Browsing by Author "Dhanya, M K"

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Compendium on cardamom
(Kerala Agricultural University, 2016) Murugan, M; Dhanya, M K; Deepthy, K B; Preethy, T T; Aswathy, T S
Eco-friendly management of Fusarium rot in cardamom and its impact on soil health and plant defense mechanism
(Department of Plant Pathology, College of Agriculture, Vellayani, 2020) Veni Krishna, K C; Dhanya, M K
Etiology and management of bacterial of anthurium
(Department of Plant Pathology, College of Agriculture, Vellayani, 2000) Dhanya, M K; Mary, C A
Bacterial blight incited by Xanthomonas axonopodis pv. dieJJenbachiae (Me Culloch and Pirone) Vauterin et al. (1995) is a serious disease of anthurium (Anthurium andreanum Linden) causing heavy economic loss to growers in Kerala. The diseased plants showed both foliar and systemic infections. The bacterium was a Gram negative, motile rod. Morphological, physiological and biochemical characters of the six isolates were same except for some characters like nature and rate of growth, virulence and hydrolysis of starch. The bacterium inciting this disease was identified as Xanthomonas axonopodis pv. dieffenbachiae based on morphological, physiological and biochemical characters coupled with pathogenicity. Potato Sucrose Agar was found to be the best medium for growth and slime production of the bacterium. Dieffenbachia sp., Philodendron oxycardium, Aglaonema robelinii, Colocasia esculenta and Syngonium podophyllum were carriers of Xanthomonas axonopodis pv. dieJJenbachiae. The pathogen survived In infected plant debris kept in soil under glass house conditions and In refrigerated conditions for about 45 days and in soil for 60 days. Under in vitro evaluation, 100 ppm streptocycline and 0.3 per cent captan were most effective in inhibiting the growth of the pathogen. Under in vivo conditions, the relative efficiency of four ecofriendly management practices namely the application of turmeric powder + sodium bicarbonate, Pseudomonas jluorescens (proprietary product), neem oil and cowdung extract at three different levels were compared with that of spraying with 100 ppm streptocycline and 0.3 per cent captan. It was observed that the use of 0.15 per cent turmeric powder + sodium bicarbonate (10 : 1 proportion) was most effective and the extent of disease control achieved after a schedule of five sprayings at one week interval was same as that of 100 ppm streptocycline.
Evaluation of beneficial fungal root endophytes against fusarium rot in small cardamom
(Department of Plant Pathology, College of Agriculture, Vellayani, 2022) Aishwarya Manoharan; Dhanya, M K
The study entitled “Evaluation of beneficial fungal root endophytes against Fusarium rot in small cardamom” was conducted at College of Agriculture, Vellayani and Cardamom Research Station, Pampadumpara during 2020-21 to evaluate the colonisation and interaction of two beneficial fungi, Piriformospora indica and Glomus fasciculatum, in cardamom and their potential to manage Fusarium rot disease of cardamom and elucidation of the role of gibberellic acid in the endophytic fungimediated disease tolerance. Fusarium infection in small cardamom is characterised by root rotting, eye shaped lesion on pseudostem and panicle rot. Fusarium oxysporum Schledt was isolated from the infected roots of the farmer’s field of Pampadumpara in Idukki district. Koch’s postulate was proved by inoculation of the pseudostem of one year plants using pinprick method where the isolate produced the typical eye shaped lesion within two weeks. A pot culture experiment was conducted at CRS, Pampadumpara to assess the interactive effect of the fungal root endophytes P. indica and G. fasciculatum on the vegetative growth of small cardamom seedlings and suckers using four treatments and five replications. Both individual and combinatorial effects of the endophytes on the vegetative characters like plants height, number