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ThesisItem Open Access Transmission, properties and hostrance of snake gourd mosaic virus(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Raghunadhan, D; KAU; Rajagopalan BSnake gourd mosaic virus disease commonly occurring in Kerala was investigated. The symptoms appeared as typical mosaic mottling with dark green and light green patches. The leaves were much reduced in size, variously crinkled and deformed. Diseased plants were severely stunted and produced only a few flowers and fruits. Transmission studies showed that the virus could be transmitted through mechanical means, grafting and by aphid vectors. The virus was found to be transmitted by the aphids, Aphis gossypii Glov., Aphis malvae Koch. and Aphis craccivora Koch. Among the three species of aphids, A. gossypii was found to be the most efficient vector. Investigations on the physical properties of the virus revealed that the virus had a thermal inactivation point between 70-750C, Dilution end point between 1:10000-1:50000, longevity in vitro between 96-120 h at room temperature (28-300C), and between 144-168 h at 100C. The minimum acquisition feeding and inoculation feeding period were found to be 30 s and 1 min respectively. But the percentage of transmission was maximum when an acquisition feeding of 20 min and inoculation feeding of 1 h were given. Influence of starvation before acquisition and inoculation feeding proved that pre-acquisition starvation for 1 h produced maximum infection but post-acquisition starvation decreased the per cent infection. The vector was found to retain the virus for 1 ½ h. A single aphid could transmit the virus to healthy test plants, but maximum percentage of transmission was obtained with 10 aphids. Host range studies showed that the virus was restricted to the members of the family chenopodiaceae, compositae, cucurbitaceae and solanaceae. Serological studies showed that snake gourd mosaic virus is related to cucumber mosaic virus and pumpkin mosaic virus. Varietal screening trial with seven varieties of snake gourd revealed that all the varieties were susceptible to snake gourd mosaic virus infection. Studies on estimation of loss revealed that early infection reduced significantly the length of vine, number of leaves, number of flowers, number of fruits and yield, whereas late infection did not produce significant effect, on both the varieties tested. There was significant reduction on leaf area and internodal length on plants inoculated at all stages of growth.ThesisItem Open Access Varietal variation for nodulation by Rhizobium in Greengram(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Padmanabhan Nair, V; KAU; Sasikumar NairThe present investigation on varietal variation for nodulation by Rhizobium in greengram was conducted at College of Agriculture, Vellayani, Trivandrum. The field trial for host varietal specificity was done at C. S. R. C Karamana of Kerala Agricultural University and in a farmer's plot at Pattom, Trivandrum. Rhizobium capable of nodulation in greengram was isolated from 10 out of 14 different soil samples collected from Alleppey, Quilon and Trivandrum Districts. The ten isolates of Rhizobium obtained initially were screened for their nodulation efficiency under aseptic pot culture conditions by using the greengram variety C0-3. In this screening it was found that the increase was maximum in R5 treatment where 188.30 nodules were formed per plant when compared to only 8.33 in the uninoculated control. The fresh and dry weights of nodules formed 455 and 119.33 mg respectively were also maximum in the R5 treatment. A significant increase in root length was obtained only in two of the above treatments R6 and R9. The Rhizobium culture R5 isolated from C.S.R.C. Karamana, Trivandrum was found superior to all other local isolates of rhizobia. Besides the required minimum increase in dry weight of plants from Rhizobium inoculation, 50 per cent increase in dry mass over uninoculated control (as per the Indian Standard Institution Specifications for Rhizobium inoculants is 0268-1976) was obtained only with this isolate of Rhizobium.ThesisItem Open Access Biology of termitomyces species and standardisation of its cultivation techniques(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Sreelatha, Nair; KAU; Bhavani, Devi SState wide survey was conducted during the South West and North East monsoon periods in 1984-85 and nine species of Termitomyces were collected and identified from thirty two localities of the State. Among the nine specices, T. heimii, T. clypeatus and T. microcarpus var. Santalensis were the first record for Kerala. Detailed description of the morphological and microscopical characters of the nine