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ThesisItem Open Access Antibiotic producing and antagonistic microorganisms in the forest soils of Kerala(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1988) Vinod, P B; KAU; Sukumara Varma, AThe antibiotic producing and antagonistic fungi, actinomycetes and bacteria in the evergreen forest soils of Ladysmith forest of Thariyode in Wynad, and Cheriyakanom forest of Thekkadi in Idukki districts of Kerala State were studied. The phanerogamic flore around the sites of soil sample collection in both localities were identified. The total microbial population was studied in relation to the depth of soil. The microbial population was maximum in the top layer and decreased with increase in depth of soil. The total microbial population was higher in Idukki and in both districts, population of bacteria was maximum followed by actinomycetes and fungi. A diversified group of fungi consisting, Mucor, Syncephalastrum, Trichoderma, Microascus, Cunningphamella, Absidia, Aspergillus, Penicillium, Talaromyces, Paecelomyces and Fusarium was present. Three types of actinomycetes viz. Streptomyces sp. with straight sporophores, flexuous sporophores and fascicled sporophores were present while four types of bacteria viz., B. subtilis. Bacillus sp. identical to B. subtilis, Bacillus sp. with small cell and fast growth in NA and Bacillus sp. with small cell and slow growth in NA were present. Antagonistic properties of the isolated were studied with the test organisms Pythium myriotylum, Phytophthora palmivora and Rhizoctonia soleni. Mucor sp. and Cunninchamella elegans showed intermingling and overgrowth with all the test organisms while Absidia corymbefera, Syncephalastrum racemosum, Aspergillus meleus, A. tarreus, Microascus cinereus and Fusarium oxysporum showed this character with P. myriotylum and P. palmivora. Intermingling and overgrowth character was observed in Paecelomyces lilacinus with P. palmivora and R. solani whereas A. versicolor and three species of streptomyces showed this character only with P. palmivora. Mutual inhibition on contact was exhibited by Talaromyces wortmannii with all the three test organisms, while A. versicolor and Streptomyces spp. with flexuous sporophores and fascicled sporophores showed this character with P. myriotylum and R. solani. This character was observed in case of A. corymbefera, S. racemosum, A. meleus, M. cinereus, F. oxysporum and Streptomyces sp. with straigtht sporophores, with R. solani while P. lilacinus showed this with P. myrootylum. Mutual inhibition at a distance was shown by Penicillium citrinum, P. simplicissimum, B. subtilis and the other three Bacillus spp. when tested with P. palmivora and R. solani, but A. terreus showed this reaction only with R. solani. Inhibition at a distance and disintegration of test organism was shown by A. niger with P. myriotylum and R. solani while P. citrinum and P. simplicissimum showed this character only with P. myriotylum. All the three spp. of Trichoderma showed die – back and disintegration of all the three test organisms, while A. niger showed this character only with P. palmivora and A. sydowii showed this character with R. solani only. streptomyces sp. with straight sporophores, B. subtilis and the other three Bacillus spp. showed this character with P. myriotylum alone. Inhibitory properties of antagonists using cell free culture filtrates were estimated and found that A. niger inhibited 100 per cent growth of all the three test organisms while P. citrinum, P. simpliciccimum and B. subtilis showed 100 per cent inhibition of P. myriotylum and a range of 67-87 per cent in case of P. palmovora and R. solani. A. terreus did not inhibit P. myriotylum and P. palmivora, but inhibites 78 per cent of R. solani. All the three Trichoderma spp. moderately inhibited all the three test organisms (13-26 per cent) while A. sydowii showed 20 per cent inhibition of R. solani only. Antibiotic property of the antagonists was determined and P. citrinum exhibited maximum, equivalent to 325 ppm tetracycline followed by Streptomyces with straight sporophores having 250 ppm. T. longibracheatum, P. simplicissimum and A. versicolor recovered antibiotic property equivalent to 150 ppm tetracycline hydrochloride while the other isolates had < 100 ppm equivalence of tetracycline hydrochloride.ThesisItem Open Access Management of sheath blight disease of rice in relation to the population of the pathogen in soil(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1987) Shaji, Alexander; KAU; Rajan, K MLaboratory, pot and field experiments were carried out to study the role of various physical, chemical and biological factors on the management of sheath blight disease of rice caused by Rhizoctonia solani Kuhn. (Thanatephorus Cucumerlis (Frank) Donk). Populations of total fungi, bacteria and actinomycetes in soil were enumerated at different