Abstract: Campylobacter jejuni has been isolated previously from market produce and has caused gastroenteritis outbreaks linked to produce. We have tested the ability of this human pathogen to utilize organic compounds that are present in leaf and root exudates and to survive in the plant environment under various conditions. Carbon utilization profiles revealed that C. jejuni can utilize many organic acids and amino acids available on leaves and roots. Despite the presence of suitable substrates in the phyllosphere and the rhizosphere, C. jejuni was unable to grow on lettuce and spinach leaves and on spinach and radish roots of plants incubated at 33°C, a temperature that is conducive to its growth in vitro. However, C. jejuni was cultured from radish roots and from the spinach rhizosphere for at least 23 and 28 days, respectively, at 10°C. This enteric pathogen also persisted in the rhizosphere of spinach for prolonged periods of time at 16°C, a temperature at which many cool-season crops are grown. The decline rate constants of C. jejuni populations in the spinach and radish rhizosphere were 10- and 6-fold lower, respectively, than on healthy spinach leaves at 10°C. The enhanced survival of C. jejuni in soil and in the rhizosphere may be a significant factor in its contamination cycle in the environment and may be associated with the sporadic C. jejuni incidence and campylobacteriosis outbreaks linked to produce.

Abstract: Samples of tree seeds, buds, and needles collected within the winter period at ambient temperatures from −11 to −17°C were analyzed for the presence of methylotrophic microflora. Thin sections of blue spruce needles were found to contain bacteria morphologically close to pink-pigmented methylobacteria. The methylobacteria that were isolated in pure cultures from samples of linden seeds and buds and pine and blue spruce needles, as well as of lilac, maple, and apple buds, were classified into the genera Methylobacterium and Paracoccus based on the data of morphological studies, enzyme assay, and DNA-DNA hybridization analysis. The methanotrophs that were isolated in pure cultures from samples of linden buds and blue spruce needles were referred to the genus Methylocystis based on the data of morphological studies, enzyme assay, DNA-DNA hybridization, and the phylogenetic analysis of the particulate methane monooxygenase gene pmoA sequences. The inference is made that aerobic methylotrophic bacteria are permanently associated with plants. At the beginning of the vegetative period in spring, the phyllosphere of coniferous and deciduous trees is colonized by methylotrophic bacteria that have wintered inside plant tissues.

Abstract: A number of nitrogen fixing bacteria has been isolated from forest phyllosphere on the basis of nitrogenase activity. Among them two best isolates are selected and identified as Corynebacterium sp. AN1 & Flavobacterium sp. TK2 able to reduce 88 and 132 n mol of acetylene (10(8)cells(-1)h(-1)) respectively. They were grown in large amount and sprayed on the phyllosphere of maize plants as a substitute for nitrogenous fertilizer. Marked improvements in growth and total nitrogen content of the plant have been observed by the application of these nitrogen-fixing bacteria. An average 30-37% increase in yield was obtained, which is nearer to chemical fertilizer treatment. Comparatively better effect was obtained by application of Flavobacterium sp.

Abstract: Rice phylloplane fungi were evaluated for their potential as biocontrol agents for rice blast disease caused by Magnaporthe grisea. A total of 1923 fungal isolates were obtained from rice plants in fields at Ishigaki and Iwama and from potted plants placed in a cedar woods in Iwama as bait. Although 82.9% of isolated fungi could not be identified, species of Epicoccum were the most prevalent among identified isolates. Of the 1923 isolates, 967 were randomly selected for screening against rice leaf blast. Nine isolates (MKP5111B, MKP5112, J2JMR3-2, K2J131-2, I5R3-1, NOP541, K1KM134-1, NOP5112, MKP33222) suppressed the disease when a conidial or hyphal suspension of both the phylloplane fungus and pathogen were simultaneously used to inoculate rice plants cultured in pots in a growth chamber. Five of the isolates originated from potted plants in the woods and four from Ishigaki, a subtropical island. Five (MKP5111B, MKP5112, NOP541, NOP5112, MKP33222) of the nine isolates strongly suppressed conidial germination of M. grisea (≦0.7%) and formed inhibition zones (3–5 mm width) in dual cultures with the pathogen. Methanol extracts from the isolates also inhibited mycelial growth of the pathogen. These results suggest that the five isolates produced antibiotic(s). These five isolates are likely identical or closely related fungal species because the sequence of their ITS regions were 100% similar. ITS sequence analysis also suggested that J2JMR3-2 was associated with a species of Fusarium. Under field conditions, J2JMR3-2 reduced both leaf and panicle blast severity, and three other isolates (MKP5111B, K1KM134-1, K2J131-2) suppressed leaf blast in one of the three experiments.

