Effects of water table depth and calcium perioxide application on cowpea (Vigna unguiculata) and soybean (Glycine max)

Summary The effects of three water table (WT) depths (0, 15 and 40 cm) and calcium peroxide (Calper) on the growth and yield of cowpea (Vigna unguiculata, L.) and soybean (Glycine max) were investigated in field lysimeters for a sandy loam soil. Cowpea growth was the best at 40 cm WT depth. Leaf area, plant height, dry matter production, number of leaves and pods, grain yield and consumptive water use of cowpea increases with deeper (lower) WT depth. Application of calcium peroxide improved per cent emergence, leaf area, dry matter, number of leaves and pods, weight of 100 seeds, grain yield and water use in cowpea. The optimum WT depth for vegetative growth of soybean was 15 cm, although the highest grain yield was obtained at 40 cm WT depth. Number of pods, grain yield and water use efficiency of soybean increased with deeper water table depth. Application of calcium peroxide to soybean increased number of leaves and pods per plant, and grain yield for the 15 cm WT depth treatment.     

Protein and free amino acids in field-grown cowpea seeds as affected by water stress at various growth stages

Summary This study was undertaken to evaluate water stress effects during vegetative, flowering, and podfilling stages of cowpea plants (Vigna unguiculata L.) grown under natural field conditions in southern California on seed yield and protein and free amino acid content of the cowpea seeds. The lowest concentration of N was found in the seeds of the control treatment plants while the seed yield from these treatments was the highest as compared with the N concentration and yield of seeds from plants subjected to water stress during flowering and podfilling stages. The concentration of N in the seeds was inversely related to the seed dry weight yield. Protein arginine,-threonine,-serine,-cystine,-valine,-methionine, and-isoleucine were significantly affected by water stress at the three growth stages. There was no consistent pattern in the effect of water stress on the individual amino acids. The sum of protein amino acids in the cowpea seeds was not significantly influenced by the various treatments since some of the protein amino acids increased and others decreased producing an averaging effect on the figures comprising the sums of the amino acids. Water stress during the flowering and pod-filling stages increased the free amino acid pool, and at the same time, inhibited incorporation of the amino acids into the protein chain-thus lowering the protein amino acid fraction simultaneously. With the exception of methionine plus cystine, the essential amino acids in the seeds were present at concentrations equal to or greater than recommended by the World Health Organization and FAO. It is of particular importance to note that the concentration of lysine in the cowpeas was substantially higher than that found in wheat grain. It is also important to note that the amount of essential amino acids per gram of protein was not measurably affected by the water stress treatments during any of the growth stages.     

Record of new host plants for Sphaceloma on cowpea in Nigeria

Sphaceloma ( Elsinoe phaseoli Jenkins), which causes scab on cowpea, occurred on 9 out of 14 major weed species growing in cowpea fields in the northern guinea savanna of Nigeria. The incidence was highest on Euphorbia heterophylla, Cassia obsitufolia, Centrosema pubescens, Ipomoea eriopcarpa and I. involucrata with 94, 76, 57, 56 and 51% of the plants examined for each weed species infected, respectively. Fungal isolates from 7 weed species were pathogenic to different degrees on cowpea plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Additional sources of resistance to groundnut rosette disease in groundnut germplasm and breeding lines

Groundnut rosette, a virus disease of groundnut (Arachis hypogaea) transmitted by the aphid, Aphis craccivora Koch, reduces yield in susceptible cultivars by 30–100%. Additional sources were sought in germplasm accessions involving 2301 lines from different sources and from 252 advanced breeding lines derived from crosses involving earlier identified sources of resistance to rosette. The lines were evaluated in field screening trials using an infector row technique during 1996 and 1997 growing seasons. Among the germplasm lines, 65 accessions showed high levels of resistance while 134 breeding lines were resistant. All rosette disease resistant lines were susceptible to groundnut rosette assistor virus. This work identified germplasm and breeding lines that will contribute to an integrated management of groundnut rosette disease. These new sources also provide an opportunity to eliminate yield losses due to the rosette disease.     

