M.Sc.

The study entitled “Nutrient based management of Chilli leaf curl virus in Chilli (Capsicum annuum L.) was conducted at Department of Plant Pathology, College of Agriculture, Vellayani from 2017 to 2019. The main objectives were to serologically and molecularly characterize the virus causing leaf curl in chilli and to study the role of nutrient application in the management of the disease. The present investigation was carried out in four experiments viz., collection of Begomovirus infecting chilli from different cultivated areas, symptomatology, serological diagnosis and molecular characterization of the virus causing chilli leaf curl and nutrient based management of chilli leaf curl. The survey was undertaken from December 2018 to March 2019 to investigate the disease incidence in major chilli growing areas of Palakkad (Vadakarapathy and Kozhinjanpara) and Thiruvananthapuram districts (College of Agriculture, Vellayani) of Kerala. In Thiruvananthapuram, the disease incidence ranged from 69.33 to 80 per cent whereas Palakkad recorded maximum incidence of 73.33 per cent in Vadakarapathy village and Kozhinjanpara village recorded the disease incidence of 55.71 to 71.70 per cent. The common symptoms of the disease were upward curling and puckering of leaves, and stunting of whole plant. Other symptoms viz., reduced leaf size, yellowing, petiole elongation, crinkling and mottling of leaves with few or no fruits were also observed.
Serological diagnosis of the disease was carried out using triple antibody sandwich – enzyme linked immunosorbent assay (TAS-ELISA) using polyclonal antisera specific to Begomovirus, Sri Lankan cassava mosaic virus (SLCMV). All the samples collected from College of Agriculture, Vellayani were detected with the virus whereas none of the samples from Palakkad district were positive to the virus. Molecular characterization of the virus using universal primers specific to coat protein of Begomovirus viz., AV-AC and DENG through Polymerase chain reaction (PCR) revealed that the DNA isolated from samples of Vellayani could yield an amplicon size of ̴ 550 bp (AV-AC) and ̴ 500 bp (DENG); thus confirming the presence of the virus. But no PCR amplification was observed in any of the samples from Palakkad district. Blast analysis with the sequence of coat protein of Vellayani revealed that the virus had 96.63 per cent similarity with Chilli leaf curl Vellanad virus. Nutrient status of healthy and diseased leaves revealed that the per cent of major nutrients viz., nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg); and micronutrients viz., manganese (Mn), zinc (Zn), copper (Cu) and boron (B) in the infected leaves was low compared to the healthy leaves but in sufficient level. Whereas, the per cent of sulphur (S) and iron (Fe) in infected leaves was high and in toxic level. Comparatively higher levels of all the major and micro nutrients were recorded in the soils collected from the infected fields than the soils from the healthy field. A pot culture study was conducted at Department of Plant Pathology in completely randomized design consisting of ten treatments and three replications with chilli variety Vellayani Athulya from May 2019 to August 2019. Cent per cent disease incidence was recorded in all chilli plants before imposing the treatments. Soil samples were taken and analysed for major and micro nutrients at pre-treatment stage. Urea, rajphos, murate of potash, lime and magnesium sulphate (MgSO4) were used as the source of major nutrients like N, P, K, Ca and Mg, respectively. Whereas, manganese sulphate (MnSO4), zinc sulphate (ZnSO4), copper sulphate (CuSO4), borax and potassium silicate were used as source for micronutrients such
as Mn, Zn, Cu, B and Si, respectively. After imposing the treatments, the highest coefficient of infection (75.0) was recorded in untreated infected plants whereas, the plants supplemented with nutrients as per package of practices (POP) + B @ 10 kg ha-1, POP + (ZnSO4) @ 20 kg ha-1 and, basal application of 1/2 N + full P + 1/2 K followed by 0.5 per cent foliar application of NPK 19:19:19 at fortnightly recorded the lowest coefficient of infection (25.0). TAS-ELISA conducted with all the experimental plants confirmed the presence of virus. Lower virus titre value was observed in the plants supplemented with nutrients as per POP recorded maximum level of major nutrients. Among the treatments highest fruit yield of 48.85 g plant1 was obtained from plants supplemented with nutrients as per POP + B @ 10 kg ha-1 was found to be most effective in reducing the coefficient of infection with better yield. Thus, the present study revealed that the serological diagnosis of the disease carried out using TAS-ELISA with antisera SLCMV and molecular characterization of the virus using primers AV-AC and DENG through PCR confirmed the presence of virus in Vellayani. The BLAST analysis of Chilli leaf curl Vellayani isolate thus showed 96.63 per cent similarity with Chilli leaf curl Vellanad virus. It was also indicated that Chilli leaf curl virus in chilli could be managed by the application of nutrients as per package of practices recommendation along with boron as borax @ 10 kg ha-1 which need to be validated under field conditions.