species collected were recorded in the data sheet along with the ethiono mycological and gastronomic details. All termitomyces species were commonly consumed by the local people during the seasons and were known by different vernacular names. Observations on the periodicity frequency and intensity of occurrence of the nine species showed that T. microcarpus, T. microcarpus var. santalensis and T. robustus were the most commonly occurring species abundantly distributed throughout the State, irrespective of soil type. Their habit of occurrence also revealed that T. robustus and T. striatus were always seen solitary while all the other species occur gregariously consisting of ten to hundred sporocarps. The results relating to the periodicity of occurrence of different species of Termitomyces indicated a post monsoon maxima for the seven species belonging to subgenus Eutermitomyces and a monsoon maxima for the two species viz. T. microcarpus and T. microcarpus var. santalensis of the subgenus pratermitomyces. Studies conducted to observe the developmental morphology of T. robustus from mycelial stage till maturity revealed that different stages of development can be divided into eight stages viz. spherule, clove bud, primordial elongation, pseudorhizal stage, epigeal button, epigeal egg, epigeal elongation and mature stage. The first four stages of development were hypogeal and took 192 h to attain the 4th stage while the next four epigeal stages took only 96 h to reach the mature stage. Critical observations of the different stages of growth and development of the sporocarp revealed the significance of pseudorhiza and perforatorium in the hypogeal development of the sporocarp. The data relating to the temperature and humidity of the comb of T. clobulus and surrounding the environment showed insignificant variations. A comparative study of the chemical composition of the comb of T. robustus and T. heimii showed little difference in the total moisture content, cellulose, carbon, nitrogen and pH. Isolation of other fungi from the termitaria obtained from different localities revealed the occurrence of 19 species of fungi belonging to 12 genera indicating their possible role in cellulose decomposition in the environment. Among the nineteen species isolated, species of Aspergillus and xylaria were found to be the predominant fungi in the combs. Species belonging to Odontotermis was found to be the most common termite associated with different species of Termitomyces in Kerala. O. obesus was always found to be associated with its fungus mutualist Termitomyces microcarpus. The beetle Amblyopus cincetipinnis was found to be the common pest of Termitomyces. The beetle was found to interest and feed the emerging as well as mature sporocarps and turn them unfit for consumption. Field trials on the effect of soil moisture for the production of sporocarps revealed that the number of sporocarps emerged from the daily irrigated plots were more when compared to the non irrigated plots. Among the eight media tested Rebeeca’s selective medium was found to be the only medium to support scanty mycelial growth of T. robustus. Maximum mycelial growth was observed at 300C. Experiments on the effect of light in mycelial growth of T. robustus showed no significant differences in growth. In vitro studies indicated that cellulose was the best source of carbon followed by maltose and lactose. Maximum protein content was observed in T. heimii when compared to other species. Trials on the suitability of different substrates for spawn production failed to support any mycelial growth of the fungus. Dehydrated sporocarps preserved in sealed polythene covers showed maximum shelf life when compared to other ‘methods of preservation. Though fresh sporocarps could be stored in polythene bags for only 48 h it was possible to extend their shelf life when preserved in brine solution. Blanching and pickling and were the other method of preservation of the sporocarps of Termitomyces tried.ThesisItem Open Access Studies on the leaf spot diseases of oil palm (Elaeis guineensis jacq.) in Kerala(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Thomas, John; KAU; Karunakaran, PA survey was conducted in the oil palm growing areas of Palode, Anchal, Kulathupuzha and Thodupuzha. Six leaf spot diseases were noticed. They include the leaf spots caused by Bipolaris hawaiiensis, Botryodiplodia theobromae, colletotrichum gloeosporioides, curvularia geniculata, fusarium pallidoroseum and phoma sorghina. All these are new records from India. Out of the six leaf spot diseases, the leaf spot caused by C.gloeosporioides was found to be the most severe causing damage in all the four plantations and it was considered to be of major economic importance. Other