Sorghum hybrids are generally considered to be drought tolerant based on their yield performance in multi-locational trials. The present study was undertaken to test this hypothesis. A short duration hybrid, CSH–6, a long duration hybrid, CSH–9, their common male parent and both female parents were evaluated in the field in India under both rainfed and irrigated conditions during the rainy seasons of 1986 and 1987. Due to the low rainfall received in these years, the unirrigated treatments experienced severe water stress during the vegetative and post-anthesis periods. The hybrids produced more leaf area and dry matter than their parents even under water stress. The values for the physiological traits examined either resembled those of one of their parents or were intermediate between them. The hybrid CSH–6 produced more grain than its female parent under rainfed conditions but, due to the severe water stress, neither CSH–9 nor its parents exhibited panicle emergence. The results suggest that crop phenology is very important for the production of grain yield under severe water stress. Given knowledge of rainfall characteristics and probable periods of drought within specific regions, it should be possible to breed phenologically and physiologically adapted hybrids for specific environments.

The growth and yield of late-season tomato was studied at Akure, Nigeria, from 1995 to 1998. In each year, treatments were 0 (bare ground) or 12 kg/ha grass mulch applied to tomatoes at densities of 1·9, 2·8, 3·7 and 5·6 plants/m2 in a factorial combination. Increase in plant density and mulching reduced soil temperature at 5 cm depth while only the latter enhanced soil moisture at 10 cm depth throughout tomato growth. The improved soil hydrothermal regime resulted in earlier onset of flowering, 50% flowering date and date of first harvest respectively and shorter fruit harvest duration in tomato grown on either bare ground or at increased plant density.

Although increased plant density reduced shoot dry weight per plant at final harvest, both root length per plant and root dry weight per plant were enhanced. Fruit yield/ha increased as plant density increased although yield of the individual plants and their components were significantly reduced. Because of compensation at higher plant population densities, it is economical to grow late-season tomato at 5·6 plants/m2. Mulching enhanced growth and yield of tomato compared to bare ground and the result emphasizes the need for early and rapid growth of late-season tomato before the onset of terminal drought.

The dynamic simulation model ‘PNUTGRO’ was used to predict groundnut growth and yield from 1989 to 1993 at Ludhiana, India. The simulated flowering, pegging and physiological maturity dates, leaf area index (LAI), pod and seed yields and shelling percentage of groundnut were compared with actual observations for the commonly grown cultivar, M-335. The simulated phenologic events showed deviations of only −3 to +3 days for flowering, −3 to +2 days for pegging and −4 to +2 days for physiological maturity of the crop. The model estimated the LAI to be within 95–108% (mean 101·5%) and shelling percentage to be within 93–108% (mean 100·5%) of the actual values. The model predicted the pod yields from 89 to 111% (mean 100%) and seed yield from 90 to 110% (mean 100%) of the observed yields. The results obtained with the model for the five consecutive crop seasons revealed satisfactory predictions of phenology, growth and yield of groundnut and hence the model ‘PNUTGRO’ can be used for prediction of groundnut production in the central plains of the Indian Punjab.

Russian wheat aphid (RWA), Diuraphis noxia is a serious pest of cereals in various regions of the world. Seventy-six barley genotypes collected from different areas in Iran were subjected to an initial mass screening test and six susceptible and 17 apparently resistant genotypes were identified. To determine resistance mechanisms, antixenosis, antibiosis and tolerance tests were conducted and selected genotypes were ranked according to their plant resistance indices.

Four crosses were made between the two most resistant lines (Shz.B-106, and Shz.B-108) and two most susceptible lines (Shz.B-105 and Shz.B-107). F1, F2 and BCF1 (backcross to the resistant parent) seedlings were screened for RWA resistance in the greenhouse by artificial infection. Resistance in Shz.B-106 was apparently controlled by a semi-dominant gene, whereas resistance in Shz.B-108 was controlled by a dominant one.

