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Open Access
Endophytic microorganism mediated systemic resistance in Cocoa against Phytophthora palmivora (Butler) Butler
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2011) Sainamole Kurian, P; KAU; Koshy Abraham
The study on 'Endophytic microorganism mediated systemic resistance in cocoa against Phytophthora palmivora (Butler) Butler was carried out during 2005-2010. The pathogen causing pod rot of cocoa was isolated from infected pods , and its pathogenicity established. Based on cultural and morphological characters, it was identified as Phytophthora palmivora (Butler) Butler. Endophytes were isolated from samples of feeder roots, tender shoots, leaves and pods of cocoa collected from various locations of major cocoa growing area of the state. The population of endophytic microflora varied among different locations and parts of the plant, and in general, the population was more in roots. Bacteriaand fluroscent pseudomonads were more abundant than filamentous fungi and yeasts. Out of the 325 endophytic isolates comprising of 116 bacteria, 153 fluorescent pseudomonads, 34 years and 22 fungi, 82 were found exerting antogonism towards the pathogen. These antagonistic endophytes were further evaluated in In vitro by dual culture and by inoculation on detached cocoa pods, and leaves. It was found that, 25 isolates were more efficient antagonists.
Open Access
Pathogenic and genetic variability in Xanthomonas oryzae pv. oryzae (Ishiyama) Swings et al. and the management of bacterial blight disease
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2013) Purushothaman, S M; KAU; Rehumath Niza, T J
Bacterial blight of rice is a major threat in rice cultivation causing huge yield loss to the crop. Realizing the practical importance, an investigation entitled on “Pathogenic and genetic variability in Xanthomonas oryzae pv.oryzae (Ishiyama) Swings et al. and management of bacterial blight disease” was carried out during 2006-2011. A series of surveys conducted in 14 locations of three major rice growing districts (Alappuzha, Palakkad and Thrissur) of Kerala during September 2007 to find out the occurrence of bacterial blight disease. High incidence was recorded in Palakkad district. During, the survey, the characteristic symptom of bacterial blight as yellow lesions on the both the margins of the leaf leaving a green area in the centre of leaf were observed. The pathogen causing bacterial blight of rice was isolated from 14 locations of the said districts and their pathogenicity was established. Based on the cultural, morphological and biochemical characters, the pathogen was identified as Xanthomonas oryzae pv.oryzae (Xoo) (Ishiyama) Swings et al. The 14 isolates showed slight variation in their cultural, morphological and biochemical characters. Pathotype studies were conducted in net house using 14 isolates on 20 popular and commonly cultivated rice varieties, six near isogenic lines having different R genes/gene combination and two rice differentials with no genes. It could distinguish the virulence spectrum of the isolates into three groups/categories namely ‘highly virulent’, ‘moderately virulent’ and ‘weakly virulent’ isolates/strains. The study on the kresek symptom also confirmed the above finding. BOX and ERIC-PCR fingerprinting depicted the existence of high level of genetic variability among the pathogen population in the rice growing areas of Kerala. In vitro sensitivity of six bactericides against the four highly virulent isolates of Xoo revealed that tetracycline 250 ppm, tetracycline 100 ppm, tetracycline 50 ppm, streptocycline 250 ppm, streptocycline 200 ppm and Bactrinashak 250 ppm were effective against the pathogen. In vitro sensitivity of different organics and agrochemicals revealed that cow dung extract 2% + vermicompost extract 2%, cow dung extract 2% + P. fluorescens 2%, vermicompost extract 2% + P. fluorescens 2%, vermicompost extract 2 %, copper hydroxide 0.15% were found effective against the pathogen, in that order. The 110 bacterial isolates obtained from rice rhizosphere, rice endosphere and cowdung and vermicompost, screened against the Polpully virulent pathogen could yield six prominent bacterial isolates viz., RE-1, RR-26, RR-53, CB-39, VB-67 and VB-69 and were tentatively identified as Pseudomonas sp. Pot culture experiment, showed that tetracycline 250 ppm, tetracycline 100 ppm, streptocycline 250 ppm, Bactrinashak 250 ppm, tetracycline 50 ppm, bacteria from cow dung (CB-39), bacteria from vermicompost (VB-69), endosphere bacteria (RE-1), rhizosphere bacteria (RR-26), cow dung extract 2% + P. fluorescens 2%, vermicompost extract 2% + P. fluorescens 