In 1977, a four-course rotation was set up at Ropsley (UK) to study crop response to eight rates of nitrogen application (35–265 kg ha−1). This rotation continued until 1990 when continuous winter wheat was introduced. Results from 1978 to 1990 provide an opportunity to study the initial phase of cumulative effects from different rates of N fertilizer application on the recovery of N by cereals and the retention of N in the soil.

From 1978 to 1990, considerable variation in the recovery of nitrogen by winter wheat was observed. Neither rainfall nor drainage, as indicators of possible denitrification or leaching losses, provided a useful explanation for this, possibly because of the relatively dry conditions prevailing after spring fertilizer application. There was no evidence of increased soil N fertility, beyond single year residues, as a result of large N applications over the 13-year period.

In order to achieve the economic optimum grain yield, it was necessary to use N applications which produced inefficient recovery of N. Thus, greater return of N in crop residues and immobilization at relatively large N applications (>150 kg ha−1) contributed to an observed build-up in soil organic N over the period of study. Plots receiving, on average, 265 kg ha−1 appeared to gain c. 250 kg ha−1 N over control plots (35 kg ha−1) after 13 years of N application. Reducing the N application rate from the economic optimum to a more biologically efficient N rate (156 kg ha−1) was calculated to result in an average yield loss of 0·305 t ha−1 and cause an estimated £17 ha−1 loss in profit.

The Rht-B1b, Rht-D1b and Rht-B1c alleles for reduced height in wheat (the Norin 10 and Tom Thumb dwarfing genes previously known as Rht1, Rht2 and Rht3) were exploited in combinations to generate a near-continuous range of plant heights, from 53 cm to 123 cm, amongst near-isogenic homozygotes and F1 hybrids. Pleiotropic yield effects of Rht genes were measured in both homozygous (intravarietal) and heterozygous (intervarietal) genetic backgrounds. Heterosis due to overdominance of Rht genes was detected among intravarietal hybrids. The effects of heterozygosity at other genetic loci (mean dominance) were determined, independently of Rht effects, from comparisons between intravarietal and intervarietal F1 hybrids.

Genotypes of intermediate plant heights gave maximum yields, in agreement with other trials of the homozygous lines, so that heterosis (hybrid exceeding best parent) for Rht yield effects was observed in crosses between tall and dwarf isogenic pairs. This heterosis combined additively with increased mean weight per grain in intervarietal crosses, generating the highest overall grain yields in hybrids with semi-dwarf stature in heterozygous genetic backgrounds. The Rht-B1c allele showed single-gene overdominance for grain yield, also the production of alpha-amylase in ripening grains of Maris Huntsman was effectively inhibited in the Rht-B1a/c intravarietal hybrid. The Rht-B1c allele thus offers advantages for both grain yield and grain quality in the heterozygous condition and should be considered as an alternative to the conventional semi-dwarfing genes Rht-B1b and Rht-D1b for F1 varieties in environments conductive to preharvest sprouting.

The suitability was assessed of various designs for field experiments investigating plant diseases caused by airborne pathogens that can be subject to interplot interference. Use of a model to describe such interference showed that the treatments with the most dissimilar effects on controlling the disease should be allocated to experimental plots furthest apart in each block, in order to minimize the interplot interference within a block. When using large square plots, rectangular blocks were more efficient than square blocks in minimizing treatment-comparison biases due to interference between neighbours. For rectangular blocks with the square plots side by side, less biased treatment comparisons were obtained from designs with complete blocks than from designs with incomplete blocks, especially when larger numbers of treatments were included in the experiment. However, when interplot variance is taken into account, incomplete blocks may give better treatment comparisons. Similarly, unbalanced designs composed only of incomplete blocks that yield less biased treatment comparisons may be better than balanced incomplete block designs when interplot variance is low. For high levels of variation, balanced incomplete block designs may be more appropriate, as increasing the precision of the treatment comparisons becomes more important than reducing the bias.

