Q.amaryllis leaf problem
One of my amaryllis plants has suddenly developed a yellow streak down the center of its leaves. I expect that the leaves will yellow completely and eventually die off. What might be causing this? (The other 9 plants appear to be fine. )

Certified GKH Gardening Expert
It is possible that the plant has amaryllis mosaic. This can cause streaking, but is typically accompanied by a molted appearance on the leaves but does not have to have that. There is no cure for this and the plant will slowly continue to fail so should be removed.
Another cause could be bulb damage from a pest of some kind.