Abstract: Numerous bacteria and fungi are able to colonize and form biofilms on plant surfaces Microbes colonizing aerial surfaces, such as flowers, stems, and leaves (phyllosphere), are generally referred to as epiphytes Bacterial colonizers of the root surface (rhizosphere) are generally referred to as rhizobacteria This chapter specifically focuses on the mechanisms involved in bacterial biofilm formation on plant roots, including pathogenic and beneficial interactions Scanning electron microscopy (SEM) is a powerful tool to visualize at the single-cell level the process of colonization and microcolonies in the rhizosphere and on sprouts showing the presence of many differently shaped bacteria The genetic background of plants should also be taken into account to gain a better understanding about how bacteria function in the rhizosphere Quorum-sensing genes have been identified in several plant-associated bacteria regulating a large variety of different phenotypes involved in pathogenicity and plant beneficial effects Hyphae of soil-born pathogenic fungi attach to the root and usually colonize the root surface before penetrating and infecting the root Biofilm formation on fungal hyphae implicates the possibility of interactions at the molecular level between the fungus and the bacterium Bacterium-fungus interactions are found widespread through nature, associated with plants and animals, where these microorganisms compete with each other, attack each other, and form consortia

Abstract: Yeasts are potential antagonists of microorganisms in the phyllosphere. Due to their osmotolerance, they should also be able to colonize apple flowers. In field experiments, we applied yeast agents against fireblight at two different sites in the southern part of Germany. They showed efficiencies 0-20% below Plantomycin (streptomycin). Co-culture experiments in liquid basal media with synthetic nectar resulted in suppression of Erwinia amylovora by yeast. This effect could not be confirmed with population studies of yeasts and E. amylovora in flower clusters. Field and laboratory experiments indicated that yeasts have antagonistic properties against fireblight but further research is needed to investigate this potential.

Abstract: The effects of changes from conventional grassland management on fenland in Germany to extensification due to reduced fertilizer inputs and cutting frequency on the microbial colonization in the phyllosphere were investigated. A delay in the first cut for silage and hay, required by a nature conservation programme, was accompanied by the senescence of grasses which significantly influenced certain microbial groups. Heterotrophic bacteria, aerobic and anaerobic spore-formers, as well as filamentous fungi, showed an increase in population densities on the mature herbage of the later cuts. Differences in the rate of fertilizer application and cutting frequency, which had an effect on the dry-matter yield, also influenced the population density of heterotrophic bacteria and, in certain circumstances, that of filamentous fungi. Chemical measures of forage quality were highly correlated with the population density of microbial groups and with the maturity of the herbage. In contrast to these results, the population dynamics of further groups of micro-organisms (yeasts, Micrococcaceae, listeria) did not show any relationship with pasture management.

Abstract: To study the effect of microenvironments on potato-associated bacteria, the abundance and diversity of bacteria isolated from the rhizosphere, phyllosphere, endorhiza and endosphere of field grown potato was analyzed. A total of 2,648 bacteria isolated during a period of two successesive seasons at three different growth stages of potatoes was screened for antagonism towards the plantpathogenic fungi Yerticillium dahliae Kleb. and Rhizoctonia solani Klihn. Antagonistic isolates were identified by FAME and by sequencing the bacterial 16S rDNA. Altogether, 41 antagonistic were identified with 21 of them being typical colonizers of endophytic microenvironments. Richness and diversity indices confinned the specificity of the microenvironments. All 349 antifungal antagonists were characterized by testing their antagonistic mechanisms and plant growth promoting mechanisms in vitro, including glucanolytic, chitinolytic, pectinolytic, cellolytic, and proteolytic activity as well as siderophore and auxin production. Evaluation resulted in the selection of five promising candidates from each microenvironment for biological control.

