suppress diseases ( Berger et al., 1996 ; Van Os & Van Ginkel, 2001 ) even in soilless systems ( Postma, 2009 ). Frequent coisolation of bacteria and Pythium and Phytophthora species suggests possible interspecies communication ( Kong et al., 2010
fluorescent pseudomonad species or which culturable bacilli species are present in the root zone. Although culturable bacteria may represent a small proportion of the total bacteria in the soil or rhizosphere ( Alexander, 2005 ), knowledge of the culturable
, the soil was inoculated with 10 g AM fungi (80 active propagules/g) or 10 mL (10 8 mix of bacteria/mL) PGPB, provided by the Soil and Water Research Institute of Iran. All plants were placed in a greenhouse with the same conditions and management
Most bacteria isolated from persistently contaminated micropropagated mint plants were Gram-negative rods identified as xanthomonads, pseudomonads, and agrobacteria based on their cultural characteristics. A few Gram-positive, non-sporeforming bacteria were also found. Inhibition of bacterial growth by gentamicin and streptomycin was greater at pH 6.5 and pH 7.5 than at pH 5.5. Inhibition by rifampicin and Timentin was less affected by pH change. Pseudomonads were uniformly resistant to Timentin at all pH's and at levels up to 1000 μg/ml. Streptomycin at 500 μg/ml was bactericidal for the pseudomonads and Gram-positive bacteria while 1000 μg/ml was required to kill xanthomonads and agrobacteria. Minimal bactericidal concentrations for gentamicin varied widely, even within groups, and ranged from 10 μg/ml to >80 μg/ml for agrobacteria. These results emphasize a need to acquire basic information about the identities and antibiotic susceptibilities of microbial contaminants before attempting treatment of infected plant cultures.
The purpose of this symposium paper is to give an overview and progress report of developments on root-colonizing bacteria to promote plant health. This topic includes such subjects as factors affecting the dynamics of root colonization, mechanisms of microbial antagonism, use of bacteria to control diseases, and commercial development of microbiological inoculants. Papers cited below and reviews (3, 5, 27–30, 34, 39) provide a more detailed account of specific investigations on root-colonizing bacteria and plant health and microbial interactions in the rhizosphere. The rhizosphere is defined as the sphere about roots that is influenced by root activities, such as the exudation of chemicals.
Phytopathogenic bacteria cause important economic losses in several horticultural crops ( Butsenko et al., 2020 ; Kim et al., 2016 ; Nandi et al., 2018 ). Currently, few phytosanitary products other than copper-based pesticides are available to
natural or added microflora and their antimicrobial products. In this sense, lactic acid bacteria (LAB) present a promising approach for several reasons: 1) they naturally occur in foods such as fresh vegetables and fruit, 2) are considered harmless to
Root inoculation of legumes with efficient nodulating bacteria of the genus Rhizobium aims to enhance biological N fixation and increase crop yield and quality. Legume inoculation with N 2 -fixing bacteria is an old practice in agriculture
The fungicide benomyl (formulated as Benlate 50 DF) has been implicated in damage to several crops grown under warm, moist conditions. Although the target pathogen may be controlled, occurrence of population shifts in rhizosphere bacteria has been documented, with benomyl application. A growth chamber study to investigate the effects of benomyl on marigold (Tagetes patula) and subsequent effects on the populations of rhizosphere bacteria of marigold was performed. A one pound per one hundred gallon rate as foliar and drench treatments were applied to marigolds. Plant growth data and rhizosphere bacteria populations were recorded. Repeated application of the benomyl treatments significantly reduced the marigold root and shoot mass, 44% and 67% respectively, compared to controls. Repeated foliar applications of benomyl also resulted in necrotic lesions on marigold leaf margins. Rhizosphere bacteria total numbers differed between treatments, having a greater population for the drench rate than the foliar rate. These results suggest application of benomyl may have harmful nontarget effects, leading to production problems associated with its use.
A white sulfur slime produced by certain sulfur bacteria clogged drip irrigation emitters when the water contained H2S. Systems were cleaned by irrigating continuously for 3 weeks after first eliminating O2 leaks. After cleanout, growths of sulfur bacteria were prevented by keeping the lines full of water and free of O2 between irrigations. Intermittent injection of chlorine to yield a free residual level of 0.5 ppm prevented sulfur bacterial growths. Lowering the pH to 6.4 with SO2 or 6.0 with HCl also inhibited sulfur bacterial growths.