The pollination requirements of West Indian cherry (Malpighia emarginata DC) were investigated in NE Brazil through observations of flower morphology, floral rewards, anthesis, anther dehiscence, stigma receptivity, pollen cross and self-compatibility and proportion of fruit set. Potential insect pollinators and their foraging behaviour were also studied, and the pollination efficiency of the most frequent flower visitor, the bee Centris tarsata Smith (Anthophoridae), was assessed using single visits to flowers. It was shown that the West Indian cherry flower has a short lifespan, thus requiring pollination on the day of anthesis, when both cross- and self-pollen grains set fruit. The flower can potentially be pollinated by an array of insect visitors, but only oil-collecting bees of the genus Centris find it very attractive. Centris tarsata appeared as the main pollinator of West Indian cherry in the area studied, and farmers are advised to encourage its presence in orchards. Despite high levels of natural pollination, only 30% of flowers set fruits. It is suggested that a high proportion of abnormal ovule development may be responsible for low fruit set where pollination is satisfactory, and that West Indian cherry varieties showing a lower percentage of such abnormalities should be selected for.

Changes in environmental conditions and the EU policy have put more emphasis on growing alternative crops in the set aside farmlands of western Europe, and sunflowers are increasingly being grown as a minor crop in the UK. However, long-term success of sunflowers as a commercial crop depends largely on the availability of early maturing, high yielding, disease resistant varieties. The present study was conducted to investigate the nature of genetic variation among the available breeding stocks that may have to be exploited to produce such cultivars. Analysis of 182 test crosses, produced by crossing 13 male sterile (CMS) lines with 14 restorer (SB) lines, has revealed that genetic variability exists for many important traits, including maturity, vigour and seed yield. Genetic differences were also detected within the male sterile and restorer groups of lines even though they were classed as early maturing. All types of gene effects, additive, dominance and epistasis, contributed to variation among the test crosses and dominance was largely unidirectional and partial. CMS and SB lines also showed some allelic complementation and the CMS exerted a modest degree of maternal control for flowering time. The test crosses were generally more vigorous and high yielding compared to their inbred parents. But they also matured significantly late, indicating that all crosses will not be suitable as potential hybrids for the UK conditions. Genotypic correlations indicated that faster growth, early flowering, high seed number and seed weight can be combined more readily in the F1 crosses.

Infection of pearl millet by downy mildew [Sclerospora graminicola (Sacc.) Schrot.] has been shown to be influenced by soil pH, soil bulk density, soil moisture content and addition of farmyard manure and nitrogen fixing bacteria. A pH value of 8·5 allowed disease to develop the most, with increases in acidity to pH 7·5 producing 70% reduction in disease. Higher soil bulk density and moisture content also led to reductions in disease but the effects were not as marked as for pH. The addition of farmyard manure to soil or the addition of Rhizobium, Azospirillum or Azotobacter inocula as combined seed and soil treatment also reduced disease with the best effects being from a cluster bean isolate of Rhizobium and from Azotobacter chroococcum. Assessment of rhizosphere microorganisms associated with the resistant and susceptible varieties of pearl millet showed that, overall, the fungal population was lower in the resistant varieties but that it was increased in both susceptible and resistant varieties by infection with downy mildew. Bacterial and actinomycete populations were also lower in resistant varieties but in this case downy mildew infection decreased the rhizosphere populations of both groups.

Dehydrogenase activity of rhizosphere soil was higher in susceptible varieties but was decreased in both variety types by infection with S. graminicola.

The results are discussed with reference to possible mechanisms to explain the observed effects.

The efficacy of insecticides derived from two local plants was tested on termites infesting maize in maize–cassava–‘Egusi’ melon intercrops in two farmers' fields in south-western Nigeria during the 1989/90 and 1990/91 cropping seasons. The intercrops consisted of 40000, 20000, and 10000 maize plants/ha, with a fixed population of 10000 plants/ha of both cassava and melon. The insecticides were aqueous extracts of ripe seeds of neem (Azadirachta indica A. Juss) and the crude seed oil of Piper guineense Schum And Thonn, each at 10% concentration at the rate of 390 litres/ha and 18 litres/ha, respectively. On the plots treated with these natural insecticides, damage by termites [Microtermes spp., Macrotermes bellicosus Smeathman = nigeriensis Sjostedt and M. subhyalinus Rambur (Isoptera: Termitidae)] was significantly lower and maize yields higher than on the control plots. The mean percentage of maize stems attacked by termites (considering all categories of termite damage) in untreated plots during the trials ranged between 0–22% in 1989 and 2–46% in 1990. Planting densities did not significantly influence termite attack on maize. Cassava and melon plants or cassava tubers were not attacked by termites in any of the trials and their yields were not affected by insecticide treatments or planting density of maize.

