Penicillium expansum

Genus/species (aliases): Penicillium expansum (Green Mold)


Classification: Ascomycete


Morphology:

Mono-verticillate branched septate conidiophores with sporulating cells (phialides)
Cell: Ellipsoid or pyriform conidia, smooth texture
Colony: Circular, smooth edges (entire margin)
Malt agar: 16-34 mm diameter colony growth.

  • Conidium color: White, Green, Grey, or Beige
  • Reverse color: Red or Brown WL:
  • CYA (Czapek Yeast Autolysate Agar): Diameter 30-40 mm;
  • Conidium color: White to Cream, Green, or Grey to Beige
  • Surface typically tufted (coremial); one or more annular bands with adjacent areas velutinous to floccose
  • Moderate conidia production

Spore: Phialides, may be acerose (lanceolet without constriction) or flask-shaped (ampulliform with constriction) 
Zygote: Asexual; no zygote produced

Ascus: Conidophores are mononematous; some strains group conidophores into fascicles or clusters

Liquid Growth: (ie dispersed, pellicle, film, clumpy)- Described as mealy or grainy film usually white or green in color.


Physiological Traits:
 (growth substrates, end products)

  • Produces mycotoxins- esp. patulin which can be degraded by SO2 and fermentation
  • Also roquefortine C, citrinin, communesins, chaetoglobosin C.
  • Production of patulin may be restricted by pH; as is the case with apple juice at pH 3.2-3.8.
  • Conidia can be transported by wind
  • Psychrophile: can grow at -2°C with strong growth at 0°C. Optimum temperature at 25°C and max near 35°C.
  • Low oxygen requirement; unaffected by levels of oxygen at levels of 2.1%.
  • Growth stimulated by as much as 15% CO2, but will rates will start to decline at higher levels.


Ecological Traits:

Secondary disease on mature grape berries after wounding or bunch rot infections. Usually occurs when berries ripen early in warm and humid climates or years. Closed bunches are more susceptible than loose bunches. Conidia are spread by wind and even subtle movement of infected clusters. The conidia will germinate on a wet berry surface as soon as a sugar is available.


Isolation has come predominantly from pome fruits, especially apples and pears. To control growth, sprays are used to curb Colletotrichum infections which permit entry by P. expansum (Pitt 1997). It has also been isolated in tomatoes, straqwberries, avocados, and mangoes.


Distinguishing Features: White pads can be observed on the berry wound. Infected berries will soften and change to an olive-green or light brown color. Berry shrinkage may occur. P. expansum is distinguished by dull green conidia, often born in coremia, smooth walled stipes on CYA, orange brown to brown exudates, soluble pigment and reverse colors. Introduction to apples and pears will induce destructive rot. P. expansum also produces a violet color on Ehrlich media (Pitt 1997)

Role in wine:  
Disease agent in vines that may impart an off-flavor to the wine. Small amounts of infected berries have been reported to contribute to a mouldy taste in wine.

Sensitivities:

  • SO2:X
  • Sorbate: X
  • DMDC: X
  • pH: X
  • Acids: X
  • Ethanol: X
  • Anaerobiosis:
  • Heat: 37°C


References:

  • Bragulat MR, Abarca ML and FJ Cabanes. 2008. Low occurrence of patulin- and citrinin-producing species isolated from grapes. LETTERS IN APPLIED MICROBIOLOGY. 47:286-289.
  • Delage N, d'Harlingue A, Ceccaldi BC, et al. 2003. Occurrence of mycotoxins in fruit juices and wine. Food Control. 14:225-227.