Groundnut Plants Research Articles

Phenolic acid metabolism of groundnut (Arachis hypogaea L.) plants inoculated with VAM fungus and Rhizobium

Mycorrhizal and Rhizobiuminoculation resulted in a significant increase in the quantities of phenoliccompounds in roots and shoots of groundnut plants, as compared to uninoculatedplants. Production of some new compounds, and increase in the activity of theenzymes peroxidase and polyphenol oxidase, following inoculation was observed.Accumulation of phenolics and the activation of oxidative enzymes were morepronounced in the dual inoculated plants.

Translocation of <sup>14</sup>C-(Labelled) Photosynthates in Groundnut (Arachis Hypogaea L.) Infected with Macrophomina Phaseoli (Maub) Ashby

At various intervals after inoculation of the roots of groundnut plants with the fungus Macrophomina phaseoli, 14CO2 was administered to branch 2 (from the base) of the plants in the light. The effects of the disease on the translocation of 14C-photosynthates out of the source branch to the rest of the plant were studied 24 h after labelling. As the plant aged and the disease symptom development became more evident, an increasing percentage of the fixed 14C-photosynthates was exported from branch 2 of the inoculated plants (IP) compared to the non-inoculated plants (NIP). The apex, main stem, and branch 1 of NIP imported more of the total fixed 14C throughout the developmental stages of the plant except for day 10 after inoculation when branch 1 of IP imported almost 76 % of the total fixed 14C. The roots of IP were the major sink and imported higher percent of the total fixed 14C than the roots of NIP.

Spatiotemporal Separation of Groundnut Rosette Disease Agents

ABSTRACT Analysis by triple-antibody sandwich enzyme-linked immunosorbent assay of groundnut samples from fields in two seasons from different regions of Malawi showed the absence of groundnut rosette assistor virus (GRAV) from some plants showing groundnut rosette disease symptoms and the presence of GRAV in some symptomless plants. Viruliferous Aphis craccivora collected from fields transmitted either GRAV alone, groundnut rosette virus (GRV) with its satellite RNA (sat RNA), or all three agents together, in different proportions. More plants became infected with all three agents when increasing numbers of potentially viruliferous aphids were used per plant, suggesting a dosage response. Electrical pentration graph studies of aphid stylet activities indicated successful transmission of GRV and its sat RNA during both the "stylet pathway phase" and salivation into sieve elements, whereas GRAV was transmitted only during the latter phase. Aphids transmitted all three agents together only during the salivation phase. Reverse-transcriptase polymerase chain reaction testing of viruliferous aphids and of inoculated plants revealed no correlation between the presence of all three agents in prospective aphid vectors and their simultaneous transmission to groundnut plants. These results show that separation of the groundnut rosette disease agents occurs over time and space.

Autophosphorylation-dependent activation of a calcium-dependent protein kinase from groundnut

Ca2+-dependent protein kinases (CDPKs) containing a calmodulin-like domain integrated in their primary sequence are present primarily in plants. A member of this family was characterized from the groundnut (Arachis hypogea) plant and called GnCDPK (M. DasGupta [1994] Plant Physiol 104: 961-969). GnCDPK specifically uses the myosin light chain synthetic peptide (MLCpep), which is the phosphate-accepting domain of smooth muscle myosin light chains (KKRPQRATSNVFS), as an exogenous substrate under in vitro experimental conditions. In this report we show that GnCDPK undergoes intramolecular autophosphorylation. This self-phosphorylation occurs in threonine residues in a Ca2+-dependent (K0.5 = 0.5 &mgr;M) and calmodulin-independent manner. The kinase activity toward MLCpep and its sensitivity to Ca2+ were unaffected by prior autophosphorylation when measured under saturating ATP concentrations. The role of autophosphorylation in the exogenous substrate MLCpep phosphorylation reaction was reinvestigated at low ATP concentrations. A pronounced lag time of 1 to 2 min, followed by a linear increase of activity for 7.5 min, was seen in the initial rate of MLCpep phosphorylation under such suboptimal conditions. Prior autophosphorylation completely abolished this lag phase, and a sharp rise of exogenous substrate phosphorylation was seen from the 1st min. Our results suggest that autophosphorylation is a prerequisite for the activation of GnCDPK.