An experiment was carried out in 1994 to examine energy and nitrogen utilization of lambs offered two contrasting grass-based diets. The two forages, which were from the same parent herbage, were grass silage and grass which was conserved by freezing. They were offered as sole diets or supplemented with either 250 or 500 g concentrates per kg total dry matter intake (DMI) to give a total of six experimental treatments. Seventy-two Dutch Texel × Greyface (Border Leicester × Blackface) lambs, consisting of 36 males which were initially 36 (S.D. 4·9) kg liveweight and 36 females which were initially 34 (S.D. 2·5) kg liveweight were used. Ensiling significantly increased apparent digestibility of dry matter, energy and nitrogen (P<0·001), but had no significant effect on methane energy loss as a proportion of gross energy intake, metabolizable energy intake (MEI), heat production, energy retained, efficiency of utilization of energy for growth (kg) or nitrogen retention. Supplementation of forage with concentrates resulted in a curvilinear decrease in heat production expressed as a proportion of MEI (P<0·05) and a linear increase in energy retention, expressed as an absolute value or as a proportion of MEI (P<0·05). Supplementation of forage tended to increase kg when calculated using Agricultural Research Council estimates of maintenance energy requirements, but had no significant effect when alternative estimates of maintenance were used. It is concluded that ensiling had no effect on efficiency of utilization of energy or nitrogen as measured by indirect calorimetry.

This study describes the development of a highly repeatable cold screening procedure for lentil (Lens culinaris Medik.) using controlled conditions which involve first, acclimation of the plants at the vegetative stage in a growth chamber and second, freeze testing in a freeze chamber. The seeds were first germinated in Petri dishes and then planted in styrofoam trays with individual cells. Initial growing temperatures in the growth chamber for two weeks were 25 °C day and 10 °C night with a 12 h photoperiod. In the third week the photoperiod was changed to 10 h and in the fourth the temperatures were changed to 10 °C day and 0 °C night to acclimate the plants. Using a modified freeze chamber (household deep freezer), a freeze test temperature of −15 °C, following a 6–8 weeks acclimation period (because both acclimation times had the same effect for cold tolerance of the genotypes), at 2 and 3 °C/h cooling rate, and an exposure time of 3 h at −15 °C were appropriate to detect significant (P<0·01) differences among several lines at a comparatively low degree of injury for the most cold-hardy genotypes.

From 1990 to 1992, diet selection and nutrient intake of Zebu cattle grazing Sahelian pasture were studied in Central Mali. Forty-five intact males and 12 oesophageally fistulated animals were separated into three groups of 15 intact and 4 fistulated animals. The control group (C) grazed natural pasture only, while the moderately supplemented group (M) additionally received 0·8–1·5 kg OM/day of crop by-products during the dry season (November–June) and the first month of the rainy season. The third group (H) was highly supplemented with 1·2–2·7 kg OM/day in the dry season and 0·8–1·2 kg OM/day in the rainy season. Oesophageal extrusa was collected during 5 consecutive days at intervals of 4–5 weeks. Samples were analysed for contents of organic matter (OM), crude protein (CP) and neutral detergent fibre (NDF). Digestible organic matter (DOM) and metabolizable energy content (ME) were calculated from in vitro gas release. Intake of organic matter (IOM) of the fistulated animals was determined from faecal organic matter excretion (FOM) and extrusa DOM content. Intake of CP (ICP) and ME (IME) were calculated from IOM and the respective nutrient contents of extrusa samples.

Extrusa CP, DOM and ME contents did not differ significantly between the three groups either in the dry or in the rainy season. The CP content was c. 230 and c. 197 g/kg OM during the rainy season, and declined to values [les ]70 and [les ]95 g CP/kg OM at the end of the dry season of 1990 and 1991, respectively. Average DOM and ME contents were c. 668 g DOM and c. 9·9 MJ ME/kg OM during rainy seasons. At the end of the dry seasons, these values decreased to <550 g DOM and <8·0 MJ ME/kg OM. Per kg of metabolic body mass, IOM of group C was c. 89 g/day during the early dry season. It was accompanied by a daily ICP of 8–10 g and by an IME of 691–765 kJ/day. Due to a higher nutrient content in the selected diet, energy intake was slightly increased and protein intake was significantly higher during the rainy than during the dry season, although IOM was only 77–81 g/day. At the end of the dry season, unsupplemented animals ingested <70 g IOM/day and the concomitant CP and ME intake were <6 g CP/day and <500 kJ ME/day, respectively. Feed intake from pasture was stimulated by a moderate supplementation, but reduced by a high supplementation. The results indicate that on slightly degraded Sahelian rangeland, the nutrient intake of cattle is in the first place limited by biomass availability and only secondly by the quality of the vegetation.

