicide. Clover contributed 4–12% of the harvested herbage in the latter treatment. This treatment also yielded c. 70 % as much N, carbohydrate and fibre as that without clover. Grain yields exceeded 7 t/ha without clover but were only 0·3 t/ha for barley and 1·1 t/ha for oats with unchecked clover; in the checked clover plots, barley yielded 60% and oats 78% as much as on the clover-free plots. Four and 5 weeks after whole-crop harvest, residual clover growth was 27 and 39% of that on unchecked plots for oats and barley, respectively.

In the second experiment, the cereals emerged thickly but were later dominated by the clover, and an equitable balance was achieved only with the larger dose of paraquat. However, the oat cultivar Emrys was suppressed less than the tall barley cultivar Dandy; the short barley cultivar Digger was the most suppressed. Mean whole-crop yields were 11 t/ha in the treatment without clover, about half this in the unchecked bases and c. 9 t/ha with the larger dose of paraquat. Differences in chemical composition reflected much larger clover contents in 1988 than in 1987. Yields of N and water-soluble carbohydrate were at least as large or larger with moderate paraquat than for the clover-free plots. Grain yields ranged from 5·6 to 6·9 t/ha for the three cereal cultivars without clover but were negligible to very small in the unchecked and band-sprayed treatments, and were 3·4 and 2·0 t/ha for oats and barley, respectively, with the larger dose of paraquat. Residual stolon weights, 70–80 days after whole-crop harvest, greatly exceeded initial values in all treatments. They were smallest following the larger dose of paraquat, and larger in Digger than in Dandy, which in turn was larger than in Emrys.

It is concluded that the concept of growing cereals in a clover base shows potential as a low input–moderate output system of cereal production. However, further longer term work is needed on regulation of the cereal–clover balance, on the release and uptake of N and the environmental effects of the technique.

The effect of cowpea green manure (CGM) and farmyard manure (FYM) on phenological events in maize grown with different rates of nitrogen (N) was evaluated at Ludhiana, India in 1988–89 as part of a long-term experiment on sandy loam. Tasselling (T), anthesis (A), silking (S), maturity (M) and appearance of leaves were recorded in 1988 and 1989 from plots of maize manured with cowpea and FYM and grown at 0, 75 and 125 kg N/ha. Time to phenological events was calculated in terms of calendar days and growing degree units (GDU).

Phenological events in maize were significantly advanced by CGM, FYM and N. The occurrence of T, A and S with CGM was earlier by 60·5, 84·5 and 114·5 GDU, respectively, than without it and the end of each of the growth stages T, A and S was advanced by 81·0, 99·0 and 78·5 GDU, respectively. Maturity was earlier than in the control by 65·0 GDU. Leaf emergence occurred earlier after organic manuring. Farmyard manure advanced development less than CGM. Changes in phenological events due to N followed the same pattern of changes as those found with organic manures. Time from sowing to onset of T, A, S and M, and the interval between T, A, S and M were significantly correlated with yield and yield-related characters. Desirable changes in the timing of phenological events are thus one of the factors contributing to the improvement in productivity caused by organic manures. Calendar day was found to be as accurate an index as GDU for evaluation of the effect of cultural practices on phenological events.

Soil chemistry in relation to yield of spring barley (Hordeum vulgare, cv. Golden Promise) was investigated in three field experiments in north-east Scotland in 1982. Previous treatments had produced a range of soil pH values from 4·0 to 6·0 (measured in 10mM-CaCl2 solution). The experiments demonstrated the values for soil acidity components below which yields were reduced. Large additions of phosphate fertilizer allowed barley to withstand larger concentrations of soluble and exchangeable aluminium (the principal acid soil toxin), thus decreasing the critical soil pH from 5·2 to 4·8 (corresponding to about 5·9 and 5·5 if measured in a water suspension), and increasing the critical soluble Al concentration from 10 to 50 UM and the critical Al saturation of the cationexchange complex from 0·025 to 0·1.