2% and cow dung extract 2% + vermicompost extract 2%, rhizosphere bacteria (RR-53) and copper hydroxide 0.15% were found best in managing the bacterial blight disease. Seven bacterial antagonists viz., RE-1, RR-26, RR-53, CB-39, VB-67 VB-69 and Pf1 when subjected to compatibility studies against Xoo under in vitro showed 17 combinations, showing synergistic effect in inhibiting the Xoo. In the compatibility study of seven antagonists with nine pesticides, 71 two way combinations were found synergestic effect against Xoo. The compatibility of 13 agrochemicals under in vitro against Xoo, revealed that 50 two way combinations showed synergistic action in inhibiting the pathogen. Three two way combinations showed compatible action in inhibiting the pathogen. In the compatibility of four fertilizers viz., urea, rajphos, muriate of potash and ammonium sulphate showed that five two way combinations proved synergistic action in inhibiting the pathogen. All the seven antagonistic bacteria and 17 agrochemicals showed the compatible reaction in inhibiting Xoo. The seven bacterial antagonists were subjected for various growth promoting characters viz., ‘P’ solubilization, NH3 and HCN production. The six isolates differed slightly for the above characters. All the isolates could produce siderophore and IAA. A few isolates could produce non volatile metabolites. The field study established the most practical finding that the tetracycline 50 ppm, tetracycline 100 ppm, bacterial consortium (RE-1+CB-39), bacterial consortium (CB-39 +VB-69), bacteria from cow dung (CB-39), endosphere bacteria (RE-1), bacteria from vermicompost (VB-69), streptocycline 250 ppm, Bactrinashak 250 ppm, cow dung extract 2% + KAU-(Pf1) 2%, rhizosphere bacteria (RR-26) and KAU-(Pf1) 2% were found promising in managing bacterial blight disease of rice. Thus, apart from bactericides, there was a variety of highly promising organic management possibilities to combat the disease.
Open Access
Efficacy of ligno-phenolic compost in the suppression of soil borne plant pathogens
(Department of plant pathology, College of horticulture, Vellanikkara, 2015) Gleena Mary, C F; KAU; Sally K, Mathew
The study on the “Efficacy of ligno-phenolic compost in the suppression of soil borne plant pathogens” was carried out at College of Horticulture, Vellanikkara during 2011 -2014. The major objectives were to develop a microbial consortium for rapid composting of lignintannin rich agrowastes and also to study the effect of these composts on the management of leaf blight of amaranth and bacterial wilt of tomato. Sample of soils and partially degraded substrates were collected from 15 sources of 34 locations. Among them, ayurvedic wastes yielded maximum population of cellulose and lignin degraders whereas, tannin degraders were more in the samples of teak plantation. A total of 378 microbial degraders were isolated which included 125 cellulose, 133 lignin and 120 tannin degraders. Actinomycetes were the predominant degraders of cellulose and fungi were dominant among both lignin and tannin with majority belonged to Aspergillus spp. and Penicilium spp. In vitro evaluation of degraders on respective selective media showed diffusion zones more than 4cm by 31 cellulose, 39 lignin and 33 tannin degraders. Fungi were the most efficient degraders of cellulose, lignin and tannin. Thirty five degraders found effective on their respective selective media showed ability to degrade all the three chemical components. In vitro decomposition of 33 degraders on respective host substrates recorded lowest maturity periods of 40 and 43 days for the degraders isolated from ayurvedic waste and coir pith. The degraders, ALF-26, CLF-13, CCB-8, ECF-2, ECA-8, TLF-8, CaLF-5 and ATY-1were most effective on their respective host substrates and also on other tested lignintannin rich substrates in vivo. All the 22 selected degraders were found mutually compatible. Based on the ability to degrade all the three chemical components, early maturity of composting, type and species of organisms and mutual compatibility, 10 degraders viz. Trichoderma harzianum, Paecilomyces variotii, Penicillium oxalicum, P. chrysogenum, Talaromyces sp., Streptomyces albus, S. niveus, Arthrobacter sp. and Massilia sp.were selected for the formulation of microbial consortium. Screening of selected consortium under in vitro and in vivo condition showed early maturity of 35 and 43 days in mixed substrate followed by coir pith with 35 and 45 days. In large scale composting of various agrowastes with microbial consortium, cow dung slurry and the combination of both, the minimum maturity period was observed with microbial consortium as compared to other treatments