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Open Access
Physiological and cultural studies on blue oyster mushroom (Hypsizygus ulmarius (Bull.:Fr.) Readhead)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2016) Sumi, I; KAU; Geetha, D
The present study entitled “Physiological and cultural studies on blue oyster mushroom (Hypsizygus ulmarius (Bull.:Fr.) Redhead)” was carried out in the mushroom unit, Instructional Farm, College of Agriculture, Vellayani during 2014-2016, with the objective to standardize the technology for cultivation of Hypsizygus ulmarius and to study its morphological and physiological aspects. The initial culture of H. ulmarius was isolated from the mushroom beds maintained in the mushroom unit of instructional farm through tissue culture method and purified by hyphal tip method. Morphological studies of H. ulmarius showed that the sporocarps were medium to large in size having a dark blue colour in the pinhead stage which became creamy white on maturity with an irregularly shaped, convex pileus with gills attached to the stem, but not decurrent and cylindrical, smooth and eccentric stipe. Microscopic studies revealed septate hypahe with clamp connection, oval shaped, hyaline basidiospores and the spore print was white. Studies on developmental morphology showed that H. ulmarius took an average of five days from the day of pinhead formation to complete maturity. The maximum mycelial growth was recorded on potato dextrose agar. A temperature of 25 0C, pH of 8 and dark conditions are found favourable for maximum mycelial growth. Evaluation of different substrates for spawn production revealed that paddy grains was the best medium in which spawn run was completed in fifteen days with thick fluffy growth and recorded less contaminants followed by wheat and sorghum. Evaluation of different substrates for mushroom production revealed that paddy straw was the best material for the cultivation of blue oyster with a total yield of 985 g kg-1 from three harvests followed by rubber sawdust (905 g kg-1). The minimum time for mushroom production was recorded for sugarcane bagasse and the maximum time for rubber sawdust. The average weight of sporocarp was maximum in mushrooms harvested from rubber sawdust and the maximum number of sporocarps was recorded in paddystraw. Beds prepared from sugarcane bagasse were heavily contaminated with Trichoderma sp. When compared with Pleurotus florida, H. ulmarius took more time (18 days) for complete spawn run in paddy grains and the yield was higher on paddy straw (1.096 kg kg-1) than P. florida (976 g kg-1). Infestation of pests viz., phorid flies (Megaselia sp.) and staphylinid beetles were prevalent during spawn run as well as sporocarp formation. The competitor moulds recorded were Trichoderma sp., Aspergillus sp. and Coprinus sp. Analysis for the proximate constituents in H. ulmarius revealed that it contains appreciable amount of carbohydrate (29 %), protein (32 %) and fibre (17.69 %). Sensory evaluation was done on steam cooked mushrooms for attributes like appearance, colour, texture, flavor and taste using five point score card and an overall acceptability score of 3.6 was obtained for H. ulmarius compared to P. florida (3.0). In the preference study conducted for both the mushrooms using Hedonic rating scale, 30 per cent of evaluators extremely liked H. ulmarius than P. florida (10 %). The study on the keeping quality of mushrooms in normal atmospheric condition indicated a shelf life of eight hours for H. ulmarius compared to six hours for P. florida. The study also showed that blue oyster mushrooms stored under refrigeration (4 0C) in perforated polythene covers had better shelf life (5 days) compared to P. florida (3 days). The present study indicated that blue oyster mushroom can be cultivated successfully in tropical areas on locally available materials like paddy straw and rubber saw dust under favourable climatic conditions viz., 26-28 0C temperature, more than 90 per cent relative humidity and good aeration. The variety is superior to the presently growing oyster mushroom (P. florida) in terms of yield, presence of appreciable amount of proximate constituents and keeping quality.
