Browsing by Author "Sainamole Kurian, P"

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Characterisation of Ralstonia solanacearum (Smith) Yabuuchi et al. infecting solanaceous vegetables in relation to physico-chemical and biological properties of soil
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2019) Anjali, V A; Sainamole Kurian, P
Ralstonia solanacearum, the causal agent of vascular wilt disease of crop plants has been ranked as the second most important bacterial pathogen in the world next to Pseudomonas syringae. The high diversity exhibited by the pathogen hampers the breeding for resistance, consequently the resistant varieties developed may not express uniform level of resistance in different geographical locations. Being a soil inhabitant, the survival of R. solanacearum is influenced by physico-chemical and biological properties of soil. Considering these facts, present investigation was carried out with the objective of characterisation of R. solanacearum from different agro ecological units (AEUs) of Kerala and to determine the effect of soil physical, chemical and biological properties on the pathogen. Purposive sampling survey was conducted in four AEUs of Kerala viz., North Central laterite (NCL), Marayur hills (MH), Southern laterite (SL) and Palakkad central plains (PCP) from March to September 2018. Two locations from each AEUs were selected for the survey. The per cent incidence in different locations ranged from 20 to 88 per cent. The pathogen was isolated from infected plant samples collected during the survey on triphenyl tetrazolium chloride (TZC) agar and pathogenicity was proved by inoculation on respective hosts. The rhizosphere soil samples of healthy and diseased plants were collected from each location. The population of the pathogen present in the soil was quantified and it ranged from 20.66 x 104 cfu g-1of soil to 137.66 x 104 cfu g-1 of soil. A strong positive correlation was observed between pathogen density in soil and per cent disease incidence (PDI). A total of eight isolates were collected, purified and maintained for all the experiments. The colony characters of different isolates on TZC agar showed considerable variation and the morphology of the bacterial cells was studied using scanning electron microscopy. Typical rod shaped cells with size 0.3-0.5 µm x 1.2-1.7 µm were observed. The molecular characterization of the isolates was done by PCR amplification and sequencing of 16S rRNA. The sequences were subjected to in-silico analysis which confirmed the identity of all isolates as R. solanacearum (Smith) Yabuuchi et al. The phylogenetic analysis revealed that the eight isolates collected from different AEUs clustered on different branches of the tree while those from the same AEUs clustered together. This indicates considerable variation among the isolates in accordance with location which can be attributed to the difference soil parameters in these locations. The isolates of the pathogen were further categorized into races and biovars based on pathogenicity on differential hosts and utilization of disaccharides and hexose-alcohols respectively. The results revealed that two isolates from Marayur hills (MH 1 and MH 2) belong to race 3, biovar II whereas two from Palakkad central plains (PCP 1 and PCP 2) belong to race 1 biovar III A. The other four isolates collected from Northern central laterite (NCL 1 and NCL 2) and Southern laterite (SL 1 and SL 2) were identified as race 1, biovar III. The physico-chemical and biological properties of the soil samples collected during the survey were analysed using standard protocols. The statistical analysis using paired sample t-test revealed significantly higher soil pH, organic carbon, available K, Ca and Fe content and soil microflora in rhizosphere soil of healthy plant compared to diseased. A significant positive correlation was observed between PDI and soil parameters viz., water holding capacity and bulk density whereas soil pH and available Ca content exhibited a negative correlation with PDI. A similar trend was observed in the case of pathogen population also. Further, multiple regression analysis was performed to assess the extent of variation contributed by different soil parameters on PDI and pathogen population. The results indicate that 96.8 per cent variation in the bacterial wilt incidence is explained by soil pH and available Ca content in the rhizosphere soil with negative correlation whereas bulk density and Ca content contributed 92.2 per cent in the build-up of population of Ralstonia solanacearum in soil. The study revealed the influence of soil factors on bacterial wilt disease incidence, population of R. solanacearum and pathogen variability. Hence, it is concluded that, manipulation of soil factors can play a major role in integrated management of the disease. Furthermore, the variability of pathogen according to geographical region, may be considered while planning resistance breeding programmes against bacterial wilt disease.