recording 30, 35, 40 and 55 days for mixed substrate, coir pith, ayurvedic waste and leaf litters respectively. Composting with microbial consortium resulted in drastic reduction of C:N ratio of the composts with 47 -81 per cent reduction from the initial and the lowest in ayurvedic compost (10.4:1) .Composts treated with microbial consortium recorded neutral to alkaline pH and high contents of N, P and K with maximum N and P in ayurvedic and K in coir pith compost. Traces of lead detected in all compost samples were below the permissible limits. Composting with consortium showed reduction in cellulose, lignin and tannin contents with maximum reduction in ayurvedic (49.38 %), coir pith (49.02%) and leaf litter composts (98.95%) respectively. The degraders of the consortium were thermophilic and recorded extra cellular enzyme activities of cellulase, lignin peroxidase, polyphenol oxidase, amylase, catalase, protease and xylanase. The selected degraders showed antagonism against six major soil borne pathogens viz. Pythium sp., Phytophthora sp., Rhizoctonia sp., Fusarium sp., Sclerotium sp. and Ralstonia solanacearum and T. harzianum was the most effective one. In the field evaluation of various composts in the management of bacterial wilt of tomato and leaf blight of amaranth, application of ayurvedic compost was effective in reducing both diseases. In addition, coir pith and leaf litter composts also reduced bacterial wilt incidence and mixture compost in case of leaf blight.
Open Access
Enhancement of resistance to bacterial wilt in tomato by endophytic microbial communities
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2015) Deepa James; KAU; Sally K, Mathew
The study on “Enhancement of resistance to bacterial wilt in tomato by endophytic microbial communities” was conducted in the Department of Plant Pathology, Department of Agricultural Microbiology, and Centre for Plant Biotechnology and Molecular Biology, College of Horticulture, Vellanikkara during the period 2011-2014. The endophytes were isolated from root and stem of healthy tomato plants from 16 locations of north, central and south Kerala. Endophytic microbial population varied with the plant samples and the population was more in root than stem. Bacterial population was higher than fungi and actinomycetes in root and stem. Among 154 endophytes isolated, 12 out of 79 bacteria, 16 out of 68 fungi, and four out of seven actinomycetes were antagonistic to R. solanacearum in in vitro. Among them, five bacteria, eight fungi, and two actinomycetes were promising in planta. Mutually compatible endophytic isolates were selected for the development of consortia and these were identified based on cultural, morphological and molecular characters. Of the five consortia tested, the one consisted of Trichoderma viride-1, T. viride-2, T. harzianum-1, Bacillus subtilis, and Streptomyces thermodiastaticus showed effect in reducing wilt incidence. Comparative study of the microbial consortium with individual endophytes showed the higher efficacy of consortium in reducing the wilt incidence. The endophytes were reisolated from soil, root, and stem of tomato plants. In pot culture experiment, the consortium applied as seed treatment + seedling dip + soil application at 45 DAP showed the minimum wilt incidence. Studies on the mechanism of antagonism of endophytic isolates showed, positive reaction towards ammonia and negative for HCN and siderophore production. The volatile and nonvolatile metabolites of the endophytes inhibited the pathogen. The endophytes showed varying levels of IAA and salicylic acid production with the maximum in T. harzianum-1 and B. subtilis respectively. Study on the effect of secondary metabolites of endophytes on the disease indicated that, seedlings dipped first in culture filtrate for 2 h and later dipped in bacterial inoculum for 30 min before planting showed the lowest per cent wilt incidence with the minimum for T. viride-2. Induction of systemic resistance was studied by assay of defense related compounds such as phenols, oxidative enzymes and PR proteins. The plants treated with microbial consortium showed higher activity of the defense related compounds with the maximum in plants inoculated with both consortium and pathogen. Field evaluation of endophytic consortium against bacterial wilt showed reduction in wilt incidence of 40.85 per cent in highly susceptible variety, PKM-1, 46.94 per cent in susceptible F1 hybrid, COTH-3, and 52.81 per cent in moderately resistant variety, Mukthi. Thus, the study revealed that, the application of endophytic consortium can enhance the resistance mechanism in tomato against bacterial wilt pathogen, R. solanacearum.