Changes in water status and osmolyte contents in leaves and roots of olive plants (Olea europaea L.) subjected to water deficit

Two-year-old olive trees (Olea europaea L., cv. Coratina) were subjected to a 15-day period of water deficit, followed by 12 days of rewatering. Water deficit caused decreases in predawn leaf water potential (Ψ_w), relative water content and osmotic potential at full turgor (Ψ _π100) of leaves and roots, which were normally restored upon the subsequent rewatering. Extracts of leaves and roots of well-watered olive plants revealed that the most predominant sugars are mannitol and glucose, which account for more than 80% of non-structural carbohydrates and polyols. A marked increase in mannitol content occurred in tissues of water-stressed plants. During water deficit, the levels of glucose, sucrose and stachyose decreased in thin roots (with a diameter <1 mm), whereas medium roots (diameter of 1–5 mm) exhibited no differences. Inorganic cations largely contribute to Ψ _π100 and remained stable during the period of water deficit, except for the level of Ca²⁺, which increased of 25% in water-stressed plants. The amount of malate increased in both leaves and roots during the dry period, whereas citrate and oxalate decreased. Thin roots seem to be more sensitive to water deficit and its consequent effects, while medium roots present more reactivity and a higher osmotic adjustment. The results support the hypothesis that the observed decreases in Ψ_w and active osmotic adjustment in leaves and roots of water-stressed olive plants may be physiological responses to tolerate water deficit.     

Heat tolerance in cowpea: effect of timing and duration of heat stress

Reproductive processes and pod yield in cowpea (Vigna unguiculata (L.) Walp), an important crop grown in semi-arid sub-Saharan Africa, are adversely affected by high temperature. Genotypic differences in heat tolerance have been identified under hot, long-days, but it was not known if this tolerance is also exhibited in hot, short-day environments typical of sub-Saharan Africa. The objectives of the work reported here were to determine whether heat tolerance identified under hot, long-days was expressed at the same stages of development under hot, short-days, and whether responsiveness to temperature was additive and quantitative. A heat-tolerant (Prima) and heat-susceptible (IT84S-2246) cultivar of cowpea were grown in controlled environments under short-days (12 h day^-1), initially at 30°C/24°C (Mod-T), and then transferred at 0, 10, 20, 30 and 40 days after emergence (DAE) to 36°C/27°C (High-T), where they remained for 5, 10 or 20 days duration before returning to Mod-T. Control plants remained at Mod-T or High-T for 50 days, when the first pods were mature and the experiment was terminated. There were significant effects of duration (D) and timing (T) (P < 0.001), and interactions between D × T (P < 0.001), T × genotype (G) (P < 0.01) and D × T × G (P < 0.05) on pod weight plant^-1. Prima was significantly (P < 0.001) more tolerant to high temperature during flowering than IT84S-2246, confirming that heat tolerance was expressed under hot, short days. The greater heat tolerance of Prima was associated with an ability to maintain peduncle and flower production at High-T, and with greater podset. The sensitive period in IT84S-2246 started at floral bud initiation (15–20 DAE), and effects of High-T thereafter were additive and quantitative.     

Sources of resistance to groundnut rosette disease in global groundnut germplasm*

About 6800 groundnut germplasm accessions originating from South America, Africa, and Asia were evaluated for resistance to rosette disease using an infector row technique between the 1990/91 and 1996/97 growing seasons. Of these, 116 germplasm accessions, including 15 short-duration Spanish types, have shown high levels of resistance to rosette disease. A high percentage of these resistant accessions were from West Africa and a few were from Asia and southern Africa. Only one out of 1400 accessions from South America showed resistance to rosette disease. All disease-resistant accessions were susceptible to groundnut rosette assistor virus. This is the first report to identify sources of resistance to rosette disease in groundnut germplasm from Asia and South America. These additional sources of resistance provide an opportunity to broaden the genetic base of resistance to rosette disease. The origins of rosette resistance in groundnut are discussed.     