Characterization and management of powdery mildew of yard long bean (vigna unguiculata subsp.sesquipedalis (L.) verdc.) under protected cultivation
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2018) Rahila Beevi, M H; Sainamole Kurian, P
Yard long bean (Vigna unguiculata subsp. sesquipedalis (L.) Verdc.) is believed to be selected and developed from cowpea (Vigna unguiculata (L.) Walp.) for its long, succulent pods which are used as a vegetable. In Kerala, it is one of the most preferred vegetables having very high amount of protein, iron, calcium, vitamin A, Vitamin C and dietary fibre. It is considered as a remunerative crop under protected condition owing to its high market demand. However, incidence of diseases is a major setback hampering the production of yard long bean under protected conditions among which, powdery mildew is the most devastating one. In this background, the present study was undertaken to characterize the pathogen causing powdery mildew of yard long bean and to formulate a management strategy for the disease under protected cultivation. Purposive sampling surveys were conducted in seven locations of Thrissur district and the disease severity varied from 1.67 to 67.33 per cent. The results of the survey indicated that the severity of disease was more during pod bearing and harvesting stage. Since powdery mildews are obligate parasites, characterization was done based on the microscopic observation of pathogen present on the leaves. The fungi produced hyaline, branched and septate hyphae. The conidiophores were erect and cylindrical on which conidia were born in chains. Variability was observed regarding conidia and conidiophore characters of powdery mildew collected from different locations, based on which the isolates were grouped into two viz., PM 1 and PM 2. PM1 type was observed in all locations except Vellanikkara. Based on the morphological characteristics of conidia and conidiophores, it was identified as Erysiphe polygoni. PM 2 type obtained only from Vellanikkara in which conidia and conidiophore characters were similar to Podosphera sp. which is very rarely reported on legumes. Hence, its identity was further confirmed as Podosphaera xanthii by molecular characterization. The rRNA-ITS sequence was deposited in NCBI Genbank database with accession number MH645799. This is the first report of powdery mildew of yard log bean incited by Podosphaera xanthii. In-vitro evaluation of 17 treatments including fungicides, biocontrol agents and botanicals by spore germination technique revealed that all the treatments caused cent per cent inhibition of conidial germination. For taking forward eight promising treatments to the field experiments, they were tested in-vitro on detached leaves by artificial inoculation of conidia from infected leaves. Based on the per cent leaf area infected, two systemic fungicides, one contact fungicide, two biocontrol agents and one botanical were selected for field evaluation. Field experiments were conducted simultaneously inside polyhouse and rain shelter to evaluate the performance of selected fungicides, biocontrol agents and botanicals against powdery mildew. Among the treatments, low disease severity of 4.33 per cent and 7.67 per cent was recorded in T1- difenoconazole and T2 – tebuconazole respectively in polyhouse and these treatments were statistically on par. In rain shelter also, T1- difenoconazole and T2- tebuconazole recorded low disease severity of 7.67 per cent and 10.67 per cent respectively. The performance of wettable sulphur at lower and higher concentration did not differed significantly. All the four non-chemical treatments were equally effective in managing the disease both in polyhouse and rain shelter. Correlation analysis between the meteorological parameters and disease severity revealed that per cent disease severity was negatively correlated with temperature and relative humidity both in polyhouse and rain shelter. Analysis of population of phylloplane microflora showed that, there was a drastic reduction in the population of phylloplane fungi and bacteria after spraying chemical fungicides which is an indication of the toxicity and non-selectivity of these chemicals. Survival ability of biocontrol agents sprayed on the leaves were studied and found out that both Trichodema viride and Pseudomonas fluorescens survived on the leaves for seven days. Residue analysis of difenoconazole, the most effective chemical fungicide revealed that the compound with initial deposition of 0.21 mg kg-1 dissipated to 0.09 mg kg-1 after seven days in polyhouse whereas, the residue after seven days in rain shelter was 0.19 mg kg-1. The faster degradation of the chemical inside polyhouse may be attributed to the higher temperature prevailed during the experiment. Evaluating the results various experiments in the present investigation, it was found that, even though chemical fungicides provided best disease control, considering their toxic effect on beneficial non target microflora on the phylloplane and the residue left on edible pods, biocontrl agents such as Trichoderma viride and Pseudomonas fluorescens which exhibited consistent performance with moderate disease control and sufficient survival on the leaf surface would be ideal to control powdery mildew of yard long bean if applied at right time. Moreover, frequent application of systemic fungicides with single site action can result in the development of resistant strains of pathogens. So such chemicals should be adopted only if the disease severity is very high and cannot be managed with biocontrol agents.
