US STOCKS-Wall St rises on Yellen; S&P on track for modest Q1 gain
* S&P on track for fifth straight quarterly advance
* Gains broad, materials and tech outperform
* Yellen says central bank commitment needed for some time
* Prana Biotech tumbles after Alzheimer's drug results
* Indexes up: Dow 0.8 pct, S&P 0.8 pct, Nasdaq 1.1 pct (Updates to afternoon trading)
By Ryan Vlastelica
NEW YORK, March 31 (Reuters) - U.S. stocks rose on Monday, with the S&P 500 on track to end the first quarter of 2014 with slight gains, after Federal Reserve Chair Janet Yellen calmed concerns about a rate hike coming earlier than expected.
Gains were broad, with nine of the S&P 500's 10 primary sectors rising on the day. Material stocks were the biggest gainers, jumping 1.8 percent, while utility stocks were up 1.6 percent.
Technology and financial shares, which along with materials are tied to the pace of economic growth, also outperformed on the day. Micron Tech climbed 7.2 percent to $23.48 while Oracle Corp added 3.6 percent to $40.98. Continuación...