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Open Access
Anthracnose disease of vegetable cowpea [Vigna unguiculata subsp. sesquipedalis (L.) verdcourt]
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1999) Praveen Kumar, M; KAU; Sally Mathew, K
A study on vanous aspects of anthracnose disease of cowpea was conducted at College of Horticulture, Vellanikkara during 1997-98. Etiological studies revealed Colletotrichum lindemuthianum (Sacc. and Magn.) Br. and Cav. as the main pathogen causing anthracnose disease in Kerala and the pathogen was found to be seed borne. Among the 50 genotypes tested, Kanakamony was found immune to the disease and seven genotypes were highly resistant to the disease. In ( disease management studies, all fungicides, botanicals and antagonist Trichoderma viride were equally effective under in vitro and field conditions. As far as disease control, yield and C:B ratio were concerned, mancozeb was found to be the best treatment. Summer season was found to be the best season for cowpea cultivation in areas where anthracnose is a problem. In crop loss assessment, significant difference was noticed between carbendazim treated and untreated plots in case of disease infection and yield, and yield loss of 53.85 per cent was recorded under natural condition due to this-disease.
Open Access
Biocontrol of rhizome rot of ginger using selected antagonists
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1999) Julie George, K; KAU; Sukumaravarma, M
Rhizome rot of ginger cas used by Pythium aphantdermatum (Edson) Fitzpatrick is one of the most destructive diseases of ginger in Kerala. The pathogen was isolated and its pathogenecity was established by Koch's postulates in ginger variety Rio-de-Jenerio. Among the various food bases evaluated, for the mass multiplication of selected antagonists, rice hull was found to be significantly superior to all others to obtain maximum growth for Trichoderma viride and Aspergillus flavus. For Aspergillus niger, rice bran was found to be significantly superior. The results on the effect of various treatments on germination showed that there was no significant difference among the treatments. The effect of antagonists on the pre- emergence rotting and post-emergence rotting (rhizome rot) were studied. In plots where antagonists (T viride, Aflavus or A. niger) or fungicides (mancozeb or copper oxychloride) were applied either as seed treatment or as soil incorporation at the time of planting, the pre-emergence rotting was not observed. The plot in which the antagonists T. vtride, A. mger and At flavus were applied in combination at 60 and 120 OAP, recorded the minimum rhizome rot incidence compared to other treatments. The plots in which the antagonists were applied twice, i.e., 60 and 120 OAP, the rhizome rot incidence was minimum compared to the plots with only one time application of antagonists. The maximum population of the pathogen P. aphanidermatum. was observed in plot where A. flavus was applied in combination with mancozeb. The multiplication of selected antagonists, 7: viride, A. flavus and A. niger in soil was found out by estimating their population at different stages. The population of T. virtde was maximum in plots where it was applied in combination with mancozeb in most of the period. The soil application of the combination of antagonists T. viride, A. flavus and A. niger did not affect the multiplication of anyone of them in soil. In general, soil incorporation of antagonists was found to helping in their mulitplication profusely compared to the seed treatment. The incorporation of the antagonists A. flavus and A. niger to the plots, twice was found to be superior than applying them only once, for getting maximum multiplication of propagules in soil. The result on the compatibility of antagonist with fungicide in field condition revealed that the antagonist T viride was quite compatible with mancozeb whereas A. flavus and A. niger were compatible with both fungicides tested (mancozeb and copper oxychloride). The treatments which was found to be superior in minimising the incidence of rhizome rot of ginger viz., T 16 (soil incorporation of T vir/de, A. niger at 60 and 120 DAP) and TI9 (soil incorporation of I: viride, A. niger and A. flavus) also recorded the maximum yield of ginger.
