When they broke apart, did a faint dark cloud appear? Almost like brown smoke? If so it could be a fungus spore. Be careful not to breathe that stuff in. If you've had fungus problems your garden may be getting too much water. Also, you may already be doing this, but when you do water, try to do it early in the morning versus in the evening. Also try and water only at the base of the plant (using either a watering can or a soaker hose) versus a sprinkler which gets the leaves wet.... which can sometimes lead to certain diseases. Hope this helps. Hang in there!