Open Access
Phenotypic and molecular characterisation of phytophthora sp. inciting leaf fall of nutmeg
(College of Horticulture, Vellanikkara, 2015) Sumbula, V; KAU; Sally, K Mathew
The study on ‘Phenotypic and molecular characterisation of Phytophthora sp. inciting leaf fall of nutmeg’ was conducted in the Department of Plant Pathology, College of Horticulture,Vellanikkara during 2014-2015. The major objectives were to study the cultural, morphological and molecular characters and variability of different isolates of Phytophthora sp. associated with leaf fall of nutmeg and also to study the host range of the pathogen and to chalkout suitable management strategies Isolation of the pathogen from 18 samples from different locations revealed the association of the fungus, Phytophthora sp. and its pathogenicity was established under lab and in vivo conditions. Inoculation of the pathogen with culture disc on injured lower leaf surface showed early infection than that with zoospore suspension. Symptoms observed on leaves, shoot and fruits were almost same under both natural and artificial conditions. Variation in virulence was noticed among the isolates collected from different locations. The isolates, PPaL-1 and PPaF-17, from Parakkadavu, Thrissur and PSrL-10 from Sreemoolanagaram, Ernakulam were highly virulent. PKoL-2, the isolate from Kodissery was less virulent and other 14 were moderately virulent. Cultural and morphological characters of the isolates of pathogen were studied with different media viz. carrot agar, potato dextrose agar, oat meal agar, coconut water agar and V8 juice agar. Variation in cultural characters among the isolates was observed only in carrot agar and the variation in growth rate was noticed among the different media. Morphologically, mycelia of Phytophthora isolates from nutmeg were branched, coenocytic and hyaline and the sporangia were borne terminally /laterally on the sporangiophore in sympodial fashion, caducous, semi papillate, ovoid/elongated-ovoid/ellipsoid in shape with average size of 31.9-49.5 x 22.3 – 27.9 μm, L/B ratio of 1.4 – 1.8 and pedicel length of 10.21 – 20.24 μm. Early sporangial production was noticed in carrot agar and potato dextrose agar and the maximum count was in oat meal agar and carrot agar. Numerous chlamydospores were observed in all media. Comparison on the cultural and morphological characters of Phytophthora isolates of nutmeg with other Phytophthora spp. such as P. meadii, P. palmivora, P. capsici, P. colocasiae, P. citrophthora and P. ramorum revealed that, Phytophthora isolates from nutmeg could not be completely fitted into the phenotypic description of any of these known Phytophthora species. However, they showed some similarity to P. meadii, P. colocasiae and P. ramorum. In molecular characterisation, out of 18 isolates of nutmeg Phytophthora, 15 showed maximum homology with P. colocasiae and three viz. PPoL-3, PMaL-4 and PVaL-15 with P. meadii. Isolates PPaL-1, PKoL-2, PVeL-5, PKtL-6, PKaL-7, PMtL-8, PThL-9, PTuL-11, PKnL -12, PPaF-17 and PMoF-18 also showed homology with P. citrophthora and PMaL-4 and PSrL-10 with P. botryosa. Host range of Phytophthora isolate of nutmeg includes, rubber, vanilla, rose, Coreopsis, Eucalyptus and Citrus. Nutmeg is also a host of P. meadii of vanilla and P. citrophthora of Citrus and non host of P. palmivora, P. capsici, P. colocasiae, P. meadii of arecanut, rubber and cardamom. Rose is also found to be a host of P. meadii isolates of arecanut, rubber, cardamom, vanilla and P.citrophthora of Citrus. The cultural, morphological and molecular characters, host range and cross infectivity studies of various Phytophthora isolates could not revealed the exact identity of these isolates, as the distinguishing features overlapped among the various Phytophthora species. In vitro evaluation of chemicals / bioagents showed complete inhibition of the pathogen with 1% Bordeaux mixture, copper hydroxide (2g/l), copper oxychloride (2.5g/l), potassium phosphonate (3ml/l), combination fungicides, iprovalicarb + propineb (1.5 and 2.0g/l), cymoxanil + mancozeb (2g/l) and Trichoderma viride -1, T. harzianum and T. viride -2, the isolates from nutmeg and the reference cultures viz. T. viride (KAU) and T. harzianum (IISR). In in vivo experiment, all treatments were superior to control of which, spraying of 1% Bordeaux mixture + soil drenching of copper hydroxide (2g/l) and spraying of 1% Bordeaux mixture and soil application of T. viride showed maximum reduction of the disease. In addition, spraying and drenching of copper hydroxide and copper oxychloride were also found equally effective.
