1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)

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    Phaeophycean seaweed extracts(PSWE): exploration of its antifungal and bio-elicitor properties against major fungal diseases of black pepper
    (Department of Plant Pathology, College of Agriculture, Padannakkad, 2023-09-15) Abinaya, B; Sajeesh, P K
    The present study entitled “Phaeophycean seaweed extracts (PSWE): Exploration of its antifungal and bio-elicitor properties against major fungal diseases of black pepper” was conducted in the Department of Plant Pathology, College of Agriculture, Padannakkad during 2021-2023. Plant samples of black pepper showing typical symptoms of foot rot and anthracnose were collected, and identified through cultural, morphological, and molecular characterizations, as Phytophthora capsici in case of foot rot and Colletotrichum sp. in case of anthracnose. Marine brown algal samples were collected, and the extracts were prepared through four different methods, including acid, alkali, solvent and hot water extraction. The antifungal activity of the phaeophycean seaweed extract (PSWE) at different concentrations was tested using the poisoned food technique (PFT). Hot water extract at 5000 ppm (PSWE (HW 5000)) was recorded as the highest inhibition (100%) of mycelial growth against P. capsici. In case of Colletotrichum sp., hot water extract at 5000 ppm exhibited 20 per cent inhibition. Further, the stability of the active principle in PSWE against high temperature and exposure to sunlight was tested using PFT and agar well diffusion assay (AWDA) against P. capsici. It was found that the active principle was degraded by the high temperature at (121℃ for 20 min.) and sunlight (min. temp. 28℃ and max. temp. 37℃). In PFT, zero per cent inhibition was recorded in high temperature, and 24.76 per cent inhibition was observed in sunlight-exposed PSWE. 17.11 per cent of mycelial inhibition was recorded when treated with high temperature, and 36.6 per cent of inhibition was recorded when exposed to sunlight. The protein and non-protein fractions of the extract were separated using the chloroform: methanol method and tested for antifungal activity. The protein fraction of the extract contributed to 40 per cent of mycelial inhibition through PFT. The molecular weight of the protein fraction was found to be more than three kDa, and the protein fraction with less than three kDa size recorded 42.5 per cent of mycelial inhibition. The size of protein fractions was analysed through SDS-PAGE as 75 kDa to 150 kDa. PSWE (HW 5000) was selected for a pot culture experiment with 12 treatments using the variety Panniyur 1 against foot rot pathogen P. capsici. The treatments were applied, and seven days after inoculation, the least per cent lesion development (PLD) of 33.33 per cent, as well as the least lesion size (3.42 cm), was recorded in PSWE (HW 5000) treatment with pre-inoculation of the pathogen through soil drenching and foliar spray. The highest PLD, 73.33 per cent, and lesion size (5.77 cm) was recorded in PSWE HW (5000) with post-inoculation of the pathogen via soil drenching. Biochemical basis of defense induction in the host plant by PSWE (HW5000) was analysed through the expression of defense-related enzymes. Application of PSWE (HW 5000) through soil drenching and foliar application with pre-inoculation of the pathogen (T5) and same treatment without pathogen inoculation (T9) expressed higher activity of defense-related enzymes such as polyphenol oxidase, peroxidase, superoxide dismutase and catalase. The presence of reactive oxygen species (ROS) was assessed using nitroblue tetrazolium (NBT) and diaminobenzidine (DAB) staining techniques. The build-up of superoxide ions and H2O2 were observed in the leaves of pathogeninoculated plants by their corresponding colour development. In both staining techniques, T5 and T6 exhibited reduced stain intensity compared to plants in control. It was found that PSWE (HW 5000) has noticeable growth promotion activity in black pepper. The growth promotion was highest in the application of PSWE (HW 5000) via soil drenching and foliar application (T9), followed by soil drenching (T7) of PSWE (HW 5000) and soil drenching and foliar application with pathogen inoculated plants (T5). The number of leaves (36.44), shoot and root length (165 and 21.83 cm), shoot and root biomass in fresh weight basis (47.66 and 14.33 g) and in dry weight basis (15.85 and 5.25 g) was higher in T9. The present study revealed that the PSWE (HW 5000) has effective inhibition activity against P. capsici and Colletotrichum sp., and it is effective in managing foot rot disease in black pepper under controlled conditions through the induction of host defense enzymes. Moreover, it enhances plant growth in black pepper. The signaling pathways associated with defense actions and growth promotion mechanisms have to be investigated.
