• I don't know wich protocols you tried, I use QIAGEN Plant Mini kits and they works well for grapes.
• Use another part of the plant, eg. stalk

Good luck! Regards, Gizella

If your samples are sticky and resinous, I would suggest pre-extracting them with acetone, hexane or chloroform. This won't affect the DNA, but it should remove most of the resinous material. 

This protocol has been validated for different types of food matrix. I used it to isolate the DNA from different plant species (rich in oil, proteins, ...) and works very well

Somma M (2004) Extraction and purification of DNA. In: Querci M, Jermini M and Van den Eade G (ed.) The analysis of food samples for the presence of genetically modified organisms. Ispra: European Commision, Joint Research Centre, Ch. 4.

From the picture, it looks very strange to me. You said that it was an isolation problem, but how come the samples were not 'randomly' good or 'randomly' bad? Why were the samples on the upper panel all bad and the samples on the lower panel were all good?

Were the samples different between the upper penal and lower penal? Ex. the plant treatments were different? age was different? different part of the leaf tissue was collected? Isolated DNA samples were treated differently?

Dear Gizella,

I have tried to extract using Qiagen Plant mini kit (50), however I haven't  any band on gel and concentration was too low on Nanodrop check

Thank you Andrew, I will keep in mind your suggestion (hexane, acetone) for my next sample isolations

Dear Viji, I used phenol:chloroform:isoamyl alcohol followed by Chloroform;Octanol, unfortunately, same result and shears under samples, but when treated with RNAsy A all shears disappear and however, excessive lost in DNA concentration.

I do agree with Yuan-Yeu. It depends on leaves which are old or young. How do you homogenize your leaf samples? We use Qiagen Tissue Lyser to homogenize leaf samples with tungsten carbide. This machine is very useful! If you have this machine, please consider to put your adaptors in minus 80 degree for min two hours. 

Second option is using liquid nitrogen. It takes more time to homogenize samples. But this method is also powerful.

@ Sovetgul Asekova,

In the last answer you gave, you said: "Unfortunately, same result and shears under samples, but when treated with RNAse A, all shears disappear and however, excessive lost in DNA concentration."

So, the 'smears' should be 'RNAs'. Were the samples in the upper panel treated RNAse A? Because, all of them with 'smears'.

1- using acetone, hexane or chloroform and isoamyl alcohol. This won't affect the DNA, but it should remove most of the resinous material.

or

2- using liquid nitrogen. It takes more time to homogenize samples. But this method is also powerful.