In a preliminary experiment, 74 faba bean genotypes including winter genotypes (autumn-sown) and spring genotypes (spring-sown) and isogenic population pairs (tannin-containing v. tannin-free and vicine/convicine-high v. vicine/convicine-low), were analysed for the chemical composition of their seeds. A large variability was found for the main constituents (starch, protein and fibre). Autumn-sown genotypes contained 2·3% less proteins but 2·5% more starch in the seed dry matter (DM) than spring-sown genotypes. The vc− gene, which lowers the vicine and convicine contents, did not significantly modify the main seed components in the isogenic comparisons. The zt1 and zt2 genes, which eliminate condensed tannins in the seed coats, lowered by 2·1% the proportion of the seed coat in the DM. In the isogenic comparisons, the zt2 gene had a stronger effect than zt1 in reducing the total seed fibre and increasing the protein content.

In a second experiment, from the original 74 genotypes, 12 contrasted genotypes were selected and multiplied for animal nutrition trials. Their chemical analysis confirmed the variability between the faba bean categories observed in Expt 1, but detailed chemical analyses illustrated the variability in amino acid, fatty acid, amylose and oligosaccharide composition, trypsin inhibitory activity, condensed tannins, lectins and phytic phosphorus contents.

The synthesis and accumulation of tannins on tomato seedlings are regulated by environmental factors. The variation in the content of tannins was sufficiently important to bring about the occurrence of significant differences in the numbers of glasshouse whitefly on the seedlings. During a 2-week experiment, the treatments included mechanical wounding (20 prickings per cm2), spraying with kinetin solutions of 10−4 mol/dm3, plant growth regulators, and the atmosphere enrichment to 680 μmol CO2/mol air, the content of tannins being increased by c. 40, 70, 10–45 and 25% above the values obtained in the control. These results were correlated with a decrease in the numbers of insects occurring on the seedlings by c. 35, 45, 8–29 and 18%, respectively. Contrary to the above results the spraying with solutions of abscisic acid, gibberellic acid, and the incubation of plants in an atmosphere containing 170 μmol CO2/mol air, reduced the content of tannins by c. 69, 22 and 25%, respectively. This was reflected in the respective increases by c. 70, 40 and 35% in the numbers of insects occurring on the seedlings. The obtained results suggest that tannins seem to have a dosage-dependent effect on glasshouse whitefly. Decreasing the host plant quality by increasing tannin content may act as an important selective agent limiting the losses brought about by glasshouse whitefly in tomato cultivation.

Near-isogenic lines of mungbean (Vigna radiata) were produced from backcrossing two Thai recommended cultivars, KPS 1 and CN 36, with the multiple leaflet line, V 5926, until BC9. The isogenic lines were evaluated against the two recipients at Kasetsart University, Thailand, in the rainy season of 1996 and the dry season of 1997. The effect of the gene controlling the multiple leaflet on physiological and agronomical characters was investigated. Seed yield, plant height, and number of pods per plant were greater in the trifoliate leaflet cultivars than in the multiple leaflet near-isogenic lines, whereas the numbers of seeds per pod and 1000-seed weights were not significantly different. Light saturation and photosynthetic rate did not differ, while light interception and dry matter accumulation were greater in the trifoliate leaflet cultivars than in the multifoliate lines. The leaf area index (LAI) of the trifoliate parents was greater at the vegetative stage but lower at the flowering and young pod stages, due to the greater number of leaflets per plant of the multifoliate lines. After the beginning of the podding stage, the LAI of the multifoliate lines was less than that of the parents, as the number of leaflets per plant of these lines hardly changed while that of the trifoliate parents increased.

