Ziziphus nummularia is known to impart dwarfness in ber. Dwarfness is due to:

Correct option is A

Dwarfness in Ziziphus nummularia (a variety of ber) is primarily due to graft incompatibility. When this variety is grafted onto other rootstocks, it causes reduced growth and small tree size, which is beneficial for certain types of orchard management.