Effect of dinitroaniline herbicides on rhizobia, nodulation and N2(C2H2) fixation of four groundnut cultivars

Field, greenhouse and laboratory investigations were conducted to determine the effect of four dinitroaniline herbicides on rhizobia, nodulation and nitrogen fixation of four groundnut cultivars. Benefin, dinitramine and nitralin used at recommended levels decreased nodule dry weight, nitrogenase activity and total nitrogen of groundnut tops and pod yield in three cultivars Kadiri 71-1, Kadiri-2, ICGS-11 and not for a fourth cultivar, Kadiri-3 of groundnut (Arachis hypogaea L.), but fluchloralin used at the recommended level increased the nodulation rate, nitrogenase activity and total nitrogen of groundnut tops and pod yield compared to untreated plants. Studies were conducted in vitro to determine the relative toxicity of the herbicides on four Rhizobium strains isolated from the nodules of four cultivars of groundnut. It was found that various strains of rhizobia differ in their sensitivity to different rates of the herbicides tested. Carbon dioxide exchange rate (CER) of all the cultivars which received herbicide treatment was measured at different time intervals to determine the relationship between photosynthesis and inhibition of nodulation. The lack of adverse effect on the CER of four cultivars when treated at recommended concentrations indicated that nitrogen fixation was affected in cultivars Kadiri 71-1, Kadiri-2 and ICGS-11 due to inhibition of nodulation.     

根癌农杆菌(Agrobacterium tumefaciens)对我国野生、半野生和栽培大豆的致瘤作用研究

本文利用三种根癌农杆菌(Agrobacterium tumefaciens)分别感染我国的野生、半野生和栽培大豆的子叶,诱发产生肿瘤.结果发现根癌农杆菌,A281、Chry5,Chry5C对我国的栽培大豆均有致瘤作用,且A_(281)对栽培大豆具有超毒作用.这一结果与其对美国栽培大豆的作用结果是一致的.而A281对半野生大豆的致瘤作用较差,对野生大豆的致瘤作用最弱.而根癌农杆菌Chry5C尽管其毒性已被弱化,但对我国的栽培大豆仍具有致瘤作用,这一结果与它对美国栽培大豆的致瘤作用是有差异的.说明我国的栽培大豆与美国的栽培大豆之间在致瘤方面存在差异.Chry和5Chry5C对我国的野生大豆和半野生大豆几乎是不致瘤的,说明了野生大豆和半野生大豆在Ti质粒致瘤方面与栽培大豆存在区别.这为进一步研究我国的大豆品质和野生大豆、半野生大豆的特性提供了另一种有效的途径,也为今后进行大豆遗传工程选择适当的受体材料提供了基础.     

Groundnut eyespot virus, a new member of the potyvirus group

A virus causing ‘eyespot’ leaf symptoms in groundnut plants was transmitted by sap-inoculation and by Aphis craccivora in the non-persistent manner. It infected 16 of 72 species from five of 12 families and was easily propagated in Arachis hypogaea and Physalis floridana. The virus has particles c. 13 × 755 nm and is serologically closely related to soybean mosaic and pepper veinal mottle viruses, and more distantly to four other potyviruses. The virus differs in host range, in vitro properties and serological properties from previously described strains of soybean mosaic and pepper veinal mottle viruses. It seems to be a distinct member of the potyvirus group and we propose the name groundnut eyespot virus.     