Root phenolic accumulation and loss of autoregulation of root nodule formation in Bambara groundnut (Vigna subterranea) following boron nutrition and cotyledon excision

Effects of boron nutrition and cotyledon removal on nodulation and N 2 fixation were investigated on Bambara groundnut (Vigna subterranea L. Verdc.) grown in the glasshouse. Nodule number was siginificantly lower in boron-deprived plants relative to those receiving 90 µM boron. As a result, the amount of N fixed was markedly reduced in the zero-boron control plants. Phenolic content, measured relative to the molar concentration of daidzein, an active phenolic nod gene inducer from this species, was significantly lower in roots of boron-deprived plants. However, with provision of 90 µM boron, plants significantly increased root accumulation of total phenolics by 37%. HPLC analysis of root extracts showed that the increase in phenolics was due to greater tissue accumulation of the nod-gene-inducing daidzein, following the supply of 90 µM boron. The correlation between nodulation performance and increase in tissue phenolics, especially daidzein, suggests that the increase in nodulation and N 2 fixation with boron supply (90 µM) to intact plants was triggered by the greater accumulation of the inducer molecule as a result of improved boron nutrition. However, removal of seedling cotyledons also affected the number of nodules formed per plant. Excision of cotyledons resulted in significantly reduced photosynthetic leaf area, followed by a marked increase in the number of nodules per plant due to loss of autoregulation of nodule formation. Boron supply and cotyledon removal both increased nodule formation in Bambara groundnut plants, but via different mechanisms.

Agrobacterium-mediated genetic transformation of groundnut (arachis hypogaea L.): An assessment of factors affecting regeneration of transgenic plants

Transgenic groundnut (Arachis hypogaea L.) plants were produced efficiently by inoculating different explants withAgrobacterium tumefaciens strain LBA4404 harbouring a binary vector pBM21 containinguidA (GUS) andnptll (neomycin phosphotransferase) genes. Genetic transformation frequency was found to be high with cotyledonary node explants followed by 4 d cocultivation. This method required 3 days of precultivation period before cocultivation withAgrobacterium. A concentration of 75 mg/l kanamycin sulfate was added to regeneration medium in order to select transformed shoots. Shoot regeneration occurred within 4 weeks; excised shoots were rooted on MS medium containing 50 mg/I kanamycin sulfate before transferring to soil. The expression of GUS gene (uidA gene) in the regenerated plants was verified by histochemical and fluorimetric assays. The presence ofuidA andnptll genes in the putative transgenic lines was confirmed by PCR analysis. Insertion of thenptll gene in the nuclear genome of transgenic plants was verified by genomic Southern hybridization analysis. Factors affecting transformation efficiency are discussed.

Detection of each of the causal agents of groundnut rosette disease in plants and vector aphids by RT-PCR

Detection of the three agents of groundnut rosette disease (groundnut rosette assistor virus, groundnut rosette virus and its satellite RNA) in plants and vector aphids by reverse transcription-polymerase chain reaction (RT-PCR) is reported. Three procedures for extraction of total RNA from groundnut were tested, of which two were found to be useful in giving RNA of sufficient quality for RT-PCR. Of these two, the total RNA extraction kit supplied by Qiagen was found to be the most versatile for extraction of all three agents from individual vector aphids ( Aphis craccivora). Both groundnut rosette assistor virus and groundnut rosette virus could be detected from total RNA extracted from a single aphid that had been exposed to either green or chlorotic rosette-infected groundnut plants. They could be detected in aphids stored in 70% ethanol for up to 30 days at room temperature. However, satellite RNA could be amplified only when total RNA extracted from two or more aphids was used. Groundnut rosette assistor virus, groundnut rosette virus and its satellite RNA were detected by RT-PCR in aphids that had been exposed only to groundnut rosette diseased plants containing all three agents. The potential of RT-PCR in studying certain key issues of rosette disease epidemiology is discussed.

Dispersal of Passalora personata conidia from groundnut by wind and rain

In experiments where groundnut plants with sporulating late leaf spot lesions were exposed to increasing ‘gusty’ and ‘steady’ wind speeds, conidia were more effectively removed by gusty winds than by steady winds of the same mean wind speed. Rain drops dislodged conidia more efficiently than wint, with large drops dispersing conidia more effectively than small ones. No conidia were caught in still air. After most of the conidia had been removed by exposure to high wind speeds, rain was found to remove additional conidia. When plants were exposed to continuous wind or rain, most of the conidia were dispersed during the first few minutes, and the concentration of conidia then declined exponentially with time. From field observations on rain-free days, airborne concentrations of conidia tended to increase as the wind speed increased during the day and with a further increase in wind speed, concentrations decreased. On rainy days, the onset of the first shower coincided with a phenomenal increase in the airborne concentrations of conidia.

