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Open Access
Management of bitter gourd mosaic by enhancing host resistance
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2015) Ashwini, K N; KAU; Vimi, Louis
Bitter gourd (Momordica charantia L.) is one of the important vegetable crops that occupy a pivotal position among fruit vegetables, particularly in south India. The fruits of this crop which have high commercial value and are being used for culinary preparations and various medicinal preparations. In spite of the economic importance of this vegetable, the research work carried out on protection of crop from viral disease is quite scanty. In many case, cent per cent mosaic incidence was recorded in the crop resulting in substantial economic loss. So the present study was focused on screening of bitter gourd accessions and management of bitter gourd mosaic by enhancing host resistance using defense inducers. The three different viruses causing mosaic in bitter gourd are cucumber mosaic virus (CMV), potyvirus and bitter gourd distortion mosaic virus (BDMV). As these viruses causes mixed infection in field, the separation of individual viruses was carried out using systemic indicator host plants. For separation of CMV and potyvirus, systemic indicator host plants used were cosmos and papaya respectively. BDMV was separated by white fly transmission. The pure cultures of viruses were maintained on the susceptible bitter gourd variety Preethi. The symptoms developed by different viruses were recorded under natural and artificial conditions were recorded CMV produced mosaic specks, yellow-green mosaic patches, leathery leaves and downward rolling of leaf margin. Symptoms of potyvirus infection were vein clearing, puckering, malformed leaf with reduced leaf size and rugosity. BDMV infection produced mosaic, puckering, leaf distortion, hairy growth on leaves and vines with reduction in leaf size and internodal length. For the screening of bitter gourd accessions against CMV and potyvirus, potassium phosphate buffer pH 7.0 was found to be the most suitable buffer. Among 22 accessions screened, three accessions viz., TCR 285, TCR 39 and TCR 53 were highly resistant to CMV; one accession Biliagala was highly resistant to potyvirus and 11 accessions viz.,TCR 285, TCR 39, TCR 493 ,TCR 416, TCR 492, TCR 494,TCR 380, TCR 202 and TCR 149, Green long and Biliagala were highly resistant to BDMV. The field experiment was undertaken with the objective of management of bitter gourd mosaic by using defense inducers. The three different defense inducers viz., salicylic acid 25 ppm, barium chloride 0.1% and Pseudomonas fluorescens 2 % were evaluated on the moderately resistant cultivar white long and susceptible variety Preethi. The mosaic symptom was recorded after 51 days of sowing in salicylic acid treated plants and after 40 days of sowing in control. A time gap of 5-10 days after spray of defense inducer was required for development of resistance in plants. The lowest disease severity was observed in cultivar White long treated with salicylic acid. The highest yield was recorded in Preethi treated with Pseudomonas fluorescens.
Open Access
Molecular detection and characterization of phytoplasma infecting brinjal (solanum melongena L.)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2015) Saranya, S S; KAU; Umamaheswaran, K
The study entitled “Molecular detection and characterization of phytoplasma infecting Brinjal (Solanum melongena L.) was conducted at the Department of Plant Pathology, College of Agriculture, Vellayani, with the objectives to study the symptom development, transmission, molecular detection and characterization of phytoplasma infecting brinjal and its relationship with phytoplasma diseases of other crop plants. Brinjal little leaf (BLL), collected from the Crop museum, College of Agriculture, Vellayani and catharanthus little leaf (CLL) obtained from Coimbatore were maintained for further studies. Symptomatology revealed the characteristic little, narrow, soft, glabrous and smooth leaves produced as clusters along with yellowing, proliferation of axillary shoots, shortened internodes, stunted bushy or rosette appearance and phyllody, the conversion of floral parts into leaf like structures. The graft transmission was found to be 100% successful while the percentage transmission by dodder was only 10% in brinjal and 20% in catharanthus. Phytoplasma was maintained in vivo in plants by grafting and in vitro by culturing the infected explants on MS media supplemented with 0.2 mg l-1 BAP, 0.6 mg l-1 NAA and 0.4 mg l-1 IAA. Biochemical analysis of healthy and diseased plants revealed that the contents of protein, phenol and chlorophyll were reduced in the inoculated plants as a result of phytoplasma infection. Carbohydrate content in brinjal increased immediately after inoculation and then decreased. The activity of peroxidase (PO) was enhanced in the inoculated plants while that of polyphenol oxidase (PPO) was reduced. The activity of phenyl alanineammonialyase (PAL) was reduced immediately after the inoculation, but enhanced at 30 and 60 days after inoculation (DAI). 