Characterization of rhizosphere and endophytic microflora from organically grown amaranth for management of leaf spot diseases
(Department of Plant Pathology, College of Horticulture,Vellanikkara, 2015) Aparna, V S; Sainamole Kurian, P
Endophytic bacteria : Potential biocontrol agents against plant pathogens
(Department of Plant Pathology, Kerala Agricultural University, Vellanikkara, 2019) Aswathy, Peethambaran; Sainamole Kurian, P
Endophytic microorganism mediated systemic resistance in cocoa against phytophthora palmivora (Butler) Butler.
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2011) Sainamole Kurian, P; 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 areas 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. Bacteria and fluorescent pseudomonads were more abundant than filamentous fungi and yeasts. Out of the 325 endophytic isolates comprising of 116 bacteria, 153 fluorescent pseudomonads, 34 yeasts and 22 fungi, 82 were found exerting antagonism 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. These included endophytic isolates of 12 fluorescent pseudomonads, nine bacteria and four fungi. The 25 efficient endophytic antagonists were evaluated for growth promoting ability in cocoa seedlings. It was observed that eight isolates had a profound effect on growth promotion. Hence, these were selected as potential endophytes and were subjected to various tests to study the attributes underlying their antagonistic and growth promoting effects. The potential endophytes consisted of isolates of two bacteria, five fluorescent pseudomonads and one fungus. These eight potential endophytes along with two reference cultures were evaluated in in vitro for various attributes, which underlay their beneficial effects. It was found that, isolates EB-35, EB-40, and EF-81 produced more ammonia. Phosphate soulubilizing ability was maximum for EB-35. The isolates EB-35, EB-40 and EB-65 produced high quantity of IAA. High score for antagonistic index was obtained by EB-31 and EB-35. Vigour index of coca seedlings was also high for EB-31 and EB-35. The plant growth promoting index worked out based on aforementioned attributes was high for five isolates viz., EB-31, EB-35, EB-40, EB-65 and EF-81, which were selected as promising endophytes and were subjected to further studies and in vivo evaluation. The promising endophytes were found to produce volatile and non-volatile inhibitory metabolites against the pathogen. Maximum inhibition through volatile production was with EB-35 and EB-31. While through non-volatiles, the maximum inhibition was by EB-35 and EB-40. Of the four promising bacterial endophytes, three emitted fluorescence under UV light and EB-31 and EB-65 produced more siderophores under iron limiting condition. A pot culture experiment was conducted to study the induction of systemic resistance and suppression of Phytophthora infection in cocoa seedlings by the promising endophytes. Here also, endophytic isolates effected growth promotion in cocoa seedlings and reduction in infection. Induction of systemic resistance was studied by assay of defense related compounds and enzymes. In general, the study revealed more accumulation of phenols and proteins in treated seedlings. Higher activity of PO, PPO, and β-1,3-glucanase was also noticed. Native PAGE analysis revealed six isoforms of PO and seven of PPO. More isoforms were present in endophyte treated plants. Promising endophytes were evaluated for efficiency in reducing Phytophthora pod rot in field in comparison with two reference cultures and chemicals. During the first phase of experiment, viz., after first spraying, maximum reduction in disease was observed in EB-65 and EF-81. Whereas, after second spraying least incidence was in EB-31. After two weeks of third spraying, minimum disease was observed in Pf1 and EB-35. However, the isolate EB-31 was the most efficient one which recorded the least disease incidence during most of the period under observation especially when the disease was at its peak. Based on cultural, morphological and biochemical characters coupled with results of molecular characterization, the promising bacterial endophytes were identified as Pseudomonas putida (EB-31), Bacillus subtilis (EB-35), P. plecoglossicida (EB-40) and P. aeruginosa (EB-65). The isolate EF-81 was identified as Penicillium minioluteum. In the radiotracer experiment, it was found that EB-35 and EB-65 entered the cocoa seedlings when applied on leaves and also inside the pods on application on the intact surface.
