What's Stronger - Poplar Along Grain or Particle Board?

I would like to use the following shelf bracket, which is made to hold a 5/8" shelf. It's hard to tell from the picture, but the shelf slips into a groove that supports 1.5" of the shelf on the bottom and .5" on top. The screw holes are in the back of the groove and get hidden by the shelf.
http://www.acehardware.com/product/index.jsp?productId 94531
I know these brackets work very well, cuz I have them in my laundry room. A 9" wide, 5/8" laminated particle board shelf that you can buy at any borg will easily hold a 300 oz container of liquid laundry detergent.
Here's my question: In my office at work, I would like to install a shelf that will match the rest of the furniture, and I know that I can stain a piece of poplar to match. BTDT
I am thinking of having a 36" length of 1 x 12 piece of poplar planed down to 5/8", but it will have to be mounted with the grain parallel to the bracket. The shelf will hold my phone, stapler, tape dispenser, etc. so there won't be a lot of weight on it. (The bracket itself is 24" long)
Do you think the grain on 36" length of 5/8" x 12 poplar, supported by 1.5" along a 24" section will be strong enough to support the phone etc?
Another option I've considered: Since the shelf will be 36" long and the bracket is 24", I could rout a 24" x 5/8" dado in the board, so that only the portion of the board supported by the bracket will be 5/8", with the 6" on either side remaining at 3/4". Do you think that will make any difference?
Thanks!
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Doesn't sound like the weight will be an issue I would be more concerned about warping, cupping, etc. Breadboard ends may help with that along with finding a piece that is close to quartersawn.
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DerbyDad03 wrote:

Yes. Even if you have an old rotary dial phone made of lead.
--

dadiOH
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You could put a few screws into the back edge of the board to strengthen it.
Bob

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