15N-labelled fertilizer was applied in spring to winter wheat, winter oilseed rape, potatoes, sugarbeet and spring beans in field experiments done in 1987 and 1988 in SE England on four contrasting soil types – a silty clay loam, a chalky loam, a sandy loam and a heavy clay. The 15N-labelled fertilizers were applied at recommended rates; for oilseed rape, a two-thirds rate was also tested. Whole-crop recoveries of labelled nitrogen averaged 52% for winter wheat, 45% for oilseed rape, 61% for potatoes and 61% for sugarbeet. Spring beans, which received only 2·5 kg ha−1 of labelled N, recovered 26%. Removals of 15N-labelled fertilizer N in the harvested products were rather less, averaging 32, 25, 49, 27 and 13% in wheat grain, rape seed, potato tubers, beet root and bean grain, respectively.

Crop residues were either baled and removed, as with wheat and rape straw, or were flailed or ‘topped’ and left on the soil surface, as was the case with potato tops and sugarbeet tops. Wheat stubble and rape stubble, together with leaf litter and weeds, were incorporated after harvest. The ploughing in of crop residues returned 4–35% of the original nitrogen fertilizer application to the soil, in addition to that which already remained at harvest, which averaged 24, 29 and 25% of that applied to winter wheat, oilseed rape and sugarbeet respectively. Less remained at harvest after potatoes (c. 21%) and more after spring beans (c. 49%). Most of the labelled residue remained in the top-soil (0–23cm) layer.

15N-labelled fertilizer unaccounted for in crop and soil (0–100 cm) at harvest of winter wheat, oilseed rape, potatoes, sugarbeet and spring beans averaged 23, 25, 19, 14 and 26% of that applied, respectively. Gaseous losses of fertilizer N by denitrification were probably greater following applications to winter wheat and oilseed rape, where the N was applied earlier (and the soils were wetter) than with potatoes and sugarbeet. Consequently, it may well be advantageous to delay the application of fertilizer N to winter wheat and oilseed rape if the soil is wet.

Total inorganic N (labelled and unlabelled) in soils (0–100 cm) following harvest of potatoes given 15N-labelled fertilizer in spring averaged 70 kg N ha−1 and was often greater than after the corresponding crops of winter wheat and oilseed rape, which averaged 53 kg N ha−1 and 49 kg N ha−1, respectively. On average, 91 kg ha−1 of inorganic N was found in soil (0–100 cm) following spring beans. Least inorganic N remained in the soil following sugarbeet, averaging only 19 kg N ha−1. The risk of nitrate leaching in the following winter, based on that which remained in the soil at harvest, ranked in decreasing order, was: spring beans=potatoes>oilseed rape=winter wheat>sugarbeet. On average, only 2·9% of the labelled fertilizer applied to winter wheat and oilseed rape remained in the soil (0–100 cm) as inorganic N (NO−3+NH+4) at harvest; with sugarbeet only 1·1% remained. In most cases c. 10% of the mineral N present in the soil at this time was derived from the nitrogen fertilizer applied to arable crops in spring. However, substantially more (c. 21%) was derived from fertilizer following harvest of winter wheat infected with take-all (Gaeumannomyces graminis var. tritici) and after potatoes. With winter wheat and sugarbeet, withholding fertilizer N had little effect on the total quantity of inorganic N present in the soil profile at harvest, but with oilseed rape and potatoes there was a decrease of, on average, 38 and 50%, respectively. A decrease in the amount of nitrogen applied to winter wheat and sugarbeet in spring would therefore not significantly decrease the quantity of nitrate at risk to leaching during the following autumn and winter, but may be more effective with rape and potatoes. However, if wheat growth is severely impaired by take-all, significant amounts of fertilizer-derived nitrate will remain in the soil at harvest, at risk to leaching.

RAPD (Randomly Amplified Polymorphic DNA) assay of 32 cultivar accessions from the ryegrass–fescue (Lolium–Festuca) complex was accomplished using ten decamer primers to assess (i) the power of RAPD technology to discriminate between individual commercial accessions and to produce cultivar fingerprinting, (ii) the degree of relatedness of accessions based on RAPD profiles in comparison with other existing classifications, and (iii) the possibility of automation of RAPD technology.