Open Access
Integrated management of rhizoctonia leaf blight of amaranthus (Amaranthus tricolor L.)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2016) Gireesh; KAU; Radhakrishnan, N V
The study entitled “Integrated management of Rhizoctonia leaf blight of Amaranthus (Amaranthus tricolor L.)” was conducted at the College of Agriculture, Vellayani and Coconut Research Station, Balaramapuram during 2014-2016 with the objective to investigate the effect of soil solarization, biocontrol agents, chemical activator, indigenous formulations and new generation fungicides on growth, yield and severity of foliar blight of amaranthus. Samples of the infected leaves showing Rhizoctonia leaf blight in amaranthus were collected from Vellayani, Kalliyoor, Venganoor and Kakkamoola locations. Among the four isolates of the pathogen, the Vellayani isolate gave significantly superior growth rate with minimum of six days for sclerotial formation. Koch‟s postulates were proved for the pathogenicity of different isolates of Rhizoctonia solani. All the four isolates have taken three days for the first symptom development but the progression of lesion size of Vellayani isolate was maximum compared to all other isolates, hence the Vellayani isolate was selected as the most virulent isolate for use in further in vitro studies. Evaluation of biocontrol agents for in vitro suppression of R. solani showed that Trichoderma harzianum completely overgrown the pathogen with maximum inhibition of 49.56 % compared to Pseudomonas fluorescens (28.30 %). Under in vitro evaluation of chemical activator, different concentrations of Acibenzolar-S- Methyl (ASM) against pathogen, 100 ppm concentration recorded the maximum mycelial inhibition of 75.67 % and 5 ppm concentration recorded the minimum mycelial inhibition of 27.70 %. Among indigenous organic formulations, turmeric powder and baking soda combination inhibited the maximum growth of the pathogen by 64.40 %. In the in vitro studies with new generation fungicides,mancozeb in cow dung supernatant (0.4 %) and tebuconazole (0.1 %) recorded the 100 % mycelial inhibition of the pathogen. Field studies on disease suppression and plant growth promotion was carried out as two experiments, one in soil solarized plots and the other in non solarized plots. Soil solarization along with soil application of ASM (75 ppm) and foliar application of ASM (100 ppm) recorded the lowest disease incidence of 30.41 % and 30.42 % respectively, which was superior when compared with foliar application of ASM (100 ppm) and soil application of ASM (75 ppm) with the disease incidence of 37.06 % and 38.84 %. Soil solarization + foliar spray of tebuconazole (0.1 %) recorded the minimum disease index of 37.85 % which was superior compared to foliar spray of tebuconazole (0.1 %) with the disease index of 39.28 %. Among the biocontrol agents soil solarization + foliar spray of Pseudomonas fluorescens (2 %) gave minimum disease index of 45.22 % which was greater compared to foliar spray of P. fluorescens (2 %) with the disease index of 51.66 %. In case of indigenous organic formulations, soil solarization + foliar spray of fish amino acid (5 %) given the maximum control of the disease with the disease index of 49.51 % which was superior to foliar spray of fish amino acid (5 %) with disease index of 63.59 %. The number of days taken for flowering in soil solarized plots ranged from 28.67 to 35 days where as the number of days taken for the flowering of amaranthus in non solarized plots was ranged from 27.27 to 31.67 days. At the time of harvest, soil solarization + mancozeb in cow dung supernatant (0.4 %) recorded maximum plant height of 127.07 cm which was higher compared to foliar spray of azoxystrobin (0.15 %) with plant height of 117.60 cm. Maximum of 78.00 number of leaves were recorded by soil solarization + foliar spray of azoxystrobin (0.15 %) which was greater compared to foliar spray of azoxystrobin (0.15 %) with 67.67 number of leaves.Soil solarization + foliar spray of azoxystrobin (0.15 %) gave the highest yield in terms of fresh weight by 26975.00 kg/ha and dry weight of 4233.33 kg/ha which was superior when compared with foliar spray of tebuconazole (0.1 %) with the fresh weight of 23375.00 kg/ha and dry weight of 3362.50 kg/ha. It is concluded that soil solarization for 31 days with the foliar application of tebuconazole (0.1%) can effectively control the Rhizoctonia leaf blight disease severity with plant growth and yield promotion under field conditions.
Open Access
Integrated management of anthracnose of snake gourd (Trichosanthes cucumerina L.)