of leaves, leaf length, leaf width, root parameters, biomass etc. were evaluated. Successful root colonization was observed in P. indica and G. fasciculatum treated roots at six and seven days after their inoculation respectively. This is the first report of colonization of P. indica in small cardamom. The study revealed that the endophytes inoculated plants were superior to control plants in which maximum shoot growth was shown by the dually colonized plants followed by the P. indica-colonized which was then followed by G. fasciculatum colonised plants. The root parameters were higher for P. indica-colonized plants compared to the combined or G. fasciculatum colonized plants in cardamom seedlings whereas dually colonized plants had better root growth in cardamom suckers. P and K analysis of the whole plant clearly indicated the enhanced nutrient uptake to root, shoot and leaf in the endophytes-colonized plants. The IAA analysis of root samples also revealed a higher IAA content in the endophytes colonized seedlings compared to the control seedlings with P. indica colonized plants recording the maximum value of 83.80 µg g-1 in seedlings and 94.30 µg g-1 in suckers; and least value being observed in control plants recording 44.80 µg g-1 in seedlings and 94.30 µg g-1 in suckers. This study stipulate a scope of better establishment of cardamom in field especially in the case of seedlings during transplantation due to well established root system. There was also a reduction in nursery period by two months in the P. indica and G. fasciculatum dually colonized seedlings compared to the non-colonized seedlings. In vitro evaluation of P. indica against F. oxysporum and in vivo evaluation of both the bioagents against F. oxysporum in small cardamom was carried out to appraise the effect of bioagents in the management of Fusarium rot disease of cardamom. In in vitro evaluation, dual culture assay of P. indica with F. oxysporum was performed in PDA in which a percent inhibition of 64.4 (%), antagonism index of 20.53 and an obscure lysis zone was observed. There wasn’t any presence of inhibition zone, antibiosis, coiling, overgrowth, sporulation etc. In in vivo evaluation, a pot culture experiment was laid out at CRS, Pampadumpara with seven treatments and three replications including a bio agent check of 2% Pseudomonas fluorescens and chemical check of 2 % carbendazim as basal drench. The study revealed that the beneficial interaction with bioagent successively decreased the disease severity and lesion size, among which P. indica treated plants showed the best result having the least disease severity of 38.07 (%) and 31.48 (%) in seedlings and suckers respectively. The disease severity of the control plants were the highest, recording 86.62 (%) and 76.77 (%) in seedlings and suckers respectively. Combinatorial and P. fluorescens treatments were the other treatments showing promising results in disease management. Total Gibberellic acid was estimated from leaf samples of challenge inoculated experimental plants to elucidate the role of GA in endophyte mediated disease tolerance and the authors couldn’t interpret any role of GA in disease development. Moreover, the GA content was higher in P. indica colonised recording 18.60 µg g-1 and 10.65 in µg g-1 in seedlings and suckers respectively; and dually colonised plants recording 18.00 µg g-1 and 9.71 µg g-1 in seedlings and suckers respectively. Thus, the present study proclaims a very pronounced plant growth promotion in cardamom seedlings and suckers by the beneficial fungal root endophytes viz., P. indica and G. fasciculatum just before transplanting to the field and therein advocating better development and establishment in the field condition. Furthermore, the results also indicates an effective management of the destructive Fusarium rot disease in small cardamom using endophyte colonization especially in P. indica colonized and dually colonized plants.
