Molecular Basis of inheritance

The correct option will be (A) i.e both A and R is true and r is the correct explanation of A this is because accumulation of soil bacteria in the vicinity of plants root occur specially on roots of legume plants This accumulation probably occurs because plant roots excrete certain growth factors into the soil. Then the bacteria either penetrate the relatively soft root hair tip or invade damaged or broken root hairs and progress in an infection thread through the cortex tissue to the immediate area of the endodermis and pericycle. Cell divisions commence in the endodermis and pericycle area and the nodule grows rapidly and pushes its way to the surface of the root.