STUDIES ON CHILLI (Capsicum annuum L.) VIRAL COMPLEX IN MAJOR CHILLI GROWING AREAS OF TELANGANA AND ITS MANAGEMENT

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Date
2022-07-02
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PROFFESSOR JAYASHANKAR TELANGANA STATE AGRICULTURAL UNIVERSITY
Abstract
Survey conducted in major chilli growing areas of Telangana viz., Warangal, Mahabubabad, Mulugu, Jayashankar Bhupalpally, Nagarkurnool and Khammam during Rabi 2019-20 and Rabi 2020-21 seasons revealed the natural occurrence of chilli viral complex in different mandals. In all the districts, the disease incidence ranged from 2 to 40 per cent being maximum in Khammam (41.59 per cent) followed by Warangal (32.80 per cent) and Mahabubabad (26.79 per cent) and minimum disease incidence of disease was recorded in Mulugu (19.18 per cent) and Nagarkurnool district (20.21 per cent). Severity of disease complex varied with the cultivars. Different types of symptoms viz., leaf curl, puckering, mosaic, shoe string and yellowing were observed in the fields surveyed. Occurrence of thrips was recorded in every field irrespective of cultivar grown and the season surveyed but comparatively the population was higher during Rabi 2019- 20 in different chilli growing areas of Telangana. Among them, Scirtothrips dorsalis was showing higher incidence during Rabi 2019-20 (24.25 per 5 terminals) than Rabi 2020-21 (20.75 per 5 terminals) followed by Frankliniella schultzei (19.5 per 5 terminals) during Rabi 2019 and 20 per 5 terminals during Rabi 2020-21 respectively. Whitefly population was also observed in all the fields surveyed, their population constituted between 4 to 20 whiteflies/plant (Rabi 2019-20) and 5 to15 whiteflies/plant (Rabi 2020-21). During both the years of study whitefly infestation was highest in Warangal (8.50 whiteflies/ plant; 6.53 whiteflies/plant) followed by Khammam (6.35 whiteflies/plant; 5.75 whiteflies/plant), Mahabubabad (7.25 whiteflies/plant; 5.26 whiteflies/plant), Jayashankar Bhupalpally (5.75 whiteflies/plant; 5.10 whiteflies/plant), Nagarkurnool (2.55 whiteflies/plant; 1.35 whiteflies/plant) and Mulugu (1.55 whiteflies/plant; 1.25 whiteflies/plant. It has been observed that there was not much difference in its occurrence in rainfed - direct sown and irrigated - transplanted crop grown in these districts surveyed. In the present study, twenty weed species were found in all the surveyed fields across locations, type of soils and seasons. Parthenium hysterophorus was found to be most prevalent in chilli fields surveyed and frequency of occurrence of P. hysterophorus was maximum (78 per cent) in all the six districts under survey over two years followed by Amaranthus tricolor, Cyperus rotundus, Portulaca oleracea, Tridax procumbens, Digitaria marginalis, Argemone mexicana, Phyllanthus niruri, Commelina bengalensis, Datura stramonium, Sida acuta and Cleome viscosa. DAC-ELISA was carried out using CMV antisera during Rabi 2019-20 and 2020-21, and results revealed that out of a total of 80 virus isolates collected from different fields of Telangana during Rabi 2019-20, 55 isolates tested positive in DAC ELISA tests. Results of Rabi 2020-21 revealed that out of 80 isolates tested, only 45 isolates were positive for CMV. PCR amplification techniques were used in the present study for the detection of leaf curl virus in the infected samples collected during survey. Upon amplification by PCR, 1000 bp size amplicon was obtained in 25 leaf curl infected chilli samples. Results confirmed the specific association of Gemini virus (ToLCV) is involved with the chilli viral complex. Similarly, during Rabi 2020-21 a total of 30 samples were subjected to PCR amplification using the specific primers. Upon amplification by PCR, 1000 bp size amplicon was obtained in 25 leaf curl infected samples. These results confirm the presence of leaf curl virus in the suspected samples. Electron microscopic studies of negatively stained purified and leaf dip preparations at 20,000X magnification revealed the presence of typical spherical particles with an average diameter falling in the range of 28-30 nm. The sap from leaf curl infected samples was partially purified and examined by transmission electron microscopy. Twinned and icosahedral virions about 20 nm in diameter were observed in the purified preparation, which were the typical morphology of virus particles in the genus Begomovirus. Infectivity assays revealed that many weed species in different families that commonly grow in or near chilli fields harbor the viruses. In most cases, the infected weeds were asymptomatic. Symptoms that could be associated with virus infection such as yellowing, leaf curling, and interveinal chlorosis were only observed in some species belonging to the genera of Amaranthus, Datura, Tridax, Parthenium and Euphorbia which tested positive. Twenty six plant species belonging to ten families were tested under artificial inoculation for their susceptibility to CMV and leaf curl under insect proof conditions. Out of twenty six species tested for their reaction to chilli mosaic and leaf curl viruses, eighteen species have expressed the visible symptoms. The host range studies clearly indicated that weed species occurring in chilli fields and in crop plants such as groundnut, cowpea, curcurbits etc. were found to be the most common CMV sources under field conditions. Appearance of CMV in fields, where no known sources of CMV in the vicinity due to the migratory aphids and thrips carrying and contributing to the long distance spread of the virus. Three different modules were formulated and tested for the integrated management of chilli viral complex at two different locations. The disease appeared in all the modules at 4 weeks after transplanting (WAT). In general, the disease incidence increased with the age of the plants and recorded maximum incidence at 9 WAT. The disease progress was gradual in all the modules and at all the periods of observation. However, per cent disease incidence (PDI) was maximum at 9 WAT and least at 4 WAT. Out of the three modules the disease incidence was significantly less in module 2 during both the years consecutively, which recorded 27.2 per cent during Rabi 2019- 20 and 25.2 per cent during Rabi 2020-21 respectively, which can be due to the treatments like spray of thiomethoxam@0.2g/l at 30, 45 and 60 days, barrier crop (fodder maize 3 rows), trap crop (marigold) and sticky traps. Where module-3 was least effective due to lack of treatments like trap crop, barrier crop and systemic insecticides. The correlation analysis for whitefly population with weather parameters during Rabi 2019-20 and 2020-21 indicated that there existed positive and significant correlation of whiteflies with minimum temperature, morning humidity and wind velocity; but negative correlation with evening relative humidity and sunshine hours. Regression analysis between whitefly population and weather parameters indicated that minimum temperature and wind velocity accounted for 39 and 46 per cent total variation in whitefly population in both the seasons respectively. A detailed study was made on the effect of the viral complex on the yield parameters and the data was recorded in different modules for both the seasons. There was significant reduction in plant height, pod per plant and also the length of the pods in different modules over the control. In the present study there was significant increase in the severity of the disease (viral complex) and there was corresponding decrease in the yield, yield attributes of the chilli crop. Further the disease complex also influenced the yield contributing factors by mainly reducing the number of the pods per plant and also the length of the pods. The results indicated that there was significant difference between the CBR of different modules in correspondence with the disease incidence which had remarkable influence on the yield and yield attributes hence on the CBR. The present investigation revealed that module 2 not only reduced the number of application of pesticides to cut down the cost of production but also enhanced the yield of fruits with improved benefit cost ratio.
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