M. Karthikeyan

Induction of phenolics and defense-related enzymes in coconut (Cocos nucifera L.) roots treated with biocontrol agents

The effect of soil application of biocontrol agents (Pseudomonas fluorescens, Trichoderma viride and T. harzianum) in combination with chitin on induction of phenolics and defense enzymes in coconut roots infected with Ganoderma lucidum, the causal agent of Ganoderma disease, was investigated. Soil application of these biocontrol formulations in combination with chitin induced a significant increase in the activities of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), chitinase and b-1,3-glucanase in the G. lucidum infected palms. Activities of both PAL and PO reached maximum levels within 3 d while the activity of PPO reached the maximum level 6 d after application of a mixture of P. fluorescens, T. viride and chitin. Isozyme analysis revealed that unique PO3 and PPO2 isozymes were induced in coconut palms treated with P. fluorescens + T. viride + chitin. Accumulation of phenolics was recorded 3 d after treatment and reached maximum levels 9 d after treatment application. Activity of chitinase was significantly increased from the third day after treatment imposition and continued to increase up to 9 to 12 d in all treatments. Chitinase isozyme analysis revealed that a unique Chit3 isoform was induced in coconut roots treated with P. fluorescens + T. viride + chitin. The b-1,3-glucanase activity was maximum 9 d after treatment application. The mechanisms by which P. fluorescens + T. viride + chitin reduced the incidence of Ganoderma disease in coconut may be related to its ability to induce defense mechanisms in coconut palms.

Genetic variability and aflatoxigenic potential of Aspergillus flavus isolates from maize

Abstract Various isolates of Aspergillus flavus collected from infected maize seeds were tested for their ability to produce aflatoxin B1 (AFB1) in vitro. The amount of AFB1 produced by the toxigenic isolates of A. flavus was ranged from 0.57 to 82.91 ng/ml. Among the 51 isolates of A. flavus tested, the isolate AFM1 produced the highest amount of (82.91 ng/ml) AFB1. Nineteen isolates did not produce aflatoxin B1. The genetic variability among the A. flavus isolates was investigated by PCR amplification of internal transcribed spacer (ITS) including ITS1, ITS2 and the intervening 5.8S rRNA region of ribosomal DNA followed by sequencing. PCR amplification of the ITS regions of the A. flavus isolates (AFM1, AFM3 and AFM5) by using ITS1 and ITS4 primers gave products of approximately 580 base pairs in length. The nucleotide sequences were compared with ITS sequences of A. flavus from Genbank database. Analysis of the genetic coefficient matrix derived from the nucleotide sequences of the ITS regions of A. flavus isolates showed that minimum and maximum percent similarities among the tested A. flavus strains were in the range of 12 and 99%, respectively. Phylogenetic analysis of ITS sequences by the unweighted pair group method arithmetic average (UPGMA) identified three main clusters (A, B and C). Cluster A consisted of only one strain and cluster C consisted of three strains including AFM5. The sequence of AFM5 was clustered with the sequence of a clinical isolate of A. flavus (AY677676) and about 76% similarity index was observed between them at molecular level. All the remaining strains belonged to cluster B, which includes AFM1 and AFM3. The genetic variability among A. flavus isolates should be considered when A. flavus isolates are required for testing in resistance breeding programmes.

Biological control of onion leaf blight disease by bulb and foliar application of powder formulation of antagonist mixture

Abstract Three antagonists: Pseudomonas fluorescens (Pf1), Bacillus subtilis and Trichoderma viride, were tested alone and in combination for suppression of onion leaf blight (Alternaria palandui) disease under glasshouse and field conditions. The average mean of disease reduction was 24.81% for single strains and 42.44% for mixtures. In addition to disease suppression, treatment with a mixture of antagonists promoted plant growth in terms of increased plant height and ultimately bulb yield. Though seed treatment of either single strain or strain mixtures alone could reduce the disease, subsequent application to root, leaves or soil further reduced the disease and enhanced the plant growth. The mixture consisting of Pseudomonas fluorescens Pf1 plus Bacillus subtilis plus Trichoderma viride was the most effective in reducing the disease and in promoting plant growth and bulb yield in greenhouse and field tests.

Endophytic Pseudomonas fluorescens Endo2 and Endo35 induce resistance in black gram (Vigna mungo L. Hepper) to the pathogen Macrophomina phaseolina

Abstract The effect of endophytic Pseudomonas fluorescens isolates Endo2 and Endo35 on induced systemic disease protection against dry root rot of black gram (Vigna mungo L. Hepper) caused by Macrophomina phaseolina was investigated under glasshouse conditions. When the bacterized black gram plants were inoculated with dry root rot pathogen, the activities of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) were stimulated in addition to accumulation of phenolics and lignin. Activity of phenylalanine ammonia-lyase (PAL) reached the maximum 24 h after pathogen challenge inoculation, whereas the activities of PO and PPO reached the maximum at 72 h and 48 h, respectively. Isoform analysis revealed that a unique PPO3 isozyme was induced in bacterized black gram tissues inoculated with the pathogen. Phenolics were found to accumulate in bacterized black gram tissues challenged with M. phaseolina one day after pathogen challenge. The accumulation of phenolics reached maximum at the third day after pathogen inoculation. Similar observation was found in the lignin content of black gram plants. In untreated control plants, the accumulation of defence enzymes and chemicals started at the first day and drastically decreased 3 days after pathogen inoculation. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restricting invasion of Macrophomina phaseolina in black gram roots.