The variation of the correlation coefficient r as the primary output from the automated RAPD-profile processing summarizes variability derived from DNA isolation, the RAPD reaction, and final computer-image processing of RAPD profiles. The AII (Accession Identity Interval) of r for accession Festuca arundinacea cv. Lekora was determined experimentally and the value obtained was accepted as a valid interval for all the other accessions studied. In order to evaluate the discrimination potential of all ten primers together, a pooled-similarity matrix was computed. Employing this approach, we achieved 100% discrimination between all 35 accessions when using all ten primers. A dendrogram for all 35 accessions was obtained using average linkage cluster analysis (UPGMA – Unweighted Pair Group Method with Arithmetic Means). This procedure successfully produced smaller groups of higher taxonomic homogeneity. The relationships between the Lolium–Festuca accessions were also revealed by principal coordinate analysis (PCO) based on absorbance profiles from the RAPD assay. Again, all accessions were well separated, recognising even subspecies relationships. In general, PCO analysis confirmed the inferences made from the UPGMA method.

We successfully applied the computer-aided system of RAPD assay, based on an IBM PC computer, for discrimination of cultivars as well as for description of DNA-based relationships of accessions from various taxonomic groups of the Lolium–Festuca complex.

A model to predict wheat growth stage is briefly described. It is based on prediction of the number of emerged leaves and the final number of leaves on the main shoot, and the co-ordination between leaf emergence and apex development, including stem elongation. The input variables are daily maximum and minimum temperatures, date of sowing and site latitude, from which thermal time, vernalization and daylength are calculated.

Selected growth stages were predicted for six sites in each of three growing seasons. The differences between observations made by independent observers and predictions were mostly 7 days or less but in three site–season combinations the average difference was >10 days. Observer errors were implicated and examined, but it is concluded that the prediction scheme must also have been partly responsible for the discrepancies.

Detailed information on the timing of terminal spikelet formation, anthesis, maturity and the rate of leaf appearance is crucial to the predictive accuracy of the AFRCWHEAT2 growth simulation model for wheat. To obtain appropriate data under different growing conditions for two spring wheat (Triticum aestivum L.) cultivars (cvs Minaret and Canon), a main field experiment was conducted comprising eight sowing dates between mid-March and late June 1994; data from single sowings of Minaret in 1992 and 1995 were also included in the analysis. Minaret is the focus of a major European study of the impact of climate change factors on the growth and development of wheat, and data of the type reported here were essential to support the modelling aspects of the project involving AFRCWHEAT2.

The accumulated thermal time from emergence to critical developmental stages was similar for all sowings of both cultivars, even though biomass was greatly reduced in the later sowings. Although final leaf numbers were comparable for all sowing dates, the rate of leaf appearance was correlated with the rate of change of day length at crop emergence in Minaret. The unmodified AFRCWHEAT2 model did not predict the timing of critical growth stages and leaf numbers well, but removal of the vernalization and photoperiod factors from the developmental sub-model greatly improved the accuracy of such predictions. These results strongly suggest that fixed quantities of thermal time may be employed successfully to predict the timing of critical developmental stages of these spring wheat cultivars over a range of sowing dates, geographic locations and climatic conditions, since development appeared to be a linear function of temperature.

Despite removing the photoperiod and vernalization functions, the model consistently over-predicted final leaf number because leaf production by the model continued until 1·8 phyllochrons before anthesis, as compared to the three phyllochrons actually recorded for Minaret. AFRCWHEAT2 could therefore be further modified to reproduce more accurately the smaller number of leaves typical of these spring cultivars.

The crop–environment resource synthesis model for wheat, CERES–Wheat, was used to simulate yields from 1985 to 1993 at Ludhiana, India. The simulated anthesis and physiological maturity dates, grain and total biomass yields of wheat were compared with actual observations for the commonly grown cultivar, HD–2329. The simulated and actual dates of phenological events showed deviations from only −9 to +6 days for anthesis and −6 to +3 days for physiological maturity of the crop. The model estimated the kernel weight within 88–113% (mean 100%) of the actual kernel weights. The model predicted the grain yields from 80 to 115% (mean 97·5%) of the observed grain yield. Biomass yields were predicted from 93 to 128% (mean 110·5%) of the observed yields. The results obtained with the model for the eight crop seasons demonstrated satisfactory predictions of phenology, growth and yield of wheat. However, the biomass simulations indicated the need for further examination of the factors controlling the partitioning of photosynthates during crop growth. The results of this study reveal that the calibrated CERES–Wheat model can be used for the prediction of wheat growth and yield in the central irrigated plains of the Indian Punjab.