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
Biocontrol of water hyacinth using fungal pathogens
(Department of Plant Pathology, College of Agriculture, Vellayani, 1997) Susha Thara, S; KAU; Naseema, A
Detailed study was conducted on the host range of the already identified fungal pathogens of water hyacinth viz. Colletotrichum gloeosporioides, Fusarium eguiseti and F.pallidoroseum on thirty cultivated plants including vegetables, pulses and oil seeds, field crops, fruits and forest crops and ornamental plants and forty one common weed plants which are seen in and around water ways infested with water hyacinth. It was observed that C. gloeosporioides could infect amaranthus, bhindi, chilli, Euphorbia hirta, Hydrocotyl asiatica and Phyllanthus niruri. Of the thirty cultivated plants and forty one weed plants tested F. eguiseti was seen to be pathogenic to amaranthus, Amaranthus viridis, Commelina . bengalensis, C. jacobi and Monochoria vaginalis. F. pallidoroseum could produce symptoms on napier grass, Axonopus sp., boerhaavia diffusa, C.benghalensis, C.jacobi, Echinochloa colonum, Euphorbia hirta, Justicia diffusa, J.prostrata, M.vaginalis and Oldenlandia umbrellata and Scorpia dulcis. For the effective destruction of the weed, lxl011 spores per ml concentration of Q. gloeosporioides, E. eguiseti and F. pallidoroseum were found to be more effective than lxl09 and lxl010 spores per ml concentration. Cell free metabolites of the pathogenic fungi were found to produce symptoms on water hyacinth plant. Metabolite produced by E. pallidoroseum caused considerable damage than by E.equiseti and C. gloeosporioides. When pathogens were applied singly and in combination on water hyacinth it was observed that the combined application of F. pallidoroseum and F. equiseti followed by F. pallidoroseum alone gave maximum intensity of infection. Eventhough C. gloeospoirioides gave least intensity of infection it can be used as a co-pathogen with E. eguiseti. Metabolite of the pathogens individually and in combination when applied on healthy water hyacinth plants, maximum damage was caused by F.pallidoroseum alone and the combination of metabolite of three fungi viz. C. gloeosporioides,F equiseti and F. pallidoroseum. Least damage was caused by metabolite of C. gloeosporioides. An experiment was conducted to find out suitable carrier materials for the mass multiplication and storage of pathogen. It was observed that for C. gloeosporioides maximum sporulation was in water hyacinth leaf followed by guinea grass straw and rice bran. But the spore viability was maximum for rice straw, and on coir pith. Maximum infection was caused by fungus grown on guinea grass straw and rice straw. In the case of E. equiseti spore counts was higher in guinea grass straw followed by coir pith. The spore germination was maximum in rice bran and coir pith. Maximum infection was produced by the fungi on guinea grass straw, coir pith and waterhyacinth leaf. E. pallidoroseum produce maximum number of spores on rice bran followed by guinea grass straw. It was observed that the germination percentage of spores were maximum on coir pith. Out of the six carrier materials used the fungus produced maximum infection when grown on rice bran and guinea grass straw. In the study for testing the storage life of metabolities, it was observed that the efficiency to produce symptom was reduced on storage in the case of C. gloeosporioides and E. pallidoroseum whereas for E. eguiseti on storage the effeciency of the metabolite to cause damage increased. Metabolite stored on refrigerated condition performed poorly for all the three fungi. Different methods of application of the three fungi were tried. Of the five treatments, placement of bits and dusting the inoculum along with the carrier materials produced maximum infection. In the experiment conducted to characterize the toxin presented in the cell free metabolite of pathogenic fungi, observed the presence of Fusaric acid in the metabolite of Fusarium spp.
Open Access
Disease resistance in the management of cowpea aphid-borne mosaic virus
(Department of Plant Pathology, College of Agriculture, Vellayani, 1999) Radhika, N S; KAU; Umamaheswaran, K
Investigations were undertaken on the virus causing severe mosaic on cowpea (Vigna unguiculata (L.) Walp) in Kerala. The characteristic symptoms appeared as vein clearing, light and dark green mottling, severe mosaic, dark green vein banding, blistering, distortion and reduction in leaf size. The virus was mechanically transmitted through sap extracted in 0.01 M phosphate buffer (pH 7.0). The virus was efficiently transmitted by the aphid vector, Aphis craccivora. Seed transmission of eleven per cent was recorded in the variety Sharika. Thermal inactivation point was recorded at a range of 60 - 65° C, dilution end point at a range of 10-3 - 10-4 and longevity in vitro for four hours at room temperature (28 ± 4° C) and six hours under refrigerated condition (8° C). A. craccivora could efficiently transmit the virus with an acquisition access of ten minutes and inoculation access of one minute. Pre-acquisition starvation increased the rate of transmission while post-acquisition starvation decreased the rate. A single aphid was capable of transmitting the virus. The virus causing severe mosaic was identified as blackeye cowpea mosaic virus by ELISA. The virus could also be detected by Ouchterlony immunodiffusion test. Electron microscopic studies revealed the presence of flexuous, filamentous particles of 750 nm in length. Two varieties Co-6 and Cc-Selection were grouped as no symptom producing among 65 genotypes screened for resistance. Fifty three F2 progenies of the cross Sharika and Co-6 and twenty five F2 progenies of the cross Co-Selection and Sharika were long poded and resistant. Biochemical changes indicated a lower carbohydrate content in resistant compared to susceptible. Chlorophyll content decreased in the susceptible variety due to virus infection. Increase in protein was observed in both resistant and susceptible. The phenol content did not show variation between the varieties. Peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase activities increased in the resistant variety. Bioassay of chemicals and neem oil on local lesion host (c. amaranticolor) indicated a per cent inhibition of 68.92 by neem oil in pre-inoculation application and 65.45 per cent inhibition by manganese chloride in post-inoculation application. On cowpea plants, pre-inoculation application of neem oil (ten per cent) concentration was found to be effective in reducing the symptoms due to viral infection.
