Ampelomyces quisqualis for grapes

1. What is Ampelomyces quisqualis?

It is a mycoparasitic (fungus that parasitizes other fungi) Ascomycete. Its primary host is the group of fungi that cause powdery mildews (Order Erysiphales), including the major grapevine pathogen Erysiphe necator (syn. Uncinula necator). The commercial strain AQ10 is a well-known biofungicide product.

2. Primary Target in Grapes: Powdery Mildew (Erysiphe necator)

• This is one of the most devastating and widespread fungal diseases of grapevines worldwide.

• It affects all green tissues (leaves, shoots, berries), causing reduced photosynthesis, stunted growth, off-flavors in wine, and crop loss.

• Conventional control relies heavily on sulfur and synthetic fungicides (e.g., sterol inhibitors, strobilurins), which can lead to resistance and have environmental impacts.

3. Mode of Action: A Precise Assassin

A. quisqualis operates through intimate mycoparasitism:

• Detection and Growth: Its spores germinate in the presence of powdery mildew mycelium, growing chemotropically toward it.

• Penetration: It directly penetrates the hyphae, haustoria (the feeding structures of the mildew inside plant cells), and reproductive organs (cleistothecia) of the powdery mildew fungus.

• Colonization and Killing: Once inside, it grows throughout the mildew structures, consuming their contents for nutrition. This destroys the mildew's ability to feed and reproduce.

• Sporulation: After killing the mildew colony, A. quisqualis itself produces its own spores (pycnidia) on the dead mildew, allowing it to spread to other mildew patches.

Key Point: It does not harm the grape plant or other non-target fungi. Its action is purely against the powdery mildew pathogen.

4. Advantages for Grape Production

• Specificity & Safety: Zero phytotoxicity, safe for workers, consumers, and beneficial insects/predators (like Typhlodromus mites used for spider mite control). Ideal for organic vineyards and IPM.

• Anti-Resistance Management: Has a completely different mode of action from chemical fungicides. It is a critical tool in resistance management programs to prolong the efficacy of synthetic chemicals.

• Suppresses Overwintering Structures: It can parasitize the mildew's sexual resting structures (cleistothecia), potentially reducing the primary inoculum for the next season.

• Zero Pre-Harvest Interval (PHI): Can be applied up to and on the day of harvest, which is crucial for managing late-season outbreaks.