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Open Access
Associative effect of azospirillum and bradyrhizobium on nodulation and growth of cowpea (viqna unquiculata (l.) walp,
(Department of Plant Pathology College of Horticulture Vellanikkara, 1992) Sunitha, Menon S.; KAU; Rajendran, Pillai M .V
Open Access
Leaf blight of banana and its control
(Department of Plant Pathology, College of Agriculture, Vellayani, 1993) Saj, KV; KAU; Sulochana, K K
Survey conducted to study the fungal pathogens causing leaf blight disease in banana in the three agricultural subdivisions of Thiruvananthapuram district, yielded seven fungal pathogens viz., colletotrichum musae, Curvularia sp, Guignardia musae, khuskia oryzae, Nodulisporium gregarium, Pestalotiopsis versicolor and Phaeoseptoria sp. Among these, Curvularia sp, Khuskia oryzae and Nodulisporium gregarium are new reports. Morphological characters and pathogenicity tests of all the seven isolated cultures were studied and described. Detailed studies were conducted on five fungal pathogens viz., C. musae, G. musae, K. oryzae, N. gregarium and Phaeoseptoria sp., since severe infections could be noticed by these fungi. Studies conducted on the growth and sporulation of pathogens on different, media indicated that Richard’s medium was the best for C. musae and G. musae, potato dextrose medium for K. oryzae and Phaeoseptoria sp. In the case of N. gregarium, potato dextrose agar and Czapek (Dox) broth were found to be the best solid and liquid media respectively for its growth. Best growth of C. musae, N. gregarium and Phaeoseptoria sp was obtained with maltose as the carbon source, whereas G. musae and K. oryzae utilized maximum starch and sucrose for their growth. Maximum mycelial weight of C. musae was obtained with sodium nitrate as nitrogen source, G. musae and K. oryzae with potassium nitrate, N. gregarium with glutamine and Phaeoseptoria sp. with asparagine. Potato dextrose broth and Richard’s solution were found to be best media for the toxin production by C. musae K. oryzae , G. musae and Phaeoseptoria sp. produced maximum toxin in Richard’s solution and N. gregarium in potato dextrose broth. Host range studies of the pathogen (s) conducted indicated that they can infect a number of economically important plants like, clove, cocoa, colocasia, nutmeg and tapioca, but none of the pathogens could infect clerodendron. Dithane M-45, calixin and Bavistin were able to inhibit the growth of the leaf blighting pathogens under laboratory conditions and under field conditions Dithane M-45 (0.2%) was found to be the best. Varietal screening trials showed that variety Rasakadali was moderately resistant/tolerant among the four popular varieties screened, whereas Nendran was the most susceptible variety.
Open Access
Vascular streak dieback of cocoa and its management
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Ajay Kumar, K M; KAU; Koshy, Abraham
Vascular streak dieback (VSD) is a destructive disease of cocoa. Corticium culture medium, Water agar, Potato dextrose agar gave promising results in isolation of the pathogen. Petiole and midrib gave maximum success in isolation. Potato dextrose agar and Corticium culture media supported the growth of the fungus. Fusarium sp. And Colletotrichum gloeosporioides were the major contaminants interfering in the isolation of VSD. The morphological characters of the pathogen were studied from the sporophores occurring on naturally infected cocoa plants. Based on these characters, the pathogen causing VSD was identified as Oncobasidium theobromae Talbot and Keane. The disease produced various typical symptoms on leaves and stems of infected plants like pale green colour of leaves and subsequent yellowing with green islets, defoliation, brown marks on the scars of fallen leaves, axillary bud growth of the infected stem, rusty discolouration of cambium, vascular streak, whitish sporophores on the leaf scar of fallen infected leaves and finally the death of the infected twig. Histopathological studies showed the presence of fungal mycelium in the xylem vessels. Transmission studies by grafting and budding revealed no establishment of buds or grafts. But there was vascular streaking. No seed transmission was observed. In general Kitazin and Bavistin as a seed treatment had an effect on the height of plant and leaf production. Evaluation of cocoa types planted at three seed gradens indicated that some of them possess resistance/tolerance against VSD. Variation in disease incidence and intensity of VSD was noted in germplasm VI. Calixin spraying had an effect in preventing the incidence of the disease in seedlings.