Open Access
Bio intensive management of blast disease of rice (Oryza sativa L.)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2012) Yamini, Varma C.K; KAU; Santhakumari
The present study on ‘Bio intensive Management of Blast Disease of Rice (Oryza sativa L.)’ was conducted at College of Agriculture, Vellayani and Regional Agricultural Research Station, Pattambi during 2008-2010. A survey conducted during kharif and rabi seasons 2008, in six panchayats from three different blocks, in Palakkad district, revealed that maximum disease incidence was in Pattithara panchayat during rabi and maximum disease severity was in Chalissery panchayat during kharif. The disease intensity and severity were high during kharif season, than rabi and in all the panchayats disease incidence occurred, 60 days after sowing. The fungus produced symptoms on leaves and neck of panicle. Sixty isolates from leaf samples were obtained from the six panchayats which proved the Koch’s postulates. After preliminary screening, thirteen isolates out of the 60 were selected. Out of the thirteen isolates, five isolates, P2, P4, P5, P9 and P12 had high virulence and these were selected for further studies. Among the five isolates the most virulent isolates like P4, P2 and P12 were having dark black coloured colonies with good growth. The isolate from Chalissery (P4) which was highly virulent, with maximum radial growth, mycelial dry weight, conidial size, and sporulating nature was selected for further studies. The isolate was tentatively identified as Pyricularia oryzae and further confirmed at IARI, New Delhi with accession number, as ITCC-7019. Among the media tested Potato Dextrose Agar was best followed by Oat Meal Agar. Among the liquid media, the Potato Dextrose broth supported maximum growth of Pyricularia. The optimum range of temperature for growth of Pyricularia was 25 – 30 °C, and pH value for maximum growth was 6.5. The most potent fungal antagonist Trichoderma sp. was obtained from Kadambazhippuram panchayat and the bacterial antagonist fluorescent pseudomonad was obtained from Thrithala panchayat. The per cent of inhibition was highest for Trichoderma sp. under in vitro conditions and hence this culture was selected as the fungal antagonist for further studies. The hyphae of the Trichoderma were found to coil around the hyphae of blast pathogen and in some areas disintegration of pathogen hyphae were also observed. Based on the morphological characteristics of the fungal antagonist the isolate was tentatively identified as Trichoderma harzianum and further confirmed at IARI, New Delhi, with accession number, as ITCC-7018. The fluorescent pseudomonad with highest percentage of inhibition was selected as bacterial antagonist for further studies. Based on the morphological, cultural, biochemical and physiological characteristics, the bacterial antagonist has been tentatively identified as Pseudomonas fluorescens biovar - 1. Among the plant products, the percentage of inhibition on the growth and spore germination of Pyricularia oryzae was significantly higher for the Palmarosa oil @ 0.5ml/ l) under in vitro conditions. Neemazal @ 5ml/ l was the second best plant product. The percentage reduction of spore germination was also highest for Palmarosa oil followed by Neemazal. Carbendazim (1.5g/ l), followed by Propiconazole (1ml/ l) were the best performing fungicides under in vitro conditions and they were selected as the best two chemical fungicides for further studies. Two blasticides viz., Isoprothiolane (1.5ml/ l) and Carpropamid (1ml/ l) were also selected as additional treatments. Salicylic acid (0.1ml/ l) and Benzoic acid (0.1ml/ l) were selected as best two resistance inducers from the pot culture experiment – I, since they reduced the disease severity significantly and increased the yield. In pot culture experiment-II, plants treated with Palmarosa oil + Carbendazim (T23) had significantly reduced the blast disease. Next best performance was when Salicylic acid combined with Pseudomonas fluorescens or Trichoderma. The two biocontrol agents, Pseudomonas fluorescens and