I Would suggest these things:

#for second PCR try to purify your PCR1 Product with PCR product purification kits. if these are primers  these would be lost during the purification.

# you know your product size , and with help of ladder  see  whether these are your product or not.

# try to run gel for more time this give more resolution and you will be able to understand that these are primer bands or product.

all the best

I would suggest as Prakash Chandra recommended that first of all confirm your product size from ladder, elute the band obtained at known product size on gel and then use it as template. If light band is their then take more volume as template. you may increase some concentration of polymerase in your PCR reaction mixture.

Dear Betty,

to figure out if the lighter band are primers/primer dimers you should verify ladder lighter size, they generally are 60 bp or less.

Regarding the 2nd PCR

1) do not use the same primers of 1st PCR or you will get a lot of non specific amplification

2) use extreme dilutions of 1st PCR as template (1:100/1000) and no need to purify

3) 1st PCR should be quite short, no more than 30 cycles

That should work

Try designing nested primers with a slightly higher TM, diluting the primary PCR after clean up at least 10 fold, The nested primers makes it less likely your secondary PCR will amplify any unwanted products your primary PCR did, even if they are not visible in a gel analysis of the primary PCR. Hope this helps. 

Sorry Alberto I had not read your response before posting mine. Looks as though we were thinking along the same lines though. 

Hi Betty,

I see your PCR-product is very weak. So I would not recommend to dilute it or to purify it for the 2nd PCR as you will end up with even less PCR-product. Using nested primers is possible but than you need to design or find somewhere nested primers and it will make your PCR-product (a bit) smaller. I would do the following: try the "band-stab-method". How? First prepare master mix like you did for the first PCR and divide it in tubes (number of tubes equals number of samples, in your case 2 tubes because you have 2 samples). Put most of your PCR-product (from 1e PCR) on agarosegel and do a normal electrophoresis. Make your band visible (DNA-dye in gel or color gel afterwards) on the illuminator (like you did for the photo). Use a pipettip to stab the gel on the position of the PCR-band, so you need to stab the PCR-product on the gel and transfer your tip into to the tube with mastermix. Repeat this with another tip for the second sample. Shake the tip gently in the master mix, remove it and repeat your PCR (= 2nd PCR). If all goes well, this will re-amplify your PCR-product without creating smear as all unwanted PCR-products, primerdimers and other things are left behind on the gel which you can throw away. Only DNA from the band you touched/stabbed will be present in the mastermix. So you can see it as a kind of purification without using a purification kit. This method works for me, even on weak products.

By the way: it is quite normal to see left-overs of primers on the bottom of your gel. The other band probably are primer-dimers. Don't worry about these too much when it is possible to create sufficient amounts of PCR-product. However, if the PCR is not performing well resulting in a very weak PCR-product, the band of primers is stronger (most primers were not incorporated in the PCR-product) or a lot of primer dimers are visible. This means that the primers are not suited very well for making the PCR-product or the design of the primerset is not optimal. In this case it would be better to design other primers. If this is not an option (on short-term), use the "band-stab-method" in stead.