To assess the progress made in modern breeding of open-pollinated sorghum cultivars, 24 contemporary and improved sorghum cultivars from ICRISAT (International Crops Research Institute for the Semi-Arid Tropics, India) were compared with 40 sorghum landraces collected in Ethiopia. The experiment was performed at Bet Dagan, Israel, in 1988 under near-potential (dripirrigated) and dryland (stored soil moisture) growing conditions. Data on phenology, biomass, harvest index, grain yield and its components were collected. ‘Drought susceptibility index’ (S) was calculated for each genotype as the reduction in yield from irrigated to dryland conditions relative to the mean reduction for all genotypes.

On average, cultivars produced about three- to fourfold more grain than landraces. Cultivars had the same mean growth duration and biomass but were 40% (irrigated) to 27% (dryland) shorter in mean plant height than landraces. This yield advantage was fully accounted for by a proportionately greater mean kernel number per panicle and harvest index, irrespective of the water regime. ‘Drought susceptibility index’ was near average for all cultivars and much more variable among landraces. Dryland yield became progressively dependent on the yield potential as the yield potential was genetically improved in the cultivars.

It was concluded that, irrespective of the water regime, the large yield improvement in modern open-pollinated cultivars of sorghum, as compared with landraces, has been achieved only through greater dry matter partitioning to the panicle accompanied by a reduction in plant height. The genetic improvement of yield in open-pollinated cultivars and hybrids of sorghum is discussed.

Growth and aflatoxin production of Aspergillus flavus in preharvest maize grown in Texas, USA in 1989 were determined after treatment with chitosan, Bacillus subtilis and Trichoderma harzianum. Individual or combined control treatments were applied at the milk stage of ear development, 48 h before or after kernel inoculation with an aflatoxigenic isolate of A. flavus. Single and combined treatments reduced A. flavus growth and aflatoxin production. Toxin accumulation was significantly (P < 0·05) reduced, in some instances to non-detectable concentrations by single pretreatments. Either B. subtilis or chitosan as independent treatments applied 48 h before inoculation with A. flavus inhibited aflatoxin production.

Apex and ear development in nine spring barley genotypes were studied at two sites in southern Spain in 1988. The genotypes were grouped into medium and early types, depending on the time from sowing to anthesis. Medium genotypes had significantly more spikelet primordia than early ones at both sites. Spikelet mortality was similar between genotypes and sites, resulting in a higher final number of grains/ear in the medium than the early genotypes.

There was a positive correlation between the maximum number of spikelet primordia and the duration of three stages of apical development: lemma-, stamen- and awn-primordia. Negative correlations were observed between spikelet mortality and the duration of certain developmental phases of the ear.

The growth and seed production potential of white clover (Trifolium repens L.) was studied in field plots in 2 years, with and without a companion grass (Lolium perenne L.). Three rates of grass suppressant, fluazifop-butyl (Fusilade), applied in early June, were compared on plots sown with the companion grass. Two clover varieties, Aberystwyth SI84 and Olwen, were compared.

Sowing a companion grass reduced the amount of clover in the sward in both the first and second harvest years, but did not affect the vigour of individual clover growing points or the number of clover inflorescences when the crop was ready to be harvested for seed.

Fluazifop-butyl, at the highest rate used (125g/ha), reduced the rates of leaf emergence and extension, and the numbers of reproductive tillers, in Lolium, without reducing the rate of leaf emergence in clover, although the weight per clover leaf was somewhat reduced. In the first harvest year, the numbers of SI84 inflorescences in June and July were increased by fluazifop-butyl, but the effect had worn off by harvest (24 August). Seed yield potential was not increased by fluazifop-butyl at the rates used.

Olwen produced heavier leaves, but fewer leaves and fewer growing points/0·1 m2 than SI84. In the first harvest year, Olwen had fewer and smaller inflorescences than S184.

