Brown heart disease is caused due to deficiency of

Brown heart disease is caused due to deficiency of Boron.
Boron regulates pentose phosphate pathway, and increases sugar translocation in plants. Due to deficiency of boron growth of roots stops and the disease 'brown heart'.
Boron deficiency affects vegetative and reproductive growth of plants resulting in inhibition of cell expansion, death of meristem and reduced fertility. Plants contain B both in a water-soluble and insoluble form.