1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)
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Item 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, PYard 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.Item 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, PThe 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)