diseases recorded during the present investigation were of minor importance. Inoculation studies with six leaf spot causing pathogens showed that injury to leaves makes the plant more susceptible to leaf spot disease. The percentage of infection was more in injured leaves than in uninjured leaves. In invitro evaluation of fungicides showed that Bordeaux mixture, Dithane M-45 and Foltaf were effective, Bavistin controlled all the pathogens, except B. hawaiienis and C. geniculata. The leaf spot disease caused by C.gloeosporioides was observed in all oil palm plantations in Kerala in a serious proportion, especially during monsoon periods. Field evaluation of fungicides against the above disease indicated that Bavistin, Dithane M-45 Foltaf and Cuman L were effective.ThesisItem Open Access Influence of soil solarisation on soil microflora plant growth and incidence of diseases(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Chandran, C R; KAU; Peethambaran, C KThe influence of solarization on soil microflora, plant growth and incidence of disease was studied during 1985-87 at Madavoor on collar rot of cowpea caused by Rhizoctonia solani Kuhn. The effectiveness of solarization was tested in open and partially shaded conditions in coconut garden using 0.05mm transparent polythene sheets as the mulch. The atmospheric temperature during the period of solarization ranged from 28.50C to 34.20C. The increase in soil temperature, as a result of solarization was more in open field than in partial shade. The soil temperature variation in open nonsolarized treatments was 100C while it was 12.50C in solarized plots. Corresponding figures for partially shaded conditions were 5.50C and 70C respectively. Maximum soil temperature recorded at 15cm depth in open solarized soil was 42.50C. Based on the experimental data two statistical models (1) for predicting soil temperature under polythene mulch and (2) for predicting collar rot of cowpea were developed during the study. Soil solarization significantly reduced collar rot of cowpea. Least incidence of the disease (3.6%) was noticed in open nonirrigated solarized treatments while maximum incidence (24%) was recorded in shade irrigated control. The interaction effect of shade, solarization and irrigation was not significant. Solarization reduced the total fungal population in open conditions while the population of bacteria was not significantly changed. In the case of actinomycetes population, a slight increase was noticed in solarized plots. The nematode population was significantly reduced by solarization in open field. Eventhough solarization substantially reduced weed population in open, it was less effective under partially shaded conditions. Growth parameters like height and number of leaves per plant were not significantly influenced by solarization. But it improved the stand of the crop and yield. An yield increase ranging from 7.62 to 21.69 per cent was obtained in solarized plots over the control. Availability of nitrogen, phosphorus and organic carbon was improved by solarization while there was no change in the level of potassium, calcium, PH and electrical conductivity.ThesisItem Open Access Epidemiology, symptomatology and control of leaf scald disease of rice(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Jayaram, K P; KAU; Chandrasekharan, MRhynchosporium oryzae, the causal organism of leaf scald disease of rice, was isolated and studies were conducted on the symptomatology, morphology, cultural characters, host range, toxin production and control of the pathogen. On rice plants, lesions were found to develop from the tips of leaves and the characteristic symptom was the formation of concentric zonations with brown margins, on the lesions. Symptoms were also found to occur on the leaf sheaths. Studies on the morphology of the fungus revealed that mycelium was hyaline, septate, and 2 to 3 µm broad. Conidia were two-celled and fusiform, measuring 10 to 14 µm x 3 to 4 µm. The organism was grown on different solid and liquid media. The studies revealed that among solid media, potato dextrose agar (PDA) was most suited for growth and sporulation of the fungus. Among liquid media, maximum dry weight of mycelium was obtained in potato dextrose broth. Sporulation was found to be maximum in potato dextrose broth and peptone glucose medium. Studies on the effect of varying levels of Nitrogen (peptone) and carbon (glucose) on growth and sporulation of the organism revealed that maximum dry weight of mycelium was obtained at 1 per cent Glucose and 1 per cent Peptone. Sporulation was maximum at lower levels of Carbon – 0.5 and 0.25 per cent. Starch was found to be the most suited source of Carbon for promoting the growth of the organism, and Peptone, the