GGR

In Industrial Craft 2, a crop's GGR score is its growth, gain, and resistance stats respectively. A crop's GGR score can be obtained by scanning it with a Cropnalyzer 4 times. This will drain an entire RE Battery however.

Changing
The only way to change a crop's GGR without 3rd party tools is through Cross Breeding. When 2 plants crossbreed, the resulting plant will have a GGR score that is similar to both "parent's" GGR. Sometimes it will also be a little bit higher. Thus, to obtain high GGR scores you must go through numerous generations of crossbreeding.

It is best to start with 4 of the plant you want in a plus-shape with an empty crossbreeder in the middle. This gives the best chance for the "child" plant to be the same as the "parents".

Using Weed-Ex on crops can potentially lower a crop's GGR score too. Thus, you should remove weeds manually if you want high GGR scores.

Growth
The growth stat on a crop affects how fast a crop reaches maturity. A higher score means a crop reaches maturity much faster.

Gain
The gain stat on a crop affects how much you get when harvesting. A higher gain stat results in a higher chance of seeds being dropped and more of the plant product being dropped.

Resistance
The resistance stat affects a crop's resistance to trampling. A higher resistance stat results in a crop that is more resistant to being trampled, along with a crop that is less likely to be taken over by weeds.