Theses

Browse

Search Results

Now showing 1 - 9 of 10

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
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
Distribution of species of phytophthora affecting coconut and pepper in Kerala
(Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Veena, S S; KAU; Peethambaran, C K
The present investigation was undertaken to correctly identify the species of Phytophthora causing bud rot of coconut and foot rot of pepper in Kerala and to find out their comparative role in causing diseases on coconut and pepper. The study also aimed at isolation of viable antagonistic agents against the pathogen, so as to utilize them in future for biological control. The study was conducted during 1992-96 at College of Agriculture, Vellayani and Indian Institute of Spices Research, Kozhikode. Detailed symptomatology of both the diseases at different locations were studied. Periodic collections were made from diseased coconut and pepper from seven districts of Kerala. The morphological characters of the isolates were studied in detail. The length, breadth, L/B ratio, pedicel length and caducity of sporangia of coconut isolates were smaller than pepper isolates. The sporangial shapes differed considerably between and among the isolates. All the isolates except those collected from Kannur and Kasaragod districts (C7 - C16), produced abundant number of sporangia on carrot agar. Phytophthora are either heterothallic or homothallic. Generally P. palmivora and P. capsici are heterothallic. But ten coconut isolates obtained from Kannur and Kasaragodu districts produced abundant number of sexual structures on carrot agar, indicating their homothallic nature and this is the first report of homothallic Phytophthora causing bud rot of coconut in Kerala. All other 52 isolates were mated with known A1 and A2 mating type and all the coconut isolates produced oospores with A1 and all the pepper isolates produced oospores when mated with A2. Zoospore production was induced from sporangia using cold treatment. The number of zoospores in sporangia ranged from 6-15 in number. Chlamydlospore production was a rare phenomenon in pepper isolates while all the coconut isolates and five pepper isolates produced chlamydospores. All the isolates were inoculated into pepper seedlings, coconut leaves, tender coconut and coconut seedlings and the time required for infection, variation in symptom expression by different isolates etc. were studied. All the sixteen coconut isolates produced foot rot in pepper. Fourty six isolates of pepper produced lesions on coconut leaves and nut rot in tender coconut, while, only six isolates of pepper produced bud rot in coconut plants. The cross infectivity of pepper isolates needed further confirmation to prove the point beyond doubt. Eight cultivated plants, 9 ornamental plants and 12 weed plants were tested for the host range of coconut and pepper isolates. Many plants belonged to the above three groups took infection successfully. The microorganisms found associated with healthy and diseased pepper and coconut plantations and microorganisms from soils of pepper and coconut gardens of different parts of Kerala were isolated. Out of more than 200 microorganisms, only 28 fungi inhibited the growth of Phytophthora in vitro. On pepper plant, 12 isolates had inhibitory action. Three organisms, viz., Verticillium chlamydosporium, Aspergillus terreus and Chaetomium sp checked the pathogen completely even after seven days of spraying with the organisms.
Open Access
Transmission, physical properties and host range of brinjal mosaic virus
(Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Surendran, M; KAU; Rajagopalan, B
Open Access
Etiology and management of damping-off of solanaceous vegetables
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Bindu, Menon; KAU; Sally, K Mathew
The etiology and management studies of damping-off of chilli, brinjal and tomato were carried out at the College of Horticulture, Vellanikkara, Thrissur during 1994-95. Bacterial wilt resistant varieties like Ujwala of chilli, Surya of brinjal and Sakthi of tomato were used for the study. Fungi like Aspergillus niger, A. flavus, Penicillium sp. And Rhizopus stolonifer were found associated with the seeds of chilli, brinjal and tomato. In addition, Curvularia lunata, Drechstera rostrata and Alternaria sp. were isolated from chilli, brinjal and tomato respectively. The pathogens responsible for pre and post-emergence-off were Rhizoctonia solani in summer and Pythium aphanidermatum, Phytophthora parasitica and Drechslera rostrata in rainy season. In varietal reaction, none of the varieties/genotypes was found to be immune to the disease. However, certain genotypes like LCA-304 of chilli, BB-60-C of brinjal and LE-79-5 of tomato showed resistance in both seasons. In in vitro studies, Bordeaux mixture (1%) and copper oxychloride (0.3%) completely inhibited the growth of P. aphanidermatum and P. parasitica whereas all six fungicides tested were found equally effective against R. solani and D. rostrata. in vitro evalution of Trichoderma viride, against all the isolated organisms of damping-off resulted in die-back and disintegration of the pathogens. Among the fungicides, seed treatment with chlorothalonil and thiram @ 2 g/kg seed gave maximum germination and minimum incidence of emergence damping-off both seasons. Bordeaux mixture (1%) and potassium phosphate (0.3%) have affected the germination of seeds especially in tomato. In rainy season, compared to all other treatments, maximum germination, and minimum pre-emergence damping-off was observed in solarized plots. Carbendazim (0.1%) and Bordeaux mixture (1%) treatments were found to be most effective in controlling post-emergence damping-off during summer and rainy season respectively. Solarization followed by application of antagonist was also equally effective as Bordeaux mixture treatment in rainy season.