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
Symptomatology and etiology of little leaf disease of pepper (piper nigrum L.)
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1995) Sree Kumari, P K; KAU; Sukumara Varma, A
Symptomatology and etiology of little leaf disease of pepper (piper nigrum L.) was conducted at the department of plant pathology, College of Horticulture, Vellanikkara, Thrissur and at pulppally in Wayanad district during 1992-94. Based on the external symptoms of the disease a disease scoring chart (0 to 4) was perfected. The diseased plants had shorter main root and less number of feeder roots. Brown discoloration was noticed on diseased roots. Internodal length as reduced which give a bushy appearance to the plant. Leaves were distorted, downwardly curved, chlorotic, brittle with wire-net type vein lets. Enen though the size and shape were normal, the number of flowers per spike decreased and the aborted flowers increased. Proper maturity was obtained by very few berries. Disease was observed to attach all age group of plants, but the intensity increased with age. Variety karimunda was highly susceptible and punniyur-1 was observed to be tolerant though the disease attacked Arakkulam munda, Aimpiriyan and Vellananamban with lesser degree than karimunda. Application of zinc did not inhibit the symptoms. When 0.2% Dienes stain was used for the phloem portion of the roots, nodes and petioles of the diseased and healthy plants, only diseased plant parts stained blue indicating the presence of mycoplasma like organisms in them. Disease could not be transmitted by sap or dodder. It could be transmitted by cuttings and by wedge grafting using diseased root stock and healthy scion not vice versa. Transmission studies with insects Austroagallia sp. Manderan beta Owarokowska aand Liothrips Karnyi were not successful. Applications of oxytetracycline hydrochloride (OTC) by drenching, spraying, dipping and wick feeding were effective at concentrations more than 500 ppm for remission of disease symptoms. OTC at 250 ppm was not effective. Above 750 ppm, the treatment caused phytotoxicity. Among methods, wicks feeding was found to be the best, which prevented reappearance of symptom even after two years where as in all the other methods, the symptom remission lasted for less than 6 months. Yield was observed to be reduced with an increase in disease intensity. The study revealed the symptomatology of little leaf disease of black pepper and resulted in the identification of etiology as mycoplasma like organism.
Open Access
Effect of management practices on the incidence and intensity of grey blight disease of coconut
(Department of Plant Pathology, College of Agriculture, Vellayani, 1997) Anupama, N; KAU; Padmakumari, G
From a detailed survey on the occurrence of leaf blight disease of coconut in Thiruvananthapuram (Coconut Research Station, Balaramapuram and Instructional Farm, Vellayani) and Alappuzha Districts (Rice Research Station, Kayarnkulam) it was revealed that Pestalotiopsis palmarum (Cooke) Stey was the major pathogen causing grey leaf blight of coconut in both the areas. Curvularia sp. were also found to be contribute to this disease. Of the various media tested, best growth of P. palmarum was seen in potato dextrose agar and broth. Among the various carbon sources tested dextrose, starch and inositol were equally effective for the growth of P. palmarum and for Curvularia sp., Sucrose, dextrose and starch were the best carbon sources. A temperature of 25°C and 35°C was found to be optimum for the growth of P. palmarum and Curvularia sp respectively. Arecanut, cinnamon, clove, guava, mango, nutmeg and sapota intercropped with coconut in the three locations were found to be host of the pathogen P. palmarum. In vitro evaluation of fungicides revealed that Bordeaux mixture (1000 ppm) and Bavistin (2000 ppm) were superior in inhibiting the growth of P. palmarum on the other hand Bordeaux mixture (1000 ppm) and Dithane M-45 (1000 ppm) effectively inhibited the growth of Curvularia sp. Monitoring of the disease intensity over a period of 12 months has shown that grey leaf blight intensity was high in palms planted at closer spacing and which received no fertilizers. The disease intensity was minimum in palms with wider spacing and with higher level of fertiliser (N2P2K2). In general higher level of fertilizers and wider spacing may be considered as a management practice for controlling the incidence and intensity of the grey blight diseases in coconut palm in South Kerala.