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    Biopriming and foliar apllication of biocontrol agents and endophytes for the management of major foliar fungal diseases of bush cowpea
    (Department of Plant Pathology, College of Agriculture , Vellayani, 2023-05-26) Aswathy ,V S.; Radhakrishnan, N V
    The study entitled “Biopriming and foliar application of biocontrol agents and endophytes for the management of major foliar fungal diseases of bush cowpea” was conducted at College of Agriculture, Vellayani and Coconut Research Station, Balaramapuram during 2020-2022. The objective was to develop best ecofriendly management practice involving biopriming, foliar application of endophytes and biocontrol agents for the control of major foliar fungal diseases in bush cowpea with special emphasis on Cercospora leaf spot and anthracnose. Symptomatology and etiology of anthracnose and Cercospora leaf spot were studied under field condition from different locations in Trivandrum district viz., Vellayani, Pappanchani, Venganoor, Balaramapuram, Nedumangad and Parassala. The pathogens were isolated and studied their morphological characteristics. Bush cowpea seeds were collected from five agro-ecological zones of Kerala viz., Northern, High range, Central, Special problem and Southern zones and the seeds were assessed for both externally and internally seed borne microflora. Percentage of infection was calculated by blotter method. The lowest percentage of infection was found in seed samples collected from Wayanad (16.7%) and the highest in Thrissur (38.2%). The diseased leaf samples showing anthracnose were collected from five locations of Thiruvananthapuram district and isolated Colletotrichum gloeosporioides from each location. Pathogenecity of isolated pathogen was proved by detached leaf assay and seedling assay. Vellayani isolate (C1) was found to be the most virulent pathogen and recorded lesion size of 4.33cm and 1.82cm in detached leaf assay and seedling assay on seventh day respectively. The isolate C1 was used for further studies. In vitro evaluation of biocontrol agents like Trichoderma asperellum T6 (KAU), Trichoderma koningiopsis (TRKR2), Trichoderma harzianum (TRMW2), Piriformospora indica (No. INBA 3202001787), Bacillus amyloliquiefaciens VLY 24, Bacillus velezensis (CBRE5), Bacillus amyloliquefaciens (CBSE5) and Pseudomonas fluorescens PN026 (KAU isolate) against Colletotrichum gloeosporioides and Cercospora sp. were carried out. Dual culture method of Colletotrichum gloeosporioides against biocontrol agent recorded highest percentage inhibition of mycelia by T. asperellum (64.76) followed by Trichoderma strain TRKR2 (52.63) which was on par with bacterial strain CBRE5 and least for Psuedomonas fluorescens. In vitro pathogen suppression by spore germination assay on Cercospora sp. by 145 biocontrol agents revealed that maximum inhibition of conidia germination was by T. asperellum (36.25 %) followed by Trichoderma strain TRKR2 and Trichoderma strain TRMW2 whereas least inhibition percentage was observed with Piriformospora indica (14.96). Peroxidase and polyphenol oxidase assay on bush cowpea pods and seeds showed that fungus infected tissues had relatively higher activity of these oxidase enzymes in comparison to healthy pods. Enzyme activities were higher in pods and seeds treated with Bacillus strain CBRE5, T. asperellum and Trichoderma strain TRKR2. Standardization of priming techniques revealed that soaking of seeds for 2h was found effective for Trichoderma asperellum, Bacillus velezensis (CBRE5) and Bacillus amyloliquiefaciens VLY 24 and 4h for Trichoderma strain TRKR2. The soaking duration is followed for the treatments in in vivo studies. Based on the in vitro studies, the best three treatments viz., Trichoderma asperellum, Trichoderma strain TRKR2 and Bacillus strain CBRE5 were taken for in vivo studies. In vivo studies on the effect of seed biopriming and spraying of biocontrol agent suspension at 4 leaf, 50 per cent, flowering and pod set stages revealed lowest disease severity of anthracnose was recorded for Trichoderma asperellum treated plants with disease suppression over control 41.74 per cent followed by carbendazim, Trichoderma strain TRKR2 and Bacillus strain CBRE5. In