Functions which predict rate of leaf emergence and final number of leaves, used in a model to predict the date at which growth stages occur, were tested in an experiment on winter wheat cv. Mercia grown with standardized husbandry at six sites in 1992/93, 1993/94 and 1994/95. A study of the number of detectable nodes on the culm and leaf length was also made.

The predicted rate of leaf emergence was mostly within 5% of the observed value. The difference between observed and predicted final number of leaves was mostly less than half a leaf but suspected errors in leaf counts resulted in some differences of more than two leaves.

Variable extension of the basal internode impaired confidence in the detection of nodes. The mean number of detectable nodes differed significantly among sites and between seasons from 3·7 to 4·8 but could not be related to sowing date or final number of leaves. Further information on factors affecting extension of the basal internode is desirable to standardize node detection and improve prediction of culm leaf appearance.

Culm leaves showed successively longer laminae up to the penultimate leaf. There was a significant relationship between length of the flag leaf and the final number of leaves, but it was positive in 1993/94 and negative in 1994/95. This may have been due to greater water stress in 1994/95.

The effects of contrasting management systems either of infrequent rotational grazing by town milk supply dairy cattle, or of frequent defoliation by continuously grazing sheep and beef cattle, on the morphology of independent plants and populations of ‘Grasslands Roa’ tall fescue in mixed pastures, were measured over 1 year (1992/93) in New Zealand. Volunteer perennial ryegrass plants were also measured for comparison.

While both species exhibited a similar pattern of clonal growth, tall fescue developed more plants of higher branching complexity than perennial ryegrass, chiefly through maintaining more connective stems, as herbage production was confined to the three youngest branching orders in both species. Greater resistance to microbial degradation of old stems through poorer quality organic matter (wide C[ratio ]N ratio) compared to perennial ryegrass may be responsible for the greater complexity of fescue plants. In addition, tillering rates in tall fescue were three times lower which was offset by greater longevity and size of leaves and tillers, compared to perennial ryegrass. As a result, seasonal fluctuation in the distribution of plants among the various branching orders in tall fescue was small, producing a more stable population relative to the distinct seasonal changes in the population of perennial ryegrass plants. Grazing management had no effect on the seasonal population structure in either species.

Differences in plant structure due to grazing management were small, with only slightly more tillers on sheep-grazed than on cattle-grazed tall fescue plants. The major effect of grazing management was on dry weight or size of plant components. Cattle-grazed tall fescue plants were 120% heavier, with greater numbers and lengths of stolons and flower heads than those under sheep grazing. For the volunteer perennial ryegrass, the difference was only 65%, possibly due to competition from the more vigorous tall fescue under rotational cattle grazing.

Both species produced stolons throughout the year, although these were primarily associated with reproductive growth in spring. In tall fescue, an additional distinction was made between stolon and rhizome, the latter occurring mainly in the summer–autumn. Their possible functions in plant growth are discussed.

Simulation of phasic development in wheat is necessary in constructing wheat growth and yield models. It is also useful for evaluating cultivar adaptation and scheduling cultural practices. This paper describes a conceptual model of wheat development based on phenological principles, as affected by vernalization, photoperiod, thermal response and intrinsic earliness, and also reports the results of sensitivity analysis and validation of the model.

The model predicts when the plant will reach double ridge, terminal spikelet and heading. In the model, the daily thermal sensitivity of development following emergence is determined by an interaction of ‘relative vernalization completion’ and ‘relative photoperiod effectiveness’ for that day. After complete vernalization is reached, the daily thermal sensitivity is determined only by relative photoperiod effectiveness, which gradually increases from terminal spikelet to heading. A multiplication between the daily thermal sensitivity and thermal effectiveness generated daily flowering time, which was accumulated to trigger a particular developmental stage. Genotypic differences were characterized as vernalization requirement, photoperiod sensitivity and intrinsic earliness.