91 92 The electrophoretic analysis of proteins using SDS-PAGE revealed the presence of two extra protein bands in the infected samples with molecular weights of 29 kDa (Kilo Dalton) and 43 kDa. The isozyme pattern analysis of peroxidase using native PAGE revealed two isoperoxidase bands in the inoculated plants with Relative mobility (Rm) values, 0.17 and 0.47, but a single band in healthy plants with Rm value of 0.17. Molecular detection was done using nested PCR. PCR products of ~1.8 kb (Kilo base) were obtained in direct PCR with phytoplasma universal primer pair P1/P7 and the nested PCR with P1/P7 followed by R16F2n/R16R2 amplified the fragment of size 1.2 kb. The presence of phytoplasma in tissue culture plants was also confirmed using nested PCR. Comparative nucleotide sequence analysis of brinjal and catharanthus isolates with the existing data base from NCBI revealed a 100% homology with brinjal little leaf phytoplasma isolates from Haryana and IARI and 99% homology with potato witches’ broom, potato purple top, tomato big bud phytoplasma etc. The 16S rDNA sequences of BLL and CLL phytoplasma shared 99.7% similarity with that of ‘Candidatus Phytoplasma trifolii (Ca. Phytoplasma trifolii)’. Thus the two phytoplasma isolates were identified as the related strains of ‘Ca. Phytoplasma trifolii’.
Open Access
Potential of fortified spent mushroom substrate for the management of soil borne diseases of tomato
(Department of plant pathology, College of horticulture,Vellanikkara, 2015) Arathikrishna, V K; KAU; Sheela Paul, T
Mushrooms are produced on natural materials taken from agricultural waste. SMS is the substrate left after harvesting of mushroom fruit bodies. SMS contains a diverse range of soil microorganisms. This is proven by its disease suppressing properties and its effectiveness in bioremediation. Additions of microorganisms to soil ultimately enhance and accelerate regular soil process such as nutrient mobilization. Among the beneficial uses of SMS the disease controlling property is quite interesting. Tomato is one of the most widely used vegetable. The bacterial wilt and damping off are the two serious soil borne diseases of this crop. The management of diseases using chemicals is not safer to environment due to residual problem. Increasing concern regarding food safety and environmental pollution has generated an interest in eco friendly practices like soil amendment and application of biocontrol agents to manage the plant diseases. Under these circumstances this study was taken up to assess nutritional and disease management aspects of fortified SMS in tomato The antagonists used for this study like Trichoderma hamatum, T. viride and Bacillus subtilis are the isolates from SMS obtained from the previous studies conducted in the Department of Plant Pathology along with reference cultures of Kerala Agricultural University viz. T. viride and Pseudomonas fluorescens. They were evaluated against major soil borne fungal pathogens like Pythium aphanidermatum, Phytophthora palmivora, Fusarium oxysporum, Rhizoctonia solani and Sclerotium rolfsii and bacterial pathogen Ralstonia solanacearum of tomato. The in vitro evaluation showed that T. hamatum was the best among three fungal antagonists. While in case of bacteria P. fluorescens was the best. A microbial consortium of these two organisms was also prepared. The selected best antagonists and consortium were applied to SMS @ 300 ml per kg and kept for biosoftening for 60 days. The fortified SMS with P. fluorescens softened the SMS to a certain level. The primary nutrients like N, P, K, secondary nutrient Ca and micro nutrient Cu were found to be decreased as the time increases. In the pot culture experiment for the management of damping off, the treatment SMS fortified with consortium gave maximum per cent inhibition against the disease. In the management of bacterial wilt also SMS fortified with consortium found to be best in disease suppression as well as plant growth promotion. All the treatments with SMS were found to posses disease management property and enhance the plant growth. From this study it is clear that fortified SMS paves a new way in disease management. For confirmative result, elaborative field study has to be conducted and the quality of SMS has to be worked out.