Dry matter intake is one of the major factors limiting milk production in dairy cows, although the quantity of food consumed by an individual cow when housed and fed as part of a group is rarely known. Such information would permit more precise ration formulation, concentrate allocation and selection of cows according to efficiency of milk production. Alkanes have been used with sheep and cattle to estimate feed intake under grazing conditions and could provide a technique for measuring intake in housed dairy cows. The purpose of this study was to examine alkanes C32 and C36, in combination with alkane C33, as indigestible markers for estimating intake of housed dairy cows fed on different diets under experimental and commercial conditions. Three experiments were conducted with hay-based diets (Expt 1), silage only diets (Expt 2) and a diet consisting of a silage-based basal ration plus concentrates (Expt 3). Animals were dosed once daily with C32 and C36, either on filter papers (Expts 1 and 2) or as part of a specially prepared concentrate (Expt 3). Faecal recoveries of alkanes ranged from 0·88 to 0·99. Over the range of intakes found in the three experiments (6–24 kg DM/d), the r2 values for estimated versus actual dry matter intakes ranged from 0·81 to 0·99. It is concluded that alkanes could provide a useful technique for estimating intake in dairy cows housed and fed in groups.

The growth of body mass and changes in empty body composition of three groups of 15 male Zebu cattle (Bos indicus) grazing natural pasture were studied in the Sahelian zone of Mali from 1990 to 1992. The control group (C) grazed natural pasture only, whereas the moderately supplemented group (M) received 0·8–1·5 kg OM/day of crop by-products during the dry season and the first month of the rainy season. Group H (high) was supplemented at 1·2–2·7 kg OM/day in the dry season and at 0·8–1·2 kg OM/day in the rainy season. Applying the deuterium dilution technique, empty body composition was measured at the beginning and end of the rainy season and in mid-dry season, using seasonal factors to correct for fill of the gastrointestinal tract (GIT). Energy retention was calculated from the contents of empty body protein and fat.

During the 2 years of study, body mass gains were 143 kg (S.E. 4·9) for group C, 196 kg (S.E. 5·8) for group M and 251 kg (S.E. 6·0) for group H. Total GIT fresh matter content accounted for 166 g (S.E. 4·6) per kg of fasted body mass (FBM) in the dry season and increased to 228 g/kg FBM (S.E. 2·9) at the beginning of the rainy season (P[les ]0·001). Throughout the period of study, the proportion of protein in the empty body varied between average values of 156 g/kg and 179 g/kg, and the proportion of empty body fat ranged from 124–257 g/kg. For all body components, the effect of supplement treatment over time was significantly different between unsupplemented and supplemented animals (P[les ]0·001). From linear regressions between metabolizable energy intake and energy retention the maintenance requirement of grazing cattle was determined at 732 kJ ME/kg0·75/day for the dry season and at 522 kJ ME/kg0·75/day for the rainy season.

It is concluded that the methodological approach yields useful results on empty body composition and energy requirement of Zebu cattle in extensive management systems.

The relationship between liveweight at mating and calving probability was examined in cattle grazing subtropical pastures in a 4 year study. The aim was to establish whether breed type, lactation, protein meal supplements, and/or pasture quality affected the relationship. Cows (n=242) of Hereford (H), Brahman (B) and Brahman×Hereford (BH) breed types were selected as maiden heifers, 20–;27 months of age, and grazed pastures of low digestibility (D), (0·45–0·62) and medium (D, 0·47–0·67) quality which are typical of subtropical grassland areas. The maiden heifers were supplemented with cottonseed meal (D, 0·67, 61 g nitrogen/kg) at 0, 750 or 1500 g/day for 130 days and mated during 90 days in the first year of the study and as cows in the following three years. There were 633 mating records of cows collected during the study.

A generalized additive model was used to describe the relationship between calving probability and mating liveweight. There was no relationship between mating liveweight and calving probability when the model included the main factors. At the mean herd mating liveweight of 430 kg the calving probability (predicted mean±S.E.) of B cows (0·59±0·034) was less than that of H (0·74±0·029) or BH cows (0·81±0·026). There were significant reductions in calving probability with lactation and from medium to low pasture quality. Calving probability was not increased significantly in BH cows by supplementation but was for B and H cows. On low quality pastures, lactation reduced predicted calving probability from 0·77 to 0·54 for non-supplemented H cows and from 0·61 to 0·35 for non-supplemented B cows. The reductions were smaller in H and B cows when supplemented at 1500 g/day. On medium quality pastures the effect of lactation and supplementation on the calving probability of cows was less than for those grazing low quality pastures.