the case of Cercospora leaf spot Trichoderma asperellum treated plants shown highest disease suppression (63.47%) over control followed by carbendazim, Trichoderma strain TRKR2 and Bacillus strain CBRE5. Bacillus strain CBRE5 recorded least disease suppression over control in anthracnose and Cercospora leaf spot while comparing other treatments. Highest number of pods per plant (34.75), seeds per pod (15.25), plant height (46.05 cm) and yield (232.47 g) were shown by bacterial strain CBRE5 treated plants. Thus, the present study indicated that the seed biopriming for 2 h along with foliar application of Trichoderma asperellum suspension at 4 leaf , 50 per cent flowering and pod set stages was most effective treatment for the management of major foliar fungal diseases like anthracnose and Cercospora leaf spot of bush cowpea whereas seed biopriming for 2 h along with foliar application of Bacillus velezensis suspension at 4 leaf stage, 50 per cent flowering stage and pod set was the best treatment in plant growth promotion in vivo which could be used as an eco-friendly measure to produce safe to eat crop.
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    Characterization,Documentation and Management of fungal diseases of selected forest nursery seedlings of Kerala
    (Department of Forest Resource Management,College of Forestry, Vellanikkara, 2024-06-04) Kiran Mohan; Gopakumar, S
    Disease free planting stock significantly ensures better field survival, thereby reducing the burden of economic loss and meeting the targets of climate change mitigation. Teak (Tectona grandis L.f.), Indian beech (Pongamia pinnata (L.) Pierree), custard apple (Annona squamosa L.), guava (Psidium guajava L.), and Indian laburnum (Cassia fistula L.), which are extensively used for afforestation programs in Kerala, are severely affected by fungal pathogens at the nursery stage. Hence, an investigation was undertaken to identify the major fungal diseases associated with the above mentioned seedlings in Kerala and to assess the efficacy of selected fungicides and bio-control agents through in vitro and in vivo studies. A purposive sampling survey was conducted in 40 forest nurseries across the state during summer (Feb-May), monsoon (June-Sept), and post-monsoon (Oct-Jan) seasons in 2021 to monitor the occurrence of fungal diseases and collect diseased samples. Out of the seven major fungal diseases, three from teak, and one each from the other four tree crops were observed respectively. Major fungal diseases noticed from teak seedlings include teak leaf rust (TLR), teak die back (TDB), and teak leaf spot (TLS). Pongamia foliar disease (PFD) from Indian beech, annona die back (ADB) from custard apple, guava leaf spot (GLS) from guava, and cassia die back (CDB) from Indian laburnum are the other selected major diseases. Teak leaf rust (TLR) was the most common and severe foliar disease observed in teak from various nurseries across the state and irrespective of the five agro-ecological zones (AEZs), the maximum Percent Disease Index (PDI) and Percent Disease Severity (PDS) (60.0% and 52.8%, respectively) recorded from Chettikkulam (AEZ IV- High Hills) in the monsoon season. Teak die back (TDB) disease (PDI 62%) was observed only from Edayazham (AEZ I- Coastal Plain) during the pre-monsoon period. Teak leaf spot (TLS) was noticed only from Kudayathoor nursery (AEZ III- Foothills) during the pre-monsoon season. In Indian beech, PFD was observed from different nurseries irrespective of AEZs during the study period, and Chettikkulam (AEZ IV- High Hills) recorded the maximum PDI (80.0%) and PDS (63.2%) in the monsoon. The major disease of custard apple seedlings, i.e., ADB, was observed from different nurseries, and the maximum PDI (55.0%) was recorded at Kanakappalam (AEZ III- Foothills). Guava leaf spot (GLS) was noticed as the common disease in guava seedlings during the survey, and the maximum PDI (60.0%) and PDS (55.0%) were recorded at Varanadu nursery (AEZ I- Coastal Plain). In Indian laburnum, CDB was found to be a common disease throughout the state, and at the location Kattamudy (AEZ IV- High Hills), it recorded the maximum PDI (50.0%). Based on the available data during the study period, TLR showed a positive correlation