Open Access
Standardization of techniques for cultivation of button mushroom (Agaricus spp.) in Kerala
(Department of Plant Pathology, College of Agriculture, Vellayani, 2015) Lishma, N P; KAU; Lulu Das
The work entitled "Standardization of techniques for cultivation of Button mushroom (Agaricus spp.) in Kerala" was conducted during the period 2013 - 2015 at College of Agriculture, Vellayani. The aim of study was to explore the possibility of cultivation of Agaricus species and develop a modified technique for the production of quality compost with alternative agricultural waste. A preliminary survey was conducted for the collection of various isolates of Agaricus spp. during and after south - west monsoon in different locations. The five isolates obtained along with the two isolates available at AICRP centre, Vellayani were sent to DMR and accession numbers were obtained for all the isolates.The isolate 7 identified as Agaricus bisporus (Lange) Imbach which showed maximum growth on potato dextrose agar as well as intensive spawn run on paddy grains was selected for further studies. Studies revealed that maximum vegetative growth was observed on potato dextrose agar and it preferred a temperature of 24 °C with a pH of 6. It was also observed that dark phase favoured the growth of A. bisporus. Among the different carbon and nitrogen sources tested, glucose and beef extract supported maximum growth of A. bisporus. The study on evaluation of different substrates for spawn production revealed that in paddy grains spawn run was completed within twelve days which was the best. Evaluation of various compost and casing material combinations revealed that pearl millet straw, poultry manure, urea and gypsum + coir pith was the best with a total yield after three harvests of 325.97 g per kg bed followed by pearl millet straw, poultry manure, urea and gypsum + tea waste (301.76 g per kg bed). No mycelial growth was observed in all combinations of sawdust, poultry manure, urea and gypsum as well as wheat bran, poultry manure, urea and gypsum with different casing materials. The pest and disease incidence during the cultivation period of A. bisporus was studied and it was observed that sciarid flies and staphylinid beetles were prevalent during sporocarp formation. The competitive fungi recorded were Trichoderma sp. and Coprinus sp. during spawn run, casing and sporocarp formation. The study also showed that mushrooms stored under refrigeration (4 °C) had maximum shelf life of 7 days compared to those stored at room temperature. Sensory evaluation of mushroom recipes were carried out by a panel of judges for attributes like colour, texture, flavor and taste using a five point score card. Among the various products mushroom soup obtained an overall acceptability of 4.7. From this study it can be concluded that growth of A. bisporus was maximum in potato dextrose agar at a temperature of 24 °C with a pH of 6 in dark phase. Glucose and beef extract were found to be the best carbon and nitrogen sources respectively. Compost prepared from pearl millet straw, poultry manure, urea and gypsum overlaid with coir pith compost as casing material supported maximum growth and yield of A. bisporus.
Open Access
Immunomolecular detection and characterisation of potyviruses infecting cowpea (Vigna unguiculata (L>) Walp.) and papaya (Carica papaya L.)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2015) Krishnapriya, P J; KAU; Umamaheswaran, K
The study entitled “Immunomolecular detection and characterisation of Potyviruses infecting cowpea (Vigna unguiculata (L.) Walp) and papaya (Carica papaya L.)” was conducted at Department of Plant Pathology, College of Agriculture, Vellayani, Thiruvananthapuram during 2013-2015 with the objective to study the symptomatology and transmission of Potyviruses infecting cowpea and papaya, along with their biological, immunological, molecular detection and characterisation. Symptoms caused by Blackeye cowpea mosaic virus (BlCMV) in cowpea include mosaic and vein banding and that of Papaya ring spot virus (PRSV) in papaya showed mosaic and shoe string on leaves and ring spot on fruits and leaves. BlCMV and PRSV were mechanically transmitted (80 and 100 per cent respectively). Seed transmission (48.5 per cent) was recorded for BlCMV in cowpea. PRSV was not transmitted through seeds. BlCMV was transmitted by Aphis craccivora Koch and Aphis gossypii Glover (30 per cent respectively). Papaya mealy bug (Paracoccus marginatus Williams and Garnara de Willink) (80 per cent) was the most efficient vector of PRSV followed by Aphis gosssypii Glover (40 per cent) and Aphis craccivora Koch (30 per cent). Host pathogen interaction studies in resistant and susceptible genotypes of the cowpea (CO6 and Vellayani Jyothika) and papaya (Pusa Nanha and local variety) indicated a significant reduction in total carbohydrates and chlorophyll contents in susceptible genotypes on inoculation with