Physiological behaviour of loquat and anger rootstocks in relation to salinity and calcium addition

The salinity tolerance of two commercial rootstocks used for loquat plants (Eribotrya japonica Lindl.), loquat and anger, was studied in a pot experiment. The plants were irrigated using solutions containing 5 and 50mM NaCl and 5 and 25mM calcium acetate for 4 months. The growth, tissue mineral content, water status, and leaf gas exchange responses to salt treatment with and without additional calcium were examined. Plant growth was not modified by salinity in anger (50mM), but was reduced in loquat; leaf biomass and stem diameter were particularly affected. However, Cl(-) levels leaf increased with salinity to a greater extent in anger, while the Na(+) content increased to the same extent in both species, indicating that ion transport from root to leaves was not inhibited in either species. Additional calcium (25mM) reduced Na(+) and Cl(-) concentrations in both species, but did not minimise the effects of salinity on the growth of salt-treated loquat plants. The decrease in K(+) concentrations had no effect on growth, as anger was the most tolerant rootstock and had lowest leaf K(+) content. Salinity reduced the Ca(2+) concentration in the roots of both species. However, when calcium was added, the concentration of Ca(2+) increased in the roots of salinised plants. Leaf water potential at pre-dawn decreased significantly in both species under saline conditions. Leaf gas exchange, stomatal conductance and, in particular, net CO(2) assimilation, decreased with salinity only in loquat, indicating that photosynthesis could be the growth-limiting factor in this species.     

Na+ accumulation in shoot is related to water transport in K+-starved sunflower plants but not in plants with a normal K+ status

Sunflower plants (Helianthus annuus L. cv Sun-Gro 380) grown in nutrient solutions with different K⁺ levels were used to study the effect of potassium status on water uptake, Na⁺ uptake and Na⁺ accumulation in the shoot. Changes in nutrient potassium levels induced evident differences in internal potassium content. When both low and normal-K⁺ plants were exposed to 22 °C and salinity conditions (25 or 50 mM NaCl) during a short time period (9 h), water uptake in low-K⁺ plants was greater than in normal-K⁺ plants. In addition, K⁺ starvation favoured the Na⁺ uptake and the Na⁺ accumulation both in the root and in the shoot. When the plants were exposed to heat stress by a sharp increase of the temperature to 32 °C during the same period of time, the stimulating effect of K⁺ starvation on the water uptake was even greater. The high temperature increased Na⁺ uptake in both types of plants, but the Na⁺ accumulation in the shoot was only favoured in low-K⁺ plants. The results suggest that Na⁺ accumulation in the shoot is more dependent on the water uptake in low-K⁺ plants than in normal-K⁺ plants, and this effect could explain the greatest susceptibility to the salinity in K⁺-starved plants under high transpiration conditions, which are typical in dry climates.     

Early responses of drought-resistant and -susceptible tomato plants subjected to water stress

Three-week-old seedlings of one drought-susceptible tomato cultivar (Lycopersicon esculentum cv. “New Yorker”) and two drought-resistant species of tomato (Solanum pennellii andLycopersicon chilense) were subjected to various degrees of PEG 8000-induced water stress from ?0.017 to ?1.0 MPa for a duration of 24 h so that their early responses to water stress could be compared. Such a comparison would determine if there was a relationship to root cytokinin levels following sudden induction of water stress in the drought-resistant species. Transpiration rates of leaves were monitored throughout the 24-h period, shoots were evaluated for leaf water potential (LWP), and roots were extracted for levels oft-zeatin riboside (t-ZR) and dihydrozeatin riboside (DHZR) using a monoclonal antibody enzyme immunoassay. Transpiration rates were evaluated gravimetrically by difference every 6 h up to 24 h. Transpiration rate decreased with increasing PEG levels and passage of time in all three species, measured at 6 and 12 h, logarithmically in the case of the twoLycopersicon species and linearly in the case ofSolanum. From 12–18 h (while plants were in darkness), transpiration rate was a function of the level of PEG only and not time in all three species. When light resumed from 18–24 h, only 5.pennellii showed no further decrease in transpiration rate over time with increasing PEG. Drought-susceptibleL. esculentum had a stronger linear decrease in LWP with increasing PEG 8000 concentration than the other two species.L. esculentum also had a higher initial transpiration rate than did either of the drought-resistant species. The two drought-resistant species showed less change in LWP with 5.pennellii having a small decrease andL. chilense having little change. OnlyS. pennellii exhibited a decrease in roott-ZR levels, which may imply a role for root cytokinin within the first 24-h exposure to water stress in this species.L. esculentum exhibited no change in roott-ZR. The levels oft-ZR inL. chilense were less than that ofL. esculentum but showed only a slight decrease with increasing PEG.S. pennellii andL. chilense, although both drought-resistant tomato species, showed different patterns of response with respect to pattern of decline in transpiration rate, LWP, and roott-ZR levels.     