Etiology and management of fruit rot of brinjal (Solanum melongena L.)
(Department of Plant Pathology, College of Agriculture, Vellanikkara, 2020-09-30) Aswathy Peethambaran; Sainamole Kurian, P
Brinjal belonging to the family Solanaceae is of great importance in human nutrition and is considered as the King of Vegetables. Despite being a versatile crop adapted to various agroclimatic regions and seasons, brinjal is affected by many diseases like Phomopsis blight and fruit rot, little leaf, damping off and bacterial wilt. In addition to these, recently a fruit rot caused by Phytophthora nicotianae is also reported from various parts of India (Jain et al., 1982 and Chowdappa et al., 2015). A preliminary study of the same has been conducted by Jose and Beena (2016). Considering the importance of Phytophthora spp. in the agricultural scenario of Kerala, the present investigation was carried out with the objectives to study the symptomatology and etiology of fruit rot of brinjal, screening popular brinjal varieties for resistance and to develop management strategy for the disease. Purposive sampling survey was conducted in different locations of Thrissur and Palakkad districts during June to October 2019, infected brinjal fruits were collected and symptoms were recorded. The incidence and severity of the disease in different locations ranged from 10 to 84 and 10 to 66 per cent respectively. Presence of a white mycelial growth was consistently observed on the infected fruits which on examination under microscope showed hyaline, coenocytic hyphae and pear shaped sporangia with papillae. The microorganism was isolated on carrot agar and pathogenicity was tested. Symptoms produced on artificial inoculation were also recorded. A total of four isolates of the pathogen were collected, purified and maintained for further studies. The isolates were named after the place of collection as VKA Ⅰ, VKA Ⅱ, KPD and NMA. Cultural and morphological characters of the isolates were studied on three different media viz., carrot agar, potato dextrose agar and coconut water agar. Colony characters like growth rate, colour, shape, texture of colony and sporulation varied among the isolates and media. All the four isolates produced coenocytic, hyaline, branched mycelium and thick walled, hyaline, globose chlamydospores. Non caducous, papillate, ovoid and obturbinate sporangia were borne terminal or intercalary on the sporangiophore in a simple sympodial fashion. Variation in dimensions of sporangia was observed among the isolates grown on different media. Based on morphology, all the isolates were identified as Phytophthora sp. Oospore production was not noticed on pairing of isolates suggesting that these belong to single mating type and express the typical heterothallic behaviour of the genus. Molecular characterisation of the four isolates revealed maximum similarity to P. nicotianae and phylogenetic analysis showed that isolates VKA Ⅰ, VKA Ⅱ and NMA are more closely related than KPD. Host range studies proved that the pathogen can infect other crops like tomato, chilli, bhindi, bitter gourd, arecanut, coconut, nutmeg, cocoa, papaya, rubber and black pepper on artificial inoculation. The most popular varieties of brinjal, released from Kerala Agricultural Universiy viz., Surya and Haritha were found to be susceptible to the pathogen. The results of in vitro evaluation showed that cymoxanil 8%+ mancozeb 64%, metalaxyl+ mancozeb, mancozeb, copper hydroxide, fosetyl- Al at 0.05 per cent concentration and Bordeaux mixture (0.5%) recorded cent per cent inhibition of the pathogen. However, azoxystrobin (0.05%) recorded 37 per cent inhibition only. Similarly Trichoderma sp. and Pseudomonas fluorescens recorded cent per cent and 69.40 per cent inhibition respectively. The leaf extracts of Capsicum frutescens and Boerhavia diffusa also gave significant inhibition of pathogen. In bioassay on detached fruits the highest disease reduction was recorded by mancozeb (72.38%) followed by cymoxanil 8%+ mancozeb 64% (66.26%). However biocontrol agent Trichoderma sp. also recorded 51.67 per cent reduction over control which was on par with fosetyl- Al, copper hydroxide and azoxystrobin. Leaf extract of Capsicum frutescens also reduced the disease by 39.18 per cent. Phytophthora fruit rot is an emerging disease and if left uncontrolled it will be a serious threat to brinjal cultivation. The study has confirmed the etiology and symptomatology of the disease and the wide host range of the pathogen. It was also proved that the four isolates of P. nicotianae collected in the study are confined to same mating type. The investigation has also revealed the efficacy of lower doses of commonly used fungicides, against P. nicotianae. Results of the study also suggested the potential of biocontrol agents and botanicals against the pathogen.
