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Subject: Plant Pathology × End date: 2004 × Start date: 2004 × Type: Thesis ×
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    ThesisItemOpen Access
    Biological management of phytophthora pod rot of cocoa
    (Department of Plant Pathology, College of Horticulture, Vellanikkara, 2004) Bhavani, R; KAU; Koshi, Abraham
    Phytophthora pod rot (PPR) is one of the serious diseases of cocoa in Kerala. Fifteen isolates of the pathogen were isolated from different locations of Thrissur district and their pathogenicity established. The cultural and morphological characters of 15 isolates of the pathogen like growth on Carrot Agar, mycelial width, length of sporangiophore, sporangial ontogeny, length and breadth of sporangia, L/B ratio, and pedicel length were studied. Based on these characters, the different isolates were identified as Phytophthora palmivora (Butler) Butler. To find out the variations among the isolates of P. palmivora the morphological, virulence and protein profile characteristics of 15 isolates were studied in addition to their sensitivity towards fungicides and antibiotics. Analysis of data on protein profiles and sensitivity towards fungicides did not show much variation among the isolates. But the isolates showed some variations with regard to their morphology, virulence and sensitivity to antibiotics. Among 225 cocoa types screened for host resistance, eight cocoa types viz., G VI 14, G VI 73, G VI 77, G VI 124, G VI 138, G VI 154, G VI 279, G VI 284 showed moderately resistant reaction. Sixty three types were moderately susceptible and rest highly susceptible. Quantitative estimation of epiphytic microflora from cocoa pods yielded more bacteria than fungi and actinomycetes. The epiphytic fungi and bacteria showed antagonistic activity against P. palmivora. Actinomycetes were not antagonistic to the pathogen. Eight fungal and seven bacterial antagonists including standard cultures of T. harzianum and P. fluorescens [Pf (K) and Pf (T)] exhibited maximum inhibition on the pathogen. Studies on the detached pods revealed the efficacy of epiphytic fungal isolate 20F and two bacterial isolates 23B and 24B against the pathogen. The efficient fungal isolate 20F was identified as T. viride Pers. ex. S.F. Gray and the bacterial isolates 23B and 24B as P. fluorescens Pelleroni. The mechanism of antagonism of epiphytic T. viride and standard T. harzianum was studied. The antagonists overgrew the pathogen and showed interactions like coiling, penetration, hyphal malformations and disintegration of host hyphae. Three P. fluorescens isolates including Pf (K) produced HCN and siderophores. T. viride (20F) and T. harzianum were compatible with Akomin 40 and Indofil M45. They were incompatible with Bordeaux mixture, Bavistin and Kocide. Fytolan was partially compatible. The two fungal antagonists were compatible with insecticide phorate, while Sevin was partially compatible. Ekalux, Nuvacron and Endosulfan were incompatible. Ammonium chloride, Rajphos and MOP were compatible with two Trichoderma spp. while ammonium sulphate was incompatible. Two native P. fluorescens (23B and 24B) and standard Pf (K) were compatible with Akomin 40, Indofil M45 and Bavistin and incompatible with Bordeaux mixture, Kocide and Fytolan. With regard to insecticides, the lower two concentrations of Sevin, Ekalux, Endosulfan and Nuvacron were compatible with the bacterial antagonists, while higher concentration was incompatible. Phorate was partially compatible. Fertilizers like Rajphos and MOP were compatible with antagonists. Urea was incompatible. Ammonium sulphate and ammonium chloride were partially compatible. Among different fungicides screened, Bordeaux mixture, Fytolan and Kocide completely inhibited P. palmivora. The lower two concentrations of Akomin 40 and Indofil M45 at all concentrations permitted slight growth. Bavistin was not inhibitory to the fungus. Nuvacron at all concentrations, the highest concentration of Ekalux and two higher concentrations of Endosulfan were inhibitory to the pathogen. Sevin and phorate exerted varying levels of inhibition. Urea and MOP were not much inhibitory to the pathogen. Ammonium chloride, ammonium sulphate and Rajphos showed partial inhibition. Field evaluation of isolates of P. fluorescens [23B, 24B, Pf (K)] and two Trichoderma spp. revealed the efficacy of fluorescent pseudomonads in reducing the incidence of PPR of cocoa. The efficacy was comparable with the recommended fungicides.
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    ThesisItemOpen Access
    Micropropagation of Dendrobium Hybrids
    (Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2004) Sivamani S; LekhaRani C
    Standardisation of protocol for the rapid in vitro propagation of Dendrobium hybrids was attempted. The studies were carried out in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani during 2002-2004. Different explants such as immature leaf segment, stem nodal segment and inflorescence axis were used. The effect of different basal media such as MS (full, half and quarter strength), VW (full strength) and KC (full strength) on these explants was studied. The effect of different levels of plant growth substances such as IAA, NAA, Kinetin and BA and different levels of CW on PLB development and plantlet growth was studied. Plant growth substance IBA along with AC was tried for in vitro rooting of microshoots. Among the various explants tried, stem nodal segment responded well showing early PLB differentiation. Since leaf segment and inflorescence axis did not respond even after 45 days of inoculation, they were abandoned and stem nodal segment explant alone was carried forward for further trials. Out of the different basal media tried with stem nodal segment explant, VW medium exhibited early culture establishment and rapid PLB development. Different levels of the hormone combination, BA and NAA tried showed that BA 2.0 mg l-1 + NAA 2.0 mg l-1 responded with the earliest plantlet development, but number of shoots produced was more in BA 8.0 mg l-1 + NAA 8.0 mg l-1. Combination of BA and IAA at different levels showed that BA 2.0 mg l-1 + IAA 4.0 mg l-1 produced plantlets in a minimum number of days. Number of shoots was maximum in BA and IAA each at 8.0 mg l-1. In the combination of KIN and NAA tried at different levels earlier plantlet development was observed in 2.0 mg l-1 each of the auxin and the cytokinin and the number of shoot produced was highest in 8.0 mg l-1 each of KIN and NAA. Among the different levels of KIN and IAA combination tried, 4.0 mg l-1 each of KIN and IAA was found to be the best for rapid plantlet development. Number of shoots produced was highest in the combination KIN 6.0 mg l-1 and IAA 2.0 mg l-1. Out of the three different levels of CW tried, CW 200 ml l-1 was observed to be the best in terms of early plantlet development and the production of more number of shoots. In vitro rooting of microshoots was the best in half strength MS medium supplemented with IBA 2.0 mg l-1. Addition of AC did not produce any significant effect on root development.