The model showed a sensitive response to environmental variables of temperature and daylength, and to genetic parameters of vernalization requirement and photoperiod sensitivity. Evaluation of the model using multiple experimental data involving various cultivars and planting dates exhibited a marked goodness of fit between simulation and observation with a root mean square error <5 days. The results indicate that the model can be used as a predictor for the major flowering stages, as well as functioning as a knowledge base for understanding the characteristics of different development components in wheat.

Lucerne (Medicago sativa L.) is the most common forage species in the world. In Italy it is grown on c. 1 million ha and is one of the most important crops for restoring soil fertility and for low-input agriculture. Landraces are still common (73% of the seed market) and 14 are registered in the National Register of Varieties. However, by 2002, landraces will be removed from the Register, seed certification will terminate and seed marketing will be forbidden. The collection, agronomic evaluation and characterization of farmer-landraces, still widespread in central Italy, were the objectives of the present work, particularly of the most important morphological and physiological characters useful for their identification. From 1993 to 1995, 20 landraces were evaluated for dry matter and seed yield in dense stands, and compared with Casalina, a local landrace, Boreal, an improved variety, and Italia Centrale, the registered landrace from central Italy. From 1992 to 1994, six landraces were evaluated as spaced plants and 48 morphophysiological characters were recorded.

Several landraces, not differing from the local control, were significantly more productive than Boreal. Univariate analysis of variance indicated that although differences were found in several characters, they could not be used to distinguish between populations. Discriminant analysis was more powerful, and five landraces out of six were clearly distinguished, with an average of correct classification of individuals in the group of origin as high as 82%.

The ex situ and in situ conservation of lucerne landraces, their potential role in future breeding programmes, and the most important characters to be used in discriminant analysis in the landrace/variety characterization of allogamous species in Hardy–Weinberg equilibrium are discussed.

Fifty-six half-sib families of perennial ryegrass (Lolium perenne), derived from wild populations in Galicia, were examined for the presence of perennial ryegrass endophytes; 28 were endophyte-infected (E+) and 28 were endophyte-free (E−). All families were established in spaced-plant nurseries and trial plots at two locations in Galicia, in 1992. E+ families had a significantly (P<0·05) higher first cut, spring and total yield than E− families at one location in the third year after planting. At this location, water deficit was about 75% higher than at the other location in all three years of study. Endophyte did not affect crown rust susceptibility or forage quality (crude protein, water-soluble carbohydrate and in vitro digestibility). Ergovaline alkaloid concentration in the 28 E+ families varied from 0 to 0·55 μg/g dry matter (DM) (mean 0·15), with 14 families containing levels of ergovaline >0·1 μg/g DM. Thus endophyte infection may benefit the host in drought-prone areas of Galicia, with an increased chance of E+ plants being favoured by either natural or artificial selection.

Wheat was grown in rotation with three different crops, namely wheat, chickpea and lentil, and with a fallow, in three consecutive seasons beginning in 1992 in NW Syria. Two rates of N fertilizer (0 and 30 kg N ha−1) were superimposed on these four rotations, giving eight treatments which were replicated three times in each season. 15N-labelled fertilizer was applied to microplots within the fertilized plots at sowing when unlabelled fertilizer was broadcast on the rest of the plot.

Yields of grain and dry matter were generally greatest when wheat followed a fallow, and least in the continuous wheat rotation; this was significant in 1993 and 1994. Applications of N fertilizer had no effect on productivity in 1992, but in the other two seasons grain yields were increased by 550 kg ha−1, on average. Depending on the season, between 8 and 26% of the 15N-labelled fertilizer was recovered in the shoot dry matter, while between 18 and 54% of the fertilizer remained as N in the soil at harvest, mostly in the 0–20 cm soil layer. More than half the fertilizer in the crop at harvest had been taken up by the end of March, although by March the plants were only c. 10% of their mass at harvest. Conversely, <35% of the soil-derived N in the crop at harvest had generally been taken up by March. This temporal difference in the pools of N utilized by the crop was attributed to the drying of the soil surface layers where most of the N fertilizer remained. Approximately 50% of the 15N-labelled fertilizer was unaccounted for in the crop and 0–40 cm soil layer at harvest.