Evaluation of phylloplane microorganisms for the management of early blight of Tomato (Solanum lycopersicum L.)
(Department of Plant Pathology, College of Agriculture, Vellanikkara, 2024-08-14) Wongamthing, R.; Sainamole Kurian, P
Tomato (Solanum lycopersicum L.) is a widely grown vegetable and the most remunerative solanaceous crop in both tropics and sub tropics of the world. It is vulnerable to various biotic diseases among which, early blight caused by Alternaria solani is a destructive one. Management of diseases using biocontrol agents is a safe alternative in the integrated disease management system. However, success of a bioagent is dependent on its comparative survivability in the new niche. Therefore, the present investigation was undertaken to identify strains of beneficial microorganisms adept on the phylloplane of tomato for use against early blight as it is a disease affecting mainly the foliage. As part of the investigation, purposive sampling survey was conducted in Thrissur and Palakkad districts of Kerala. It was found that early blight is prevalent in all the areas surveyed and the disease severity on foliage varied from 23 to 78 per cent at various locations. Though several fungi were found to be associated with the disease, only six isolates collected from Pudukkad, Valapad, Mundathikode, Vadakarapathy, Nenmara and Parrisakal were identified as Alternaria sp.(PDK), A. alternata (VAL), Fusarium oxysporum (MUN), A. solani (VAD and NEM) and Corynespora cassiicola (PAR) which could be proved as pathogens on tomato. Phylloplane microorganisms were isolated from both the healthy and diseased leaves collected from plants at various locations and a total of 132 isolates were then subjected to preliminary in vitro screening for their ability to suppress A. solani and 59 were selected as they could antagonize the pathogen in various degrees. The antagonists thus selected were further screened by dual culture technique and 36 showed more than 60 per cent inhibition. The antagonism exerted by phylloplane isolates was clearly discerned by limited growth, or the complete absence of fungal mycelium in the inhibition zone between the pathogen and the test isolate. Out of the 36, five were selected as promising potential antagonists as they could give more than 80 per cent inhibition of the pathogen. The selected five are identified as Trichoderma spp. (PF2 and PRF1), Bacillus subtilis (MNB2), Bacillus mojavensis ii (TB1) and Ochrobactrum sp. (EB1) which showed per cent inhibition of 91.2, 90, 89.4, 88 and 85 respectively. Furthermore, when these isolates were tested for growth promotion on tomato, the vigour index of tomato seedlings varied from 2110 (Trichoderma sp., PF2) to 1676 (Bacillus mojavensis, TB1). As next step, selected antagonists were tested for induction of systemic resistance (ISR) on tomato by conducting a pot culture experiment. Increased accumulation of peroxidase (PO), polyphenol oxidase (PPO) and, phenylalanine ammonia-lyase (PAL) was observed in plants treated with phylloplane antagonists. Higher activity of PO and PPO was induced by Trichoderma sp. (PF2) and B. subtilis (MNB2) at fifth day after inoculation (DAI) of pathogen. The phylloplane antagonists Trichoderma sp. (PF2) and B. subtilis (MNB2) recorded 169.54 min-1 g -1 and 152.56 min-1 g -1 respectively for PO and 199.19 min-1 g -1 and 172.24 min-1 g -1 respectively for PPO. Higher activity of PAL at fifth DAI was obtained by Pseudomonas fluorescens (KAU) followed by Trichoderma sp. (PF2) and B. subtilis (MNB2) recording 209.86 min-1 g -1 , 198.59 min-1 g -1 and 180.85 min-1 g -1 respectively. However, the highest per cent reduction of early blight after the first spray (68.58) was effected by Trichoderma sp. (PF2) followed by (64.92 and 60.22) B. subtilis (MNB2) and Ochrobactrum sp. (EB1), respectively. The disease reduction at early stage was reflected on yield of tomato and the same treatments; Trichoderma sp. (PF2), B. subtilis (MNB2) and Ochrobactrum sp. (EB1) gave 410 g, 389.33 g and 340 g fresh tomatoes per plot respectively. Hence these three phylloplane antagonists were selected for further evaluation. An experiment was carried out under rain shelter to evaluate the efficacy of the selected antagonists, conventional biocontrol agents such as Trichoderma sp. (KAU) and P. fluorescens (KAU) and a chemical check, propineb (0.2 %). The results showed that the phylloplane antagonists Trichoderma sp. (PF2) and B. subtilis (MNB2) offered significant effect against the disease