Abstract
Crown gall and leafy gall disease caused by phytopathogenic Agrobacterium tumefaciens and Rhodococcus, respectively, are a significant, costly, and chronic problem in the ornamentals nursery industry. Crown gall has been particularly troublesome in crops that are clonally propagated. Losses are due to the lack of effective chemicals for control of diseases caused by these bacteria. In an attempt to provide growers with viable options for disease prevention, we embarked upon a program to test various botanical extracts for use against A. tumefaciens and Rhodococcus. We investigated the antibacterial activity Achillea millifolium (yarrow), Withania somnifera (ashwagandha), Artemisia absinthium (wormwood), Centaurea cyanus (bachelor's button), Matricaria recutita (chamomile), Taraxacum officinale (dandelion), Celtis boninensis and Strobilauthes cusia. Extracts of these plants were prepared and tested using agar diffusion and micro-dilution assays. We found that a number of extracts from these plants have good antimicrobial activity against R. fascians, indicating their potentials to be used as green alternatives to synthetic agrochemicals for treating plants. The present results encourage further effort to investigate plant-derived bioactive compounds that may possess good antibacterial properties against these gall-forming plant pathogens.