The yield benefit of growing wheat in rotation with a fallow or either grain legume rather than continuously, ranged from nothing to the equivalent of a fertilizer application of at least 30 kg N ha−1 to continuous wheat, depending upon the season and the previous crop. Only in the season where the residual effect of the rotation on wheat yields was greatest (1993) did the preceding grain legume crop or fallow appear to contribute between 10 and 20 kg N ha−1 to the wheat crop. Otherwise they contributed no N at harvest. While a fallow may increase the availability of water to the succeeding wheat crop, the benefit from the preceding grain legumes may lie in their effect on the soil physical structure or on the increased availability of other limiting nutrients rather than additional N.

Stolon death, often caused by grazing or winter-kill, is a major factor determining the survival and persistence of white clover (Trifolium repens L.), the most important forage legume in UK agriculture. Since stolon morphology apparently affects stolon survival, this study was designed to assess the genetic variation for stolon characters within a white clover population from Switzerland and to assess the effects of two generations of selection for stolon characteristics on that population. Bidirectional selection was carried out simultaneously for stolon diameter (as the primary criterion of selection) and total stolon length i.e. the product of the length of the longest stolon and stolon number. Four selection lines were established: (a) plants with thick sparse stolons, (b) plants with thick profuse stolons, (c) plants with thin sparse stolons and (d) plants with thin profuse stolons. Realised heritabilities for stolon diameter, estimated in both directions and over both generations of selection, were found to lie within the range 0·28–0·44; significant shifts in population means for stolon diameter were demonstrated. Selection for thin profuse stolons and for thick sparse stolons was effective, but because of negative correlations between stolon diameter and both stolon length and number, selection for thin sparse stolons or thick profuse stolons was ineffective.

The water-use model (watyield) was used to estimate a number of variables which were then related to the actual yields recorded in long term sugarbeet experiments carried out at several sites in England over the last 30–40 years. Nine functions were developed which are based on yield/water-input, yield/crop evaporation and (the equivalent of) relative yield/relative crop evaporation relationships. In all cases, highly significant linear correlations were obtained but the levels of precision, and degree of site specificity, varied. For irrigation planning and water allocation, three approaches are recommended with increasing sophistication and, in general, precision. These are (1) relating yield increases to the estimated irrigation need; (2) relating actual yields to crop evaporation totals; and (3) determining actual yields for rainfed and irrigated crops from the calculated seasonal totals of the ‘effective’ solar radiation intercepted by the crop canopy. These values can be estimated with the model using standard weather and soil physical data appropriate to the locality and the crop.

Field experiments were conducted at Cuttack, India during 1991–94 to study the effect of tillage, methods of crop establishment and weed control at varying levels of N fertilizer on the performance of rice under flood-prone lowland conditions (0·60 cm water depth). The loss in grain yield of direct-sown rice caused by unchecked weed growth ranged from 18·2 to 59·2% in the different years, and was greater when N fertilizer was applied and when the conventional practice of ploughing the fields just before sowing was followed. Increasing the number of tillage operations before sowing improved the crop stand, reduced weed infestation and, thereby, increased the yield significantly compared with that achieved by conventional tillage. Summer ploughing rather than conventional tillage decreased weed dry weight at harvest by 15·8–53·2% and increased grain yield by 47·4–56·3%. A pre-emergence application of thiobencarb at 2·0 kg/ha, hand weeding once at 20 days of growth and post-establishment inter-crop cultivation at 37–42 days provided effective weed control and increased yield by 32·7–34·7, 36·7 and 28·7–83·9%, respectively. The efficiency of weed control and the resulting increase in rice yield were comparatively greater under puddling than with inter-crop cultivation and herbicide application. The loss in yield due to weeds was negligible when the crop was transplanted due to the incorporation of weeds during puddling and a greater water depth in the later growth stages. Therefore, the grain yield of rice was highest with transplanting followed closely by the direct-sown crop with post-establishment inter-crop cultivation. The response of direct-sown rice to N fertilization up to 60 kg N/ha decreased with fewer ploughings when no weed control measures were adopted. However, the grain yield increased significantly with N application up to 40 kg N/ha when weeds were controlled by cultural or chemical methods. The results suggested that an integrated weed management strategy involving summer ploughing, thiobencarb application and inter-crop cultivation is essential for effective weed control in direct-sown, flood-prone, lowland rice, in order to ensure higher N-use efficiency and crop productivity.