Identification of resistance to Peanut bud necrosis virus (PBNV) in wild Arachis germplasm

Eighty three wild Arachis germplasm accessions, belonging to 24 species of five sections and one natural hybrid derivative of a cross between the cultivated and a wild Arachis species, were evaluated along with a susceptible groundnut cultivar for resistance to Peanut bud necrosis virus (PBNV) in a replicated field trial at ICRISAT, Patancheru, India. Thirty days after sowing, the percentage of infected plants were recorded for all the accessions and subsequently young leaflets from all these accessions were tested for the presence of the virus by enzyme linked immunosorbent assay (ELISA). One accession each of A. benensis and A. cardenasii, and two accessions of A. villosa, in the section Arachis, two accessions of A. appressipila in the section Procumbentes, and one accession of A. triseminata under section Triseminatae were not infected by PBNV. These seven field‐resistant accessions were tested under glasshouse conditions for virus resistance by mechanical sap inoculations. One accession of A. cardenasii and two accessions of A. villosa did not show systemic infection. Similarly, in another glasshouse test, where 13 A. cardenasii accessions of section Arachis were evaluated, two accessions did not show systemic infection. In all these resistant accessions, the inoculated leaves showed infection, but the systemic leaves did not show the presence of virus in spite of repeated mechanical sap inoculations. So, the resistance in these accessions appears to be due to a block in systemic movement of the virus. To our knowledge this is the first report on the identification of resistance to PBNV in wild Arachis species. Since both A. cardenasii and A. villosa are the progenitors of cultivated groundnut and can be hybridised with the latter, the resistant accessions are being utilised in conventional breeding programmes to transfer PBNV resistance to widely adapted groundnut cultivars.     

Enhanced Expression of <Emphasis Type="Italic">AtNHX1</Emphasis>, in Transgenic Groundnut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.) Improves Salt and Drought Tolerence

Salinity and drought are main threat to agriculture productivity, to avoid further losses it is necessary to improve the genetic material of crops against these stresses In this present study, AtNHX1, a vacuolar type Na⁺/H⁺ antiporter gene driven by 35S promoter was introduced into groundnut using Agrobacterium tumefaciens transformation system. The stable integration of the AtNHX1 gene was confirmed by polymerase chain reaction (PCR) and southern blot analysis. It was found that transgenic plants having AtNHX1 gene are more resistant to high concentration of salt and water deprivation than the wild type plants. Salt and proline level in the leaves of the transgenic plants were also much higher than that of wild type plants. The results showed that overexpression of AtNHX1 gene not only improved salt tolerance but also drought tolerance in transgenic groundnut. Our results suggest that these plants could be cultivated in salt and drought-affected soils.     

Micropropagation and in vitro conservation of wild <Emphasis Type="Italic">Arachis</Emphasis> species

Wild species of Arachis constitute potential sources of novel genes for groundnut improvement programs and some of them are also considered as new agricultural usage. The majority of these species occur in regions under intensive human activity and their areas of distribution are being drastically reduced, thus requiring effective conservation measures. Conservation of Arachis germplasm is usually carried out in seed banks or as live plants. However, seed renewal can be impaired by loss of germinative potential, and plant multiplication under field conditions can be limited by specific soil and environmental requirements or by low seed yield. Therefore, complementary in vitro methodologies represent an important tool for ex situ conservation of Arachis germplasm. In this work, we analyse the state of art of micropropagation and the use of in vitro conservation methodologies for wild relatives of the groundnut.     

Evaluation of bacteria and Trichoderma for biocontrol of pre-harvest seed infection by Aspergillus flavus in groundnut

Pre- and post harvest aflatoxin contamination of groundnut caused by Aspergillus flavus is a major problem in the semi-arid tropics. Fluorescent Pseudomonas, Bacillus and Trichoderma spp. potentially antagonistic to A. flavus were isolated from the geocarposphere (pod-zone) of groundnut and used successfully for the control of pre-harvest groundnut seed infection by A. flavus. In greenhouse and field experiments, inoculation of selected antagonistic strains on groundnut resulted in significant reduction of seed infection by A. flavus, and it also reduced >50% of the A. flavus populations (as cfu) in the geocarposphere of groundnut.     