stages of growth of the crop in order to assess their role in reducing the intensity and incidence of sheath blight disease. Results of the investigation revealed that the pathogen can be managed by deeper ploughing followed by submergence of the soil for a minimum period of two months. Amendments like glyricidia leaves, rice husk, lime and non edible oil cakes of marotti, neem and punna were useful in reducing the severity and spread of the disease. Fungicides like carbendazim and ediphenphos and the herbicide benthiocarb were also efficient in managing the disease. Rotation of rice with crops like tapioca, banana and brinjal was also useful. It was seen that amendments stimulated the population of saprophytes like Trichoderma viride in soil which are antagonistic to R. solani resulting in a subsequent reduction in population of the pathogen. In spite of the reduction in severity and spread of the disease, grain and straw yields were not enhanced by the treatments. More elaborate field trials are to be undertaken before landing on any ultimate conclusion regarding the use of these practices as tools for disease management.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 Studies on the seed borne diseases of rice in Kuttanadu(Department of Plant Pathology, College of Agriculture, Vellayani, 1986) Jose Joseph; KAU; Susamma PhilipSeveral fungi were isolated from the seeds of twelve varieties/cultivars of rice collected from different localities of Kuttanadu, the major rice growing tract of Kerala. Fungi were encountered extrenally as well as internally. Among the externally seed borne fungi, Aspergillus flavus was the most common with its occurrence on nine varieties followed by Bipolaris oryzae and Curvuleria lunata. Other fungi included Rhizopus stolonifer, Chaetomium gracile, Syncephalestrum racemosum, Fusarium moniliforms, Trichoderma virde, Sarocladium oryzae. Aspergillus niger, Alternaria padwickii, Fusarium gramineazum, Piricularia oryzae, A. fumigatus, A. quadrilineatus, Nigrospora oryzae and Penicillium spp. Among the varieties Jaya was found to harbour the maximum fungal population. The germination percentage was not found to be affected due to seed inoculationwith the predominant fungi viz. A. flavus, A. padwickii, B. oryzae, C. lunata and S. oryzae.ThesisItem Open Access Epidemiology and control of sheath rot disease of rice(Department of Plant Pathology, College of Agriculture, Vellayani, 1986) Krishnakumaran Nair, B; KAU; Chandrasekharan Nair, MStudies on symptomatology, epidemiology and control aspects of sheath rot disease of rice caused by Serocladium oryzae Cams & Hawksworth (= Acrocylindrium oryzae Saw.) were done in detail. The disease initiated as purplish-brown oblong lesions on the sheath of the flag leaf. At maturity lesions enlarged in size with grey -white centres and often covered the entire flag leaf sheath. Panicle often did not emerge but choked inside the affected sheaf itself. Artificial inoculation studies showed that under sufficient humid conditions the pathogen took an average five to eight days for initiation and 15 to 20 days for the complete development of the disease in rice plants. The pathogen was isolated from four naturally infected rice varieties, collected from three different culture (isolates viz., S1, S2, S3, S4, S5, S6 & S7) were selected based mainly on symptomatological variations and their comperative morphological characters were studied in detail. No appreciable differences were noticed in the morphological characters between isolates.ThesisItem Open Access Properties, host-range and control of cowpea mosaic virus(Department of Plant Pathology, College of Agriculture, Vellayani, 1987) Sreelakha, L; KAU; Balakrishnan, SStudies were conducted on the cowpea mosaic virus disease commonly occurring in cowpea plants (Vigna unguiculata (L.) Walp) in Kerala The major symptoms caused by cowpea mosaic virus infection in cowpea plants were vein banding, inter- veinal chlorosis mosaic mottling and general stunting of the plants. Transmission studies showed that the virus could be transmitted through mechanical means, grafting, through seeds and by means of aphid vectors. The virus was found to be transmitted by the aphids, Aphis craccivora. Aphis gossvpii and Aphis malvae. Among the three species of aphids, Aphis craccivora was found to be the most efficient vector. The percentages of transmission obtained by A. craccivora, A. gossypii and A. malvae were 90,65 and 45 respectively. Studies on the physical properties of the virus revealed that the virus had a thermal inactivation pointbetween 50 and 55°C, dilution end point between 10“"* and —2 10 , longevity in vitro of 8 h at room temperature and24 h at 8°C. The minimum acquisition feeding and inoculation feeding period were found to be 30 s each. But the percentage of transmission was maximum when an acquisition feeding of 10 rain and inoculation feeding