Trichoderma were effective when individually combined with plant products like, Palmarosa oil, or Neemazal, or resistance inducer, Salicylic acid. The biometric observations like, height of the plant, number of total and productive tillers, grain yield and straw yield were also considerably higher for the above treatments. The best nine treatments with lowest PDI and highest yield from this experiment were selected for field experiments. Palmarosa oil and Neemazal was compatible with Trichoderma, but the systemic fungicide, Carbendazim inhibited growth of Trichoderma followed by Propiconazole. Pseudomonas fluorescens was compatible with the two plant products, Palmarosa oil and Neemazal as well as two fungicides, Carbendazim and Propiconazole. It was also found that T. harzianum and Pseudomonas fluorescens were compatible to each other. Field Experiment-I showed that 75 DAT, T23 (Palmarosa oil + Carbendazim) had significantly lowest percentage of disease incidence and this was on par with T21 (Palmarosa oil + Salicylic acid), T36 (Trichoderma + Pseudomonas fluorescens + Salicylic acid) and T34 (Trichoderma + Pseudomonas fluorescens + Palmarosa oil). The treatment T23 (Palmarosa oil + Carbendazim) had the highest effect on reducing the PDI, 75DAT along with four treatments viz., T21, T27, T36 and T34 which were on par in their effects. The treatment T23 (Palmarosa oil + Carbendazim), produced significantly more height, higher number of total tillers, and productive tillers. Significantly higher grain yield /ha was obtained for T23 and T34. Significantly maximum straw yield /ha was also obtained for T23 In the diseased plants there was a steady decrease in chlorophyll ‘a’, ‘b’ and total chlorophyll. But in the uninoculated healthy plants, chlorophyll content remained same throughout the observation period. The activity of defense related enzymes viz., peroxidase, poly phenyl oxidase and phenyl alanine ammonia lyase activity, was significantly higher in rice plants on 5th day after inoculation for the treatment Trichoderma + Pseudomonas fluorescens + Palmarosa oil followed by Trichoderma + Pseudomonas fluorescens + Salicylic acid. Enzyme activities were least in the un inoculated plants. In the second experiment (kharif 2010) 75DAT, T23 (Palmarosa oil + Carbendazim) had significantly lower percentage of disease incidence. Two additional blasticides were also on par with T23 The biometric observations also followed the same trend. Significantly maximum grain yield and straw yield /ha was obtained for T23. The pooled analysis during two succeeding years, (kharif 2009 and 2010) revealed that, T23 had the lowest PDI with highest efficiency in reducing the blast disease. Four treatments viz., T21, T27, T36 and T34 which were on par in their effects, with T23. The B:C ratio was highest for T23 (Palmarosa oil + Carbendazim) followed by T21 (Palmarosa oil+ Salicylic acid), T27 (Neemazal + Carbendazim) (2.5), T34 (Trichoderma + Pseudomonas fluorescens + Palmarosa oil), T36 (Trichoderma + Pseudomonas fluorescens +Salicylic acid) and fungicidal check T41 (Tricyclazole). Exactly the same value of the maximum B:C ratio was obtained for Isoprothiolane. The relationship between blast disease severity and weather factors during kharif 2010, indicated positive correlation between disease severity and maximum temperature, relative humidity, rainfall, and number of rainy days but negative correlation with minimum temperature. The outcome of this research work which can be recommended in the rice organic farming techniques, are the following 1. Trichoderma + Pseudomonas fluorescens + Palmarosa oil 2. Trichoderma + Pseudomonas fluorescens +Salicylic acid 3. Palmarosa oil + Salicylic acid The result of molecular diagnosis of five selected cultures of blast pathogen, based on the D1/D2 regions in PCR analysis showed 99% similarities for 4 cultures (P2, P4, P9 and P12) and 97% similarities in one culture (P5) with the Magnaporthe oryzae, which accurately proved the identity of blast pathogen.
Open Access
Characterization and management of viral diseases of black pepper(Piper nigrum L.)
