Alternaria alternata

Genus/species: Alternaria alternate (Torula alternata, Alternaria tenuis, Macrosporium erumpens, Alternaria erumpens, Macrosporium meliloti, Macrosporium polytrichi, Macrosporium seguierii)

Classification: Ascomycete

Morphology:

  • Cell:
  • Colony: Malt agar: Brownish Grey to black with white edges, producing a “suede-like” coating of spore stalks.
  • WL: Will produce “masses of vegetative mycelium”. This type of growth is rarely seen in nature, and is not as useful for identification, since the conidia are more often used.
  • Spore: Large, brown, multicelled, obclavate (larger at one end, sort of like a squeeze bulb), may be beaked, may be solitary or much more often in branching Longicatenatae (L. catenae, chains): chains of 10 or more spores (See photo)
  • Zygote:
  • Ascus:
  • Liquid Growth: (ie dispersed, pellicle, film, clumpy)

 

Physiological Traits:

Characteristic Secondary Metabolites: Altenuene – soluble in Acetone/1M NaOH, alternariol, alternariol monomethyl ether, altertoxin I, tentoxin and tenuazonic acid (Bottolico and Logrieco, 1998).

Ecological Traits:

Ubiquitous, usually saprophytic but capable opportunistic parasite/pathogen. On grapes can appear as a black smut on the surface.

Distinguishing Features:

Conidia Morphology (see above description), Secondary metabolites (see above)

Role in wine: 

Normal vineyard/winery flora.  Likely present with other molds on wet/injured fruit.  Can contribute to rot.  Not amenable to growth under wine/fermentation conditions but can produce a moldy taint in wines made from infected clusters.  A. alternatapresents more of a hazard to the health of employees, as it has been associated with asthma symptoms in US homes, and may cause skin legions.

Sensitivities:

A. Alternaria is not a concern in wine.  Like other molds, it is quickly killed by SO2 and the fermentative process.  Fungicide sprays are effective in the field.

References:

Tags

Yeast & Mold