New uses of natural fibres in industrial processes have increased the demand for linseed fibre which is normally discarded. In this investigation, 18 linseed and 10 flax varieties are evaluated for 13 developmental, seed yield and fibre yield traits with a view to identifying suitable genotypes which may have high yields of both seed and fibre, and therefore can be used as dual-purpose varieties and/or are likely to provide a suitable foundation for breeding new cultivars with an ability to produce high yields for seed as well as fibre.

Comparison of linseed and flax varieties has revealed that the two plant types have diversified to a great extent, particularly for those traits which have been subjected to direct or indirect selection during the past decades. However, considerable variation still exists among the linseed and flax varieties, and linseed shows more heritable variation than flax, for both seed and fibre traits. On the other hand, persistent selection of linseed and flax for commercially desirable phenotypes has not modified the genetic correlations to any appreciable level and both crops display almost identical correlations which do not differ significantly for any pair of traits. None of the flax or linseed varieties has shown such outstanding performance for seed yield as well as fibre weight which would have allowed them to be considered suitable for cultivation as a dual-purpose variety. In general, linseed × linseed and linseed × flax crosses would constitute better source materials for breeding high yielding dual-purpose cultivars compared to flax × flax crosses, particularly when seed will be the primary commercial product and fibre/straw a secondary commodity of such varieties.

The changes in weight and quality of sugarbeet roots stored in 18 clamps, mostly in eastern England during the winters of 1992/93 to 1994/95, were studied on farms using best commercial practice. Storage usually started in early December, at about the last recommended date of harvesting, and continued until the end of the beet-processing campaign at the local sugar factory (usually in February). Random samples of beet, in open-weave nets, were either analysed at the outset or were buried in a predetermined pattern in the clamp for up to 84 days. Periodically, samples were removed from the clamps for analysis. Beet weight hardly changed but sugar was lost as a reduction in sugar concentration: this declined at c. 0·02% per day. The concentration of reducing sugars, which are important impurities, increased fourfold during storage. Most other beet quality parameters remained unchanged. Sugar and adjusted weight was lost at 0·143 and 0·187% per day respectively. This relationship was highly significant, but a relationship between sugar loss and accumulated thermal time (0·0188% per °C day) accounted for more of the variation (73%). Temperature changes within the clamps, and the differences between clamps in accumulated thermal time, were not predictable. Some clamp insulation materials appear to allow more heat to accumulate than is desirable.

Experiments using cultivars with differing degrees of striga resistance were conducted at two sites at Kamboinse in 1988 and at two locations (Kamboinse and Kouare) in 1989 in the Sudan-Savannah region of Burkina Faso. At each site, striga-free (SFP) and striga-infested plots (SIP) were selected. Two factors, location and genotype, were found to be associated additively with yield losses in soils infested by striga. The location effect was probably due to lower soil fertility in the SIP than the SFP plots under farming conditions. Yield losses in SIP relative to SFP ranged from 3·1%, at the experimental station, to 44·2% under farmers' field conditions. The genotype effect was evident at all locations. Depending on the susceptibility of the cultivars, it varied from 3·1 to 36·5% of the mean yield of SFP with an average of 31·4% in susceptible cultivars. The location effect was evident only at Kouare, where SIP plots were under continuous cultivation without appropriate soil fertility maintenance and/or restoration measures. This amounted to c. 19·4% of the mean yield in the SFP. To reduce yield losses in soils infested by striga, it appears to be necessary to grow high yielding, striga-resistant cultivars using agronomic practices which are known to improve soil fertility.