|I plant a seed from a very sweet orange, it grows and bear fruits but I wonder why the fruits are terribly sour just like lemon, and also it is infected by white thing at the back of the leaves and the top of the leaves turn black, i am worried it might get to my other trees.
|Even though the seed you planted was from a sweet orange, the orange tree has become a rootstock rather than a sweet orange tree. The oranges from your tree will never be sweet so don't grow it for its fruit but for its flowers and evergreen leaves. What you describe on the undersides of the leaves are insects. Either mealybugs or scales. As they feed they excrete a sticky substance called honeydew. It eventually turns black (called sooty mold). It won't hurt the leaves but it doesn't look very attractive. If you control the insects, the sooty mold will weather away and no more will appear. Use insecticidal soap to kill off the insects. Best wishes with your citrus tree!|