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    ThesisItemOpen Access
    Integration of bioinoculant technology with micropropagation of black pepper (Piper nigrum L.) and standardization of production of arbuscular mycorrhizal fungi (AMF) in transformed roots
    (Department of Plant Pathology, College of Agriculture, Vellayani, 2004) Simi, R; KAU; Sivaprasad, P
    The present investigation was undertaken to evaluate the effect of inoculation with various microbial inoculants such as arbuscular mycorrhizal fungi (AMF), Azospirillum and fluorescent pseudomonads in different combinations on establishment, growth and foot rot tolerance of micropropagated black pepper plantlets and also to standardize transformed root culture technique using Agrobacterium rhizogenes for AMF inoculum production in selected host plant. A general improvement in growth and establishment of the plantlets was observed due to inoculation with AMF, Pseudomonas and Azospirillum. The combined inoculation of the three microbial inoculants showed a significant effect on survival rate and growth characteristics such as plant height and leaf area. There was significant effect on physiological and biochemical characteristics of the plantlets such as stomatal conductance, leaf temperature, relative water content, total phenol, orthodihydroxy phenol, total soluble protein and total carbohydrate content due to inoculation with microbial inoculants which favoured better survival, growth and disease tolerance of the plantlets. All the treatments involving AMF showed a minimum stomatal conductance at early stages of hardening and later it was steadily increased and reached the maximum. The leaf temperature was found to decrease due to treatments with microbial inoculants. Inoculation with the organisms resulted in consistently high values of relative water content at different stages of observation. Combination involving all the three organisms recorded maximum. The total phenol content in plant tissues was highly stimulated by AMF followed by Azospirillum and Pseudomonas. The orthodihydroxy phenol, total soluble protein and total carbohydrate content of the plantlets were also significantly improved by inoculation with all the three organisms. Foot rot disease incidence and intensity was significantly reduced by inoculation with Pseudomonas either singly or in combination with others. AMF alone or in combination also showed relatively low mortality due to foot rot disease. Azospirillum was not effective in suppressing foot rot disease. In the attempt made to make use of transformed root culture technique using Agrobacterium rhizogenes for AMF inoculum production, cucumber was found as the most sensitive host plant. The co-culturing of transformed root with AMF through root colonization was not successful. Further studies are needed to analyse the physiological reasons for the failure of AMF colonization in transformed roots. The present investigation vividly showed that inoculation with microbial inoculants – AMF, Pseudomonas and Azospirillum – is highly beneficial to tissue culture plantlets of black pepper and significant increase in survival rate, growth and tolerance to foot rot disease was achieved. The treatment combination involving all the three organisms was most effective.
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    ThesisItemOpen Access
    Purification and immunodetection of banana bract mosaic virus
    (Kerala Agricultural University;Thiruvananthapuram, 2004) Dhanya, M.K.; KAU; Rajagopalan, B.
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    ThesisItemOpen Access
    Improvement of strains and production technologies for paddy straw mushrooms (Volvariella Spp.)
    (Kerala Agricultural University;Thiruvananthapuram, 2004) Pramod, R.; KAU; Balakrishnan, B.
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    ThesisItemOpen Access
    Evaluation of fluorescent pseudomonads for the management of sheath rot of rice
    (Department of Plant Pathology, College of Agriculture, Vellayani, 2004) Sundaramoorthy, M; KAU; Sulochana, K K
    The study entitled ‘Evaluation of fluorescent pseudomonads for the management of sheath rot of rice’ was carried out at three stages i.e., under in vitro condition, green house condition, and field conditions. First two were conducted at the college of Agriculture, Vellayani, and the third one was conducted at CSRC, Karamana. The pathogen Sarocladium oryzae was isolated from the sheath portion of naturally infected rice plants and its identity was confirmed based on the cultural and morphological studies. Twenty different isolates of fluorescent pseudomonads were isolated from, rhizosphere and phyllosphere of healthy rice plants collected from various locations of southern Kerala. They were screened against Sarocladium oryzae under laboratory condition following duel culture technique. Based on the inhibition zone formation six best isolates were selected. In green house studies, six selected isolates were made into a talc based formulation and applied as seed treatment, seedling root dip and foliar spray. Here, the isolate Pf 16 performed well over other isolates and proceeded further for study under field condition. In the field, powder based formulation of selected isolate Pf16 in three different methods of application viz., seed treatment (ST), seedling root dip (SRD) and foliar spray (FS) in nine combinations were applied. Among the different combinations tried combined application of seed treatment + seedling root dip + foliar spray (ST+SRD+FS) gave considerable reduction in disease incidence and improved biomass yield. Based on the preliminary biochemical studies conducted the isolates Pf16, Pf19 and Pf8 were tentatively identified as Pseudomonas fluorescens biovar II, Pseudomonas aeruginosa, Pseudomonas fluorescens biovar I respectively. The metabolite of promising isolate Pf16 extracted and it formed a clear inhibition zone around the pathogen when antagonism was done.