Activation of tomato plant defence responses against bacterial wilt caused by Ralstonia solanacearum using DL-3-aminobutyric acid (BABA)

In this study, we investigated the ability of DL-3-aminobutyric acid (BABA) to protect tomato against bacterial wilt caused by Ralstonia solanacearum. This was combined with studies of accumulation of total phenolic compounds, free and total salicylic acid (SA), and activity of enzymes related to plant defence, i.e., polyphenol oxidase (PPO) and catalase (CAT). Under greenhouse conditions, tomato plants pre-treated by soil drenching with BABA profoundly reduced disease severity of bacterial wilt compared to plants receiving a soil drench with water. Thus, BABA reduced leaf wilting index by 75.3 % and vascular browning index by 69.9 %, without any in vitro inhibitory activity on the pathogen. BABA treatment significantly reduced the population of R. solanacearum in stems of tomato plants and additionally also significantly increased both fresh and dry weight of roots and shoots of tomato plants compared with the inoculated control. Application of BABA resulted in a high increase in PPO activity both in plants with and without inoculation. Compared to water-treated plants, treatment with BABA also induced a significant increase of total phenolic compounds as well as of free and total SA in leaves of both inoculated and non-inoculated tomato plants at all sampling times. CAT activity decreased in tomato plants treated with BABA in comparison with the water-treated control plants and the decrease in activity correlated with an increasing total SA accumulation. These findings suggest that BABA treatment resulted in induction of resistance to bacterial wilt in tomato.