Germplasm Preservation of Wild Arachis Species through Culture of Shoot Apices and Axillary Buds from In Vitro Plants

A study was conducted to evaluate in vitro techniques for germplasm preservation of wild species of Arachis. Nodal segments excised from in vitro-grown plants of A. retusa, A. macedoi and A. burchellii were used to examine the effects of explant position and age of the donor plant. Explants were excised from plants maintained in culture for 30, 60, 90 or 180 d, numbered I – V from top to bottom and cultured on MS medium supplemented with 2.7 µM NAA or different BAP concentrations (0, 4.4, 13.2 and 22 µM). The age of the donor plant has not influenced the responses of the four genotypes studied. In contrast, shoot regeneration ability was significantly affected by the original explant position, decreasing from top to bottom. In media supplemented with different BAP concentrations, multishoot formation was induced from apical segments at low frequencies (10 – 20%) and segments of all positions originated calluses at the explant basis after 30 d of culture. The culture of nodal segments in the presence of 2.7 µM NAA as the sole growth regulator is recommended for the multiplication of in vitro collections of wild groundnut species in order to avoid callusing and adventitious shoot formation.     

Parasitism of grain legumes by Alectra species (Scrophulariaceae)

In glasshouse pot experiments in the United Kingdom, the host preference of nine seed samples of Alectra vogelii from Eastern, Western and Southern Africa and of two samples of A. picta from Cameroon and Ethiopia, to cultivars of cowpea, groundnut, bambara and mung bean, was assessed. A susceptible cowpea cultivar, Blackeye, and four cultivars of groundnut were attacked by all samples of both parasitic species regardless of whether the host of origin was cowpea, groundnut or bambara. Five “strains” of A. vogelii were distinguished using two criteria: their ability to parasitise bambara and/or mung bean and their ability to parasitise cowpea B301 and bambara TVU 870. The latter proved in an associated experiment to be resistant to collections of the parasite from some locations. Strain 1, including populations from Mali, Nigeria and Cameroon, attacked all groundnuts, cowpea cultivar Blackeye, but not cowpea line B301, mung bean or bambara. Strain 2, from Botswana, differed in attacking B301 and mung bean. Three other strains were identified which attacked susceptible lines of all four legume species. Strain 3 from Kenya failed to attack either cowpea B301 or bambara TVU 870, strain 4 from Malawi attacked cowpea B301, but not bambara TVU 870, while strain 5 from Northern Transvaal, South Africa, attacked bambara TVU 870, but not cowpea B301. Cowpea B359 was resistant to A. vogelii samples from all locations and also to A. picta, which has a similar host preference to strain 1 populations of A. vogelii from West Africa. Two out of 13 groundnut lines tested showed low susceptibility to A. vogelii from Cameroon suggesting there is scope for selecting resistance in this crop also.     

Involvement of phenazines and lipopeptides in interactions between Pseudomonas species and Sclerotium rolfsii, causal agent of stem rot disease on groundnut

Aims: To determine the role of phenazines (PHZ) and lipopeptide surfactants (LPs) produced by Pseudomonas in suppression of stem rot disease of groundnut, caused by the fungal pathogen Sclerotium rolfsii. Methods and Results: In vitro assays showed that PHZ‐producing Pseudomonas chlororaphis strain Phz24 significantly inhibited hyphal growth of S. rolfsii and suppressed stem rot disease of groundnut under field conditions. Biosynthesis and regulatory mutants of Phz24 deficient in PHZ production were less effective in pathogen suppression. Pseudomonas strains SS101, SBW25 and 267, producing viscosin or putisolvin‐like LPs, only marginally inhibited hyphal growth of S. rolfsii and did not suppress stem rot disease. In contrast, Pseudomonas strain SH‐C52, producing the chlorinated LP thanamycin, inhibited hyphal growth of S. rolfsii and significantly reduced stem rot disease of groundnut in nethouse and field experiments, whereas its thanamycin‐deficient mutant was less effective. Conclusions: Phenazines and specific lipopeptides play an important role in suppression of stem rot disease of groundnut by root‐colonizing Pseudomonas strains. Significance and Impact of the Study: Pseudomonas strains Phz24 and SH‐C52 showed significant control of stem rot disease. Treatment of seeds or soil with these strains provides a promising supplementary strategy to control stem rot disease of groundnut.     