Identification of major fungal pathogens of dragon fruit and management of its major disease
(Department of Plant Pathology, College of Agriculture, Vellayani, 2023-12-29) Kovvuri Janakadatta Reddy; Dhanya, M K
The research study entitled "Identification of fungal pathogens of dragon fruit and management of its major disease" was carried out at the Department of Plant Pathology, College of Agriculture, Vellayani, from 2021 to 2023 to identify and characterize the prevailing fungal pathogens of dragon fruit plants grown in Southern Kerala and develop an integrated management strategy against its major diseases. Two dragon fruit cultivating regions, AEU 09 (south-central laterite) and AEU 12 (southern and central foothill) in Kerala, were surveyed to identify the major fungal pathogens and associated symptoms on dragon fruit plants. Stem canker, characterized by yellow spots that further progressed into orange-brown lesions with yellow haloes, was observed in plantations of Palode and Vembayam regions of Thiruvananthapuram district. In the Vellavoor block of Kottayam district (AEU 12), a widespread outbreak of a wilt disease caused by Rigidoporus spp. was recorded. In Palode region (AEU 09), Fusarium infection was prevalent, where soft rot symptom was observed near the soil line and brownish-red lesions on the stems/cladodes. Neoscytalidium spp, Fusarium spp, and Rigidoporus spp were isolated from the infected samples collected from various locations. Three isolates of Neoscytalidium spp (I1, I3, I5) were obtained from Palode, Vembayam, and Pala regions respectively. Among them, the isolate (I1) was found to be more virulent, and hence selected for further studies. The pathogenicity of these isolates was confirmed by artificial inoculation on healthy dragon fruit cladodes and fruits, and Koch's postulates were established. The morphological and cultural characteristics of each isolate was examined on potato dextrose agar (PDA) medium. Neoscytalidium isolates (I1, I3, I5) exhibited greyish colonies with dark grey to black pigmentation. The average growth rate of these isolates was about 1.06 cm per day. Their hyphae were characterized by brown colour, branching pattern, and septation. Conidia of various shapes and colours were formed in chains (arthroconidia). The Isolate I2 had white aerial mycelium with concentric rings and sickle-shaped conidia. The Isolate I4 produced dense cottony white mycelia with an average growth rate of 0.87 cm per day. Molecular characterization with ITS primers indicated that isolates I1, I3, and I5 had 97.21 Per cent similarity with Neoscytalidium spp reported from Malaysia, and China respectively. The isolates I2 and I4 showed 95.29 Per cent and 100 Per cent similarity with Fusarium spp and Rigidoporus spp reported from India and Malaysia respectively. DNA of isolate I2 on amplification in PCR with ITS and TEF primers revealed 100 per cent similarity to F. fujikuori Potential of biocontrol agents, including Bacillus amyloliquefacians, Pseudomonas fluorescens, Trichoderma asperellum (KAU isolate), and T. harzianum (IISR isolate), were tested against the above pathogens. T. harzianum significantly inhibited the hyphal growth of Rigidoporus sp. whereas T. asperellum showed 75.62 Per cent inhibition against Fusarium spp and 66.85 Per cent inhibition against Neoscytalidium spp. In vitro studies with fungicides revealed that even lower concentrations of the Bordeaux mixture (0.25%) completely inhibited the growth of Neoscytalidium spp. Among systemic fungicides, Difenoconazole (0.2%) showed 100 Per cent inhibition, whereas carbendazim + mancozeb (0.05%) was identified as the best combination fungicide against the pathogen. Against Fusarium spp and Rigidoporus spp, given lower concentrations of fungicides i.e., BM (0.25%), Difenoconazole (0.025%), and Trifloxystrobin + Tebuconazole (0.013%) gave 100 Per cent inhibition. Among the chemicals, all concentrations of potassium phosphonate, calcium chloride, and sodium carbonate showed 100 Per cent inhibition of Rigidoporus spp. All doses of calcium chloride showed cent percent inhibition for Fusarium spp, while recommended and double doses of calcium chloride and potassium phosphonate were found effective against Neoscytalidium spp. Compatibility of promising fungicides and chemicals with potent bioagents was carried out based on the results of an in vitro study. Calcium chloride and potassium phosphonate showed maximum compatibility with B. amyloliquefacians and T. asperellum respectively. A pot culture study was conducted to find out the effective treatments against stem canker disease of dragon fruit which is identified as the most prevalent and devastating disease during the study period. Prophylactic application of T. asperellum enriched FYM @100 g plant -1 as well as combined application of calcium chloride (0.7 g/l) and B. amyloliquefacians (600 ml/1.5 ×10 8 CFU) significantly reduced disease severity under in vivo condition. Thus, the present study identified successful management strategies for the fungal pathogens of dragon fruit through proper employment of bioagents, chemicals, fungicides and their combinations. These findings contributed valuable insights for the development of an economical and environment-friendly strategy against the dragon fruit diseases prevailing in southern Kerala.
