Pathogens in the foliar environment

Epiphytic bacteria were isolated from strawberry plants cultivated in the field or in the greenhouse in order to investigate their interaction with leaf-surface transport properties. Colonization of lower leaf sides was higher on field-grown plants, whereas upper leaf sides were more densely colonized on plants cultivated in the greenhouse. Fungal isolates significantly contributed to total microbial biomass on leaf surfaces of greenhouse-grown strawberry plants, whereas these organisms were rarely abundant on field-grown plants. Microscopic investigations of bacteria in the phyllosphere revealed that the highest densities of bacteria were observed on living trichomes, which obviously provide a source of nutrients. Isolated strains were characterized by colony morphology, microscopy and histochemistry. About 324 isolated bacterial strains were grouped into 38 morphotypes. Of the morphotypes, 12 were identified by 16S rRNA gene sequencing. Dominating bacteria belonged to the genus Pseudomonas, Stenotrophomonas, Bacillus and Arthrobacter. Cuticular water permeability of isolated cuticular membranes and intact leaf disks was measured before and after treatment with one of the most prominent epiphytic bacteria, Pseudomonas rhizosphaerae. Results showed that cuticular transpiration was significantly increased by P. rhizosphaerae. This shows that leaf-surface properties, such as cuticular water permeability, can be influenced by bacteria, leading to improved habitable conditions in the phyllosphere.

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“…media). This might be the reason for the lack of Xanthomonas and Erwinia species, that are very common in the phyllosphere [27].…”

Section: Identification Of the Strainsmentioning

confidence: 99%

Epiphytic microorganisms on strawberry plants (Fragaria ananassa cv. Elsanta): identification of bacterial isolates and analysis of their interaction with leaf surfaces

Krimm

Abanda-Nkpwatt

Schwab

et al. 2005

FEMS Microbiology Ecology

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“…The age (in weeks ± 2) of each leaf sampled was determined from plant maps to compare average leaf ages among treatments. Because filamentous fungi, some of which are pathogenic, can invade plant tissues by germinating on the plant surface (Blakeman 1993), phylloplane spore counts were conducted microscopically on samples taken by affixing transparent tape across the widest portion of the adaxial leaf surface of 10 control plants and from 10 treatment plants from which ants had been excluded.…”

Section: Methodsmentioning

confidence: 99%

ANTS, STEM-BORERS, AND FUNGAL PATHOGENS: EXPERIMENTAL TESTS OF A FITNESS ADVANTAGE INPIPERANT-PLANTS

Letourneau

1998

Ecology

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This study tests experimentally the hypothesis that Pheidole bicornis ants increase the fitness of Piper ant‐plants (Piperaceae) in Costa Rican forests. In two experiments with naturally occurring Piper ant‐plants, ∼50 individuals were randomly selected and maintained either as controls (with ants) or as ant‐exclusion plants (without ants) for 2 yr. Leaf replacement rates and seed production, as measures of relative plant vigor and reproductive potential, were significantly greater in control plants with intact ant colonies than in plants from which ant colonies were experimentally excluded by periodical treatment with dilute insecticide. A series of experiments was designed to assess the relative contribution of antiherbivore defense, nutrient procurement, and antipathogen defense as potential mutualistic functions of the ants. To assess the fitness effects of antiherbivore defense, leaf replacement rates and seed production were measured on plants to which artificial folivory was applied over a 2‐yr period (33% of each leaf blade removed), and stem‐boring weevil damage was monitored on plants with and without ants. Nutrient procurement by ants was estimated quantitatively, and net leaf production was monitored experimentally on control plants (with ants), on plants without ants, and on nutrient‐enriched plants with ants (microquantities of fertilizer added to lower stem). Epiphyll loads, phylloplane spore densities, and disease incidence were compared on experimental plants with and without ant colonies. The results indicate that folivory, the classical parameter measured in ant‐plant studies, was not related to differences in fitness in Piper ant‐plants; instead, ant disruption of stem‐borers and ant foraging on inflorescences to reduce fungal invasion were identified as probable mechanisms by which ants conferred an average fitness advantage of at least 60 and 10%, respectively, in the 2nd yr of the comparison. Although neither antifolivore defense nor nutrient provisioning by ants appeared to benefit Piper plants, they may contribute synergistically or may operate on temporal or spatial scales not included in the study. For example, nutrient provisioning may allow Piper ant‐plant species to occupy and compete favorably in poor‐soil habitats not evaluated in these experiments.

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“…Most abundant bacterial species which have been described belonged to the genera Corynebacterium, Erwinia, Pseudomonas, Xan-thomonas and Bacillus (Ercolani 1991;. Cladosporium, Alternaria and Aureobasidium have been described as being abundant filamentous fungal species and Cryptococcus and Sporobolomyces were described as abundant yeast species in the phyllosphere (Andrews and Harris 2000;Blakeman 1993). …”

Section: Leaf Surface Colonisation and Species Compositionmentioning

confidence: 98%

“…Pronounced succession in leaf surface colonisation has been described by several authors (Ercolani 1991;Kinkel 1991;Blakeman 1993). Normally, the first detectable microorganisms are bacteria starting to colonise the leaf surface (Blakeman 1991).…”

Section: Leaf Surface Colonisation and Species Compositionmentioning

confidence: 98%