this is because of degradation of genomic DNA. If you have gel photo attach here then I will clarify this thing

@Phani kashyap S thank you for your answer.

this is our electrophoresis photo. Sorry for darkness and low quality, but we clearly saw band-thing in real sight.

@Kalpana Korde thank you for your answer.

We used CTAB method for high concentration. We did use liquid nitrogen and we got quite a good quality DNA. 

Purity was about 1.2, so it was not that good. maybe is this reason for smearing?

If it is, then do we have to purify our DNA?

Your g-DNA simply degraded. Reasons might be thousands.

If you want clear things.. After isolation You just check the DNA quality by agarose gel electrophoresis.....load 2-3 micro liters each sample.

 If you find intact DNA, the problem would be High voltage,, generally long run always recommendable 25-30V (southern).

If you did not find intact DNA then it would g-DNA isolation handling problem. Mechanical shearing...other factors as well...

Hope you will find the solution soon.. If you follow

In addition to all reasonable causes mentioned by yourself and others here, I think the agarose gel is too fresh, the size marker does not show very sharp bands, so there is at least some (little) room for improvement in the electrophoresis conditions. Perhaps you let your agarose gel solidify for a longer period (e.g. over night) or use it after some storage in the refrigerator (4 °C) - or try a different agarose sample. Of course, a slow, long run with low voltage is good.

its better to use cur tips to avoid degradation 

and see the attached file for manual method for DNA isolation.

voltage is not a matter because DNA is stable eve at 150V 

but when u run for southern then u have to run at 30Vf or differentiation of band  

 Use liquid nitrogen to grind plant material.

Too high voltage can increase the temperature of the gel - and melt it...

Dear Somin,

Smearing indicates degradation of the genomic DNA. Since the 1 kb ladder is sharp and fine, the degradation could have happened during extraction process and not during electrophoresis. Hope you have used DNAse inhibitors  while extracting the genomic DNA.

In our lab we use a modified Doyle & Doyle protocol (1990) for DNA extraction, and works very well for fungi, some bacteria and animals. One of the main reasons of smears in our gels are RNAs, and when whe treat our samples with Ribonuclease A (RNAse A) after'cell lysis, bands become clear and sharp. You could add 40ug of RNAse per tube after cell lysis, and incubate for 30 min at 37ºC, and then continue your DNA extraction. 

I was facing a similar issue when I was extracting gDNA from Wuchereria bancrofti parasites. There were two modifications that we made to troubleshoot this streaky gDNA.

1) we included a little extra RNAse A, 60ul and incubated it for 15 mins in a shaking dry bath at 37*c.

2) we changed the elution buffer to water(trpled distilled, deionised).

It worked when i used different water, my band was clear when i used sigma water and triple distilled deionised water.

One more thing is storage of the gDNA, it is best prepared fresh and used fresh, long storage leads to denaturing of the DNA.

Good luck.

Smears are usually formed if the DNA has not been handled properly during the extraction. There could be other possible reasons too.

I am getting such a smeared band please help me out with this

My labmate gel also smearing. I helped him to check his DNA concentration via NanoDrop. Surprisingly the result of purifying and concentration pretty high and good. Therefore, I suspect maybe smearing happen because of aneling temperature during PCR or primer.

Thank you.