(College of Agriculture, Vellayani, 2010) Ayisha, R; KAU; Joseph, P J
A detailed survey was undertaken to study the occurrence and distribution of viral diseases in black pepper in Thiruvananthapuram and Kollam districts of Kerala. Disease incidence (DI) and per cent disease index (PDI) were determined during survey which showed that per cent DI varied between 0-57 and PDI between 0-18. The disease was prevalent in both the districts. Most of the local cultivars and improved varieties were susceptible to the disease. The characteristics symptoms of disease were chlorotic spots on emerging younger leaves, vein clearing, scattered chlorotic flecks followed by chlorotic mottling along veins leading to interveinal chlorosis and characteristic twisting and curling of leaves. The infected leaves were also observed to be small, crinkled, and brittle with reduced internodal length, leading to typical stunting of plants. Most of the diseased plants were found to be infected with both Cucumber mosaic virus (CMV) and Pepper yellow mottle virus (PYMo V). The presence of these viruses was confirmed through conducting enzyme linked immunosorbent assay (ELISA) on representative samples collected from different locations. The virus was not mechanically transmitted to healthy pepper seedlings. However the virus was found to be transmitted through grafting, insect vectors and also through seeds. The mealy bug, Ferrisia I virgata was found to be the efficient vector although aphid, Toxoptera aurantii, was also found to be transmitting the virus. Thermal inactivation point was recorded at a range of 40-450C and dilution end point between 10-3 and 10-4 for CMV. Host range studies revealed that virus could be readily transmitted to other species in Piperaceae family as well to some of the weed hosts. The virus was partially purified and antiserum was produced with a titre of 1:128. Identification and serological characterization of the virus was done using ELISA and DIBA. Molecular detection of the virus was also performed using PCR and a PCR product of amplicon size 500 bp and 300 bp were obtained for primers specific to CMV and banana streak virus (BSV) respectively. The pathophysiological studies revealed that virus infected plants showed increased phenol, carbohydrate and protein content. The chlorophyll content was found to be less in infected samples. The activity of defence related enzymes like peroxidase, polyphenol oxidase and phenylalanine ammonialyase were found to be more in infected plants. Electrophoretic analysis of virus infected samples through SOS-PAGE revealed the presence of two novel proteins in diseased samples. Analysis of isozymes through native gel revealed the production of an additional isoform of peroxidase and over expression of polyphenol oxidase in infected plants. In screening of varieties for the source of resistance Panniyur, 2, 3 and 4 were found moderately resistant and Karimunda was highly susceptible. Piper colubrinum showed resistance to the virus. Meristem culure attempted was unsuccessful and could not be used as a viable strategy for eliminating the virus infecting black pepper as the meristems were seen contaminated with the pepper badnavirus.
Open Access
Epidemiology and management of false smut of rice (Oryza sativa L.) in Kerala
(College of Agriculture, Vellayani, 2014) Rashmi, C R; KAU; Gokulapalan, C
The study entitled 'Epidemiology and management of false smut of rice (Oryza saliva L.) in Kerala' was conducted during the period 2010-2013 at College of Agriculture, Vellayani, Trivandrum and the field experiments and varietal evaluation trials were carried out at the Regional Agricultural Research Station, Pattambi, Palakkad, Rice Research Station, Moncompu, Alappuzha and at Farmers fields at Vilayur (Palakkad) and Chambakkulam (Alappuzha). The results of the surveys conducted at Alappuzha and Palakkad indicated that maximum disease was observed at the upper Kuttanad area of Alappuzha. A new collateral host for the pathogen, Oryza spontaneum was observed at Alappuzha during the survey. Isolation of the pathogen was made from the samples collected during the survey. The method of isolation of the pathogen was standardized. Surface sterilization of smut balls with 0.1 % HgCb for 3.5-4 minutes followed by three serial washings with sterile water and dusting of the chlamydospores over YPPDA, and pure culturing after observation under a light microscope after 24 hrs was the method devised for isolation. Ideal conditions for culturing of the fungus under in vitro conditions were found to be the use of YPPDA medium of pH 6.5 at 28°C under full darkness. An indigenous medium viz., rice extract sucrose agar was developed for the culturing of the pathogen. The pathogen, Ustilaginoidea virens was observed to be producing smut balls and chlamydospores in culture similar to that produced under field conditions. Stromatic heads of the fungus was observed under in vitro conditions for the first time in India. Sequencing of the ITS region of pathogen gave 100% similarity with the known sequences of U. virens on BLAST analysis and thus the pathogen was conformed to be U. virens. The pathogen isolates were identified and deposited at ITCC, New Delhi, and the accession numbers ITCC-7335 (Pattambi, Palakkad) and ITCC-7334 (Moncompu, Alappuzha)were obtained for the isolates. Laboratory trials revealed the efficacy of five chemical fungicides, different species of Trichoderma and three bacterial strains