Potyviruses, whereas resistant genotypes showed no significant difference. However, phenol, protein and defense related enzymes showed a significant increase in resistant genotypes on inoculation, compared to the susceptible genotypes. Sodium dodecyl sulphate-Polyacrylamide gel electrophoresis (SDS-PAGE) and native-PAGE were conducted for the comparison of proteins and isozymes respectively, in resistant and susceptible genotypes. Eleven novel proteins were induced in CO6 whereas ten new proteins were observed in Vellayani Jyothika. Nine and eight induced proteins were identified in Pusa Nanha and local variety of papaya respectively. Three isoperoxidases with Relative mobility (Rm) values of 0.13, 0.20 and 0.27 were unique for CO6. There was no unique isozyme on inoculation in Vellayani Jyothika. Isoperoxidases with Rm values of 0.08 and 0.23 were unique for Pusa Nanha. However no specific isozyme was observed in local variety of papaya. Chenopodium amaranticolor and Chenopodium quinoa were identified as indicator plants for the biological detection of BlCMV and PRSV. Immunological studies using Direct antigen coating-Enzyme linked immunosorbent assay (DAC-ELISA) and Dot immunobinding assay (DIBA) and molecular detection viz. Reverse transcription-Polymerase chain reaction (RT-PCR) identified the Potyviruses as Bean common mosaic virus (BCMV) strain Blackeye and PRSV respectively. Comparative amino acid sequence alignment revealed a 95 and 100 per cent homology with coat proteins of BCMV and PRSV respectively. The transmission studies revealed that Potyviruses were transmitted mechanically and by insects. Present study also revealed that BlCMV was transmitted through seeds while, PRSV was not seed transmitted. The host pathogen interaction studies identified phenol, protein and defense related enzymes along with induced proteins and isoforms of peroxidase could be used as biochemical markers to identify resistance and susceptibility in plants. The present molecular study confirmed that BlCMV infecting cowpea was closely related to BCMV, a strain of Blackeye. PRSV in the present investigation was found related to PRSV isolates reported from other parts of India. Comparative sequence analysis of BlCMV and PRSV Potyviruses showed that the sequences were entirely different and showed only a 51.12 per cent similarity at nucleotide levels. Serological and sequence studies thus suggest that BlCMV caused the mosaic disease in cowpea and PRSV, the ring spot disease in papaya.
Open Access
Integrated management of anthracnose in chilli (Capsicum annuum L.)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2015) Shilpa, Treasa Chacko; KAU; Gokulapalan, C
The study entitled “Integrated management of anthracnose in chilli (Capsicum annuum L.)” was conducted at Department of Plant Pathology, College of Agriculture, Vellayani, Thiruvanathapuram during 2013-2015 with the objective to evolve an integrated management package for anthracnose in chilli. Nine isolates of the pathogen causing chilli anthracnose were isolated and based on morphological characters like colony colour, conidial shape and dimensions, the pathogens causing fruit rot disease of chilli were identified as Colletotrichum capsici (Syd.) Butler and Bisby and Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. which was further confirmed and deposited at Agharkar Research Institute, Pune with accession number NFCCI- 3411 & NFCCI- 3412, respectively. Pathogenicity was proven following Koch’s postulates and virulence rating was done. From this the most virulent isolate C2, an isolate of C. capsici was selected for the further studies. The results of standard blotter test and standard agar plate method revealed that C. capsici and C.gloeosporiodes infection in chilli is seed borne in nature. The results also indicated the dominance of C. capsici (44.66 per cent) followed by C. gloeosporioides (12.00 per cent), Alternaria sp. (0.50 per cent). Saprophytic fungi recorded were Penicillium sp. (0.16 per cent) and Aspergillus sp. (0.16 per cent). The study showed that C. capsici survived for 77 days in the infected fruits and leaves in the soil and 42 days in the lab condition. The host range studies revealed that the solanaceous crops brinjal (Solanum melongena L.) and tomato (Solanum lycopersicum L.) at fruiting stage were found to be alternative hosts of C. capsici under natural conditions. However on artificial inoculation of C. capsici, brown lesions were observed on leaves of green gram (Vigna radiata L.), ivy gourd (Coccinia indica L.), sesame (Sesamum indica L.), black gram (Vigna mungo L.) and sweet potato (Ipomoea batatus L.). Natural incidence of disease was observed on weeds Richardia scabra L. (Tropical girdlepod) and Commelina benghalensis L. (Tropical spiderwort). The predominant micro-organisms isolated from chilli phyllosphere, pomoplane and rhizosphere Penicillium citrinum, Trichoderma viride, Bacillus and Pseudomonas