The Effect of Groundnut rosette assistor virus on the Agronomic Performance of Four Groundnut (Arachis hypogaea L.) Genotypes

The effect of Groundnut rosette assistor virus (GRAV), in the absence of the other two agents (Groundnut rosette virus and its satellite RNA) of the groundnut rosette disease virus complex, was evaluated on the agronomic performance of four groundnut (=peanut) genotypes (CG‐7, ICGV‐SM‐90704, JL‐24 and ICG‐12991) with different botanical characteristics. All genotypes infected with GRAV showed mild yellowing/chlorosis of leaves and the symptoms persisted throughout their growth period. ELISA absorbance values indicated lower amounts of GRAV antigen in ICGV‐SM‐90704 than in the other genotypes. The reduction in leaf area due to GRAV infection varied between 15.5% and 21.7%, whereas the plant height was decreased between 11.3% and 13.4% among the four genotypes. GRAV infection caused 28.4%, 16.9%, 21.7% and 25.5% reduction in the dry weight of haulms in CG‐7, ICGV‐SM‐90704, JL‐24 and ICG‐12991 respectively. Plants infected with GRAV showed greater reduction in seed weight in CG‐7 (52.2%), followed by JL‐24 (46.1%), ICG‐12991 (40.7%) and ICGV‐SM‐90704 (25.7%). These results provide evidence for the first time that GRAV infection, without GRV and sat RNA, affect plant growth and contribute to yield losses in groundnut.     

Use of monoclonal antibody to potato leafroll virus for detecting groundnut rosette assistor virus by ELISA*

Three of 10 monoclonal antibodies (MAbs) produced to potato leafroll luteovirus (PLRV) were found to react in triple antibody sandwich ELISA (TAS-ELISA) with groundnut rosette assistor luteovirus (GRAV), though none reacted with four other luteoviruses (barley yellow dwarf, bean leaf roll, beet western yellows or carrot red leaf)- The most effective PLRV MAb, SCR 6, was used in TAS-ELISA to detect isolates of GRAV from groundnut plants with chlorotic, green and mosaic forms of rosette from Nigeria and Malawi. The test also detected GRAV in extracts of single Aphis craccivora.     

Evaluation of some fungal diseases and yield of groundnut in groundnut-based cropping systems

A study on the evaluation of some fungal diseases and yield of groundnut in groundnut-based cropping systems was conducted in 2002 and 2003 planting seasons. Analysis of variance indicated that intercropping was highly significant on leaf spot disease severity 0.76; 0.75, rust 2.75; 2.69, as well as percentage defoliation 78.42%; 78.10% in 2002 and 2003, respectively. Plant population was significant on leaf spot severity 4.52, 4.60 rust 2.76; 366 and defoliation 226.5; 441.1 fungal as well as yield, while interactions were not significant on the fungal diseases and yield. Sole groundnut recorded significantly high severity of the fungal diseases investigated but low yield, when groundnut was intercropped with maize and melon and recorded the lowest yield in 2002 and 2003 respectively. 250,000 plants/ha recorded the lowest severity of the diseases investigated, while 444,444 plants/ha recorded the highest. Sole groundnut also recorded the highest percentage defoliation 79.37%, 79.25% when groundnut was intercropped with maize recorded the lowest 77.06%; 77.60%. 250,000 plants/ha had the lowest defoliation when 444,444 plants/ha had the highest 80.75% 82.13% in 2002 and 2003, respectively. Sole groundnut recorded the lowest in the majority of yields when intercropped with maize and with melon recorded a high yield and yield components in 2002 and 2003, respectively. The microorganisms identified were Cercospora spp., Aspergillus linked and Blastomyces.     