with temperature and a negative correlation with rainfall. However, PFD showed a negative correlation with temperature and a positive correlation with rainfall and ADB showed a positive correlation with rainfall as well as relative humidity. In the case of GLS, no common trend was detected, and CDB showed a negative correlation with relative humidity. The typical orange colour urediniospores on the backside of the affected teak leaf characterizes TLR symptoms. Meanwhile, TLS is noticed as scattered black spots with a greyish center. Whereas TDB originates as leaf blight and subsequently spreads throughout the seedlings. Symptoms of PFD are observed as irregular chlorotic spots on the adaxial side and black dot-like sporodochia on the abaxial side. Leaf yellowing, followed by inward curling and the further spread of a necrotic area throughout the seedling, is the typical symptom of ADB. Meanwhile, GLS is noticed as grey to cream-colored blighted region surrounded by black, brown, or violet round margin. In the case of CDB, the initial symptom of leaf blight later spreads throughout the seedling. The pathogenicity of the major foliar diseases (TLR, TLS, PFD, GLS) was proven using Mycelial Bit Inoculation Method (MBIM), Micro Droplet Inoculation Technique (MDIT), and inoculation with the infected leaf method. Spore suspension method and mass multiplied pathogen in the substrate method were adopted for major root diseases (TDB, ADB, CDB). The obligate parasite (TLR) was identified as Olivea tectonae based on the morphological characters of urediniospores and all other major pathogens were identified upto the species level based on cultural as well as morphological characters, coupled with characters of amplified gene regions (ITS region and LSU region). The TDB pathogen was thus identified as Colletotrichum fruticola, TLS pathogen as Corynespora cassiicola, PFD pathogen as Cladosporium tenuissimum, ADB pathogen as Colletotrichum siamense, GLS pathogen as Colletotrichum siamense, and CDB pathogen as Alternaria alternata. In vitro evaluation studies revealed that carbendazim 12% + mancozeb 63%, mancozeb, and propineb stood out against major foliar diseases. However, in vivo experiment results showed that carbendazim 12% + mancozeb 63%, mancozeb, hexaconazole, and Trichoderma asperellum were observed to be efficient against major foliar diseases. Similarly, carbendazim 12% + mancozeb 63%, mancozeb, Bordeaux mixture, and hexaconazole showed promising results against major root diseases during in vitro as well as in vivo experiments.
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    Fungal diseases of selected medicinal plants of Kerala
    (Department of Plant Pathology, College of Horticulture, Vellanikkara, 1991) Sukumara Varma, A; Abi Cheeran
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    Studies of fungal diseases of forage grasses
    (Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Sasidharan, R K; Padmakumari, G
    A study of different fungal diseases of various forage grasses cultivated in Kerala showed that H. gramineum, F. graminearum and C. trifoli are prominent pathogens. Best growth of H. gramineum and F. graminearum were in Czapek (Dox) agar, while Curvularia trifoli grew best in Richards medium. All the pathogens were favoured by a temperature of 250 C. All the graminaceous hosts studied were susceptible to H. gramineum and F. graminearum. However, Curvularia trifoli infected paddy, congosignal and para grass, among the graminaceous hosts. Susceptibility to non-graminaceous hosts indicated that none of the pathogen’s could infect eupatorium, clerodendron, Papaya and Jack. In vitro evaluation of fungicides revealed that Bordeaux mixture 1 per cent and 1.5 per cent were found to be superior in inhibiting the growth of H. gramineum, F. graminearum, and C. trifoli. A field trial carried out has shown that blight disease caused by H. gramineum in hybrid napier was least in treatment combination of Dithane M-45 0.3 per cent, with NPK @ 200:50:62.5 kg/ha. In general, higher dose of potash favoured disease management. A fungicidal trial carried out revealed that Dithane M-45 0.3 per cent and Bordeaux mixture 1 per cent were effective in controlling blight disease of hybrid napier.