(Department of Plant Pathology,College of Agriculture, Vellayani, 2016) Aswani Devi; KAU; Kamala Nayar
The objective of present study entitled “Integrated management of anthracnose of snake gourd (Trichosanthes cucumerina L.)” was to make a comparative evaluation of foliar application of newer fungicides and biocontrol agents for the management of anthracnose disease of snake gourd. Surveys were conducted during October 2015 in snakegourd fields of five different locationsof Thiruvananthapuram district , viz., Instructional Farm, College of Agriculture,Vellayani, Department of Olericulture, College of Agriculture, Vellayani, Kalliyoor, Kakkamoola and Palapoor. Maximum disease incidence (90.00 per cent) and disease severity/ percentage disease index (44.22) were recorded in the snake gourd fields of Instructional Farm, Vellayani whereas disease parameters were minimum (21.89 per cent and 70.00 per cent) in the fields of Palapoor Pathogenicity tests revealed that the isolate C1 obtained from Instructional Farm, Vellayani produced maximum lesion size both on detatched leaf (2.53 cm2) as well as and on intact leaves of 30-days old potted plant (10.06 cm2). The smallest lesion size of 1.33 cm2 on detatched leaf and 1.53 cm2 on 30 days old potted plant was produced by the isolate C4 from Kakkamoola. Based on lesion size and virulence rating, C1 was screened as the most virulent isolate. Results of the cultural studies among the five isolates, showed that potato dextrose medium, oat meal medium and Richard’s medium were screened as the best media both in solid and liquid states for the growth of the tested isolates. Effect of different light sources (Fluorescent light: 253.7 - 185 nm, L.E.D light: 365 nm and UV light: 10 - 380 nm) on growth and sporulation of anthracnose pathogen indicated that the cultures exposed to fluorescent light and darkness for alternate cycles of 12 h of each day resulted in maximum mycelial growth and minimum days for sporulation for all the isolates. Growth was less when the cultures of the isolates were exposed to UV light for a period of 45 min. The morphological characters studied indicated that average conidial size of isolate C1, C2, C3 and C5 ranged from 11.40μm- 13.14μm x 4.48μm-4.82 µm and that they were cylindrical in shape with obtuse ends. The isolate C4 was ellipsoidal in shape and had a conidial size of 10.52μm x 4.40 µm. The isolates C1, C2, C3 and C5 were further identified at National Fungal Collection Culture India (NFCCI) - Pune, as C. coffeanum F.Noack and the isolate C4 was identified as C. musae (Berk. & M.A. Curtis) Arx. Isolate C1 of C. coffeanum which was earlier screened as the most virulent isolate was used for the subsequent studies conducted for the management of anthracnose disease in snake gourd. In the invitro assayconducted for screening of newer fungicides and bio control agents, effective for the inhibition of the isolate C1 of C. coffeanum, the nutrient potassium silicate (0.5 per cent) and fungicide mancozeb (0.4 per cent) resulted in hundred per cent mycelial inhibition while, KAU talc based formulations of the bio control agents viz., P. fluorescens (2 per cent) and T. viride (2 per cent) resulted in inhibition of 88.33 per cent and 87.33 per cent respectively and were selected for further evaluation in green house study. Minimum spore germination was recorded due to amendment of medium with T. viride (1.33 per cent). Conidia were also reduced in size when growth medium (PDA) were amended with tested chemicals and bio-control agents. In the green house studies using the snake gourd variety Kaumudi, maximum disease suppression was observed when plants were sprayed with 0.5 per cent potassium silicate (89.12 per cent) and 0.4 per cent of fungicide mancozeb (84.99 per cent) at fifteen days interval. Biometric parameters observed were also maximum for plants sprayed with 0.5 per cent potassium silicate followed by mancozeb and KAU talc based formulation of bio-control agents P. fluorescens and T. viride. Anthracnose affecting the foliage of snake gourd is a serious disease in snakegourd fields of Thiruvanathapuram district. The nutrient potassium silicate which was tested for the first time in Kerala against a plant pathogen, Colletotrichum sp. is found to be a promising chemical for management of the disease. The present study has also revealed the prospects of utilizing the mineral nutrient, potassium silicate for control of anthracnose disease as well as attainment growth promotion, flowering behavior, yield components and increases in yield of snake gourd which is an important vegetable crop of Kerala. Besides, this study also has highlighted the scope for integrating the fungicide mancozeb with bio-control agents like P. fluorescens and T. viride which were was also highly beneficial for the disease management as well as in improving the growth parameters of the crop under green house conditions. Such integration of fungicide mancozeb with bio-control agents will also be useful in minimizing the detrimental effects of continous and intensive use of this fungicide which is otherwise very effective in disease management. In the background of the promising results obtained from this thesis project especially from the use of potassium silicate, trials for confirming the beneficial effects of the treatments in field grown snake gourd plants would be useful for the vegetable growers in Kerala.
