S. Nakkeeran

Induction of plant defence compounds by Pseudomonas chlororaphis PA23 and Bacillus subtilis BSCBE4 in controlling damping-off of hot pepper caused by Pythium aphanidermatum

Abstract Bacillus subtilis strain BSCBE4 and Pseudomonas chlororaphis strain PA23 (=P. aureofaciens) were effective biocontrol agents against Pythium aphanidermatum, the causal agent of damping-off of hot pepper (Capsicum annum L.) in greenhouse vegetable production systems. Application of strains BSCBE4 and PA23 at the rate of 20 g kg−1 of seed significantly increased the growth of hot pepper seedlings. The efficacies of various carriers in sustaining the population of these strains in storage were assessed. Both the antagonists survived up to 180 days of storage in peat and talc-based formulations. The two bacterial strains induced development of plant defence-related enzymes including phenylalanine ammonia lyase, peroxidase, polyphenol oxidase, phenol content, suppressed incidence of damping-off and increased growth of hot pepper seedlings.

PGPR MEDIATED MANAGEMENT OF STEM BLIGHT OF PHYLLANTHUS AMARUS (SCHUM AND THONN) CAUSED BY CORYNESPORA CASSIICOLA (BERK AND CURT) WEI

Bacillus subtilis (BSCBE4), Pseudomonas chlororaphis (PA23), endophytic P. fluorescens (ENPF1) inhibited the mycelial growth of stem blight pathogen Corynespora casiicola (Berk and Curt)Wei under in vitro. All these bacterial isolates produced both hydroxamate and carboxylate type of siderophores. But the siderophore production was maximum with the isolate ENPF1. Delivering of talc based formulation of BSCBE4 through seedling dip and foliar application effectively reduced stem blight disease incidence and increased the dry matter production under pot culture and field conditions. Application of BSCBE4, PA23 and ENPF1 increased the defense related enzymes such as peroxidase, polyphenol oxidase, chitinase and β-1,3 glucanase in P. amarus up to ten days after challenge inoculation with C. cassicola. Native gel electrophoretic analysis revealed that challenge inoculation of pathogen with BSCBE4 and PA23 induced both peroxidase and polyphnol oxidase isoforms.

Antagonistic potentiality of Trichoderma viride and assessment of its efficacy for the management of cotton root rot

Mutants of Trichoderma viride were developed by exposing the conidia of T. viride – Tv 6 (Tv. WD) to physical and chemical mutagens such as UV rays, gamma rays and nitrosoguanidine. The mutants were screened for antagonistic potentiality by developing an antagonism index. Antagonism index is the product of competitive saprophytic ability, colonization behavior, percent inhibition of pathogen, propagule lysis, speed of overgrowth on pathogen and inhibition zone, where AI = CSA x CB x PI x PL x SOOP x IZ. Strains MG3, MG6, UV10 and MNT7 recorded the highest antagonism index ranging from 192 – 480 with increased activity of cellulase, chitinase, β- 1, 3 glucanase and IAA. Delivering of MG6 through seed and soil recorded the lowest root rot incidence with increased yield and dry matter production of cotton under field conditions.

Development of biomanure for the management of turmeric rhizome rot

Abstract MG 6 strain of Trichoderma viride was found to be effective in inhibiting the growth of P. aphanidermatum, the causal agent of turmeric rhizome rot. Maximum population of T. viride was recorded in chaffy paddy grain. Among the various substrates, FYM well supported the growth of T. viride in situ. Changes in the C/N ratio, cellulose, lignin and micronutrients were noticed during the incubation period. Rhizome rot incidence was found to be reduced in plants applied with FYM-based biomanure under glass house conditions.

Antiviral action of Harpulia Cupanioides and Mirabilis Jalapa against tomato spotted wilt virus (TSWV) infecting tomato

Mirabilis jalapa and Harpulia cupanioides remain as an unexploited potential to be tapped, as sources of antiviral principles. The antiviral protein from M. jalapa (MAP) and H. cupanioides (HAP) were highly effective in inhibiting TSWV at 60 and 80% saturation. A minimum concentration of 400 μg/ml of MAP was sufficient to inhibit TSWV. HAP at 800 μg/ml recorded 98.41% inhibition of lesion formation. The plants treated with M. jalapa and H. cupanioides challenged with TSWV did not show significant variation in absorbance values when compared to uninoculated healthy plants, indicating the absence of detectable virus through indirect DAS ELISA thus indicating the effectiveness of AVPs. Pre-application of MAP and HAP induced the activity of phenols, PO, PPO and PAL leading to the suppression of TSWV on local lesion and systemic host.