A single dominant gene for Fusarium wilt resistance in protoplast-derived tomato plants

Summary Autotetraploids were established from 8 diploid wild species of section Arachis. In all the autotetraploids the chromosomes paired largely as bivalents even though they possess the ability to pair as multivalents. Pollen and pod fertility in the C₁ generation were not directly associated with chromosome pairing. The C₂ generation autotetraploids showed a gradual increase in bivalent associations and pollen and pod fertility. The identification of two genomes, A and B, in the diploid species and in the tetraploid, A. hypogaea, of the section Arachis, a fairly good crossability, and the type of chromosome associations observed in hybrids between A. hypogaea and the autotetraploids of wild Arachis species indicated good prospects of utilizing autotetraploids as genetic bridges in transferring desired traits from these taxa into groundnut.Submitted as Journal Article No. 516 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Components of resistance to Cercospora arachidicola and Cercosporidium personatum in groundnuts*

The reactions of four groundnut cultivars to inoculation with two leaf spot pathogens (Cercospora arachidicola and Cercospodirium personatum) were investigated. Resistant cultivars showed longer latent periods, reduced sporulation and less defoliation; however, none of the cultivars was resistant to both pathogens. Numbers of lesions, time to leaflet loss and the percentage of spores which produced lesions were influenced by the concentration of C. personatum inoculum applied to the leaves and there were significant cultivar differences in lesion numbers at the lowest inoculum level. Only the first two characters were affected by applied spore concentration in the study with C. arachidicola. Generally it was found that lower inoculum levels gave a better separation of cultivars. The level of resistance was similar to that found in the slow resting reaction of cereal crops and should be useful in a groundnut breeding programme.     

Ethyl Methanesulfonate Mutagenesis–Enhanced Mineral Phosphate Solubilization by Groundnut-Associated <Emphasis Type="Italic">Serratia marcescens</Emphasis> GPS-5

Twenty-three bacterial isolates were screened for their mineral phosphate–solubilizing (MPS) ability on Pikovskaya and National Botanical Research Institute’s phosphate (NBRIP) agar. The majority of the isolates exhibited a strong ability to solubilize hydroxyapatite in both solid and liquid media. The solubilization in liquid medium corresponded with a decrease in the pH of the medium. Serratia marcescens GPS-5, known for its biocontrol of late leaf spot in groundnut, emerged as the best solubilizer. S. marcescens GPS-5 was subjected to ethyl methanesulfonate (EMS) mutagenesis, and a total of 1700 mutants, resulting after 45 minutes of exposure, were screened on buffered NBRIP medium for alterations in MPS ability compared with that of the wild type. Seven mutants with increased (increased-MPS mutants) and 6 mutants with decreased (decreased-MPS mutants) MPS ability were isolated. All seven increased-MPS mutants were efficient at solubilizing phosphate in both solid and liquid NBRIP medium. Among the increased-MPS mutants, EMS XVIII Sm-35 showed the maximum (40%) increase in the amount of phosphate released in liquid medium compared with wild-type S. marcescens GPS-5, therefore, it would be a useful microbial inoculant in groundnut cultivation. EMS III Sm W, a nonpigmented mutant, showed the lowest solubilization of phosphate among the 6 decreased-MPS mutants.     

Fungi associated with stored unprocessed cowpea and groundnut varieties available in Borno State, Nigeria.

Five stored unprocessed cowpea (Vigna spp) and four groundnut (Arachis hypogeae) varieties available in Borno State were examined for the mould flora. The degree of infestation of the grains ranged from 31% to 100% and 68% to 86% for surface sterilized cowpea and groundnut respectively. The mould flora commonly encountered were species of the genera Aspergillus. Penicillium species, Scopulariopsis species and Trichoderma species were also found. The flora of the cowpea was dominated by Aspergillus niger while Aspergillus flavus was the dominant mould on groundnut.     