Open Access
Etiology and management of mosaic disease in ginger (Zingiber officinale Roscoe)
(Department of Plant Pathology, College of Agriculture, Vellayani, 2018) Ananthu, N; KAU; Umamaheswaran, K
The study entitled ‘Etiology and management of mosaic disease in ginger (Zingiber officinale Roscoe)’ was conducted at the Department of Plant Pathology, College of Agriculture, Vellayani during 2015-2018 with the objectives to identify, characterize and sequence the genes of Ginger mosaic virus infecting ginger along with the management of the disease. As part of the study, the symptoms produced by the virus in ginger plants collected from the field and grown in glass house were observed. The symptoms on the leaves appeared as small light green flecks. These flecks eventually increased in size and formed streaks. The streaks were arranged parallel to the veins. The appearance of too many streaks on the leaves led to severe chlorosis and the leaves showed necrotic symptoms in the advanced stage. Transmission of the virus was tested in rhizome (seed material collected from infected plants) and mechanical inoculation was done using infected leaf sap to the healthy plants. The infected rhizomes resulted in 100% transmission and mechanical transmission failed to transmit the virus. Changes in total carbohydrates, chlorophyll, phenol, total soluble proteins and defense related enzymes namely peroxidase, polyphenol oxidase and phenylalanine ammonialyase were carried out at 30, 60, 90 and 120 days after infection. The study revealed an increase in the content of phenols and defense related enzymes in infected plants. An increase in carbohydrates, chlorophyll and protein in healthy plants was also observed. Protein profile study using sodium dodecyl sulphate- polyacrylamide gel electrophoresis (SDS- PAGE) indicated the presence of a novel protein with molecular weight of 20 kDa in the infected plant sample. The immunological detection techniques direct antigen coating- enzyme linked immunosorbant assay (DAC- ELISA) and dot immunobinding assay (DIBA) were carried out. Since the etiology of the virus was unknown, seven suspected viruses were tested in DAC- ELISA and antibodies specific to two viruses namely Banana bract mosaic virus (BBrMV), Cucumber mosaic virus (CMV) gave an absorbance value of 0.15 and 0.19 respectively which was three times more than the absorbance shown by the healthy leaf (0.05 and 0.07). The infected leaf tested for the presence of African cassava mosaic virus (ACMV) by triple antibody sandwich ELISA (TAS-ELISA) gave an absorbance of 0.0425 while the healthy gave an absorbance of 0.017. DIBA analysis gave positive reaction to BBrMV. Polymerase chain reaction ( PCR) was carried out with both total DNA and RNA isolated from infected ginger leaf sample. The PCR experiment was positive to Begomoviruses and negative to PVY (Potato virus Y) and BBrMV isolates. An amplicon of size 550 bp was obtained for the sample DNA using begomo degenerate primer. The sequence was subjected to BLAST analysis which indicated 74 per cent similarity to Tomato leaf curl virus Bangalore isolate. The management studies were conducted with antiviral principles like botanicals, chemicals and that of microbial origin against the virus. The experiment was conducted in completely randomized design (CRD) with 13 treatments and three replications. Karthika was the variety used for the study. Perfekt (a botanical extract-76%) at 0.5 ml L-1 and 1ml L-1, chemicals namely aspirin, salicylic acid, barium chloride, at 100 and 150 ppm concentrations and botanicals namely ten per cent leaf extracts of Mirabilis jalapa and Bougainvillea spectabilis, two per cent neem oil garlic emulsion and two per cent PGPR mix II were used in the experiment. The treatments were given at fortnightly interval. Before each spray the efficacy of the treatments were evaluated using Vulnerability Index (V.I) developed by Bos (1982). The treatments with Perfekt at the rate of 0.5 ml L-1 and 1.0 ml L-1 and ten per cent leaf extract of Mirabilis jalapa were found effective for the management of the disease. The study indicates that the mosaic disease in ginger is transmitted through rhizomes, the virus has been molecularly characterized and shows only 74% identity with Tomato leaf curl virus (TLCV) and management of the disease can be done by application of Perfekt at 0.5 ml L-1 or 10% leaf extract of Mirabilis jalapa at fortnightly interval.