Open Access
Strain variation in Colletotrichum gloeosporioides (Penz.) Penz & SAcc.
(Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Alice, K J; KAU; Karunakaran, P
Colletotrichum gloeosporioides (Penz.) Penz. & SAcc. Is observed as a major pathogen infecting a number of crop plants, ornamentals and weeds. Detailed studies on the variability of this pathogen on important vegetables and ornamental plants in different locations of Thiruvananthapuram and Thirissur districts of Kerala were undertaken to distinguish different strains of C. gloeosporioides. Studies on the symptoms and pathogenecity tests of the 69 isolates showed that there were variations in the exoression of symptoms and in initiating symptoms indicating that the isolates were highly variable. Great variability in growth rate, colony characters, degree of sporulation and size of conidia were observed in different isolates. Based on the protein production and enzyme activity three groups of isolates could be distinguished. The isolates varied in their growth under varying temperature and relative humidity. Light intensity had no significant effect on the growth of the pathogen. Among the solid media tested, all the selected isolates exhibited the maximum growth on PDA. Richard’s medium was found to be the best liquid medium for mycelial growth. The degree of sporulation of selected isolates was the highest at 92.9 per cent RH and the lowest at 100 per cent RH. The highest sporulation was observed when exposed for 24 h of continuous light (125 lux) and poor when exposed for 24 h darkness. Basal medium was found to be best for sporulation. The results of host range studies and cross inoculation studies showed that the selected isolates were not host specific even though there were variations among the isolates in the intensity of infection. Inhibition of germination of selected seeds was observed when bioassayed with exotoxin. The purified toxin produced more or less identical symptoms as did by the casual organism. Coon’s medium was found to be the best for production of endotoxin. The maximum production of toxin was observed in 25 day old cultures. Biological groupings of all the 69 isolates studied were done based on the correlation matrix of different characters. Eight different groups of isolates could be distinguished and designated as G1, G2, G3, G4, G5, G6, G7 and G8 strains of C. gloeosporioides.
Open Access
Development of inoculant cultures of azospirillum for rice (Oryza sativa L.) in Kuttanad
(Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Sasikumar, S; KAU; Sivaprasad, P
Azospirillum was isolated from the rice roots of twenty five different locations of Kuttanad, Kerala in order to develop acid and salt tolerant inoculant cultures suited for the locality. The isolates were identified as A lipoferum and A brasilense. All the isolates showed good salt tolerance up to 2% NaCl concentration and good acid tolerance up to pH 5.0 and some isolates tolerated up to pH 4.0. The nitrogen fixing capacity in vitro by the isolates ranged between 11.20 and 2.28 mg/g malate and 1AA production between 24 µg 1-1 and 55 µg 1-1. Four isolates of them were selected for pot culture trials based on efficiency of nitrogen fixation, 1AA production, root elongation and acid and salt tolerance. The inoculated plants showed increased height, number of productive tillers and beneficial influence on root parameters. All these reflected in the final grain yield and AZR 15 gave highest yield followed by AZR 37. A saving of 25% nitrogen can be made by inoculation with these cultures in rice. The acridine orange curing of plasmids conducted to know the genetic basis of salt tolerance showed that the character is plasmid borne.
Open Access
Varietal screening host range and control of downy mildew of Bittergourd caused by Rostow
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Mini, SImon; KAU; Sally K, Mathew
A study was conducted at the College of Horticulture, Vellanikkara, during 1993-95, on varietal screening, host range and control of downy mildew of bittergourd (Pseudoperonospora cubensis (Berk. & Curt.) Rostow). Varieties obtained from the Department of Olericulture were screened for disease resistance and it was found that all the varieties tested were moderately susceptible to the disease. A preliminary screening of 174 genotypes of bittergourd available at NBPGR was conducted during August 1994 and all the genotypes were found to be infected. Only 32 genotypes were moderately resistant to the disease. Host range studies revealed that P. cubensis from bittergourd can infect other cucurbitaceous crops, such as bottlegourd, pumpkin, cucumber, snakegourd, ashgourd, watermelon and ivygourd. Four fungicides and four plant extracts were tested in in vitro, pot culture and field conditions to find out their effectiveness in reducing downy mildew infection. Among the fungicides, chlorothalonil (0.2%) was found to be the most effective as it gave maximum disease control, maximum yield and highest cost: benefit ratio. Among the botanicals, Ocimum leaf extract (10%) gave maximum reduction of the disease. In crop loss assessment, it was found that the highest CODEX of 60.22 per cent could cause an yield loss of 45.7 per cent under natural condition.

Theses

Browse

Thesis Type

Type

Author

Date

Subject

Search Results