Agar isolation techniques — wedging, FAE, and avoiding contamination
34 replies · Cultivation
Agar work is the skill that separates consistent growers from people who get lucky sometimes. I've been doing agar isolation for 3 years and I want to share what actually works. The basics: wedging healthy mycelium from a sector of growth you like (fast growth, dense rhizomorphic pattern) and transferring to fresh agar. The real learning curve is identifying what healthy growth looks like vs. early contamination vs. normal variation. What are your agar techniques?
Rhizomorphic vs. tomentose growth on agar: rhizomorphic (thin, spreading, almost fern-like) tends to colonize faster and fruit more vigorously. Tomentose (fluffy, dense) can still be fine. When doing isolation, I always pick from the leading edge of rhizomorphic sectors. Don't isolate from the center of the colony — that's older mycelium, possibly senescent.
Contamination identification on agar: Green/blue = Trichoderma (most common, very aggressive). Black spots = Aspergillus. Yellow to orange sectors = bacteria. Pink/red = Neurospora. If you see any of these, the plate is lost. There's no saving a contaminated agar plate. Don't try to cut around it — contamination spreads through the agar below the surface.
My FAE (fresh air exchange) setup for agar work: I use a still air box with 70% isopropyl alcohol wiped down inside, let it settle for 10 minutes before opening anything. No flow hood needed if you're careful and work quickly. Flame the scalpel until red hot, let it cool for 3 seconds, then make your transfer. Speed is everything — the longer a plate is open, the higher the contamination risk.
For long-term storage of isolated cultures: once you have a clean, vigorous isolate you like, make multiple backup plates and store them sealed with Parafilm in the refrigerator (not freezer for agar). I also do grain-to-grain transfers before storing. A good isolate is worth protecting — I've had favorite genetics for 5 years by maintaining them carefully.
30 more replies — forum posting coming soon.