Open Access
Characterization, host range and management of papaya ringspot virus (PRSV)
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2018) Atheena Harish; KAU; Anita Cherian, K
Papaya is an important fruit crop which is cultivated extensively both in tropics and subtropics. During the last decade, the area under papaya cultivation has dramatically increased due to the introduction of superior varieties. A major setback subsequent to the introduction of such new varieties has been the incidence of papaya ringspot disease caused by Papaya ringspot virus (PRSV) which leads to almost 100 per cent yield loss. Considering the importance of the disease, the project was undertaken with the objectives of characterization of the virus, molecular and immunodiagnosis along with disease management. The research project was initiated with purposive sampling surveys conducted in different papaya orchards of Thrissur district in order to document the symptoms under natural conditions, to assess the incidence and severity of the disease and to collect infected samples for further studies. The maximum disease incidence and disease severity recorded were 99.6 and 96.67 per cent on papaya variety Red Lady from Vellikulangara and Puthur respectively. The development of symptoms was studied under artificial conditions also through mechanical inoculation of healthy papaya seedlings with virus inoculum maintained in insect proof net house conditions. The salient diagnostic symptoms of the disease observed on leaves were chlorotic spots, mottling, vein thickening, puckering, leaf distortion, shoestring symptom along with presence of oily streaks on the petiole. The fruits of infected plants presented typical oily concentric or broken ringspots on fruit surface along with malformation. Histopathological studies of infected leaves revealed disruption of the epidermis, disorganization of parenchyma, disintegration of chloroplasts and deposition of crystalline bodies. The studies on virus transmission confirmed that it is transmitted through plant sap from infected to healthy papaya plants. Seed transmission studies revealed that PRSV is not seed -borne. Twenty one plant species including weeds seen in and around papaya orchards were tested for studying the host range of the virus and only five plant species viz., Cucumis sativus, Cucurbita moschata, Trichosanthes cucumerina, Momordica charantia and Chenopodium amaranticolor developed symptoms after artificial inoculation of PRSV and thus proved to be the hosts of the virus. Morphological characterization done using electron microscopy showed the presence of typical flexuous rod particles of size 807.74 nm x 12 nm which indicated that the virus belongs to genus Potyvirus and the etiology of the disease was confirmed as Papaya ringspot virus. Immunodiagnostic technique was validated using Direct Antigen Coating - Enzyme Linked Immuno Sorbent Assay (DAC-ELISA) and infected samples showed positive reaction to PRSV antiserum and could be detected at 1:200 dilution of primary antibody and 1:10,000 dilution of secondary antibody. Molecular characterization of PRSV was also carried out through Reverse Transcription Polymerase Chain Reaction (RT-PCR). The nuclear inclusion b (NIb) gene and the coat protein (CP) gene were amplified using reported primer pairs which yielded amplicons of approximate size of 1700 bp. The PCR products were outsourced for sequencing and in silico analysis of the sequences obtained revealed that the isolates of present study are more similar to Calicut isolate of PRSV, PRSV- Ca (DQ666640.1) A pot culture experiment under insect proof conditions was also conducted to evaluate the effects of selected botanicals, chemicals and biocontrol agents for disease management. Among the fourteen treatments, Bougainvillea leaf extract, 10 per cent (T7) was the most effective with lowest disease severity (6.67%) followed by foliar spray and soil drenching with Pseudomonas fluorescens 2 per cent (T3) with a disease severity of 11.11 per cent as against 97.77 per cent recorded in untreated control plants. Plant height recorded after each treatment application revealed that both 10 per cent Bougainvillea leaf extract (T7) and 2 per cent P. fluorescens are equally superior to all other treatments. However, with respect to mean girth of stem, maximum value (2.91 cm) was recorded in P. fluorescens (T3) The data on virus titre of all treated plants assessed through DAC-ELISA revealed that the concentration of virus particles was minimum in plants treated with T7 and T3. The outcome of this study would facilitate early detection and elimination of source of virus infection and thereby prevent the spread of disease in the field. The information generated on molecular characterization of PRSV isolates under could be applied in genetic engineering. The project also revealed the potential of botanical, Bougainvillea spectabilis leaf extract and biocontrol agent, Pseudomonas fluorescens for the ecofriendly management of papaya ringspot disease.