Open Access
Survival of Xanthomonas campestris pv. Oryzae and its Control in Kuttanad
(Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Mary, C A; KAU; Sasikumar Nair
The present investigation was taken up to understand the factors responsible for the recurrence of bacterial blight disease in a severe from only during the additional crop season in Kuttanad. The mode of survival of the pathogen during and in between the two major cropping seasons of Kuttanad region were also studied in detail. An extensive survey was also conducted among 115 farmers in 12 Krishibhavans of Kuttanad taluk for this purpose to collect specific informations on existing cultural practices, crop variety, nature and distribution of weed flora and self sown rice plants in and around rice fields and on wether data from June 1992 to March 1994. The efficacy of two different methods of spraying, prophylactic and curative using streptocycline, mixture of streptomycin and oxytetracycline in the proportion 1:9, Bactrinol – 100 cowdung extract on the control of bacterial blight disease was tested under field condition at Nedumudi in Kuttanad. The survey showed that there was considerable variation in the incidence of bacterial blight in Kuttanad taluk. Among the 12 Krishibhavan areas the disease incidence was maximum in Ramankari and Nedumudi and minimum in Kavalam, Kainakary and Muttar. In Neelamperoor and Thalavadi areas there was no incidence of this disease during the period of survey. Between the two major cropping seasons the disease incidence was more during the additional crop season than during Punja season. Red Triveni and Jyothy were the most popular varieties cultivated in the area and more than 50% of the farmers cultivate Red Triveni. It was observed that the variety Red Triveni as highly susceptible to bacterial blight disease. The isolate of the pathogen Xanthomonas oryzae pv. Oryzae from the rice variety Red Triveni was capable of both gelatin liquefaction and starch hydrolysis. The pathogen X. oryzae pv. oryzae was found to survive for a maximum period of 42 days in infected seed, 105 days in infected straw, 56 days in infected stubbles at room temperature, 24 days in infected stubbles under dry land condition and 14 days under wet land condition. The pathogen did not survive in soil and water. Weeds like Oryza sativa var. fatua and Paspalum conjugatum served as alternate host for the pathogen. Bacterial blight infected self sown rice plants could be seen in Kuttanad during the cropping and non cropping seasons. Due to certain specific reasons, the cultivation practices were often found to extend beyond the normal cropping seasons in the region resulting in the chances of survival of bacterial blight pathogen in the host plant itself. The specific weather conditions during the additional crop season played an important role for the severity of bacterial blight desease in this season in Kuttanad. The pathogen X. oryzae pv. oryzae was tested for sensitivity to antibiotics, Bactrinol – 100 and cowding extract under in vitro conditions. The maximum growth inhibition was obtained with oxytetracycline followed by chloramphen icol which was statistically on par with oxytetracycline. The effect of increasing concentrations of oxytetracycline in combination with streptomycin on growth of X. oryzae pv. oryzae was studied with 100, 250 and 500 ppm concentrations. The growth inhibition increased not only with the concentrations of antibiotic from 100–500 ppm but also with increasing concentration of oxytetracycline. The maximum zone of growth inhibition was obtained with 1:9 proportion of streptomycin and oxytetracycline. The five treatments selected for field evaluation trial included streptocycline at 500 ppm, streptomycin + oxytetracycline (1:9) at 250 ppm and 500 ppm, Bactrinol -100 at 500 ppm and fresh cowdung extract at 20g/1. Two different spraying methods, prophylactic and curative were evaluated in two rice varieties, T(N) 1 and jyothy. The reduction in disease index by prophylactic and curative sprayings was maximum after spraying with cowdung extract 20g/1. As regards to two methods of spraying, significant reduction in per cent disease index was obtained with curative spraying. The maximum per cent increase in grain yield over control was obtained after curative spraying with 500 ppm streptomycin and oxytetracycline mixture in jyothy followed by cowdung extract 20 g/l. In T(N) 1 and jyothy both by prophylactic and curative spraying, the thousand grain weight was maximum with cowdung extract 20 g/1. As regards to two method of spraying, significant increase in grain yield and thousand grain weight was obtained after curative spraying. In T(N) 1, both by prophylactic and curative spraying the per cent increase in straw yield was maximum with a mixture of streptomycin and oxytetracycline at 500 ppm and jyothy with cowdung extract 20g/1. In T(N)1 significant reduction in chaff per cent was recorded by prophylactic spraying while in Jyothy no significant difference was obtained by the two methods of spraying. In both these varieties the reduction in chaff per cent was maximum by spraying with cowdung extract (20g/1). It was observed that two prophylactic spraying with selected bactericidal agents, neither resulted in any significant reduction in disease index nor increase in yield as compared to curative spraying. This could be due to the fact that in Kuttanad bacterial blight disease usually occurred only around the panicle initiation stage or even later. Therefore a need based curative spraying schedule would be most effective for the control of bacterial blight disease in Kuttanad. On working out the economic benefits of controlling bacterial blight it was observed that there will be economic return only from spraying infected plants of both (T(N) 1 and jyothy with cowdung extract 20g/1. The return from plants sprayed with all other treatments in the investigation was low when compared to unsprayed control plants. Thus it will be economically advantageous to use cowdung extract to control bacterial blight of rice.
