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20183
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Subject: Plant Pathology × End date: 2018 × Start date: 2018 × Thesis Type: Ph.D ×
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    Epidemiological studies on Alternaria blight of marigold
    (Punjab Agricultural University, Ludhiana, 2018) Mailem, Y.S; Amarjit Singh
    Marigold (Tagetes erecta L.) is an important multipurpose flower crop grown throughout India. Its production is affected by various biotic and abiotic factors of which Alternaria blight caused by Alternaria tagetica plays an important role in economic production. The pathogen affects almost all parts of the crop under severe condition. It was found that the disease affects plant at all stages of growth with increased severity in older plants compared to younger plants. The optimum inoculum load of the fungus for disease development was 4 x 104 conidia/ml of water, although incidence and severity increased with increased inoculum load. Leaf wetness duration and temperature were also found to play a role in disease development. Temperature of 25± 1oC and wetness period of 12 h was found to be optimum creating high disease pressure. Marigold seeds were found to play role in the transmission of the disease when naturally and artificially infected by the pathogen. The pathogen also showed survivability under different conditions. Maximum survival was observed under room conditions where there were no soils during storage. Progression of disease was more towards South-eastern and North-western direction due to flowing of North-westerly and South-easterly winds during the two crop seasons. Among twenty-one marigold cultivars evaluated, four cultivars viz. Pusa Arpita, Double Dwarf Lemon, Harmony Boy and French Banita were found to be resistant under field conditions. All other remaining cultivars, except Pusa Narangi Gainda were found to be moderately susceptible. Morphological characters of marigold plant were found to show non-significant role in disease development. Biochemical analysis of defense related enzymes viz. peroxidise, polyphenol oxidase and phenylalanine ammonia lyase among eight cultivars showed that these enzyme activities were greatly reduced in susceptible marigold cultivar in comparison to resistant and moderately susceptible cultivars.
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    Identification, characterization and management of major virus(es) associated with cucurbits in Punjab
    (Punjab Agricultural University, Ludhiana, 2018) Dhkal, Manmohan; Sharma, . Abhishek
    Viral disease was reported to be major constraint in the cucurbits cultivation under Punjab conditions. Disease survey conducted during February-August 2017 and 2018 in different cucurbits growing areas of Punjab revealed maximum viral disease incidence in district Pathankot (100%) during 2017 and Ludhiana (36.5%) during 2018. During survey blistering, yellows, leaf curl, mosaic, puckering and necrosis were observed as common viral symptoms on cucurbits. Among these, yellows and leaf curl were most prevalent symptoms on cucurbits in different districts of Punjab, whereas watermelon showed necrotic symptoms. Musk melon samples with yellows and leaf curl symptoms showed seronegative reaction against antisera of commonly occurring viruses and was found positive in PCR for whitefly transmitted begomovirus infection. Musk melon and tinda were identified as new host of begomovirus in India. Tomato leaf curl New Delhi virus (ToLNDV), Tomato leaf curl Palampur virus (ToLCPMV) and Seena leaf curl virus were characterized from musk melon showing yellows and leaf curl symptoms. ToLNDV infection was found to be associated with tinda and cucumber causing yellows and leaf curl symptoms. In watermelon, Groundnut bud necrosis virus (GBNV) was serologically detected with samples showing necrosis symptoms. Among different methods of transmission ToLCPMV associated with yellows and leaf curl symptoms was found to be transmitted only by whitefly, whereas one percent seed transmission of necrosis symptoms caused by GBNV was observed in watermelon. Out of 75 melon accessions SM/IC-267375 and WM-11 showed high resistance response against ToLCPMV in artificial screening as no symptom observed even after 45 days of sowing as compared to susceptible checks. Three watermelon accessions viz., WM-6-2-2-1-1-2, WM-36 and WM-829833 produced mild necrotic symptom during natural screening. Among different natural products used for management of viral disease in musk melon, buttermilk was found to be highly effective at 20% concentration with least per cent disease incidence (50.8%) as compared to 10 % (64.2 %) and 5 % (71.1%) concentrations. Besides buttermilk, kaolin was also found to be effective in the management of viral diseases of musk melon. Among different dates of sowing least incidence of viral disease was observed on late sown or transplanted musk melon crop 15 March (38.96%) followed by the 5 March (46.7%) sown crop. Among different methods of planting, tray transplanted musk melon crop showed less incidence (48.3%) compared to directly sown crop (50.4%) whereas, normally transplanted crop showed maximum disease incidence of 55.7 per cent.
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    Molecular and biochemical bases for resistance to sclerotinia stem rot in introgressed Brassica juncea lines
    (Punjab Agricultural University, Ludhiana, 2018) Gill, Rupeet; Sandhu, Prabhjodh Singh
    Sclerotinia rot caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary is one of the most serious and damaging diseases of oilseed Brassicas and there is keen interest worldwide to identify Brassica genotypes with resistance to this pathogen. In this study, introgression lines derived from hybridization of wild crucifers with Brassica juncea were evaluated for response to stem rot. These were challenged against local Sclerotinia sclerotiorum isolate and 24 lines giving variable reaction were selected. Apart from this a total of 58 isolates of S. sclerotiorum were collected from different Brassica growing states (Punjab and adjoining states). These were evaluated for their pathogenicity on susceptible B. juncea cultivar RL1359 and based on disease progression; they were divided into five groups. Further 24 isolates were chosen from these groups and analysed for biochemical parameters. It was found that oxalic acid production significantly correlated with the pathogenicity of the isolates and lesser/no correlation was observed for pectinase enzymes. These 24 isolates were then used to further evaluate the selected 24 introgression lines. The observation on progression of lesion length revealed a variable response of lines to different isolates. Disease scoring was done and thus lines were categorised as resistant, moderately resistant and susceptible. Qualitative analysis was carried out on lines from different categories for genes NPR1, COI1 and EIN2. Upregulation in COI1 gene after fungal infection in resistant lines indicates the possible induction of jasmonic acid mediated defence response. Four lines from each category were selected for biochemical analysis involving SOD, POX, PAL, total phenols and lignin. All of these had a negative correlation with disease and the genotype with a greater level of resistance was superior to the susceptible one in regard to phenol and lignin production and the activities of defence enzymes. These results suggest that a combination of these defence responses in Brassica may contribute to greater plant resistance to S. sclerotiorum and that these enzymes have potential use in selection of resistant genotypes.