Apple shares tumble more than 6%

NEW YORK/SAN FRANCISCO - Apple Inc shares tumbled more than 6% on Wednesday, chalking up their biggest single-day loss in four years as fears grow about intensifying competition in the mobile device market. The sell-off, fuelled by a forecast by an influential research firm that the iPad maker is continuing to cede ground to rival Google Inc Android gadgets, rounded off a bleak 10 weeks for the most valuable U.S. company. The stock was one of Wednesday's biggest percentage losers on the S&P 500, shedding $35 billion US of market value as more than 37 million shares changed hands -- blowing past the company's average daily volume over 50 days of 21 million. Apple's shares, once among the most desirable of portfolio holdings, have headed steadily south since September on growing uncertainty about the company's ability to fend off unprecedented competition. This year saw a surge in sales of Amazon.com Inc's cheaper Kindle Fire and Microsoft Corp's first foray into the tablet market with its Surface. Meanwhile, Samsung Electronics continues to chip away at the iPad's dominance with its Galaxy line. The assault on Apple's consumer-electronics home turf presents a stiff challenge for CEO Tim Cook, who was elevated shortly before the death of Silicon Valley legend Steve Jobs and is now charged with keeping the world's largest technology company humming. "This is not going to be a short-term trend. This is a management test, of how well they can perform without Steve Jobs," said Brian Battle, director of trading at Performance Trust Capital Partners in Chicago. Referring to Apple's new iPad mini, which is only a smaller version of the existing iPad, Battle said the company needs "another home run" for shares to return to levels around $700. "They need another new product that hits it out of the park. Without that, they could get a gradual grind-down in confidence," he said. On Wednesday, research firm International Data Corp said Apple most likely shed market share in the tablet computer space in 2012. Its worldwide tablet market share will slip to 53.8% in 2012 from 56.3% in 2011, while Android products would increase their share to 42.7% from 39.8%, IDC said. Concerns that tax rates on dividends and capital gains may rise next year were also cited as contributing to the Apple sell-off. The stock's massive market value meant Apple was almost single-handedly responsible for Wednesday's 1.1% decline in the Nasdaq 100 Index. Apple is still up 33% this year, but is down nearly 24% from its record high of $705.07, hit on Sept. 21. The stock slid more than 6.4% on Wednesday to close at $538.7923.