It proved feasible to measure the weight of new leaf produced per week and the nett additions to stolon and inflorescence dry matter (DM). The estimate of nett addition to stolon DM was increased by increasing the number of visible internodes included in the calculation, up to the maximum number recorded (nine). The rate of leaf emergence was slower on young branches than on main axes.

Two experiments, each involving a set of six sweet potato clones, the first set developed in sites differing in altitude, and the second in sites differing in soil type, were done at three locations in 4 years in Cameroon. Data obtained were subjected to analyses of variance to determine the presence of genotype × environment (G × E) interactions, and to joint regression analyses to measure the performance of clones across environments. The first experiment produced higher yields and contained more stable clones than the second. In both experiments, mean yields were almost twice as high in 1984 (21·1 t/ha) as in each of the other years (c. 11·0 t/ha), and highest at Nyombe (18·0 t/ha). In Expt 1, the G × E interaction mainly concerned interaction with location, whereas in Expt 2 it concerned interaction with years.

Clones 1611 (Expt 1) and 048 (Expt 2) yielded above average and gave linear regressions significantly above unity (b > 1·0) for most traits, indicating specific adaptation to high-yielding environments and hence below average stability. Clones 1112, 1639 and TIbl (Expt I) yielded above average and had regression slopes equal to unity (b = 1·0), indicating average stability and thus general adaptability. Clones TIb2 (Expt 1) and 1487 (Expt 2) produced below average yields (b < 1·0), indicating specific adaptation to low-yielding environments. Since sweet potato is grown mainly for human consumption in Cameroon, a preferred clone must have stable marketable yields. Only clones 1112, TIbl and 1639 could be considered desirable for release to growers.

The effect on soil fertility and crop performance of different organic fertilizers; paddy straw (PS), farmyard manure (FYM), water hyacinth compost (WHC) and tank silt (TS), at different rates of application and in combination with N fertilizer, was studied in a rice-based cropping system on an acid lateritic soil at Kharagpur, India, during 1985/86. Organic manuring of wet-season rice (first crop) with 5 t PS/ha 10 days before transplanting and 10 t FYM or 10 t WHC/ha at transplanting increased grain yield as much as the application of 30 kg N/ha. Increasing the rates of FYM and WHC application up to 15 t/ha increased yield but increasing the rate of PS beyond 5 t/ha did not. Response to increasing amounts of N was not linear; there was a significant increase up to 90 kg N/ha and a decrease when N was applied in conjunction with organic fertilizers. There was a significant increase in the N uptake of the rice but a decrease in the recovery of applied fertilizer N with the application of increasing rates of organic and N fertilizer.

The organic C content of the soil after the rice harvest increased significantly after PS application, whereas there was more available N after WHC and FYM. Increasing the rate of application of PS up to 15 t/ha increased organic C but not available N. Mineral N fertilizer had little effect on fertility build-up. Grain yields of wheat and gram (Cicer arietinum), grown after rice without any additional fertilizer, increased significantly. The residual N effect of the previous crop on wheat or gram yield was small and adding fertilizer directly is considered essential for higher productivity in these crops in a rice-based cropping system.

Experiments were carried out between 1983 and 1987 in a cool but dry environment in Tasmania to evaluate the growth, development and yield of chinoli compared with the Brassica napus cultivar, Marnoo. In 1983/84 chinoli plants became large, with many pods, but then lodged at the stage of peak pod development. Seed yields were less than half those of the B. napus lines and only slightly better than that of B. campestris, ‘Jumbuck’. In subsequent experiments, lodging was either delayed or completely eliminated, either by the application of plant growth regulators, particularly PP333, or by using low populations or late sowing. However, these remedial measures were all associated with lower seed yields. Early flowering before the achievement of adequate plant size and then the setting of a large number of pods resulting in few seeds in each were identified as the main reasons for the low seed yields in chinoli. Irrigation after anthesis increased numbers of seeds/pod and thus gave better seed yields, but still not as high as those of Marnoo.