recording 40.74 and 37.04 reduction in per cent disease severity (PDS) which in turn resulted in per cent yield increase of 32.63 and 28.10 respectively. Enumeration of phyllopane microflora proved that, there is drastic reduction in microbial population on leaf surface after iii spraying with propineb whereas the population increased after application of bioagents. Further, it was found that Trichoderma sp. (PF2) and B. subtilis (MNB2) are compatible with P. fluorescens (KAU) but B. subtilis (MNB2) is not compatible with Trichoderma sp. (KAU). Trichoderma sp. (PF2) is weakly inhibited by propineb (0.2 %), but azoxystrobin (0.1 %) could reduce its growth by 58 per cent. However, B. subtilis (MNB2) could not be affected by any of the two fungicides used against leaf blight. Hence, based on the results of various experiments in this study, phylloplane antagonists, especially, B. subtilis (MNB2) seems to be suitable for inclusion in IDM for early blight of tomato. Enumeration of culturable microflora on tomato leaves revealed that, bacteria are more on healthy leaves while fungi are more on the infected leaves. However, metagenomic analysis of the phylloplane revealed great difference in density and diversity of microbial taxa between healthy and infected leaves. This indicates that, specific functions of the phylloplane microbes and their antagonistic potential are also important in determining their efficacy as biocontrol agents. The study also revealed the presence of plant pathogenic fungal genera like Cladosporium, Corynespora, Pseudocercospora, Conidiosporomyces and Ustilago on tomato leaves. Both healthy and diseased tomato leaves harbour great microbial diversity and the phylloplane dwellers include well-known antagonists like species of Bacillus, Pseudomonas, Trichoderma and Penicillium. Presence of members of genera like Klebsiella and Enterobacter which are human pathogens was also revealed by metagenomic analysis. However, they are beneficial to plants as N fixers, P and K solubilizers and siderophore and IAA producers. Phylloplane dwellers also include species of Methylobacterium, Sphingomonas and Massilia and they are reported to produce different pigments and antibiotics besides being plant growth promoters, and antagonists to plant pathogens. Furthermore, species of Staphylococcus, Cladosporium, Coprinellus and Moesziomyces are also detected from tomato phylloplane and are reported to have antifungal properties with goo plant growth attributes, while species of Meira are reported as potential biological control agents against phytophagous mites
Management of downy mildew (Pseudoperonospora cubensis (Berk. & Curt.) Rostov.) of cucumber under protected cultivation
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2016) Reshma Raj, T; Sainamole Kurian, P
The present study entitled “Management of downy mildew (Pseudoperonospora cubensis (Berk. & Curt.) Rostov.) of cucumber under protected cultivation” was conducted in the Department of Plant Pathology, College of Horticulture, Vellanikkara during the period from October to April 2015-16. The major objective was to assess the incidence and severity of downy mildew of cucumber under protected cultivation and to formulate eco-friendly management package against the disease. A survey was conducted in Thrissur district during January to December 2015 in nine polyhouses. During the survey, incidence of downy mildew was noticed in all the polyhouses where cucumber was cultivated irrespective of the season and the disease severity varied from 11.33 to 35.75per cent. There is a significant positive correlation between the disease incidence and severity with relative humidity (RH) inside the polyhouse and negative correlation with temperature. Morphological characterization of the pathogen present on the diseased leaves collected during survey revealed that sporangiophores are dichotomously-branched at acute angles that tapered to curved pointed tips. Large lemon shaped, brownish yellow sporangia are borne singly at the tip of the sporangiophore. Field experiments were conducted simultaneously inside the polyhouse and rain shelter for management of downy mildew with 12 treatments and three replications. The treatments included two biocontrol agents (Trichoderma viride and Pseudomonas fluorescens), cowdung supernatant, two biofungicides (garlic and calphomil) and two systemic (potassium phosphonate + hexaconazole and cymoxanil + mancozeb) and one contact (mancozeb) fungicide. Soil solarisation inside