Epidemiology of grey mildew and Alternaria blight of cotton

Grey (Areolate) mildew (Ramularia areola) and Alternaria blight (Alternaria macrospora) are two important fungal foliar diseases affecting cotton in India. Both the diseases are polycyclic in nature. The primary inoculum for grey mildew is through conidia or ascospores from infected debris and/or perennial cottons and the secondary spread is through primarily infected leaves. Whereas for Alternaria blight the spread is initially from seed-borne inoculum (in Gossypium herbaceum and Gossypium arboreum cottons) and/or crop debris and the secondary spread is from sporulating lesions on older leaves. Both R. areola and A. macrospora require a temperature regime of 20–30 °C with prolonged high humidity (>80%) and frequent rains for infection and disease development. However, it has been observed that cool weather coupled with prolonged dewy periods in the absence of rains has also been found conducive for the development of both the diseases. So, suitable epidemiological tools and models are required to predict the disease development, spread and to design suitable management practices.

Effect of combination of bio-agents and mineral nutrients for the management of alfalfa wilt pathogen Fusarium oxysporum f. sp. medicaginis

Abstract Biological and nutrient management of soil borne disease is increasingly gaining stature as a possible practical and safe approach. Inhibitory effects of fungal and bacterial antagonists were tested under in vitro conditions against the wilt pathogen of alfalfa Fusarium oxysporum f. sp. medicaginis. Trichoderma harzianum and Pseudomonas fluorescens (PI 5) were found to be effective against the alfalfa wilt pathogen. Manganese sulphate at 500 and 750 ppm inhibited the mycelial growth of F. oxysporumf. sp. medicaginis under in vitro conditions. In pot culture studies, manganese sulphate at 12.5 mg/kg reduced the wilt incidence (23.33%). Combined application of manganese sulphate 12.5 mg/kg + T. harzianum 1.25 mg/kg of soil significantly reduced the wilt incidence accompanied by improved plant growth and yield in pot culture. The mixture of manganese sulphate (25 kg/ha) + T. harzianum (2.5 kg/ha) significantly reduced the wilt incidence when applied as a basal dose in the field conditions. The average mean of disease reduction was 62.42% over control.

Influence of phylloplane colonizing biocontrol agents on the black spot of rose caused by Diplocarpon rosae

Abstract An attempt was made to study the biocontrol efficacy of antagonistic microorganisms in phylloplane of rose cv. Edward to manage the black spot (Diplocarpon rosae) disease. Eight antagonistic microorganisms were tested in vivo against the black spot pathogen. Among these, Trichoderma viride and Pseudomonas fluorescens pf1 reduces the mycelial growth significantly. These two biocontrol agents were evaluated for their ability to induce defense-related enzymes and chemicals in plants. Increased activity of phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO) and total phenolics were recorded in all the biocontrol agents treated leaves. P. fluorescens Pf1 recorded early and increased synthesis of the entire defense-related enzymes and total phenol within 6 days. The application of biocontrol agents induced the defense-related enzymes involved in phenyl propanoid pathway in addition to direct antagonism, which collectively contribute for enhanced resistance against invasion of Diplocarpon rosae in rose.

Occurrence of aflatoxin contamination in maize kernels and molecular characterization of the producing organism, Aspergillus

Aflatoxins are toxic metabolites produced mainly by Aspergillus flavus and Aspergillus parasiticus. Aflatoxin B1 (AFB1) is a potent carcinogen, teratogen and mutagen. 660 pre- and post- harvest maize samples were collected from major maize growing areas in Tamil Nadu, India. Aflatoxin contamination was observed in 40.22% of the samples tested of which, 22.97% of pre-harvest and 53.93% post-harvest maize samples were found to be infected with AFB1 and 12.05% of the total samples exceeded WHO permissible limit of 20 μg/kg. AFB1 contamination ranged from 0 to 149.32 µg/kg. 28 A. flavus isolates were isolated and grouped into three sets based on aflatoxin producing potential viz., highly aflatoxin producing isolates, medium producing isolates and no aflatoxin producer or traces of aflatoxin producing isolates. The genetic coefficient matrix analysis using random amplified polymorphic DNA (RAPD) with ten random primers revealed minimum and maximum percent similarities among the tested A. flavus strains ranging from 35 to 89%. Cluster analysis separated the three sets of isolates into two groups (groups I and II) with each two subgroup confirming the genetic diversity among the A. flavus isolates from maize.

Analysis of variability among the isolates of Peronosclerospora sorghi from sorghum and cornbased on restriction fragment length polymorphismof ITS region of ribosomal DNA

Abstract Downy mildew, caused by Peronosclerospora sorghi [Weston and Uppal (Shaw)], is one of the most serious diseases of sorghum and corn worldwide. Pathogenic variability among various isolates of P. sorghi has been reported. However, the molecular relationships between the isolates from sorghum and corn are unknown. In the present study DNA was extracted from P. sorghi isolates from sorghum and corn collected from different locations of Tamil Nadu, India, and their genetic variability was investigated using restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified internal transcribed spacer (ITS) region of ribosomal DNA. PCR amplification of the ITS regions of the P. sorghi isolates from sorghum and corn gave products of approximately 550 base pairs in length with slight variations in a few isolates. Restriction fragment length polymorphism analysis of the ITS regions of nuclear rDNA of P. sorghi with HhaI, EcoRI and MspI confirmed the heterogeneity among the P. sorghi isolates from sorghum and corn.

User Intended Privacy Preserving Models in Online Social Networks

The proposed system introduces new social network privacy management models and it measures their human effects. Here it introduces a mechanism using clustering techniques which helps users to group their friends using policy management. Then it introduces new privacy management model which will give policies to other friends to find similar friends in the network. And thereby explored various ways that help users to find example friends. In addition, it will help to find privacy management models which can be further enhanced and also it helps to detect privacy sentiment of user. Assistant friend grouping will be done for effective friendship establishment. In a network user privacy will be maintained by setting privacy techniques. Privacy management models can be routinely customized to the privacy sentiment and done according to the needs of the user.