Plants respond to bacterial pathogen attack by activating various defence responses, which are associated with the accumulation of several factors like defencerelated enzymes and inhibitors which serve to prevent pathogen infection. The present study focused on the role of the defence-related enzymes phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) in imparting resistance to tomato against bacterial wilt pathogen Ralstonia solanacearum. The temporal pattern of induction of these enzymes showed maximum activity at 12 h and 15 h for PAL and PPO, respectively, after the pathogen inoculation (hpi) in resistant cultivars. Twenty different tomato cultivars were analyzed for PAL, PPO and total phenol content following pathogen inoculation. The enzyme activities and total phenol content increased significantly (P < 0.05) in resistant cultivars upon pathogen inoculation. The increase in enzyme activities and total phenol content were not significant in susceptible and highly susceptible cultivars. The role of PAL and PPO in imparting resistance to tomato against bacterial wilt disease is discussed.

Phenylalanine ammonia lyase (PAL) activity was studied in different genotypes of tomato with varying degrees of resistance and susceptibility to bacterial canker disease after inoculation with Clavibacter michiganensis ssp. michiganensis. In resistant genotypes the enzyme activity increased significantly 21 h after bacterial inoculation, whereas in the susceptible genotypes the activity decreased. The increase or decrease in PAL activity correlated well with the degree of host resistance along with total phenol contents. The role of PAL in imparting resistance to tomato against bacterial canker disease is discussed. KEY WORDS: Phenylalanine ammonia lyase; Clavibacter michiganensis ssp. michiganensis; tomato; bacterial canker. Plants possess a variety of active defense responses, which contribute to resistance against a range of pathogens. Strengthening the endogenous defense capabilities of plants, viz., synthesis

Field surveys undertaken in major tomato growing districts of the Karnataka state, located in southern part of India, revealed a high incidence of bacterial wilt caused by Ralstonia solanacearum and it is one of the most destructive bacterial diseases of economically important crops. Across all the tomato cultivars under evaluation, the disease incidence in plants ranged from 9% to 39% whereas the incidence in seeds ranged from 4% to 18%. The effects of tomato seed treatments with Pseudomonas fluorescens in the control of bacterial wilt under greenhouse conditions revealed that the treatments protected plants against soil-borne infections of the bacterial wilt organism. Seed treatment with antagonistic P. fluorescens strain significantly improved the quality of seed germination and seedling vigour. The disease incidence was significantly reduced in plants raised from P. fluorescens treated seeds followed by challenge inoculation with R. solanacearum. Periodic field surveys for the incidence of bacterial wilt of tomato could be recommended to monitor the populations of the bacterial wilt pathogen. Workable measures are presented that could lead to the reduction of the prevalence of this serious disease in affected fields of the small farm-holders.

The elimination of disease-causing microbes from the food supply is a primary goal and this review deals with the overall techniques available for detection of food-borne pathogens. Now-a-days conventional methods are replaced by advanced methods like Biosensors, Nucleic Acid-based Tests (NAT), and different PCR-based techniques used in molecular biology to identify specific pathogens. Bacillus cereus, Staphylococcus aureus, Proteus vulgaris, Escherichia coli, Campylobacter, Listeria monocytogenes, Salmonella spp., Aspergillus spp., Fusarium spp., Penicillium spp., and pathogens are detected in contaminated food items that cause always diseases in human in any one or the other way. Identification of food-borne pathogens in a short period of time is still a challenge to the scientific field in general and food technology in particular. The low level of food contamination by major pathogens requires specific sensitive detection platforms and the present area of hot research looking forward to new nanomolecular techniques for nanomaterials, make them suitable for the development of assays with high sensitivity, response time, and portability. With the sound of these, we attempt to highlight a comprehensive overview about food-borne pathogen detection by rapid, sensitive, accurate, and cost affordable in situ analytical methods from conventional methods to recent molecular approaches for advanced food and microbiology research.

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