Open Access
Screening Of Fungal Pathogens For Biocontrol Of Water Hyacinth (Eichhornia Crassipes (MART.)Solms)
(Department of Plant Pathology, College of Agriculture, Vellayani, 1994) Santhy Kammath S; Naseema A
A survey was conducted in and around Trivandrum district viz., in veli, Ambalathara and Akulam to obtain the fungal pathogens of water hyacinth for its biocontrol. Colletotrichum gloeosporioides (Penzig) Penzig and Sacc Curvularia lunata (Wakker) Boedjin, Fusarium equiseti (Corda) sacc., Fusarium semitectum Berk and Rav, Fusarium solani (Mart) sacc., R. solani Kuhn and sterile fungus were found infecting the plants. The seasonal occurrence of the fungi isolated was studied and it was found that Fusarium spp. were present throughout the period of study. C. gloeosporioides and R. solani were present in the rainy season only. The pathogenicity of all the above fungi to the water hyacinth plants was established by artificial inoculation. Host range studies revealed that R. solani had a wide host range, which included amaranthus, cowpea, rice Monochoria vaginalis and panicum repens. The host range of C. gloeosporioides included chilli, Commelina benghalensis, Hydrocotyl asiatica and Ludwigia parviflora Fusarium spp. were found to infect Monochoria vaginalis only. Among the fungal pathogens isolated from water hyacinth, F. semitectum caused highest intensity of infection of 51.10 per cent followed by F. equiseti and F. solani (48.88 per cent) C. gloeosporioides and R. solani caused 44.44 and 45.76 per cent intensity of infection respectively. Curvularia lunata caused the lowest intensity of infection of 20 per cent. An experiment was conducted to fix the concentration of inoculam required for effective destruction of water hyacinth. The spore concentration of 10 9 spores/ml was the most effective one in the case of F. equiseti, F. semitectum and F. solani For C. gloeosporioides spore concentration of 2 x 109 sporce/ml was the most effective one. Different carrier materials were tried for mass multiplication and storage of the promising fungal pathogens of water hyacinth. The different carrier materials tested were coir pith, paddy straw, peat moss, rice bran and wheat bran. Wheat bran was found to be the most suitable media for F. equiseti, F. semitectum and F. solani. In wheat bran, the spore count and viability of the spores of these fungi were maximum. For C. gloeosporioides, in rice bran maximum spore count was obtained whereas, in the case of viability of the spores, rice bran and wheat bran were on par. In peat moss none of the fungi grew. In the field tests conducted to try different methods of application of the fungi viz., C. gloeosporioides, F. equiseti, F. semitectum and F. solani, applying bilts of inoculum of the fungi and spraying of the inoculum of the fungi were found to be the best methods. Whereas, dusting of the inoculum produced very poor symptoms. The field performance of the fungi in different carrier materials showed that rice bran and wheat bran inoculum caused good symptom development on water hyacinth plants whereas, coir pith inoculum caused poor symptom development. All the three Fusarium spp. viz., F. equiseti, F. semitectum and F. solani were found to produce toxin. Which could cause similar symptoms on the water hyacinth leaves as those produced by inoculating the culture bits.