Open Access
Influence of microflora associated with earthworm (Eudrilus eugeniae kinberg) and vermicompost on growth and performance of chilli. (capsicum annuum L.)
(Department of Plant Pathology, College of Agriculture, Vellayani, 1999) Suja, P R; KAU; Sasikumar Nair
The present investigation on 'Influence of microflora associated with earthworm (Eudrilus eugeniae Kinberg) and vermicompost on growth and performance of chilli (Capsicum annuum L.) was done at College of Agriculture, Vellayani during 1997-99 as part of a Science, Technology and Environment Department (Government of Kerala) funded research project. Among the surface microflora of Eudrilus eugeniae, the total number of bacteria, fungi and actinomycetes were maximum on 45 day of compost formation. However, the number of nitrogen fixing bacteria was more on 60 day. Similarly, in the case of gut micro flora, the total number of bacteria and fungi were maximum on 45 day of composting. However, the number of actinomycetes was more on 30 day. Nitrogen fixing bacteria could be isolated only on 15 day. In the vermicompost, the total number: of bacteria fungi and actinomycetes were maximum on 30,45 and 60 day respectively. The number of phosphate solubilizing bacteria and nitrogen fixing bacteria were more on 15 and 30 day of sampling. However, soilborne pathogens such as Pseudomonas solanacearum, Pythium spp. and Phytophthora spp. were absent. There were significant differences in the growth rate of various isolates of nitrogen fixing bacteria in Jensen's nitrogen free broth. The mean optical density for isolate 3 was significantly higher than rest of isolates. The nitrogen fixing ability of this isolate was also higher. The isolate 3 was selected for enrichment of vermicompost. Based on various morphological and physiological characters, this isolate was tentatively identified as Azotobacter sp. Among the different isolates of phosphate solubilizing bacteria, the isolate 1 which showed maximum solubilization of tricalcium phosphate in modified Pikovskaya's broth was selected for enrichment of vermicompost. Based on the various morphological and physiological characters, the isolate 1 was tentatively identified as Pseudomonas sp. In the study on the enrichment of vermicompost with nitrogen fixing bacteria on growth of chilli, the shoot fresh and dry weights were significantly high in the treatment combination receiving vermicompost enriched with Azotobacter sp. along with 50 per cent nitrogen (N3P1K+VN) when compared to the control treatment. The per plant yield was significantly high in the treatment combination with 100 per cent nitrogen and vermicompost enriched with Azotobacter sp. (NIP1K+VN) followed by that receiving 75 per cent nitrogen and vermicompost enriched with Azotobacter sp. (N2P1K +VN). In the study on the use of vermicompost enriched with phosphate solubilizing bacteria, there were significantly earlier onset of flowering and significantly higher number of fruits formed per plant in the treatment combination of 100 per cent phosphorus along with vermicompost enriched with Pseudomonas sp. There were no significant differences between treatments in the keeping quality of chilli harvested from treatments with enriched vermicompost. III the interaction study between Eudrilus eugeniae or Megascolex sp. and Pythium aphanidermatum, there was 100 per cent seedling mortality in treatments such as. POP(F)+P and POP(V)+P where the application of Pythium aphanidermatum was coupled with surface injury in the collar region of seedlings. But in the absence of such an induced injury, there was no incidence of damping off. However, in these treatments the plant growth was generally poor in height, fresh and dry weight of roots. At the same time, the plant growth was better in treatments without pathogen inoculation. The number of branches formed was significantly high in POP(F)+E and POP(V)+E treatments where Eudrilus eugeniae was applied when compared to that of the control treatment. The treatment with vermicompost alone (POP (V» recorded significantly earlier onset of flowering. The number of fruits formed per plant and per plant yield were significantly higher in the treatment with farm yard manure and Eudrilus eugeniae (POP (F)+E) compared to the control. Significant differences between treatments were observed in the onset of flowering, number of fruits formed and in the per plant yield of chilli due to the combined application of Megascolex sp. and Pythium aphanidermatum. Flower initiation was earlier as well as the number of fruits formed were also significantly high in the treatments with vermicompost either alone (POP (V» or in combination with Megascolex sp. (POP(V)+M). The treatment with vermicompost alone recorded the highest per plant yield. There were no significant differences between treatments in the keeping quality of chilli harvested from treatments with or without the application of either Eudrilus or Megascolex sp. and Pythium aphanidermatum.

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