flourescens exhibited 56.23 per cent, 64.45 per cent, 88.88 per cent and 73.33 per cent inhibition of the pathogen respectively under in vitro conditions. In vitro assay of fungicides with poisoned food technique revealed that propiconazole (0.15 per cent), difenoconazole (0.05 per cent) and mancozeb (0.2 per cent) completely inhibited the mycelial growth of C. capsici. It was followed by azoxystrobin (0.15 per cent), captan+hexaconazole (0.1 per cent), carbendazim (0.1 per cent) with mycelial inhibition of 97.77 per cent, 88.30 per cent and 83.33 per cent respectively. No mycelial growth of the pathogen was observed in chlorothalonil (0.1 per cent) amended media. Among organic preparations, panchagavya provided complete inhibition of the growth of the pathogen at all the concentrations tested. Jeevamruth provided complete inhibition only at 10 per cent concentration, whereas, the amendment of media with fish amino acid did not affect the mycelial growth of the pathogen. Chilli seedling assay of different bioagents for the control of disease on seedlings revealed that the percentage seedling mortality was lowest for the seeds treated with the biocontrol bacterium Bacillus sp. (10.46 per cent) isolated from phyllosphere and pomoplane followed by the KAU released biocontrol agent Pseudomonas flourescens (15.36 per cent). Piriformospora indica treated seeds exhibited 45.36 per cent mortality.Seedling assay with fungicides revealed that seeds treated with propiconazole (0.1 per cent) exhibited the lowest seedling mortality (10.37 per cent). A pot culture study conducted with chilli variety Vellayani Athulya to evaluate the efficacy of organic preparations, biocontrol agents and fungicides and it revealed that maximum disease suppression was provided by foliar spraying of 0.1 per cent propiconazole (62.85 per cent) and 0.05 per cent difenoconazole (61.06 per cent) at fortnightly intervals. Among the biocontrol agents, Bacillus sp. was found to be superior in suppressing the disease (59.59 per cent) and among organic preparations, panchagavya gave the maximum suppression of the disease (57.06 per cent). Based on the results of the study, an integrated management package for anthracnose in chilli is proposed as follows: Seed treatment with systemic fungicides like propiconazole (1 ml kg-1) or biocontrol agents like Pseudomonas fluorescens 10 g kg-1 prevent seed borne infection , removing infected crop debris and destroying alternative hosts such as tomato, brinjal, green gram, black gram, sesamum, ivy gourd and sweet potato and weed hosts such as Richardia scabra and Commelina benghalensis prevent disease incidence and foliar spraying of propiconazole (1 ml l-1) or difenoconazole (0.5 ml l-1) or panchagavya (2.5 ml l-1) at fortnightly intervals after the onset of the disease controls the disease.
Open Access
Integrated management of sigatoka leaf spot disease of banana caused by Mycosphaerella musicola R. leach ex J. L. mulder
(College of Agriculture, Vellayani, 2015) Nayana, K; KAU; Radhakrishnan, N V
Banana (Musa spp.), being the fourth most important food after rice, wheat and maize products, it tolls up as a major fruit crop of India. Among the various diseases of this crop, Sigatoka leaf spot disease is a serious factor limiting the productivity of the same. It causes losses by reducing the functional leaf surface of plant, which results in small bananas that fail to ripen and may fall. Hence a field study entitled “Integrated management of Sigatoka leaf spot disease of banana caused by Mycosphaerella musicola R. Leach ex J.L. Mulder” was conducted at Coconut Research Station, Balaramapuram with an objective to study the effect of Pseudomonas fluorescens, the secondary nutrient magnesium, the micronutrients, zinc and boron and new generation fungicides on growth, incidence of Sigatoka leaf spot disease and yield of banana as intercrop in coconut gardens. The parameters studied were grouped into four main categories namely disease factors, weather factors, biochemical or physiological responses and growth and yield characteristics. Studies were conducted to assess the effect of treatments on disease intensity and incidence revealed that, there was a reduction in disease factors during all months with respect to treatments in contrast with the control plots. In both the case of disease incidence and disease intensity all the treatments were significantly superior over control. With respect to the disease incidence studies, it is clear that fungicide alone or combination treatments of the same along with Micronol or Mg + Zn + B is highly effective to lower the disease incidence. Disease intensity studies indicated that, foliar spray of new generation systemic fungicides such as tebuconazole, propiconazole or the contact fungicide copper hydroxide gave better disease suppression of yellow Sigatoka disease. The pathophysiological studies of chlorophyll content revealed that there was an