for suppression of the pathogen in vitro. Correlation studies on the influence of weather parameters on the development of the disease revealed that the disease was negatively correlated with the minimum temperature during SO % flowering. Results of the survival studies of the pathogen revealed that the smut balls of the pathogen can survive for eight months at room temperature. At field level, the fungus was found to be surviving on the ratoon rice emerged from the stubbles of the previous crop. Under the varietal evaluation trials conducted at Alappuzha and Palakkad, the varieties Vaishak and Harsha were found resistant to the disease and the varieties PTB 10 and Makom were moderately resistant. The varieties, Uma, Remanika, Gouri and Bhagya were the most susceptible ones. RAPD profiling of the resistant and susceptible varieties with 10 random primers showed polymorphism with five primers OPK-I4, OPG-I8, OPC-IS, OPB-IO and OPD-I8. Field trials conducted at Alappuzha and Palakkad showed that spraying of Propiconazole 12Sg a.i./7 SO L or TebuconazoleO.I87 S kg a.i./SOO L or Copper Hydroxidel000 g a.i./7S0 L or Pseudomonas flourescens @ 2% of the talc based formulationat SO% flowering could control the disease effectively. Tebuconazole 0.187S kg a.i./SOO L gave significant yield increase over the control. Biochemical studies like SDS PAGE and NA TIVE PAGE were conducted. SDS PAGE showed conspicuous bands of the pathogen proteins and NATIVE PAGE revealed increased activity of peroxidase and polyphenol oxidase on the diseased grams. Based on the research results, a management package was developed for effective control of the disease at the field level as follows: 1) avoiding use of paddy grains harvested from severely affected fields as seed material 2) avoiding continuous cultivation of the most susceptible rice varieties like, Uma, Remanika, Gouri and Bhagya 3) use of resistant varieties like Harsha, Vaishak or Makom 4) Weed management to control the collateral hosts like wild rice 5) biological control by spraying of Pseudomonas flourescens @ 2% of the talc based formulation at 50% flowering 6) spraying of Propiconazole125 g a.i./750 L or Tebuconazole 0.1875 kg a.i./500 L or Copper Hydroxide 1000 g a.i./750 L at 50% flowering.
Open Access
Integrated management of fusarium wilt and anthracnose of vegetable cowpea (Vigna unguiculata subsp. sesquipedalis (L.) Verdcourt) using new generation fungicides
(College of Agriculture, Vellayani, 2014) Sreeja, S J; KAU; Girija, V K
The study entitled “Integrated management of Fusarium wilt and anthracnose of vegetable cowpea (Vigna unguiculata subsp. sesquipedalis (L.) Verdcourt) using new generation fungicides” was carried out in the Department of Plant Pathology, College of Agriculture, Vellayani during 2011 - 2014 with an objective to test the efficacy of new generation fungicides for the management of Fusarium wilt and anthracnose of vegetable cowpea and to develop an integrated management strategy using effective fungicides compatible with ecofriendly tactics. Isolation, characterization and identification of the pathogens revealed that, Fusarium oxysporum, F. equiseti and F. solani were associated with wilt of cowpea while, Colletotrichum gloeosporioides was associated with anthracnose. In vitro evaluation of new generation fungicides indicated that tebuconazole (0.1 %), carboxin + thiram (0.4 %), and mancozeb (0.25 %) completely inhibited the mycelial growth of F. oxysporum and C. gloeosporioides. Pot culture experiments conducted to evaluate the efficacy of new generation fungicides for the management of Fusarium wilt and anthracnose revealed that soil drenching of flusilazole (0.1 %), tebuconazole (0.1 %) or carbendazim (0.1 %) totally suppressed the incidence of wilt while, the foliar application of flusilazole (0.1 %) recorded the lowest index (5.60) of anthracnose which was on par with the treatment with tebuconazole (0.1 %). A field experiment conducted to develop an integrated disease management package Fusarium wilt and anthracnose of cowpea indicated that soil solarization, application of Trichoderma enriched neem cake organic manure mixture and soil drenching of either tebuconazole (0.1 %) or carbendazim (0.1 %) recorded the lowest (0.00) disease index of Fusarium wilt whereas, three rounds of foliar application of either flusilazole (0.1 %) or tebuconazole (0.1 %) recorded the lowest (0.93) anthracnose index. The studies on persistence and degradation of fungicide residues indicated that tebuconazole (0.1 %) was having the shortest waiting period (0 days) indicating its safety to the vegetable. Considering the overall efficacy of fungicides against two diseases, associated yield increase, safety to the crop as well as economic benefits the following integrated management package was developed for the control of Fusarium wilt and anthracnose of cowpea in disease prone areas as: 1) Seed treatment with carbendazim (2 g/kg seed) 2) Soil solarization for a period of 45 days using transparent polythene sheets during warm season 3) Application of Trichoderma enriched neem cake organic manure mixture @ 1 kg/pit 15 days after seed emergence 4) Application of tebuconazole (0.1 %) at 30, 45 and 60 days after seed emergence. In order to counter the possibility of resistance build up due to repeated use of the triazole fungicide, the contact fungicide copper oxychloride (0.2 %) may be used in rotation.

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