Solute accumulation in leaves and roots of woody plants subjected to water stress

Summary Young seedlings of English Oak, Quercus robur L., and Silver Birch, Betula verrucosa Ehrl., were subjected to a number of consecutive periods during which water was withheld. During one 14-day period leaf-and soil-water potentials and leaf- and root-solute potentials of two groups of plants were sampled at noon of each day. One group of plants was watered every day while water was withheld from the other group. Solute accumulation in roots and leaves of oak seedlings subjected to water stress resulted in maintenance of turgor and high leaf conductance as the soil dried. In birch seedlings turgor was only maintained by stomatal closure at high soil water potential.Fourteen consecutive water stress cycles greatly reduced the growth of birch seedlings but had little effect on oak seedlings other than to alter root morphology. Water stress treatment resulted in the production of long thin roots in this plant. Stomatal behaviour in oak and birch seedlings during the 14-week stress period was consistent with observed changes in leaf water and solute potentials. Daily solute accumulation in oak leaves was presumably responsible for the maintenance of plant growth as water potentials fell.     

Early responses of drought-resistant and -susceptible tomato plants subjected to water stress

Three-week-old seedlings of one drought-susceptible tomato cultivar (Lycopersicon esculentum cv. New Yorker) and two drought-resistant species of tomato (Solanum pennellii andLycopersicon chilense) were subjected to various degrees of PEG 8000-induced water stress from –0.017 to –1.0 MPa for a duration of 24 h so that their early responses to water stress could be compared. Such a comparison would determine if there was a relationship to root cytokinin levels following sudden induction of water stress in the drought-resistant species. Transpiration rates of leaves were monitored throughout the 24-h period, shoots were evaluated for leaf water potential (LWP), and roots were extracted for levels oft-zeatin riboside (t-ZR) and dihydrozeatin riboside (DHZR) using a monoclonal antibody enzyme immunoassay. Transpiration rates were evaluated gravimetrically by difference every 6 h up to 24 h. Transpiration rate decreased with increasing PEG levels and passage of time in all three species, measured at 6 and 12 h, logarithmically in the case of the twoLycopersicon species and linearly in the case ofSolanum. From 12–18 h (while plants were in darkness), transpiration rate was a function of the level of PEG only and not time in all three species. When light resumed from 18–24 h, only 5.pennellii showed no further decrease in transpiration rate over time with increasing PEG. Drought-susceptibleL. esculentum had a stronger linear decrease in LWP with increasing PEG 8000 concentration than the other two species.L. esculentum also had a higher initial transpiration rate than did either of the drought-resistant species. The two drought-resistant species showed less change in LWP with 5.pennellii having a small decrease andL. chilense having little change. OnlyS. pennellii exhibited a decrease in roott-ZR levels, which may imply a role for root cytokinin within the first 24-h exposure to water stress in this species.L. esculentum exhibited no change in roott-ZR. The levels oft-ZR inL. chilense were less than that ofL. esculentum but showed only a slight decrease with increasing PEG.S. pennellii andL. chilense, although both drought-resistant tomato species, showed different patterns of response with respect to pattern of decline in transpiration rate, LWP, and roott-ZR levels.     

