It looks like it is going to seed. Those little "buds" on the left will flower and once that happens you might find that it starts wilting. If you pluck these off you can often get the basil to last a bit longer.
I've read elsewhere that simply scratching the green to see if it is only on the surface will help to find out whether it is just normal lichen type surface cover.
One possible reason for leaves being lost on citrus is 'irregular' watering. If the trees / soil dries out and then gets watered - the tree can shed its leaves. On the other hand - overwatering can also trigger leaf loss.
I know this doesn't answer your question but that evil plant (bougaiinvillia) has stabbed me far too many times through my gardening gloves to warrant saving!!!