What is the apple of discord mentioned in the passage?

Read the given passage and answer the questions that follow.
A potential flashpoint in the long-running boundary dispute between Maharashtra and
Karnataka was averted when the scheduled visit of two ministers in the Maharashtra
government to Belgavi was called off. Unfortunately, this will not end the disruption endured
by people in the area. Prohibitory orders have been imposed, public transport disrupted, and
the atmosphere remains charged. The immediate trigger for this round of flare-ups is the
conduct of senior functionaries in both governments and organisations with a stake in the
issue.
The dispute goes back to reorganisation of states on linguistic lines in the 1950s. Multilingual
regions were demarcated and Maharasthtra’s governments have been unsatisfied with the
allocation of Belgavi to Karnataka. A joint effort by governments in the two states in the 1960s
to find a solution did not fructify. The dispute currently is in the Supreme Court. In other
words, no amount of grandstanding by politicians on both sides is going to result in redrawing
borders. However, that hasn’t prevented them from periodically raking it up with the
consequences borne by people in the region. As is the case with border areas, many
inhabitants speak both languages even as politicians are ostensibly fighting the cause of
speakers of one language.
India does need a more active national interstate council to manage tensions that arise out of
disagreements over maps. However, an inactive council cannot condone the conduct of
senior politicians as heated rhetoric causes collateral damage. India’s painstaking transition to
dismantling interstate fiscal barriers through the roll-out of GST is undermined when physical
movement of goods and people get disrupted by escalating tension. The political class that
set aside differences to arrive at a grand bargain and created a common market in India
should not undo their achievement. One of India’s strengths is the extent of multilingualism
even when internal borders have been determined largely on linguistic basis. Politicians need
to learn from common Indians.