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Maria L. Burgos-Garay, Chuanxue Hong, and Gary W. Moorman

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

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Monica L. Elliott, J.A. McInroy, K. Xiong, J.H. Kim, H.D. Skipper, and E.A. Guertal

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

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W.G. van Doorn and Y. de Witte

Cut rose (Rosa hybrida L.) flowers placed in water often wilt prematurely, which is partially due to bacterial accumulation in the stems. Bacterial strains in the stems are mainly pseudomonads and enterobacteria. The possible sources of these organisms were investigated in `Sweet Promise' (trade name Sonia) roses. No bacteria were found in the xylem of intact plants. Cutting the stems with sterile secateurs introduced no bacteria at the cut surface or the stem interior, but cutting with nonsterile secateurs used by rose growers did. The secateurs sampled at rose growers contained Enterobacter agglomerans along with several other bacteria not found inside the xylem of cut flowers but did not contain pseudomonads. Although the plant surface may contain bacteria, freshly cut stems placed in water introduced no bacteria. Bacteria rapidly developed on the cut surface and inside the water-conducting elements when rose stems were placed in tap water, even when the stems had been surface-sterilized. However, there were no bacteria in vase water when the water and the stem surface had been sterilized. Since the stem and the secateurs are not a main source of bacteria inside stems and tap water contains pseudomonads and Enterobacter spp., we conclude that tap water is the main source of the bacteria inside cut rose stems.

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Azadeh Behrooz, Kourosh Vahdati, Farhad Rejali, Mahmoud Lotfi, Saadat Sarikhani, and Charles Leslie

, 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

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M. N. Schroth and A. R. Weinhold

Abstract

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.

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Liang Cheng, Ning Zhang, and Bingru Huang

effective to mitigate stress damages. Some plant growth–promoting bacteria (PGPB) such as B. phytofirmans and B. gladioli contain deaminase enzymes that use ACC as a nitrogen source, breaking down ACC and reducing ACC availability for ethylene synthesis

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Patricia M. Buckley and Barbara M. Reed

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.

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Maxime Delisle-Houde, Pascal Dubé, Awa Barro, Valérie Tremblay, and Russell J. Tweddell

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

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Anna Marín, Anne Plotto, Lorena Atarés, and Amparo Chiralt

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

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Charis-Konstantina Kontopoulou, Sofia Giagkou, Efthalia Stathi, Dimitrios Savvas, and Pietro P.M. Iannetta

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