Vermicompost-based bioformulation for the management of sugarbeet root rot caused by Sclerotium rolfsii

Vermicompost-based bioformulations of bacterial and fungal biocontrol agents were examined against sugarbeet root rot caused by Sclerotium rolfsii. The result showed that the Pseudomonas fluorescens strain Pf1 in combination with either Trichoderma asperellum strain TTH1 or Bacillus subtilis strain EPCO-16 performed better in reducing disease next to the chemical difenoconazole. Similarly, enhanced yield was observed in the same combination treatments under both pot and field conditions.

Rhizobacterial-mediated induction of defense enzymes to enhance the resistance of turmeric (Curcuma longa L) to Pythium aphanidermatum causing rhizome rot

Rhizobacteria isolated from the rhizosphere soil were evaluated for their ability to control rhizome rot in turmeric (Curcuma longa L). These isolates were characterised as Pseudomonas fluorescens and Bacillus subtilis. Under in vitro condition, two isolates, namely P. chlororaphis (PcPA23) and B. subtilis (BsCBE4), showed maximum inhibition of mycelial growth of Pythium aphanidermatum, were found effective in reducing rhizome rot of turmeric both under greenhouse and field conditions and increased the plant growth and rhizome yield. Both the isolates were further tested for its ability to induce production of defense-related enzymes and chemicals in plants. Increased activities of phenylalanine ammonia lyase, peroxidase, polyphenol oxidase, chitinase and β-1,3-glucanase were observed in PcPA23 and BsCBE4 pre-treated turmeric plants challenged with P. aphanidermatum. Moreover, higher accumulation of phenolics was noticed in plants pre-treated with PcPA23 and BsCBE4 challenged with P. aphanidermatum. Thus, the present study shows that in addition to direct antagonism and plant growth promotion, induction of defense-related enzymes involved in the phenyl propanoid pathway collectively contributed to enhance resistance against invasion of Pythium in turmeric.

First report of leaf blight of noni caused by Alternaria alternata (Fr.) Keissler

A severe outbreak of leaf blight was observed in noni crop for the first time in Tamil Nadu and Karnataka states of India during 2008–2009. Based on pathogenicity, morphology and ribosomal DNA spacer sequences, the pathogen was identified as Alternaria alternata (Fr.) Keissler. This report is the first of Alternaria leaf blight of noni.

First report of anthracnose on noni caused by Colletotrichum gloeosporioides in India

Noni, an important medicinal plant grown in southern India suffered heavy loss due to anthracnose disease in 2008–2009. Based on their pathogenicity, morphological and cultural characters and ribosomal DNA spacer sequences, the pathogen was identified as Colletotrichum gloeosporioides. This is the first report of anthracnose on noni in India.

Effect of biocontrol agent, plant extracts and safe chemicals in suppression of Mungbean Yellow Mosaic Virus (MYMV) in black gram (Vigna mungo)

Pseudomonas fluorescens (Pf1), plant extract and bioactive compound treatments on induction of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) and accumulation of phenolics in black gram to suppress the natural incidence of Mung bean yellow mosaic bigeminivirus (MYMV) was studied. Leaf extracts of Mirabilis jalapa, Datura metel and neem (Azadirachta indica) oil provided reduced incidence of MYMV with increased yield in black gram under field conditions. The bio-compatible products actigard® (acibenzolar-S-methyl), disodium hydrogen phosphate and alum (aluminium potassium sulphate) also suppressed MYMV on black gram and increased yield compared with nontreated plants under field conditions. The mean disease incidence of the two field trial shows that the foliar spray of P. fluorescens and M. jalapa recorded the lowest disease incidence of 39.14 and 41.48% with yields of 718 and 716.5 kg per hectare, respectively. Induction of systemic resistance as evident from the increased accumulation of pathogenesis related (PR) proteins and other defense related compounds was observed in black gram plants following application of Pf1, plant extracts and bioactive compounds after incidence of MYMV during 30 and 45 days after planting. Black gram with these treatments exhibited a significant increase in activities of enzymes PAL, PO, PPO along with rapid and distinct accumulation of toxic phenolic compounds than the control plants. These results suggest that the enhanced activities of defense enzymes and elevated content of phenolics may contribute to the protection of black gram against MYMV. Further, the inverse correlation of reduced MYMV disease incidence with significantly high chlorophyll content and total sugar contents in Pf1, plant extract and bioactive compounds treated plants also suggest the potential of these treatments to use for managing MYMV in the field.