Flower production and growth in groundnut plants

Groundnut flowering was analyzed on plants whose growth was modified by changing planting density or by shading exposure during different periods of the growth cycle. Flowering was assessed at the level of the plant, branch, and inflorescence. The results showed that flowering progression along the branch reflected the flowering dynamics of the entire plant. The number of flowers produced was determined by the rate of progression of flowering along the branches and by the period from the beginning to the end of blooming. These features were closely dependent on plant growth conditions. Increasing the planting density slowed the flowering rate and shortened the blooming period. This allowed a better synchronization of pod maturity. Exposure to shade before flowering decreased the rate of production of flowers but prolonged its duration, whereas exposure at mid-flowering halted flower production. It is suggested that the different reproductive organs (flowers and pods) may compete for assimilates, thus explaining the various effects observed on daily flower production.

Selection and regeneration of groundnut plants resistant to the pathotoxic culture filtrate ofCercosporidium personation through tissue culture technology

Callus cultures were established from immature leaf expiants ofArachis hypogaea on MS medium supplemented with 2.0 mg/L of NAA and 0.5 mg/L of BAP of the susceptible cultivars namely VRI-2 and TMV-7. Three-week-old calli were subjected to mutagenic treatments (gamma rays: 50–250 Gy and EMS: 5–25 mM). Mutagen-treated calli were subcultured to fresh medium containing various concentrations (25–100% v/v) of pathotoxic culture filtrates. Calli were challenged in vitro with pathotoxic culture filtrate of the fungal pathogen and were assessed by visible growth ratings expressed as the percent response to the doses/concentrations of mutagen. Selected mutagen-treated calli showed resistance in vitro on media containingCercosporidium personatum pathotoxic culture filtrate. Resistance calli were then transferred to MS regeneration medium supplemented with BAP (2.0 mg/L) and NAA (0.5 mg/L) for shoot bud regeneration. The progeny of the plants produced 13 disease-resistant plants (R2) in both the cultivars. Among the eight R2 populations studied, 70.2–82.5% of the plants exhibited enhanced resistance. This study suggested that groundnut plants with resistance to C.personatum can be selected

Down-regulation of Groundnut Rosette Virus Replication by a Variant Satellite RNA

Symptom production in groundnut plants infected with groundnut rosette virus (GRV) depends on the presence of satellite RNA (sat-RNA) in the GRV culture, and sat-RNA variants that induce only mild symptoms are known. One such variant drastically diminished the replication of GRV genomic RNA in infectedNicotiana benthamianaplants. This down-regulating ability did not involve either of the two open reading frames in the sat-RNA but was controlled by a region near its 5′ end, which is required for sat-RNA replication. WhenN. benthamianaplants were inoculated with GRV and the mild satellite and challenged by inoculation with a GRV isolate (YB) containing a sat-RNA that induces yellow blotch symptoms, no symptoms appeared and little GRV genomic RNA or sat-RNA was detected in the plants, provided the two inoculations were no more than 2 days apart. A GRV isolate containing a sat-RNA that neither induces symptoms inN. benthamiananor affects genomic RNA accumulation also provided protection against yellow blotch symptom production if inoculated before or up to 2 days after isolate YB. However, in this case protection was incomplete and both GRV RNA and sat-RNA accumulated to normal levels. It is suggested that sequences from the mild sat-RNA may provide a novel source of resistance against rosette disease.

Characterization of Two Strains of Cowpea Mild Mottle Virus Naturally Infecting Groundnut (Arachis hypogaea L.) in India

AbstractTwo viruses were isolated from commercial groundnut plants showing mild mottle (MM) and severe mottle (SM) symptoms in the Rayalaseema area of Andhra Pradesh State, India. The host range of both the isolates was restricted to Fabaceae. The physical properties of both isolates were: DEP 10‐6 to 10‐7. TIP 70–85 C and LIV 5–8 days. Partially purified virus preparations contained slightly flexuous filamentous particles. In ELISA and gel diffusion tests both isolates reacted similarly with anusera to the carlaviruses cowpea mild mottle, cassia mild mosaic and potato M. Particle morphology. sedimentation coefficient, and estimated sizes of the coat proteins and RNAs gave additional evidence that the viruses were carlaviruses. Bemisia labaci transmitted only the MM isolate and the two isolates also differed in electrophoretic mobility of intact particles and amino acid composition of the coat proteins. The isolates are identified as distinct strains of cowpea mild mottle virus.