of 15 rain were given. Pre-acquisition fasting up to a period of 2 h increased the percentage of transmission, whereas the post-acquisition fasting decreased the efficiency of transmission. The vector was found to retain the virus for 1-2 h. Maximum percentage of transmission was obtained with 10 aphids and the symptoms appeared within 14 days after inoculation. Host-range studies revealed that the virus is restricted to the family Leguminosae and Chenopodiaceae. Varietal screening trial with ten different varieties of cowpea showed that all the ten varieties were susceptible to virus infection. C-152 was found to have the highest susceptibility of 100 per cent infection. C.G.104 showed some resistance with 13.33 per cent infection. In serological studies the cluster bean mosaic virus and sword bean mosaic virus were found to be related to cowpea mosaic virus. The antiserum titre and end point of virus in the present study were found to be between 1;1024 and 1:2048 and 1:512 and 1:1024 respectively. Studies on the effect of virus infection on growth of cowpea plants showed that there was significant reduction in height of the plant, number of pods produced and length of pods. Observations on natural incidence of cowpea mosaic virus indicated that cowpea mosaic virus is the major disease among the different virus diseases affecting t cowpea. Among the infected plants 57 per cent showed cowpea mosaic virus. The results of the experiments to find out the effect of leaf extract sprays on cowpea mosaic virus infection indicated that the disease could be effectively controlled by pre-inoculation sprayings with leaf extracts of Bougainvillea sp. and Eupatorium odoratum.ThesisItem Open Access Effect of root-knot nematode Meloidogyne incognita on nodulation in cowpea(Department of Plant Pathology, College of Agriculture, Vellayani, 1986) Nirmala Moni, D; KAU; Sasikumar NairAn investigation was carried out at Colloge of Agriculture , Vellayani, Kerala, to study the effect of Infeatation with Meloidogyne incognita on nodulation and 1 1 formation in cowpea. Ten varieties of cowpea, New Era Pathenettumaniyan, HG-22, PTB-1 PTB-2, 0-152, Sundari, V-16, V-37 and V-240 were initially screened for resistance to this nematode. She plants were inoculated with 1000 second stage larvae of H.incognita on 14th day and various observations on gall number, gall fresh weight, nodule number, nodule fresh weight leaf number plant height, root length# fresh and dry weight of shoot and nematode population in infested root and soil were taken on 50th day of plant growth. Eight varieties namely Pathinettumaniyan HG-22 PSB-1 0152 Sundari V-16 V-37 and V-240 were found resistant while two varieties new Era and PTB-2 were highly susceptible to this nematode.ThesisItem Open Access Effect of inoculation of vesicular-arbuscular mycorrhiza on nodulation and phosphorus uptake in cowpea(Department of Plant Pathology, College of Agriculture, Vellayani, 1987) Meena Kumari, K S; KAU; Sasikumar NairA study on the effect of inoculation of vesicular- arbuscular mycorrhiza and Rhizobium on nodulatlon, phosphorus uptake and yield in coupe a was conducted at College of Agriculture, Vellayani, Trivandrum during 1983-85. Three separate pot culture experiments were conducted during this Investigation; Initially, ten cowpea varieties were screened for the natural incidence of YA-mycorrhiza., There were significant differences between varieties in their mean mycorrhizal index; The infection was maximum in C-152 which had an average index of 1.19. This was significantly higher than that of varieties such as CG-11, HG-22, PTB-1, RC-25, S-488, IT-16 and V-38; The application of rock phosphate had a significant effect in enhancing the mycorrhizal infection in all varieties except in S-488. The cowpea variety which had the maximum mycorrhizal index under natural conditions m s further used to study the effect of age of host plant on mycorrhizal infection. This ms significantly higher on 45th day. The application of rock phosphate at the rate of 30 kg P2 O5/ha had a uniform significant effect in enhancing the mycorrhizal infection at different stages of plant growth. In the last part, a detailed study on the combined effect of VA-mycorrhiza and Rhizobium inoculation on nodulation, phosphorus uptake and yield in cowpea was conducted. Observations were taken at two stages of plant growth, on. 45th day and at the time of harvest. A uniform treatment effect on various plant characters studied was observed only at the time of harvest. The number of nodules formed per plant and their fresh (and dry weights were significantly higher in the treatment combination consisting of the standard culture of VA-mycorrhiza, Rhisobium inoculation and the application of rock phosphate at the rate of 30 kg P205/ha. The fresh and dry weights of plants and the mean mycorrhizal index were also maximum in this (MSR+RP) treatment.