Abstract: Plant-associated microbial diversity encompasses symbionts, protecting their host against various aggressions. Mycorrhizal and rhizospheric microorganisms buffer effects of soil toxic compounds and soil-borne pathogens. Endophytic bacteria and fungi, some of which are vertically inherited through seeds, take part in plant protection by acting directly on aggressive factors (mainly pathogens and herbivores) or by enhancing plant responses. Plant protective microbial symbionts determine the ecological success of plants; they drastically modify plant communities and related trophic webs. This review suggests approaches to improve the inventory of diversity and functions of in situ plant-associated microorganisms. To cite this article:

Abstract: The microbiology of the aerial portion of plants supports a diversity of microorganisms, including bacteria, fungi and archeae. In addition there are direct interactions with eukaryotic species that feed off the plant. The abundance of life in the phyllosphere is matched by the habitat range that plants occupy in both terrestrial and aquatic environments. Plant leaves provide the greatest surface area on the planet tolerating geographic and climatic extremes that can fluctuate on a daily cycle from sub-zero night time temperatures to leaf surface temperatures that exceed 50°C in direct sunlight. Plants are found in over 90% of the approximately 2 × 108 km2 terrestrial surface of the planet where the surface area of leaves (the phylloplane) approaches 1 × 10 km2 [ref. 75]. It is a statement of fact that those bacteria that have adapted to life in the phyllosphere must exhibit a range of phenotypic characteristics to mitigate against the effect of these physical parameters. These are perhaps greater that those experienced by soil or rhizosphere bacteria. However resource limitation, in respect to nutrient supply and water availability are common selective factors that dictate the range and functional capacity of microbial life at plant surfaces. To understand more about the wider context of leaf microbiology the reader is directed to the conference proceedings of the two most recent symposia on phyllosphere microbiology66,78, and recent reviews that cover a number of related issues that have not been dealt with in depth here64,65.

Abstract: We developed a polyclonal antibody (PAb) based-ELISA system to accurately and rapidly monitor inocula on plant surface before onset of anthracnose. Titer of mouse antisera against conidia of Colletotrichum gloeosporioides was determined by using indirect ELISA. It was high enough to be detectable up to × 12,800 dilutions. Absorbance readings exceeded 0.5 even at a 10(?5) dilution. Sensitivity of PAb was precise enough to detect spore concentration as low as 50 conidia/well by indirect ELISA. PAb1 and PAb2 proved to be very sensitive and highly specific to the target pathogen, C. gloeosporioides, apparently discriminating other unrelated pathogens, or epiphytes. Absorbance values for original isolate exceeded 1.0, but no reaction was detected with other isolates, except three other anthracnose fungi: C. gloeosporioides (pepper strain), Glomerella cingulata (apple strain) and C. lagenarium. Our data suggest that PAb1 and PAb2 bind with the protein epitope that partially contains residues of amino acid, arginine, and lysine. This kit fulfills the requirements for detecting inoculums before infection and during onset of anthracnose on sweet persimmon.

Abstract: The impact of plant genotype on plant-microbe interactions has been widely examined in the realm of plant pathogenic organisms, and many of these interactions have been studied to elucidate the mechanisms of pathogenesis and the genetics of host resistance. The capacity of plant genotype to influence interactions with beneficial plant-associated microorganisms has received less extensive consideration, and has primarily been limited to examination of the rhizobia-legume interaction and the symbiotic relationship between plants and arbuscular mycorrhizal fungi. Consideration of host specificity in interactions between plants and other non-symbiotic plant-beneficial microorganisms has received scant attention. Conventional thought has been that these relationships are quite unspecialized, however recent lines of evidence suggest varying degrees of specialization may exist among plant interactions with saprophytic elements of the soil microbial community. Support for host genotype specialization in these plant-microbe interactions include the observation that plant cultivars differing in susceptibility to pathogens demonstrate differences in composition of the antagonistic microflora recovered from the rhizosphere; the observation of cultivar-specific induction of soil suppressiveness to various soilborne diseases; differences in expression of antibiotic biosynthetic genes by biocontrol bacteria in the rhizosphere of different plant cultivars; and the identification of quantitative trait loci in tomato inbred lines which explain a portion of the variation in biocontrol of Pythium torulosum achieved via the application of the biocontrol strain Bacillus cereus UW85. These findings demonstrate a significant impact of plant genotype in determining the genetic composition of certain elements of the resident soil microflora and its important role in determining the efficacy of biological controls. The identification of genes involved in plant host selection of beneficial microorganisms could lead to breeding strategies that optimize these plant-microbe interactions, resulting in an effective means to enhance plant growth and control soilborne diseases in an environmentally sensitive manner.