the protected structures was included as part of treatments viz., T1 (soil solarisation + seed treatment and soil application + foliar spray with T. viride) and T2 (soil solarisation + seed treatment and soil application + foliar spray with P. fluorescens). It was found that soil temperature at 10 cm depth was higher in solarized soil when compared to nonsolarised soil by 4 oC and 3.5 oC inside polyhouse and rain shelter respectively. It was also recorded that the population of soil microflora was reduced due to solarisation in protected structures. Among the treatments, T10 (foliar spray with cymoxanil + mancozeb- 0.2%) was the most effective for management of downy mildew in both polyhouse and rain shelter followed by T11 (foliar spray with mancozeb-0.2%) and T1 (soil solarisation + seed treatment and soil application + foliar spray with T. viride) and these were statistically on par. Moreover, highest yield was recorded in T1 followed by T2 (soil solarisation + seed treatment and soil application + foliar spray with P. fluorescens). Correlation analysis was performed with the meteorological data and per cent disease severity (PDS) at periodic intervals and it was confirmed that there is significant positive correlation between PDS and RH and negative correlation between PDS and temperature inside the structure. Economic analysis of the field experiments suggested that the treatments with biocontrol agents recorded the highest B:C ratio. Analysis of population of phyllolane microflora proved that there was drastic reduction in the population of phylloplane fungi and bacteria after spraying with chemical fungicides whereas the population increased after spraying with biocontrol agents. Survival of biocontrol agents on the phylloplane of cucumber was also studied and it was found that both T. viride and P. fluorescens, survived on the leaf surface upto 15 days after foliar application. Results of the survey and field experiments indicated that, there is a chance of incidence of downy mildew inside the structure if the RH is ≥ 79 per cent. Downy mildew of cucumber inside the protected structures could be effectively managed by biocontrol agents, which gave a reduction in disease severity comparable to that of systemic fungicide. Powered by TCPDF (www.tcpdf.org)
Management of early blight disease of tomato (Solanum lycopersicum L.) under protected cultivation
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2020) Sumbula, V; Sainamole Kurian, P
Management of fungal diseases of capsicum (capsicum annuum L.) under protected cultivation
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2017) Deepa Pawar; Sainamole Kurian, P
Phyllosphere microorganisms for the management of anthracnose disease of Cowpea (Vigna unguiculata (L.) Walp.)
(Department of Plant Pathology, College of Agriculture, Vellanikkara, 2022) Anupama, P R; Sainamole Kurian, P
Microorganisms associated with aerial parts of plants such as stems (cauloshere), phylloplane (leaves), anthosphere (flowers) and carposphere (fruits) which are collectively known as phyllosphere. Phyllosphere microbes includes bacteria, filamentous fungi and yeasts. They offer natural biological control of diseases affecting aerial plant parts. Being better adapted to the phyllosphere niche, they are potential biocontrol agents which are under exploited in agriculture which allow them to adapt to the phyllosphere environment and inhibit the growth of microbial pathogens, thus sustaining plant health. Hence, microbial biocontrolbyphyllosphere microorganisms is a fast growing field of research. Considering the importance of the potential of phyllosphere antagonists, the research project entitled “Phyllosphere microorganisms for the management of anthracnose disease of cowpea (Vigna unguiculata (L.) Walp.).” was carried out. Phyllosphere microbiome enhance plant tolerance to withstand biotic and abiotic stress conditions in the current facet of climate change. A purposive sampling survey was conducted in 21 locations of Kerala where cowpea and/or yard long bean are grown as a vegetable crop. The survey covered six districts namely, Thrissur, Palakkad, Malappuram, Kozhikode, Kannur and Kasaragod and five agro ecological units. Fungi associated with anthracnose symptoms and phylloshere microrganisms associated with healthy and symptomless plants from the fields were isolated. On pathogenicity test, six fungi were confirmed as pathogens and they were identified as Colletotrichum Siamense, three isolates of Colletotrichum