Open Access
Triazole,strobilurin and its combination fungicides for the management of anthracnose and fruit rot of chilli
(Department of Plant Pathology, College of Agriculture, Vellayani, 2018) Anjana, R S; KAU; Joy, M
A study entitled ‘Triazole, strobilurin and its combination fungicides for the management of anthracnose and fruit rot of chilli’ was conducted during 2016 - 18 at Department of Plant Pathology, College of Agriculture, Vellayani with the objectives to study the host range of the pathogen Colletotrichum capsici and to develop management strategy to control the disease using new generation fungicides. A survey was conducted at Vellayani, Kumarakom, Thrissur, Pattambi, Ambalavayal and Padanakkad during 2016 – 17 to screen the most virulent isolate of C. capsici in chilli (Capsicum annuum). During the survey period, C. capsici was found causing the disease in five and C. gloeosporioides in one locations. The maximum disease incidence (70 %) and severity (45 %) by C. capsici was recorded from Padanakkad. Except from Ambalavayal, five pure cultures of C. capsici (C1 to C5) were obtained and Koch’s postulate is proved. C. capsici produced white to dirty white, sparse mycelial growth on PDA, which later turned into dirty grey colour. Days taken to cover petridish (9 cm radius) ranged from 7.4 to 8.3 days. Mycelium was hyaline, septate and branched. Black colored acervuli were produced after 20 - 30 days of incubation and its diameter ranged from 21.85 - 45.82 μm, with 18 - 47 dark setae of 72.50 - 110.41 μm length. Conidiophores are hyaline, short and cylindrical with sickle shaped single celled conidia having an oil globule at the centre. The average size of the conidia was 20.04 - 23.48 μm x 2.58 - 3.22 μm. Based on screening of isolates through leaf and fruits inoculation of chilli variety ‘Vellayani Athulya’, C3 was identified as the most virulent isolate. The identity of C. capsici (C3) was confirmed by PCR using ITS primers, sequencing of amplicon, BLAST and phylogenetic analysis. The best solid and liquid media for growth and sporulation of C. capsici was potato dextrose medium, the optimum temperature was 30oC and pH was 6.5. The growth of C. capsici was studied under different light conditions and the fungus growth was maximum in 8 hour light and 16 hour dark under white light at 20 lux intensity. Host range of C. capsici was studied in different vegetable crops viz. Capsicum chinense, C. frutescens, cowpea, brinjal, tomato and bhindi. C. capsici infected all the host plants tested and brinjal was found as the ideal host plant. Among eight KAU varieties of chilli viz. Vellayani Athulya, Jwalamukhi, Jwalasakhi, Ujwala, Anugraha, Keerthi, Vellayani Thejus and Vellayani Samrudhi, screened against C. capsici with leaf and fruits inoculation, Vellayani Athulya was found to be the most susceptible variety to the disease, whereas Vellayani Thejus and Vellayani Samrudhi were found comparatively resistant to leaf and fruit infection. Under in vitro evaluation of new generation fungicides by poisoned food technique, azoxystrobin 11 % + tebuconazole 18.3 % SC at 10 ppm, pyraclostrobin 20 % WG at 50 ppm and hexaconazole 5 % EC + pyraclostrobin 20 % WG at 100 ppm completely inhibited the mycelial growth and proved to be most effective. All fungicides significantly inhibited spore germination of C. capsici. Hexaconazole 250 ppm completely inhibited germination. Pyraclostrobin 20% WG at 10 ppm, hexaconazole 5 % EC + pyraclostrobin 20 % WG at 50 ppm, tebuconazole 25.9 % EC and hexaconazole 5 % EC at 100 ppm were also equally effective in inhibiting germination of spores and were statistically on par. A pot culture study was conducted with chilli variety ‘Vellayani Athulya’ to evaluate the efficacy of selected new generation fungicides. The selected treatments were imposed only once, after 18 days of flowering when at least 25 per cent of fruits were at maturity stage. At recommended dose, the maximum disease suppression was recorded with 0.24 % of copper oxy chloride 50 % WG (90.59 %), followed by 0.1 % of hexaconazole 5 % EC + pyraclostrobin 20 % WG (73.50 %), 0.15 % of azoxystrobin 11 % + tebuconazole 18.3 % SC (70.94 %) and 0.1 % of tebuconazole 25.9 % EC (68.70 %). At higher (double the recommended) doses of respective fungicides, disease suppression was more. Biocontrol agents were also effective, but the disease suppression was less with 22.22 per cent for Trichoderma viride and 43.58 per cent for Pseudomonas fluorescens compared to the new generation fungicides. Hence anthracnose and fruit rot of chilli can be effectively managed by foliar spray of hexaconazole + pyraclostrobin combination fungicide and it may be subjected to mutlilocation and multiseasonal trials before recommendation.