Field experiments were conducted at the farm of Qinghai Academy of Animal and Veterinary Science, Xining, China during 1996/97 to determine the effects of level of food intake on the urinary excretion of purine derivatives (PD), creatinine and nitrogen in yaks (Bos grunniens). Two experiments were carried out with three female yaks (initial body weight 173–187 kg, age 5 years). For Expt 1 a 3×3 Latin square experimental design was used with three levels of oat hay (nitrogen 13·5 g/kg dry matter (DM)) intake treatments, i.e. 0·3, 0·6 and 0·9 of voluntary intake (1·3–3·5 kg DM/d). Each treatment lasted for 17 days and the samples were collected during the last 7 days of each period. For Expt 2 the animals were fed the same oat hay as in Expt 1 for 3 weeks at a level equivalent to the estimated energy maintenance requirement (M) (1·5–2·2 kg DM/d). The intake was then reduced to 0·6 M on day 1, 0·3 M on day 2 and zero from day 3 until day 10. The animals were re-fed in the reverse order for 3 days. Of the PD, only allantoin and uric acid were present in the urine. The proportions of allantoin and uric acid were 0·86 and 0·14 respectively for both experiments. There was no response of creatinine and nitrogen excretions to feed intake. The rates of PD excretion per kg digestible organic matter (DOM) or digestible dry matter (DDM) were 13·5 and 13·6 mmol respectively. As expected, urinary PD excretion increased significantly (P<0·001) with increasing intake of DDM and DOM. The daily fasting PD, creatinine and nitrogen excretions amounted to 0·22±0·02 (S.E.), 0·25±0·01 mmol/kg W0·75 and 314±24·2 mg/kg W0·75 respectively. The results suggest that it is possible to establish a method for estimating intestinal microbial protein flow based on PD excretion in yaks.

Nitrogen fertilization of okra (Abelmoschus esculentus) when intercropped with cassava (Manihot esculenta) and maize (Zea mays) was studied using three N rates (0, 60 and 120 kg/ha) in two field experiments in Nigeria between 1995 and 1997. The okra was grown between the cassava and maize rows. The effect of using two contrasting maize cvs. TZE Composite 3 Cl (less-tall, early-maturing with narrow leaves) and DMRSR-Y (tall, late-maturing with broad leaves) on N response of okra in the mixture was also investigated. Intercropping with maize or cassava and maize significantly increased stem elongation, delayed pod harvest, and decreased branch or pod formation and marketable pod yield in okra. In the cassava/maize/okra combination, maize had greater effect than cassava in determining most growth and pod yield attributes of the okra crop, regardless of N rate. However, the effect was relatively less severe in mixtures with early-maize cv. TZE Composite 3 Cl than with late-maize cv. DMRSR-Y. Although applied N at rates above 60 kg/ha in intercropping increased maize grain and cassava tuber yields, this did not result in a further significant gain in pod yield of the associated okra crop. The present recommendation of 60 kg/ha for N fertilization of cassava/maize intercrop was found to be applicable to okra grown between the cassava/maize rows using the less-tall, early-maize cultivar with relatively narrow leaves, and possibly reduced leaf area.

Two field experiments were conducted during 1996–98 at Bangalore, India to study the effect of soil moisture regimes (0·3, 0·6 and 0·9 IW:CPE ratios) irrigation water:cumulative pan evaporation (IW:CPE) ratios and three rates of nitrogen application (0, 100 and 200 kg/ha) and in another experiment, three soil moisture regimes (0·3, 0·6 and 0·9 IW: CPE ratios), two rates of nitrogen application (100 and 200 kg/ha) and modified urea materials [prilled urea (PU) and dicyandiamide coated urea (DCDCU)] on oil content, herbage, oil yield and quality of geranium grown on altisols. Soil moisture maintained at 0·6 IW:CPE ratio significantly increased the herbage and oil yields of geranium. Application of 200 kg N/ha gave the maximum herbage and oil yield compared with those obtained from 0 and 100 kg N/ha. DCDCU produced higher yield than PU. The concentration and quality of essential oil were not influenced either by soil-moisture regime, rates or carriers of N.