sp., Ectophoma multirostrata and Curvularia verruculosa based on cultural, morphological and molecular characterization.C. siamense and Ectophoma multirostrata infecting cowpea is the first report in the world. Similarly, first report of Curvularia verruculosa infecting cowpea and producing anthracnose symptoms from India. Enumeration of phyllosphere microorganisms on cowpea grown at different locations showed that population of fungi distributed on all plant parts and more abundant on flowers. Likewise, bacteria are more abundant on cowpea flowers, and fluorescent pseudomonads and yeasts are more abundantly seen on cowpea pods. Based on colony characters, a total of 183 different isolates of phyllosphere microbes were made into pure cultures and were screened for antagonism towards C. siamense. Forty one isolates expressed antagonism in varying degrees which were again subjected to dual culture screening in vitro. Five promising anatgonists were selected based on per cent inhibition of mycelium of the pathogen on PDA. The five were identified as Trichoderma longibrachiatum, Trichoderma asperellem, Bacillus amyloliquefaciens, Bacillus velezensis and Candida tropicalis based on cultural, morphological and molecular characterization. Cell free culture filtrates of promising phyllosphere antagonists showed maximum growth inhitbion of C. siamense ranging from 86 per cent for Candida tropicalis to 100 per cent for Trichoderma longibrachiatum and Trichoderma asperellem In order to study the induction of systemic resistance in cowpea by phyllosphere antagonists, a pot culture experiment was conducted and the results showed that all the antagonists accelerate the production of defence related enzymes such as peroxidase, polyphenol oxidase and phenylalanine ammonia lyase when challenge inoculated with the pathogen. Bacillus amyloliquefaciens induced higher activity of peroxidase (1.2 min-1g-1 fresh tissue over control), similarly polyphenol oxidase by Candida tropicalis (0.5min-1g-1 fresh tissue over control) and phenylalanine alanine by Trichoderma asperellem (0.8 μmol of transcinnamic acid formed g-1 fresh tissue over the control). To test the biocontrol efficacy and plant growth promotion of phyllosphere antagonists against C. siamense causing cowpea anthracnose, a field experiment was conducted. The semi trailing cowpea variety ‘Anashwara’ was used in the experiment. The treatments included conventional biocontrol agents such as Trichoderma sp. (KAU) and Pseudomonas fluorescens (KAU) and chemical check with hexaconazole (systemic), mancozeb (contact) and carbendazim + mancozeb (systemic +contact) and a control without treatments were also included along with five phyllsophere antagonists such as T. longibrachiatum, T. asperellem, B. amyloliquefaciens, B. velezensis and C. tropicalis. All the treatments were given as seed treatment, and foliar spray. Higher vigour index of seedlings was recorded in the treatment with Bacillus amyloliquefaciens (1408). Biometric observations such as plant height, number of main branches, number of pods per plant, number of seeds per pod, fresh weight of pods, pod length, days to first harvest, days to last harvest and total yieldand per cent disease incidence and severity were recorded at regular interval. Results of the field experiment indicated significant reduction in disease incidence and severity effected by phyllosphere antagonists such as T. asperellem, B. amyloliquefaciens, B. velezensis, C. tropicalis, Trcihoderma sp. (KAU), Pseudomonas fluorescens, hexaconazole, mancozeb and carbendazim + Mancozeb. In terms of yield all the five antagonists along with Trichoderma sp. (KAU) recorded significant yield increase in cowpea compared to other treatments. The bacteria, B. amyloliquefaciens has gained more attention and an emerging evidence has identified its health beneficial effects as probiotics, hence farmers can safely use this as a biocontrol agent. Focusing on efficient and safer (non pathogenic nature), the phyllosphere antagonists such as T. asperellem and B. amyloliquefaciens are selected as the best among all the treatments. So, it can be concluded that out of the eleven treatments, T. asperellem and B. amyloliquefaciens could promote the growth of the plants and reduce the disease incidence and severity than the other treatments. However, multilocational field studies should be conducted to validate the findings of the current study, so that these bioagents can be formulated and made available to the farming community.