The induction of 1,3-β-glucanases and other enzymes in groundnut leaves infected with Cercospora arachidicola

Infection of groundnut leaves with the early leaf spot pathogen Cercospora arachidicola leads to a marked increase in extracellular 1,3-β-glucanase activity, limited to the infected tissue. Three isoforms of low molecular weight and extreme pI values, typical of pathogenesis-related proteins, were induced. These β-glucanases, when acting together, were capable of degrading the pathogen cell wall in vitro. Glucanases from homogenates of infected leaf tissue were partially purified by ion-exchange chromatography to give enzymes with molecular weights of 35, 32 and 20 kDa and pI values of 3·8, 3·6 and > 9, respectively. They were electrophoretically identical to the β-glucanases found in the intercellular washing fluid. Treatment of groundnut plants with 200 μM mercuric chloride induced the accumulation of identical extracellular β-glucanases. During the course of the infection an increase in peroxidase activity was also observed, but chitinase activity remained more or less constant.

The toxicity of phytotoxins from Cercospora arachidicola and cercosporin from Cercospora species to tobacco, Swiss chard and groundnut plants

Nine of the 12 species of Cercospora isolated from various plants produced cercosporin. Some Cercospora spp. also produced a yellow fraction and C. arachidicola produced orange and yellow-orange fractions but not cercosporin. Neither cercosporin nor the orange fraction were host specific and caused similar damage on Swiss chard, tobacco and groundnuts. The amount of damage and toxin concentration were positively correlated. The orange fraction caused considerably less damage in the dark than in the light and young leaves were more resistant to damage than older leaves. The yellow-orange fraction was only weakly phytotoxic.

Effects of sulfur dioxide and ozone on intact leaves and isolated mesophyll cells of groundnut plants (Arachis hypogaea L.)

Difference between effects of sulfur dioxide (SO2) and ozone (O3) on groundnut plants (Arachis hypogaea L.) was studied by use of an exposure system of enzymatically-isolated mesophyll cells. SO2 inhibited photosynthesis of intact groundnut leaves but induced no visible injury on leaves. SO2 also inhibited photosynthesis of isolated mesophyll cells but did not kill the cells, suggesting that SO2 inhibits photosynthesis by attacking rather specifically the photosynthetic apparatus in chloroplasts. O3 inhibited photosynthesis of intact leaves and at the same time induced visible injury corresponding to the extent of photosynthesis inhibition. O3 also inhibited photosynthesis of isolated mesophyll cells and killed the cells to the extent corresponding to photosynthesis inhibition, suggesting that O3 inhibits photosynthesis not directly by attacking the photosynthetic apparatus but indirectly by killing cells. Since the response of intact leaves to each pollutant resembled that of isolated mesophyll cells, the difference between responses of intact leaves to both pollutants may considerably reflect that of mesophyll cells.

Soil acidity in relation to groundnut-Bradyrhizobium symbiotic performance

Effects of soil acidity on groundnut-Bradyrhizobium symbiotic performance were studied in a potted, sandy soil in a glasshouse in Zimbabwe. The soil was limed to soil-pH levels of 5.0 and 6.5. Soil acidity negatively affected plant development, measured as leaf area and plant dry weight, while nodulation was enhanced. This acidity-enhanced nodulation was most evident when nodulation was caused by the indigenousBradyrhizobium population. Effects of soil acidity differed between groundnut cultivars andBradyrhizobium spp. strains, the former having greater importance. TwoArachis hypogaea L. Spanish-type cultivars, Falcon and Plover, performed equally well at neutral soil pH, but Falcon was more acid tolerant. Comparison of the symbiotic performance in neutral versus acid soil of twoBradyrhizobium spp. strains, MAR 411 (3G4b20) and MAR 1510 (CB 756), showed that MAR 411 performed superiorly in neutral soil, but MAR 1510 in acid soil. The indigenousBradyrhizobium population was more effective than was inoculation with strains MAR 411 or MAR 1510. Comparison of twelveBradyrhizobium spp. strains for their symbiotic performance in acid soil showed that some strains were totally ineffective under acidity stress (MAR 253, MAR 967 and MAR 1506), while others performed well.Bradyrhizobium spp. strain MAR 1576 (32 H1) ranked highest for nitrogen accumulation, plant dry weight and leaf area, with strains MAR 1555 (TAL 11) and MAR 1510 following closely. Nitrate fertilisation of groundnut plants led to soil alkalinisation, while nitrogen fixation resulted in soil acidification. Soil acidity in combination with soil sterilisation gave rise to symptoms associated with Al and Mn toxicity.