Field experiments were conducted at Fagu and Shimla in India in 1983 and 1984 to study the effect of thiourea (0 and 5 kg/ha) on tuber yield of potatoes and uptake of P with different rates of fertilizer P (0, 22, 33, 44 and 66 kg/ha). Application of phosphorus and thiourea, both alone and in combination, increased tuber yield and uptake of P significantly at both the locations in both years.

The effect of phosphorus fertilizer on the performance of an improved semi-dwarf (100 cm), long duration (170 days), photosensitive rice variety CR 1016, grown under conditions of intermediate deepwater (15–50 cm) and simulated flash flooding (80 cm), was investigated at Cuttack, India in 1985, 1987 and 1988. Growth and yield of rice subjected to overhead flash flooding (complete submergence) at the vegetative stage for 10 days was decreased significantly compared with partial submergence in water of intermediate depth. The adverse effect of complete submergence was due to greater tiller mortality and lower number and/or weight of panicles at maturity. Rice plants fertilized with P tolerated flooding better and produced significantly higher grain yields than when no P was applied. There was no significant effect of P application on the crop grown under natural unsubmerged conditions, except when it was raised in the same plots as the previous year and may therefore have benefited from residual effects. Therefore, application of 8.7–17.5 kg P/ha along with 60 kg N and 16.7 kg K/ha at sowing was essential to overcome the deleterious effects of submergence on rice grown under waterlogged conditions.

A Brassica napus line that produces flowers with virtually no petals (Apetalous) was compared for its physiological significance with Marnoo, a related cultivar bearing conventional yellow petals. Experiments between 1984 and 1987 used different growth regulators, plant population densities and irrigation treatments. Apetalous allowed 30 % more short-wave radiation to reach the base of the inflorescence, and reflected only half as much radiation as Marnoo at peak flowering. This allowed leaves to persist and remain active for longer. Apetalous then consistently retained more seeds/pod, each of greater mean weight, at all heights within the crop canopy, resulting in substantially greater yields than Marnoo in most instances. At the highest population density, it retained productive secondary branches, whereas Marnoo had none. Irrigation after flowering increased the yields of both lines by allowing more seeds/pod to be retained, particularly at lower heights in the canopy. In Apetalous, however, even without irrigation, yields remained high. Apetalous does have larger flower parts, other than petals, which could contribute to the larger pods and seeds. This, combined with lower plant populations than Marnoo in some experiments, could have explained some of the effects seen, but the characteristic is worthy of further study in a range of genetic backgrounds and environments.

Experiments were conducted in controlled environment cabinets and in the field at Cambridge, UK, in 1987–90 and in Valencia, Spain 1989–90 with several varieties of potato. The initiation of leaf primordia and flowers was recorded in sprouts stored for long periods at 13°C with constant illumination and in sprouts exposed to different photoperiods and periods of cold storage. In field experiments, the effects of a wide range of planting dates, differences in physiological age, the time at which seed tubers were sprouted and of imposing an 8 h photoperiod were investigated.

More than 40 leaf primordia were initiated in the sprouts of Home Guard and Arran Comet stored at 13 °C, but, in other varieties, fewer leaves were initiated. Flowers were initiated in the sprouts of some varieties. In field-grown plants, the number of nodes to the first flower differed between varieties and was increased by ageing sprouts before planting. Stems from physiologically old seed of all varieties had more nodes below ground than young seed but the number of aerial leaves to the first flower increased only slightly with increasing physiological age. The number of aerial leaves to the first flower was lower and less variable in Estima than in Maris Piper.

Initiation of flowers usually occurred before tuber initiation and within two weeks of emergence but was earlier in some varieties than others. There was little influence of photoperiod on the time to initiation of flowers and tubers in most experiments but, with low levels of radiation, flowering was completely inhibited in the variety Maris Piper.