* Opposition party accuses Gandhi husband of undue wealth
* Stock prices affected for companies with perceived links to politicians
NEW DELHI, April 28 (Reuters) - India's main opposition party has used the emergence of Priyanka Gandhi as a star election campaigner for the troubled Congress party to criticise the wealth amassed by her businessman husband and score points in a wrangle over crony capitalism.
Cosy ties between business and politics are a big issue in the elections after a run of scandals weakened the Congress-led government, paralysed decision-making and stifled investment.
Gandhi, who bears a striking resemblance to her grandmother, former prime minister Indira Gandhi, is seen by many as the Congress party's best hope to revive its fortunes after a lacklustre campaign led by her brother, the standard-bearer for the Nehru-Gandhi dynasty.
Halfway through the five-week election, the party thrust her into the limelight after opinion polls showed the Congress-led government was set for a crushing defeat at the hands of opposition candidate Narendra Modi's Bharatiya Janata Party (BJP).
She went on the offensive at the weekend, mocking the stocky Hindu nationalist's boast that India needed a strong leader like him to bring change: "A 56-inch chest is not needed to run this country, a big heart is needed to run it," she said.
That brought a swift response from the BJP, which stepped up its offensive on her husband, Robert Vadra, with a mocking video alleging that states ruled by the Congress party had awarded him sweetheart land deals.
"Farmers cannot clear their debt all their lives, but the son-in-law became a billionaire overnight. We want to know what is the Robert Vadra model of business," BJP spokesman Ravi Shankar Prasad said.
It demanded an explanation for how Vadra had built up a real estate portfolio worth billions of rupees over the past five years and questioning his links to real estate developers DLF . The video showed a well-dressed Vadra working out, contrasting it with poor farmers whose land he bought.
DLF denies any wrongdoing in its dealings with Vadra.
Seeking to take the moral high ground, Congress has in turn suggested infrastructure billionaire Gautam Adani was granted favours in the state of Gujarat, where Modi has been chief minister since 2001.
Adani told Reuters in a recent interview that the state may have been a facilitator for his business, but working with the government did not make him a crony capitalist.
Regardless, the perception of close ties has affected both companies. DLF shares have crashed 13 percent so far in April, underperforming rivals, with traders blaming the losses on the company's perceived links to Congress. Adani Enterprises market value has jumped by 79 percent since February, outperforming rivals.
Vadra has previously come under scrutiny for land transactions that anti-graft activists say were helped by local politicians and officials in the Congress-ruled states of Haryana and Rajasthan.
Congress spokesman Abhishek Manu Singhvi said courts had dismissed three public interest litigations calling for investigations into Vadra's businesses.
"The BJP have spent the last months trying to dig up something. And all they have come up with is innuendos," he said. "Just because someone is related to the family does not make him a sinner. All the land deals are above board."
Gandhi's election-trail aggression has enlivened a campaign led by her brother, Rahul Gandhi, who has struggled to connect with voters impatient for change as economic growth bumps along at its lowest levels in a decade.
Priyanka, who is not standing for election, also attends strategy meetings and helped select candidates, party insiders say.
"She's playing a very big role. She's fine-tuning and managing the entire campaign," said Ambika Soni, a former government minister and party official. (Additional reporting by Aditya Kalra and Aditi Shah; Editing by John Chalmers and Frank Jack Daniel)