most suited source of Nitrogen. Studies showed the temperature of 300C and PH of 6.5 were optimum for the growth of the organism. Sporulation was found to be maximum at 25-300C. Of the twelve rice varieties tested, Mo-6 and Cul-25331 were found to be most resistant, and Mo-7, cul-204, Cul-153-1 and Jaya proved to be most susceptible. Studies conducted on the toxin produced by R. oryzae in culture revealed that the toxin by itself was able to cause typical leaf scald symptoms when sprayed on healthy rice plants. The toxin also inhibited germination of brinjal and paddy seeds and caused an appreciable decrease in the length of radical and plumule of paddy seeds. Host range studies showed that Cynodon dactylon, Cyperus rotundus, Hemidesmus indicus and Panicum repens developed scald symptoms when inoculated with the fungus. Laboratory studies revealed that cent per cent inhibition of spore germination was obtained by using Carbendazim at 500 ppm, 1000 ppm and 1500 ppm, Tridemorph at 1500 ppm, Captafol at 2000 ppm, 2500 ppm and 3000 ppm and Mancozeb at 2000 ppm, 2500 ppm and 3000 ppm. Studies following poisoned food techneques showed that Carbendazim at 500 ppm, 1000 ppm and 1500 ppm Tridemorph at 1000 ppm and 1500 ppm, Mancozeb at 2000 ppm, 2500 ppm and 3000 ppm, caused cent per cent inhibition of radial growth of R. oryzae. Pot culture trial with five fungicide revealed that after 2 sprays, Carbendazim, Mancozeb and Captafol were superior to Tridemorph and Carboxin in keeping the disease under check. Field trial showed that all the four different fungicides were effective in reducing disease intensity. The plots sprayed with Carbendazim recorded the least disease intensity. Studies on antagonistic activity of phylloplane mycoflora of rice on R. oryzae showed that Chaetomium globosum and Penicillium oxalicum might have some antagonistic effect on R. oryzae.ThesisItem Open Access Studies of fungal diseases of forage grasses(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Sasidharan, R K; KAU; Padmakumari, GA 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.ThesisItem Open Access Biological control of Rhizoctonia solani Kuhn on rice using mycoparasites(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Viswakumar, P; KAU; Chandrasekharan Nair, MThe present investigation was undertaken to assess the effects of mycoparasite-fungicide combinations on the intensity of sheath blight disease, and also the effect of the same on the rhizosphere and phylloplane mycoflora of rice. An attempt has also been made to identify efficient mycoparasites of Rhzoctonia solani naturally present on the rhizosphere and phylloplane of rice plants. Several fungi isolated from the rhizosphere and phylloplane of rice plants were found to exhibit strong antagonistic action against R. solani, in vitro. Antagonistic fungi such as Trichoderma viride, T. harzianum, Aspergillus niger caused granulation, vacuolation and finally disintegration of R. solani hyphae. The ability of the antagonists to produce volatile as well as diffusible metabolites was also assessed. T. viride was found to be very efficient in inhibiting the growth of R. solani, as a result of the diffusible as well as volatile metabolites produced by the fungus. T. harzianum was also very efficient in inhibiting growth of R. solani. When the antagonist T. viride was mass cultured in various growth substrates and tried for their efficacy as potential biocontrol agents of sheath blight disease of rice, rice bran as well as wheat bran turned out to be the best growth substrates. Under pot culture conditions, where the efficacy of various mycoparasite- fungicide combinations in checking sheath blight was assessed, T. viride was the best mycoparasite and edifenphos the best fungicide. The rhizosphere mycoflora was enhanced by application of mycoparasite, especially T. viride and T. harzianum. Among fungicides application of edifenphos resulted in increased rhizosphere mycofloral population. In the case of phyllooplane mycoflora application of mycoparasites have a suppressive effect. Treatments of edifenphos increased phylloplane mycofloral population. Under field conditions also T. viride emerged as the best mycoparasite and ediphenphos as a superior fungicide in checking sheath blight. T. viride + ediphenphos was also found to be very efficient in controlling sheath blight disease. The highest grain and straw yields were obtained in treatment with the mycoparasite T. viride, and fungicide edifenphos. The treatment combination T. viride + edifenphos also gave the highest yield. In the case of rhizosphere mycoflora application of mycoparasites enhanced the population. Mycoparasites were found to have a suppressive effect on the fungal population on the leaf surface.