Open Access
Effectiveness of soil solarization for the control of soft rot disease in ginger
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Vilasini, T N; KAU; Peethambran, C K
The effectiveness of soil solarisation for the control of soft rot disease in ginger was studied at the College of Horticulture, Vellanikkara, Thrissur during March 1992 to December 1993. The beds were inoculated with Pythium aphanidermatum, five days before the solarisation. Transparent, 150 guage polyethylene sheets were used for solarizing the beds. Maximum soil temperatures recorded were 63.00, 59.00 and 46.50 at 5, 10 and 15 cm depths in solarized soil, while, that in non-solarized soils were 49.50, 43.00 and 40.00C, respectively, at 5,10 and 15 cm depths. Temperature in the solarized soil at 5 cm depth was above 50.00 C for the entire solarisation period and above 55.00 C for 38 days, while, at 10 cm depth the temperature was above 50.00 C for 35 days and above 55.00 for five days. The soil temperature at 15 cm depth never reached 50.00 C during the solarisation period. Based on the soil and air temperature recorded, two simple regression equations at 5 and 10 cm depths, one simple equation at 15 cm depth and one multiple regression equation at 10 cm depth were developed for predicting soil temperature under polyethylene mulch. Rate of germination in ginger was enhanced by solarisation. Significant effect of solarisation was observed in controlling the pre and post-emergence rotting in ginger. Increasing the period of solarisation from 30 to 45 days did not result in a corresponding reduction in the pre-emergence rotting. Trichoderma incorporated neem cake amended 30 day solarized treatment was highly effective and recorded cent percent control of the soft rot disease, while, maximum disease incidence (90.67%) was in Trichoderma incorporated neem leaves amended 45 days solarized plots. Reduction in Pythium population ranging from 79.49 to 99.1 per cent was observed in solarized plots immediately after the removal of polyethylene sheets. Solarization reduced the total fungal, bacterial, actinomycetal and Pseudomonas sp. population in the field. Plants grown in solarized plots showed better colonization of VAM and Azospirillum. Significant reduction in the nematode population was recorded by solarisation. Solarization had a profound suppressive effect on the weed population and it lasted till harvest. Solarization effect was more pronounced in dicots. Eventhough, solarisation substantially reduced weed population, its effect was less in the edges. Bulbostylis barbata, Cynodon dactylon and Cyperus rotundus survived the solarisation effect. Increased growth response of ginger plants was observed as a result of solarization. Growth parameters like height, number of leaves/plant, number of tillers, number of roots, leaf length, leaf breadth, fresh weight of shoots and rhizomes were influenced by solarisation. Significant increase in the yield was obtained through solarisation. Trichoderma incorporated and neem cake amended 30 days solarized treatment gave the maximum yield/plant (623.23 g) and also per plot yield (10159.57 g), which was 5361 per cent more than that of control. Availability of nitrogen, phosphorus and potassium was improved by solarisation. The initial cost of solarization is comparatively high, an amount of Rs. 52,500/- is required for solarizing one hectare of ginger field. An additional profit generated from this technique was Rs. 40,136/ha for 30 days solarisation.
Open Access
Combatibility of certain fungicides and insecticides used for the control of major diseases and insect pests infesting the rice crop
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1992) Kalpana, T A; KAU; Sally Mathew, K
The efficacy of four fungicides and four insecticides alone and in combination was studied at different concentrations recommended, three-fourth and half the recommended concentrations against two major diseases of rice namely, rice blast caused by Pyricularia oryzae Cavara and sheth blight caused by Rhizoctonia solani kahn. And two major insect-pests namely, leaffoldar Cnaphalocrocis medinalis medinalis Guen. And brown planthopper Nilaparvatha lugens stal. At tillering, panicle initiation and flowering stage of the crop. The experiment was conducted in vivo and in vitro conditions during 1989-91, at the college of Horticulture, Vellanikkara, Thrissur. In general combind application of fungicides and insecticides controlled the diseases and insect-pests more effectively than the treatments given separately. At tillering stage, a synergistic effect of fungicide was observed, when it was sprayed along with insecticides. Among different combinations tried, tridemorph (o.1 per cent) + monocrotophos (0.0375%) and carbendazim (0.075 ) + guinalphos (0.025 per cent) were the best combinations against blast and sheath blight respectively. In the case of leaffolder and brown planthopper, quinalphos was found to be the best insecticide, when used alone and also in combination with fungicides. At panicle initiation stage, combined sprays of higher concentrations of carbendazim and monocrotophos was the best combination in controlling both R. solani and N. lugeas. But ediphenphos-phosphamidon combination was found to be the superior against N. lugens. When combind spraying was given at flowering stage, captafol (0.225 per cent) + quinalphos (0.0375 per cent, and carbendazim (0.075 per cent) + monocrotophos (0.0375 per cent) were found to be the best combinations against P. oryzae and R. solani respectively. But, combination of recommended doses of quinalphos with tridemorph and ediphenphos and, phosalone with ediphenphos were the effective treatments in controlling C. medinalis and N. lugens respectively. In in vitro studies, a total inhibition of the test organisms, viz.P. oryzae and R. solani were observed in all the treatments. Whereas, in the case of C. medinalis recommended doses of quinalphos in combination with ediphenphos and carbendazim and phosalone with tridemorph recorded highest mortality; while, highest dose of quinalphos with captafol and phosalone with ediphenphos were the superior combinations against N. lugens. From the above findings it could be concluded that, the fungicides viz. ediphenphos, carbendazim, captafol and tridemorph are compatible with all the four insecticides tried viz. Phosphamidon, quinalphos, phosalone and monocrotophos in controlling the diseases, blast and sheath blight and insect pests leaffolder and brown planthopper.