Occurrence of rotting disease in anthurium
(Kerala Agricultural University, Vellanikara, 2001) Santha Kumari, P; Mary, C A; Dhanya, M K
Purification and immunodetection of banana bract mosaic virus
(Department of Plant Pathology, College of Agriculture, Vellayani, 2004) Dhanya, M K; Rajagopalan, B
The study entitled “Purification and immunodetection of banana bract mosaic virus” was conducted in College of Agriculture, Vellayani, Thiruvananthapuram during 2000-2003. Survey conducted in Thiruvananthapuram district revealed that banana bract mosaic virus (BBrMV) is widely prevalent in different taluks of the district. Zero to 100 per cent variation was observed for disease incidence and per cent disease index was significantly different between taluks. The disease was found to increase with progress of time. Studies on varietal reaction revealed that none of the commonly cultivated varieties were resistant to BBrMV. Symptomatological studies showed that the characteristics symptoms of banana bract mosaic disease were longitudinal irregular reddish streaks on pseudostem, chlorosis of leaves, necrotic streaks on petiole and bract, travellers’ palm appearance, severe reduction in bunch size and formation of malformed fingers. Mechanical transmission of BBrMV through different means, graft transmission and soil transmission were unsuccessful. The aphid Pentalonia nigronervosa Coq. was identified as efficient vector of BBrMV (40 per cent transmission) with pre-acquisition fasting of one hour and acquisition threshold of 30 minutes. Carbohydrate content was less in BBrMV infected plants compared to healthy at all stages of analysis except at bract stage. The phenol content was more in infected banana plants at six months after planting and flag leaf stage whereas it was higher in healthy plants at three months after planting and at bract stage. Content of OD-phenol, protein, activity of peroxidase, polyphenol oxidase and phenylalanine ammonialyase were found to be more in banana bract mosaic virus infected plants. Electrophoretic analysis of BBrMV infected samples through SDS-PAGE revealed the presence of three extra bands (of virus) with molecular weight of 31, 32 and 39 kDa. Electrophoretic analysis of isozymes through native gel revealed the production of peroxidase isozyme in infected plants and the over expression of polyphenol oxidase isozyme in plants infected with BBrMV. Bioassay of endogenous growth regulators showed that the content of auxin, cytokinin and gibberlic acid was less in BBrMV infected fruits compared to healthy. The virus, BBrMV was purified from infected young leaf and the antiserum was developed in New Zealand white rabbit by giving intramuscular injection of partially purified virus. Titre of antiserum was tested using DAC-ELISA and it was determined as 1 : 1024. Electron microscopic studies of infected plant sample revealed that the virus particles were long flexuous rods with an average size of 725 x 12 nm. Detection of BBrMV infected plant parts was done using various immunological techniques like chloroplast agglutination, microprecipitin, Ouchterlony’s agar gel double diffusion test, DAC-ELISA and dot immuno binding assay and all were found to be efficient for the detection of BBrMV. Germplasm collection at Banana Research Station, Kannara were screened for banana bract mosaic disease resistance and found that varieties with ‘A’ genome were found to be more susceptible to the disease compared to those with ‘B’ genome. Screening of varieties at Instructional Farm, Vellayani showed that all of the commonly cultivated varieties were susceptible to BBrMV. For the production of virus free planting material meristem culture technique was attempted using meristems of BBrMV infected suckers. Virus free nature of the developed plants was confirmed through DAC-ELISA and it was found that about 100 per cent plants developed through meristem culture were free of BBrMV. Based on the survey and screening of germplasm collection, it was concluded that strict phytosanitation and use of virus free planting materials, preferably meristem cultured plants will help to manage the disease to a great extent.