Planting pattern of two pigeonpea (Cajanus cajan) cultivars when intercropped with groundnut (Arachis hypogaea)

SUMMARYField experiments were conducted during the two monsoon seasons of 1985 and 1986 at Kharagpur, West Bengal, to investigate the effect of pigeonpea cultivars and their planting pattern on the performance of a groundnut–pigeonpea intercrop. In intercropping the crops were also sown at 100% population of their sole crops. Groundnut plant growth and development was affected by intercropping with pigeonpea and the decline in pod yield ranged from 7 to 50% of the sole crop yield. The compact, short-statured and short duration pigeonpea cultivar, ICPL87, intercepted only 50% of the incoming solar radiation as against the 70% intercepted by LRG30 at the peak vegetative stage. The significantly higher groundnut yield (48%) obtained from the intercrop with the former pigeonpea cultivar as compared to the latter justifies the belief that the performance of the groundnut was light-related. This was further confirmed when the light interception by pigeonpea was reduced by increasing the row spacing from 90 to 150 cm and there was a consequent increase in groundnut yield. The cultivar and row arrangement of pigeonpea that allowed equal utilization of light by both crops gave increased productivity.

The effect of root damage caused by simulated white grub attack on the growth, yield and water-use of groundnut plants

White grubs (larval scarabaeids) are now recognized as being important pests of groundnut (peanut) in many parts of the world because of their ability to damage roots. A method of simulating white grub damage to groundnut plants was developed to obtain an indication of how the feeding activity of these insects influences plant growth. The effect of root cutting and drought stress on water uptake and biomass production was evaluated, with roots being cut at three depths in the late vegetative and early podfilling stages. As groundnut plants are often grown under conditions of drought stress, the effects of which would be accentuated by root damage, this factor was introduced into the experiment. Plant water-use measurements indicated that the root systems of plants cut 30 days after emergence (DAE) and watered twice a week became fully functional again after 40 days. Pod and total biomass production were however significantly less than those of the uncut control plants, with drought stress reducing yields below the well-watered controls, particularly when cut at 10 cm below the soil surface. The root systems of plants cut 51 DAE did not regrow to any appreciable extent, and rates of plant water-use remained less than half of the uncut control plants. Over all treatments, there was a strong positive correlation between total (and pod) biomass and plant water-use. It was concluded that the phenological stage of the plant at which root damage occurred had a profound influence on the subsequent recovery in root growth and function, and ultimately on pod yield.

EFFECT OF SEED TREATMENT WITH Trichoderma Viride AND MOISTURE LEVELS ON ROOT ROT DISEASE IN GROUNDNUT

Trichoderma seed treatment reduced the root rot caused by Macrophomina phaseolina in groundnut at different moisture levels with maximum disease at 40per cent moisture holding capacity. The population of M.phaseolina in the rhizosphere of groundnut plants was highest at the same moisture level. The rhizosphere population of the antagonist Trichoderma viride was favoured at moisture levels of 40 to 60 per cent. Significant reduction in disease was observed with increasing moisture levels. At 100 per cent MHC all the plants survived, without any disease. The root rot incidence increased with increase in plant age. Higher moisture levels were not favourable for the pathogen as well as the antagonist

Effect of fluchloralin on protein synthesis, free amino acids and hydroxyproline content in groundnut (Arachis hypogaea L.)

SUMMARYCultivar TMV‐2 of groundnut plant {Arachis hypogaea L.) was grown in a nutrient solution containing fluchloralin at the rate of either 2 mg litre‐1 or 4 mg litre“1. Protein synthesis and hydroxyproline content in the cell walls of roots, stem and leaves were determined. Free amino acids content and total ammonia in leaves and roots were also analysed. Presence of fluchloralin did not adversely affect protein synthesis. No significant effect of herbicide was observed on hydroxyproline content of a purified cell wall fraction of groundnut roots, stem and leaves. The total amount of ammonia increased in roots and leaves of plants which received the higher concentration of fluchloralin. With the exception of aspartic acid, asparagine, glutamic acid and glutamine, free amino acids content decreased considerably with herbicide treatment. Alanine and glycine were strongly reduced. It is suggested that transamination reactions could be affected and the process of senescence may be enhanced.