Abstract: Biological control of plant pathogens presents a compellingmethod of increasing plant yields by suppressing ordestroying pathogens, enhancing the ability of plants toresist pathogens, and/or protecting plants against pathogens.Micro-organisms antagonistic to plant pathogens may bederived from the resident microbial community or may be offoreign origin. Although there are concerns towards therelease of an organism of foreign extraction, in general,biological control presents a myriad of benefits such as beinga component of the environment, resistant to development ofchemical pesticide resistance, being relatively safe and riskfree, and by being compatible with sustainable agriculture.Arbuscular mycorrhizal fungi (AMF) form one such group oforganisms that can act as bioprotectors of plants. Thesezygomycetous fungi that form specialized structures such asarbuscules and/or vesicles are obligate biotrophs and utilizehost photosynthates for their growth. They are ubiquitousand co-exist with over 80% of terrestrial plants includingagricultural or horticultural crops. Their interactions withrhizosphere flora and fauna influence the growth and fitnessof the associated plants (Azcon-Aguilar and Barea 1992;Fitter and Sanders 1992). An incompatible associationbetween the host plant and the indigenous AMF communitycan lead to serious losses in crop yields, indicating thesignificance of AMF in crop production. In contrast, acompatible association can result in enhanced plantproductivity, through enhanced host P nutrition (Ravnskovand Jakobsen 1995), prevention or control of plant diseasescaused by soil-borne pathogens (Caron 1989a; St-Arnaudet al. 1995), and/or enhancement of plant hormonal activity(Frankenberger and Arshad 1995).The rhizosphere, a zone of soil loosely surrounding theroots, is a dynamic environment wherein complex chemicaland microbiological activities occur (Lynch 1990). Themycorrhizosphere is the region of the rhizosphere that issubjectedtomodificationsfollowingAMFcolonizationofthehostplant(Linderman1988).Inducedbiochemicalchangesinthe plant as a result of AMF root colonization is collectivelytermed the “mycorrhizosphere effect.” The mycorrhizosphereeffect typically results in a transient or permanent shift in theresident microbial community that may favor the eliminationorproliferationofpathogens(Edwardsetal. 1998;MeyerandLinderman 1986; Nemec 1994; Paulitz andLinderman 1989).In general, these changes are mediated by modifications inhost root membrane permeability that subsequently leads tomodifications in root exudate composition (Graham et al.1981; Ratnayake et al. 1978). Meticulous management of themycorrhizosphere may serve as an effective, safe, andenvironmentally friendly alternative to conventional methodsof plant disease control.

Abstract: Pink-pigmented facultatively methylotrophic bacteria (PPFMs), persistent colonizers of plant leaf surfaces, belong to the genus Methrlobacterium and are mostly transmitted through seeds. Plant growth-promoting activity of methylotrophic bacteria and their effects on disease suppression were evaluated on rice under greenhouse conditions. Rice seeds were inoculated with Methylobacterium sp. strain PPFM-Os-07 and seed germination was evaluated in terms of morphometric measurements, seedling growth, rate of germination (R(subscript G)), and seedling vigour index (SVI). Another experiment was carried out to study the induction of pathogenesis-related proteins (PR-proteins) in rice plants that were inoculated with methylotrophic bacteria by seed imbibition or foliar spray. In the third experiment, sixty-day-old rice plants grown in pots were challenge inoculated with Rhizoctonia solani strain TNAU-01. Methylobacterium inoculation promoted seed germination and plant growth. Increased plant height, number of tillers, plant biomass, and grain yield were observed. The average yield increases for seed imbibition and phyllosphere spray were, respectively, 22.1% and 24.3% greater than control. The bacteria also significantly reduced the sheath blight incidence when applied as either bacterial culture through seed imbibition and or phyllosphere spray. The percent disease reduction recorded for seed imbibition alone and for combined applications of seed imbibition and phyllosphere spray were 17.8% and 23.5%. Rice plants sprayed with PPFM-Os-07 strain showed increased presence of PR-proteins and phenolic contents on day 1 after application. Maximum phenylalanine ammonia lyase (PAL) and peroxidase activity on day 4 and β-1,3-glucanase and chitinase activity on day 5 were recorded. The results suggest that Methylobacterium inoculation may alter rice susceptibility to R. solani. This work emphasizes the importance of evaluating induced systemic resistance while studying plant-associated growth promoting bacteria.