Translocation and metabolism of glycine betaine by barley plants in relation to water stress

The glycine betaine which accumulated in shoots of young barley plants (Hordeum vulgare L.) during an episode of water stress did not undergo net destruction upon relief of stress, but its distribution among plant organs changed. During stress, betaine accumulated primarily in mature leaves, whereas it was found mainly in young leaves after rewatering. Well-watered, stressed, and stressed-rewatered plants were supplied with [methyl-¹⁴C]betaine (8.5 nmol) via an abraded spot on the second leaf blade, and incubated for 3 d. In all three treatments the added ¹⁴C migrated more or less extensively from the second leaf blade, but was recovered quantitatively from various plant organs in the form of betaine; no labeled degradation products were found in any organ. When 0.5 mol of [methyl-¹⁴C]betaine was applied via an abraded spot to the second leaf blades of well-watered, mildly-stressed, and stressed-rewatered plants, ¹⁴C was translocated out of the blades at velocities of about 0.2–0.3 cm/min which were similar to velocities found for applied [¹⁴C]sucrose. Heat-girdling of the sheath prevented export of [¹⁴C]betaine from the blade. When 0.5 mol [³H]sucrose and 0.5 mol [¹⁴C]betaine were suppled simultaneously to second leaf blades, the ³H/¹⁴C ratio in the sheath tissue was the same as that of the supplied mixture. After supplying tracer [¹⁴C]betaine aldehyde (the immediate precursor of betaine) to the second leaf blade, the ¹⁴C which was translocated into the sheath was in the form of betaine. Thus, betaine synthesized by mature leaves during stress behaves as an inert end product and upon rewatering is translocated to the expanding leaves, most probably via the phloem. Accordingly, it is suggested that the level of betaine in a barley plant might serve as a useful cumulative index of the water stress experienced during growth.     

Antioxidant responses and water status in Brassica seedlings subjected to boron stress

The effect of boron (B) on growth, water status and oxidative damage was investigated in the leaves and roots of 7-day-old seedlings of Brassica juncea var. Varuna. For this seedlings of Brassica were grown in solution culture with variable boron supply (0.033, 0.33, 3.3 and 33 mg B L^?1) under controlled conditions in green house. Photosynthetic pigments were found to be decreased more under excess (3.3 and 33 mg B L^–1) than deficient boron supply (0.033 mg B L^–1) when compared to control (0.33 mg B L^–1). Accumulation of hydrogen peroxide and thiobarbituric acid reactive substances content in both leaves and roots under deficient and excess boron supply suggested oxidative damage due to excessive production of reactive oxygen species. Increased activity of antioxidative enzymes: superoxide dismutase, catalase and peroxidase along with polyphenol oxidase was observed in leaves and roots under boron deficiency and excess than in control. Increased proline concentration, decreased total water content and water saturation deficit also indicated the water deficit condition in leaves and roots of boron-stressed Brassica seedlings.     

Physiological responses of groundnut (Arachis hypogea L.) to drought stress and its amelioration: a critical review

Groundnut (Arachis hypogea L.), is an important legume cash crop for the tropical farmers and its seeds contain high amounts of edible oil (43–55%) and protein (25–28%). Even though it is a fairly drought-tolerant, production fluctuates considerably as a result of rainfall variability. To develop a water stress response function in groundnut, research works have been done to improve the performance under varying degrees of stress at various physiological stages of crop growth. This review summarizes recent information on drought resistance characteristics of groundnut with a view toward developing appropriate genetic enhancement strategies for water-limited environments. It is suggested that there are considerable gains to be made in increasing yield and stabilizing the yield in environments characterized by terminal drought stress and by shortening crop duration. Many traits conferring dehydration avoidance and dehydration tolerance are available, but integrated traits, expressing at a high level of organization are suggested to be more useful in crop improvement programs. Possible genetic improvement strategies are outlined, ranging from empirical selection for yield in drought environments to a physiological–genetic approach. It was also suggested that in view of recent advances in understanding drought resistance mechanisms, the later strategy is becoming more feasible. It is summarized that application of knowledge into practice in a systematic manner can lead to significant gains in yield and yield stability of the worlds groundnuts production. Research is needed to develop transferable technology to help farmers of arid and semi-arid regions. Increasing soil moisture storage by soil profile management and nutrient management for quick recovery from drought are some of the areas that need to be explored further.     

