Population biology of Aureobasidium pullulans on apple leaf surfaces

Authors: Andrews J.H.; Spear R.N.; Nordheim E.V.

Source: Canadian Journal of Microbiology, Volume 48, Number 6, June 2002 , pp. 500-513(14)

Publisher: NRC Research Press

Abstract:

Colonization of apple leaves by the yeast-like fungus Aureobasidium pullulans was studied in the field on eight dates over 2 years. Population densities from adaxial leaf surfaces were approximately log₁₀ 0.5–2.6 U higher when enumerated directly along line transects as microscopic counts of A. pullulans cells specifically identified by fluorescence in situ hybridization (FISH) than indirectly as CFU obtained by plating leaf washings from comparable surfaces onto nutrient media. Site-specific mapping of the leaf landscape colonized by A. pullulans was facilitated by use of geographic information system (GIS) software. Colonization was plotted and analyzed both qualitatively (as occupancy) and quantitatively (as density). Overall, when expressed as mean occupancy per date, 22–42% of the microscope fields (each 0.196 mm²) contained <img src="/cisti/journals/rp/gifs/gr.gif">1 A. pullulans cell. Occupancy on a microscope field basis was greater over the midvein (47–89%) or smaller veins (49–65%) than over interveinal regions (11–21%). Intensity of colonization, whether expressed as percentage of total A. pullulans cells associated with a particular leaf feature or as cell density per unit area, was also significantly greater (P &lt; 0.05) over the veinal areas compared with the interveinal areas. The primary fungal morphotypes involved in colonization were blastospores, swollen cells, and chlamydospores; only infrequently were hyphae or pseudohyphae seen. Numbers of microcolonies (<img src="/cisti/journals/rp/gifs/gr.gif">10 clustered cells) and percentage of total A. pullulans cells that occurred as microcolonies increased over the growing season and were significantly greater (P &lt; 0.05) over veinal regions compared with interveinal regions. Locally high concentrations of A. pullulans were associated with naturally occurring micro-wounds in interveinal areas. We conclude that A. pullulans colonizes the phylloplane predominantly as single cells and groups thereof in a highly heterogeneous fashion and that sites exist that are relatively conducive (veins; wounds) or nonconducive (unwounded interveinal areas) for epiphytic fungal growth.Key words: phylloplane, yeast, phyllosphere, Aureobasidium, colonization.

Nous avons étudié la colonisation des feuilles de pommier dans le champ par le champignon levuriforme Aureobasidium pullulans à huit moments sur un période de 2 ans. Les densités de population des surfaces foliaires adaxiales étaient 0,5–2,6 U log₁₀ supérieures lorsqu'elles étaient dénombrées directement le long des transects linéaires par comptage microscopique des cellules A. pullulans identifiées spécifiquement par hybridation in situ à fluorescence (FISH), par rapport à un comptage des unités formant des colonies obtenu en ensemençant sur un milieu nutritif des lavages de feuilles provenant de surfaces analogues. Une cartographie de la topographie de la feuille colonisée par A. pullulans a été rendu possible grâce à un système d'information géographique (SIG). La colonisation a été tracée et analysée à la fois qualitativement (par l'occupation) et quantitativement (par la densité). En général, lorsqu'exprimée en occupation moyenne par date, de 22% à 42% des champs microscopiques (chacune d'une superficie de 0,196 mm²) contenaient <img src="/cisti/journals/rp/gifs/gr.gif">1 cellule d'A. pullulans. L'occupation basée sur le champs microscopique était plus élevée au-dessus de la nervure centrale (47–89%) ou des nervures plus petites (49–65%) qu'au-dessus des régions entre les nervures. L'intensité de la colonisation, soit exprimée en pourcentage des cellules d'A. pullulans totales associées à une partie de la feuille ou en densité cellulaire par unité de superficie, était également significativement plus importante (P &lt; 0,05) au-dessus des nervures que des régions inter-nervures. Les morphotypes fongiques principaux impliqués dans la colonisation étaient des blastospores, des cellules gonflées et des chlamydospores; des hyphes et des pseudohyphes furent rarement observés. Le nombre de microcolonies (<img src="/cisti/journals/rp/gifs/gr.gif">10 cellules regroupées) et le pourcentage des cellules d'A. pullulans totales se retrouvant sous forme de microcolonies a augmenté au cours de la saison de croissance et était significativement plus élev&eacu

Keywords: phylloplane; yeast; phyllosphere; Aureobasidium; colonization; phylloplane; levure; phyllosphère; Aureobasidium; colonisation

Language: English

Document Type: Research article

Publication date: 2002-06-01

• Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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