How to Do an Agar Transfer (Sector Isolation): A Step-by-Step Guide

About 1 hour active work, plus colonization time

An agar transfer is the move where you take a small wedge of mycelium off one plate and place it on a fresh sterile plate. Sector isolation is the same physical move with a specific goal: pick the single best-looking patch of growth on a mixed plate, transfer it, and ignore everything else. Done two or three times in a row, this is how you turn a wild, contaminated, or genetically scrambled plate into a clean, stable isolate you can name and keep around for years.

By the end of this tutorial you will have a fresh agar plate inoculated with a hand-picked sector, plus a labeling and tracking system you can carry through the rest of the lab pipeline. The whole transfer takes about 30 seconds at the bench once you are set up, and the wedge will recolonize a 100 mm plate in 5 to 10 days for most cubensis-style genetics. Two to three transfers in is where most growers settle on their working culture. This skill stacks directly with pouring your own agar plates and making liquid culture; an agar isolate is the cleanest source either of those workflows will accept.

What you'll need

Materials

Source plate, 1 (a colonized agar plate, contaminated or otherwise)
Fresh sterile agar plates, 3 to 5 (MEA or PDA, 100 mm)
70% or 91% isopropyl alcohol, in a spray bottle
Lint-free wipes or paper towels
Parafilm or micropore tape, 1 roll
Nitrile gloves, 1 fresh pair
Surgical mask, 1
Permanent marker, 1

Equipment

Scalpel with #11 blade, or an inoculation loop
Butane or alcohol lamp, 1
Still air box (SAB) or laminar flow hood, 1
Cutting surface or sterile tile (optional, for resting the scalpel)

Step 1: Read the plate before you cut anything

The transfer itself takes seconds. The decision of where on the plate to cut from is the entire game. A bad sector choice costs you 5 to 10 days of recolonization for nothing. Spend two full minutes looking at the plate before you ever pick up a scalpel.

Hold the plate up to a light source, lid still on. You are looking for three things: the leading edge, the dominant growth pattern, and any contaminants.

Leading edge. The outermost ring of mycelium, where it is actively pushing into fresh agar. Cells here are young and metabolically active. They recover faster on a new plate than older central mycelium that is already running out of food.
Dominant growth pattern. Two main shapes show up. Rhizomorphic mycelium looks like ropes, strings, or root-like cords radiating outward. Tomentose mycelium looks like fluffy cotton or a soft white carpet. Neither is “wrong.” Both fruit. But rhizomorphic growth is denser, colonizes grain faster, and makes contamination easier to spot, so most growers select for it when they have the choice. If your plate is fully tomentose, that is fine. Pick the most vigorous patch and move on.
Contaminants. Anything that is not white or off-white mycelium. Green dust is Trichoderma. Black sporulating heads are Aspergillus. Slimy wet patches with no fluff are bacterial wet spot. Pink or orange dust is usually Neurospora. Yellow liquid droplets on top of healthy mycelium are not a contaminant; that is just metabolite (“myc piss”) and is fine to transfer through.

A “sector” is a wedge-shaped patch on the plate that looks meaningfully different from the rest of the growth. On a spore-germinated plate you will often see four or five sectors radiating from the center, each one a slightly different phenotype because each grew from a different mating event. Sectoring is choosing one of them and leaving the rest behind. On a clone plate or a contaminated rescue, the “sector” is just the cleanest, fastest patch you can find that is not touching the contamination.

Mark your target sector on the bottom of the plate (not the lid) with a small dot or arrow in permanent marker. Lid markings travel if you ever swap lids; bottom markings stay locked to the agar.

Safety note before Step 2

Open flame plus alcohol vapor in a still air box is a real fire hazard. Spray your alcohol, wait 60 seconds for the vapor to settle, then light the lamp. Never spray alcohol while the lamp is burning. Keep the alcohol bottle outside the SAB while the flame is lit. The flame stays small and stable; the second something flares blue and tall, kill it and re-air the box before you continue.

If you decide the plate is too far gone, that is also a valid outcome of Step 1. A plate with 30%+ contamination by surface area is not worth the risk. Toss it (autoclave bag, then trash) and start over from a cleaner source. The next step assumes you have at least one clean sector roughly a thumb-nail wide.

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