Open Access
Characterization and management of yellow mosaic disease of black gram (vigna mungo (L.) hepper)
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2018) Divya Jayakumar, V J; KAU; Sumiya, K V
Black gram (Vigna mungo (L.) Hepper) is one of the important pulse crop in India and an excellent source of good quality protein. Yellow mosaic disease (YMD), caused by a whitefly transmitted geminivirus is the major constraint for black gram cultivation. Yellow mosaic disease of pulses is extensively studied from different parts of the country. But no study has been conducted in Kerala. Hence, the present study was undertaken to characterize the virus causing yellow mosaic disease in black gram in Kerala and to evolve suitable strategies for its management. Purposive sampling surveys were conducted in black gram growing areas of Palakkad and Malappuram districts, covering 13 fields at nine locations to study the incidence and symptomatology of yellow mosaic disease. The disease incidence in the fields varied from 12 to 100 per cent. Common symptoms observed in the field were typical yellow mosaic, puckering and cupping of leaves, distortion of leaf lamina and drastic reduction in size of younger leaves. Irregular whitish discolouration of leaves which turned papery white on maturity was also observed in some fields. Complete yellowing of leaves along with brown discoloration between the veins and vein banding symptoms which were not reported by earlier workers were also observed in the field. Electron microscopic studies revealed the presence of geminate particles of 15-18 x 30 nm size in infected black gram samples suggesting the association of a geminivirus with the disease. Whitefly transmission of the virus to healthy black gram plants was attempted and 80 per cent transmission was achieved. PCR amplification using virus specific primers revealed the presence of Mungbean yellow mosaic virus (MYMV) and Horsegram yellow mosaic virus (HYMV) in the samples. MYMV was detected in infected samples from nine fields out of the 13 fields surveyed. HYMV was detected in six fields, which include five fields in which MYMV was also detected revealing the occurrence of mixed infection in the field. Five representative isolates were sequenced at Agrigenome Labs, Kakkanad, Ernakulam. In silico analysis of these sequences revealed that the coat protein region of the isolates showed more than 90 per cent homology with MYMV isolates. This confirmed the presence of MYMV as the major virus in yellow mosaic disease of black gram in Kerala. Phylogenetic analysis revealed that the isolates from the present study are more closely related to MYMV isolates from southern parts of India and distantly related to Mungbean yellow mosaic India virus (MYMIV) isolates, which were reported from northern parts of India. Host range studies conducted in insect proof cages under glass house condition showed that the virus could be transmitted through whiteflies only to horse gram. Symptoms were observed in horse gram and Synedrella nodiflora, a predominant weed found in the field 20 -25 days after inoculation. But the presence of virus was confirmed by PCR only in symptomatic horse gram and not in Synedrella nodiflora. A field experiment was conducted during Rabi 2017-18 at RARS, Pattambi and evaluation of effectiveness of botanicals, biocontrol agents and other organic products revealed that application of Pseudomonas fluorescens as seed treatment @ 10g/kg seed and foliar sprays @ 10g/l at fortnightly intervals starting from 15 days after sowing or foliar sprays of 10 per cent aqueous extract of leaves of Bougainvillea spectabilis or roots of Boerhaavia diffusa at fortnightly intervals starting from 15 days after sowing are effective in reducing the yellow mosaic disease. The present study reveals that MYMV is the virus associated with the YMD of black gram in Kerala and it can be effectively managed by prophylactic application of Pseudomonas fluorescens, 10 per cent leaf extract of Bougainvillea spectabilis or 10% root extract of Boerhaavia diffusa. This is the first report on identification of MYMV associated with yellow mosaic disease of black gram in Kerala.