increase in chlorophyll content in all the treatments. Mainly the combination treatments of fungicides with Mg + Zn + B and Bio control agent (PGPR mix II). There was an increase in magnesium content, boron content and zinc content in all combination treatments when compared to the alone treatments and from the untreated plants. But in case of protein content analysis, there was a decrease in total protein content in treated plants, mainly in the plants treated with systemic fungicides. The activity of defense related phenol and OD - phenol study exhibited that, there was an increased phenol content in treated plots. Effect of treatments on plant height and plant girth indicated that all treatments resulted in higher height and girth observed in control at harvest stage. Study of the other growth parameters like number of leaves and number of functional leaves also resulted in the same conclusion that a 1.5 to 2 fold per cent increase in number of functional leaves at harvest stage where as 0.5 fold per cent increase in number of leaves in all the treated plants when compared to the absolute control. The study of yield per plant revealed that, 0.5 to 1 fold per cent increase in bunch weight. The other yield parameter studies revealed that the total number of hands, fingers per bunch and number of suckers were more than in untreated plots whereas, the number of days took for bunch emergence and bunch maturity was comparatively lower in case of treatment with maximum bunch yield, T5, Mg + Zn + B plus tebuconazole @ 0.1%. The maximum number of days took for bunch emergence and bunch maturity was in absolute control. Hence the results of integrated management for banana Sigatoka disease with respect to disease management, yield attributing characteristics were effective in the field trial that conducted. The economic analysis also revealed that the best inorganic treatment is application of Mg + Zn + B plus tebuconazole (0.1%) which recorded the highest yield, net income and benefit cost ratio which is followed by Mg + Zn + B plus PGPR (20 g l-1) under organic treatments. For the integrated management of banana Sigatoka leaf spot disease (caused by M. musicola R. Leach ex J.L. Mulder) in humid tropical southern zone of Kerala, the best treatment was found to be; Mg (2 g l-1) + Zn (3 g l-1) +B (2 g l-1 ) plus tebuconazole (0.1%) with aspect of maximum disease suppression, disease intensity reduction and highest yield.
Open Access
Characterization of rhizosphere and endophytic microflora from organically grown amaranth for management of leaf spot diseases
(College of Horticulture, Vellanikkara, 2015) Aparna, V S; KAU; Sainamole, Kurian P
Amaranth is the most important and popular leafy vegetable of Kerala. Rapid growth, quick rejuvenation after each harvest, higher yield per unit area and easiness in cultivation make it the cheapest vegetable which is rightly described as the ‘poor man’s spinach’. However, leaf spots and blights caused by fungal pathogens are serious threats to amaranth growers. The present investigation was carried out to explore the influence of various organic sources of nutrients on leaf spot diseases and to characterize potential antagonists from organically grown amaranth for management of these diseases. During the study, the pathogen causing leaf blight disease was isolated as this was the only foliar disease observed on amaranth plants grown for the field experiment. The cultural and morphological characters of the pathogen along with pathogenicity on amaranth confirmed it as Rhizoctonia solani (Kuhn). Population of fungi, bacteria and actinomycetes present in different organic sources of nutrients viz., farm yard manure, neem cake, vermicompost and poultry manure were estimated. Poultry manure contained the highest number of microflora per unit weight. A field experiment was conducted to study the effect of different organic sources of nutrients on leaf blight, growth and yield of amaranth. The results revealed that, there was no significant difference among organic sources of nutrients on disease severity. However, rate of growth indicated by various biometric parameters was the highest in plants grown with poultry manure (T5) as organic nutrient source. The population of rhizosphere microflora was estimated at periodical intervals i.e. pre-treatment, 30, 60 and 75 days after transplanting. The results revealed that, after application of organic sources of nutrients the microflora increased in the rhizosphere up to 60 days after transplanting. Bacteria were predominant in rhizosphere followed by fungi and actinomycetes. The pre-treatment fungal, bacterial, fluorescent pseudomonad and actinomycete population was not significantly different. But the population varied significantly among the treatments throughout the period of experiment. The endophytic microorganisms from stem and roots showed that endophytes were lesser in number compared to rhizosphere