Further properties of peanut clump virus and studies on its natural transmission

Purified preparations of particles of peanut clump virus (PCV) had A₂₆₀/A₂₈₀ values (corrected for light scattering) of 1.00. They contained rod-shaped particles with sedimentation coefficients of 183 S and 224 S, and a density in CsCl of 1.32 g/ml. PCV infected 36 species in 8 plant families. No serological relationship was detected between PCV and barley stripe mosaic, beet necrotic yellow vein, Nicotiana velutina mosaic and tobacco mosaic viruses. PCV was seed-borne for two generations in groundnut (Arachis hypogaea) but was not seed-borne in great millet (Sorghum arundinaceum), Phaseolus mungo or Nicotiana benthamiana. Seedlings of groundnut, great millet and wheat (Triticum aestivum) became infected when grown in soil from groundnut fields with outbreaks of clump disease, and the infectivity of soil survived air-drying at 25°C for 3 months. Groundnut seedlings became infected when grown in sterilised soil contaminated with washed roots of naturally-infected S. arundinaceum but not in soil to which roots of naturally infected groundnut or shoots of infected groundnut were added, or in which mechanically inoculated groundnut seedlings were grown at the same time. The patchy distribution of PCV in a crop was related to the infectivity of the soil for groundnut and to the presence of Polymyxa graminis resting spores which could be detected in the roots of S. arundinaceum bait seedlings, but not in those of groundnut. The results indicate that PCV is transmitted by a vector that is resistant to air-drying and closely associated with S. arundinaceum roots. For these reasons P. graminis is thought to be the vector of PCV.     

Chitin-supplemented Foliar Application of Serratia marcescens GPS 5 Improves Control of Late Leaf Spot Disease of Groundnut by Activating Defence-related Enzymes

Chitinolytic Serratia marcescens GPS 5 and non‐chitinolytic Pseudomonas aeruginosa GSE 18, with and without supplementation of chitin, were tested for their ability to activate defence‐related enzymes in groundnut leaves. Thirty‐day‐old groundnut (cv. TMV 2) plants pretreated with GPS 5 and GSE 18 (with and without supplementation of 1% colloidal chitin) were challenge inoculated after 24 h with Phaeoisariopsis personata, the causal agent of late leaf spot (LLS) disease of groundnut. GPS 5 and GSE 18, applied as a prophylactic spray, reduced the lesion frequency by 23% and 67%, respectively, compared with control. Chitin supplementation had no effect on the control of LLS by GSE 18, unlike GPS 5, which upon chitin supplementation reduced the lesion frequency by 64%, compared with chitin alone. In a time course study the activities of chitinase, β‐1,3‐glucanase, peroxidase and phenylalanine ammonia lyase were determined for the different treatments. There was an enhanced activity of the four defence‐related enzymes with all the bacterial treatments when compared with phosphate buffer and colloidal chitin‐treated controls. In correlation to disease severity in bacterial treatments, chitin‐supplemented GSE 18 was similar to GSE 18, whereas chitin‐supplemented GPS 5 was much more effective than GPS 5, in activation of the defence‐related enzymes. The high levels of enzyme activities following chitin‐supplemented GPS 5 application continued up to the measured 13 days after pathogen inoculation.     

Effect of Bradyrhizobium, VA mycorrhiza and fertilisers on seed composition of groundnut

A field experiment was carried out to investigate the effect of Bradyrhizobium and mycorrhizal (Glomus sp.) inoculation compared to adding urea and super phosphate on proximate composition, in vitro protein digestibility (IVPD) and tannin content of groundnut. The results showed that mycorrhizal inoculation and/or superphosphate significantly (P≤ 0.05) increased both oil and protein content of groundnut seeds. Bradyrhizobium and/or nitrogen fertiliser significantly (P≤ 0.05) increased protein content and significantly decreased the oil content. Bradyrhizobium and/or mycorrhizal inoculation significantly (P≤ 0.05) increased the ash, crude fibre, IVPD and tannin content. Biological and chemical fertilisers significantly (P≤ 0.05) increased IVPD. Superphosphate fertilisers significantly (P≤ 0.05) increased the tannin content. The moisture content was not affected by any treatment.