Open Access
Etiology and control of seedling blight of cocoa
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1995) Edwin Prem, E; KAU; Koshy, Abraham
The seedling blight is a serious nursery disease of cocoa. The fungus causing seedling blight of cocoa was isolated and Koch’s postulates were established. On carrot agar medium, the fungus produced sparse, striate growth. The mature sporangia were near spherical to ovoid with round base, papillate, caduceus with an average L/B ratio of 1.74. Sporangia were borne terminally in a sympodial fashion. It had a short and thick stalk with an average length of 4.1µm. Based on these characters, the pathogen causing seedling blight of cocoa was identified as Phytophthora palmivora (Butler) Butler. For maximum growth of the fungus, oat meal and corn agar were the best. But, for maximum sporangial production, carrot agar and oat meal agar were good. Among the liquid media, oat meal and corn meal broth supported good growth of the fungus. The disease produced various type of symptoms on leaves and stem of seedlings and budded plants like water soaking, leaf blight, defoliation, black discolouration, cotyledonary infection, wilting and die back. Stem of budded plants were more prone to infection than that of seedlings. The seedlings blight pathogen infected plants such as Piper nigrum L., Cocos nucifera L., Hevea brasiliensis L., Bougainvillea sp. And Colocasia esculenta L. but did not infect Areca catechu L., Piper betle L. and Piper longum L. on artificial inoculation. The youngest seedlings of age group less than 18 days after germination were more vulnerable to infection. Similarly, the youngest budded plants of age group 45 days after budding showed maximum infection. Among the 62 cocoa types screened for host resistance the cocoa types GIV-36.6 (local), GVI-23 (P9 x P4), GIV-4.6 (local) and S-45.5 (local) showed minimum percentage of mortality. Among the different fungicides/antibiotics screened in in vitro, Fytolan, Captaf, Bordeaux mixture, Akomin and Ridomil at all concentrations and 0.3 per cent Foltaf and, Chloramphenicol and Terramycin each at 400 and 500 ppm completely inhibited the growth of the fungus. Indofil-M.45, Aureofungin and Amoxycillin exhibited less inhibitory effect. Foltaf, Fytolan and Akomin each at 0.3 per cent concentration showed better effect in cheching the lesion development on detached cocoa leaves. Result of the different in vivo control experiment indicated that, the fungicides like Akomin, Foltaf, Fytolan and Bordeaux mixture had promising effect in checking the incidence and severity of the disease.
Open Access
Investigations on mosaic disease of bitter gourd
(Department of Plant Pathology, College of Agriculture, Vellayani, 1994) Purushothaman, S M; Kau; Rajagopalan, B
Bitter gourd mosaic virus disease commonly occurring in Kerala was investigated. The symptoms appeared as typical mosaic mottling with dark green and light green patches. 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., Myzus persicae Sclz. And aphis craccivora Koch. Among the four species of aphids, A. gossypii and A. malvae were found to be the most efficient vectors. Investigations on the physical properties of the virus revealed that the virus had a thermal inactivation point between 50 and 600C, dilution end point between 1:1000 and 1:10000, longevity in vitro between 12 and 24 h at room temperature (28 - 300C) and 48 and 72 h at 100c. The minimum acquisition feeding and inoculation feeding period of the vector A. malvae were found to be 30s and I min respectively. But the percentage of transmission was maximum when an acquisition feeding period of 30 min and inoculation feeding period of 2 h were given. Influence of starvation before acquisition and inoculation feeding period proved that pre – acquisition starvation for 2 h produced maximum infection but post- acquisition starvation decreased the per cent infection. The vector could retain the virus for I h only. 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 Araceae, Chenopodiaceae, Cucurbitaceae, Musaceae, Polygonaceae and Solanaceae. Datura metal acted as a symptomless carrier of bitter gourd mosaic virus. Serological studies showed that bitter gourd mosaic virus is related to cucumber mosaic virus, pumpkin mosaic virus and snake gourd mosaic virus. Varietal screening showed that all the varieties and collections were susceptible to biter gourd mosaic virus infection, but the variety Arka Harit and the collections 87 green long 1 C 68234, 61 white medium 1C 45358 and 177 green medium 1C 68324 were least susceptible. Studies on estimation of loss revealed that early infection of bitter gourd plants by the virus significantly reduced the number of leaves, leaf area, intermodal length, thickness of vines, length of vines, number of branches, number of flowers, number of fruits and other fruit characters viz., length of fruits, girth of fruits, weight of fruits and total yield of fruits.

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