microorganisms and bacteria are predominant in the endosphere of amaranth plants. In general, both fungi and bacteria are more in roots. Actinomycetes could not be isolated from any of the samples. Based on colony characters, 123 different isolates were collected from rhizosphere and endosphere of amaranth plants in which 25 fungal and 36 bacterial isolates showed antagonistic activity against R. solani. These were further evaluated under dual culture. From rhizosphere the bacterial isolate RB-21(65.33%) had the highest per cent inhibition against R. solani immediately followed by RB-14 (63.33%). From endosphere EB-2 (62.66%) showed maximum per cent inhibition and the fungal isolate, EF-8 recorded cent per cent inhibition of the pathogen. These were selected for evaluation in pot culture experiment. A pot culture experiment was conducted to study the efficacy of organic sources of nutrients and selected antagonists on management of leaf blight of amaranth. Even though there was 100 per cent disease incidence in all the treatments, significant difference was observed in the case of per cent disease severity. The plants treated with RB-14 (T8) at 15 DAT, EF-8 (T9) at 30 DAT and RB-14 (T6) at 45 DAT exhibited less disease severity during the period of experiment. It was observed that T10 (Trichoderma viride of KAU) had the highest value for most of the biometric parameters and T9 (EF-8) was the second best in promoting plant growth. Based on cultural, morphological and biochemical properties, the selected bacterial isolates, RB-21 and RB-14 were tentatively identified as fluorescent Pseudomonas sp. and EB-2 as non-fluorescent Pseudomonas sp. Based on conidia and conidiophore characters, the fungal isolate (EF-8) was identified as Trichoderma sp.
Open Access
Choanephora pod rot of cowpea and its ecofriendly management
(College of Agriculture, Vellayani, 2015) Milsha, George; KAU; Girija, V K
The study entitled “Choanephora pod rot of cowpea and its ecofriendly management” was undertaken in the Department of Plant Pathology, College of Agriculture, Vellayani during 2013-2015 with the objective to study the symtomatology, etiology and to develop an ecofriendly management strategy for Choanephora pod rot of cowpea. The pathogen causing the pod rot of cowpea was isolated from the diseased pods, leaves, peduncle, stem and flowers. Pathogenicity was proven following Koch’s postulates, virulence rating was done and the C3 isolate obtained from cowpea pods were found to be the most virulent isolate. Based on cultural and morphological characters, the pathogen was identified as the Choanephora cucurbitarum (Berk. &Ravenel) Thaxt., which was further confirmed by ITS sequencing. The study revealed that the C. cucurbitarum had wide host range encompassing other vegetable crops such as bhindi, cucurbits, chilli, amaranthus and brinjal. Natural incidence of the disease was not observed on any weeds in and around the cowpea fields. However, on artificial inoculation of the pathogen, the spreading hogweed (Boerhaavia diffusa L. Noms. Cons) took up infection. The dual culture technique to study the antagonism of the saprophytic mycoflora isolated from the rhizosphere and fructosphere through serial dilution and plating indicated that Trichoderma virens and Pseudomonas fluorescens exhibited 79.50% and 55% percentage inhibition of the pathogen. The effectiveness of organic preparations such as panchagavya, jeevamruth, fish amino acid, vermiwash and compost tea was tested at different concentrations by poisoned food technique. Amendment of media was also done with autoclaved and filtered organic preparations. Vermiwash at 2.5%, 5% and 10% filtered as well as incorporated to media as such, significantly suppressed C.cucurbitarum. Jeevamruth (10%) and Panchagavya (10%) gave complete inhibition of the pathogen. Panchagavya (10%) incorporated after filtration and autoclaving also gave 100% and 94.4% suppression of the pathogen respectively. The application of effective dose of organic preparations on excised pods showed that panchagavya (10%) caused maximum suppression of pod rot (60.64%). Among the biocontrol agents, the selected bacterial antagonist i.e., P. fluorescens showed complete suppression of the disease when applied on the excised pods. A pot culture study was conducted to evaluate the efficiency of organic preparations, biocontrol agents and fungicides. The maximum disease suppression of 99.72% was observed in plants sprayed with copper hydroxide. The organic preparation, fish amino acid suppressed the disease to 87.33%. Application of effective biocontrol agent T. virens yielded 75.27% suppression of pod rot. The ecofriendly management of the disease can be achieved by application of fish amino acid (10%) or T. virens (106cfu/ml) or fungicides such as copper hydroxide (0.2%), mancozeb (0.3%) and propiconazole (0.1%) during the pod formation stage.

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