Biocontrol of bacterial speck of tomato by aqueous extract of Tagetes erecta

Biocontrol of plant diseases has emerged as an eco-friendly measure of plant protection and has experienced a lot of devotion in the last two decades. Biocontrol agents include application of microbial agents, their secretion products and natural extracts from different parts of several plants. The present study, therefore, aimed at evaluating the potency of aqueous extracts of Tagetes erecta L. (marigold) in controlling bacterial speck disease in tomato plants. The experimental design consisted of two groups of 50 plants each: group 1 – sprayed with sterile water (control); and group 2 – sprayed with marigold extract. Spraying was performed under aseptic conditions at the third node from the base of each plant. Challenge inoculation with the bacterial speck pathogen Pseudomonas syringae pv. tomato was performed to analyze the disease severity on the test plants. The parameters of study were analysis of alteration in the activity and gene expression of peroxidase (POX), phenyl ammonia lyase (PAL), and polyphenol oxidase (PPO), as well as isoform expression of POX and PPO. The results demonstrated strong inductive effects of the extract on the activity and genes of POX, PAL and PPO. De novo expression of POX and PPO isoforms following marigold extract treatment was also observed. The observations indicate that marigold extract could be a promising biopesticide.