Open Access
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; KAU; 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.
Open Access
Exploitation of abiotic stress tolerant strains of trichoderma spp. for the management of soil borne fungal pathogens
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 2018) Stella Doncy, P P; KAU; Reshmy Vijayaraghavan
Soil borne phytopathogenic fungi are known to cause severe yield loss of several crops. To mitigate these crop ailments, farmers mostly rely on chemical methods of disease control such as fungicides and other pesticides which are deleterious to the environment. To date, biological control is an ecofriendly approach for the effective management of crop diseases. The fungi belonging to the genus Trichoderma are one among the most exploited biocontrol agents in the field of agriculture. However, the performance of Trichoderma spp. gets reduced when it is exposed to abiotic stressed conditions such as drought, high temperature, salinity, acidity and fungicides. Hence, this study was proposed to identify and exploit stress tolerant isolates of Trichoderma spp. with antagonistic potential in Kerala. Intensive soil sampling surveys were conducted across different stressed ecosystems of Kerala viz., Palakkad, Alappuzha, Vytilla, Kumarakom, Wayanad and Thrissur for the isolation and enumeration of native Trichoderma spp. A total of 24 isolates were obtained from 52 soil samples collected from different locations. Based on the number of Trichoderma spp. obtained from each district, they were serially numbered and abbreviated according to the name of the location. Accordingly, PAT 1 to PAT 6 represents number of isolates of Trichoderma spp. from Palakkad district, ALT 1 to ALT 3 from Alappuzha, VYT 1 and VYT 2 from Ernakulam district, KUT 1 from Kottayam district, WAT 1 to WAT 8 from Wayanad and THT 1 to THT 4 from Thrissur district. Cultural and morphological identification of these isolates were carried out under in vitro conditions. Isolates of Trichoderma spp. were subjected to in vitro screening for abiotic stress tolerance such as high temperature, drought, acidity, salinity and also to test their sensitivity towards copper fungicides. The isolates PAT6 and WAT2 were found as thermotolerant, VYT2 and ALT 1 as drought tolerant, ALT 3 and ALT 1 as acid tolerant and saline tolerant and the isolates ALT1, ALT3 and PAT 1 as copper fungicide tolerant. The selected six isolates were further subjected to biochemical tests and the study showed that the isolates VYT 2, ALT 3 and ALT 1 showed highest cellulase, β- 1, 3 glucanase and protease activity. Likewise, isolates PAT 1, ALT 1 and ALT 3 were found as best producers of ACC deaminase and PAT 1 and ALT 1 as the best cytokinin producer. The best performing isolates (ALT 1, ALT 3, PAT 1, PAT 6 and VYT 2) after enzyme study were subjected to dual culture experiment with five major soil borne pathogens to test their antagonistic potential. The isolates ALT 3, ALT 1, PAT 6 and PAT 1 showed more than 70 per cent inhibition of R. solani whereas, isolates ALT1 and VYT 2 showed only 57.78 and 55 per cent inhibition of S. rolfsii respectively. However, no significant difference was noticed among the isolates when grown against F. solani. Cent per cent inhibition of P. aphanidermatum was noticed with Trichoderma isolates PAT 1 and ALT 1. All five isolates showed 100 per cent inhibition on the growth of pathogen, P. capsici. Among the five, four isolates viz., ALT 1, ALT 3, PAT 1 and PAT 6 with best antagonistic potential were subjected to molecular characterization at Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram and the isolates showed homology with the nucleotide sequence of Trichoderma asperellum. A pot culture experiment was laid with the selected isolates viz., ALT 1, ALT 3, PAT 1 and PAT 6 to test the growth promotion of cowpea and biocontrol efficacy against Rhizoctonia solani. It was observed that the isolate PAT 6 coated seeds showed 100 per cent germination and also recorded better biometric characters and yield. Moreover, the lowest per cent disease incidence of 11.11 per cent was only recorded with both the isolates ALT 3 and PAT 6. Thus, the study has enlightened our knowledge on the existence of abiotic stress tolerant isolates of T. asperellum which can be employed in future for the biocontrol of soil borne pathogens in such conditions.

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