Inheritance of resistance to groundnut rosette virus in groundnut (Arachis hypogaea L.)

A method of field screening groundnut seedlings for resistance to groundnut rosette virus (GRV), by means of which over 97% incidence was induced in rows of susceptible test plants, was developed at Chitedze Research Station in Malawi. Two GRV-resistant Virginia cultivars (RG 1 and RMP 40) were crossed with three susceptible cultivars, one from each of the Spanish (JL 24), Valencia (ICGM 48) and Virginia (Mani Pintar) botanical groups. Twelve F₁ reciprocal crosses and their F₂ and backcross generations were produced and the material screened in nurseries in 1985/86 and 1986/87. Seedlings raised from plants which did not become infected in the field were inoculated in the glasshouse in order to eliminate susceptible escapees. The numbers of diseased and healthy individuals in each population were subjected to χ² tests. In the majority of the F₂ populations a good fit was obtained for a ratio of one resistant to 15 susceptible plants, a ratio to be expected if resistance to GRV were determined by a pair of independent complementary recessive genes. This was further supported by data from backcross generations.     

A comparison of nitrogen-fixing ability of peanut,cowpea and siratro plants nodulated by different strains of Rhizobium

Summary Acetylene reduction activity and nitrogen accumulation in the plant top per unit nodule mass were compared among peanut, cowpea and siratro plants nodulated by six different strains of Rhizobium. Peanut was found to have several fold higher values than cowpea and siratro for both parameters for all strains of Rhizobium which nodulated it effectively, but the bacteroid content of the peanut nodules was similar to those of cowpea and siratro.     

盐胁迫下丛枝菌根真菌对玉米水分和养分状况的影响

在ＮａＣｌ胁迫下无论接种ＡＭ真菌与否玉米植株生物产量均减少,但不接种处理的减少幅度比较种处理的高１０个百分点左右,盐胁迫下接种ＡＭ真菌的玉米根系和地上部的干重、叶片水热均高于不接种处理、叶片脯氨酸含量低于不接种处理,在盐胁迫下真菌菌丝对玉米植株营养的贡献由４５．３％降为４２．６％,ＡＭ真菌对植株生长的效应反而由３０．９％提高到６３．５％,说明ＡＭ真菌主米耐盐性的机理与改善植株的水分状况和Ｐ营养状况     

Changes in phosphorus content of two aquatic macrophytes according to water velocity,trophic status and time period in hardwater streams

We examined the influence of water velocity, trophic status, and time period on the phosphorus content of two aquatic macrophytes. We sampled Berula erecta (Huds.) and Callitriche obtusangula (Le Gall.) from 17 oligosaprobic hardwater streams in the Alsatian Rhine floodplain of northeastern France. Sampling was conducted on a monthly basis during a 9-month period from August 1996 to April 1997. For B. erecta, phosphorus content of shoots and roots were correlated to water phosphorus content but not to sediment phosphorus content. The range of phosphorus shoot content of C. obtusangula was similar to that of B. erecta. Phosphorus shoot content of C. obtusangula was not correlated with water and sediment phosphorus content. In one stream where both species were present on the same sampling dates, shoot phosphorus content decreased when water velocity was high, particularly for C. obtusangula. Additionally, a significant effect of time period was observed for both species when the water velocities were low. The effect of water velocity was only significant from spring (April) to autumn (October) when plant phosphorus content was highest. Handling editor: S. Magela Thomaz