Watch the Mixolydian online guitar lesson by Chris Buono from Modes That Matter
Southern rock is gritty, guttural, raw and real. Those qualities owe a lot to Mixolydian and it’s b7. While you could see the D-C-G progression in the jam track as V-IV-I in G it really is a I-bVII-IV in D. Try playing both D Mixolydian and G Ionian modes over the changes and in the end you’ll hear the D Mixo approach delivers the right vibe. Now you might be thinking, “aren’t those the same notes?” Yes, but it’s up to you to phrase the notes so that D is the root. Try making sure you play 3, 5 and b7 of D ensuring a dom7 arpeggio is heard in your lines. Also, don’t be afraid to slur the 3rd (b3 to 3 instances) furthering the blues-based vibe southern rock is founded on.
As an added experiment try playing G Mixolydian over the changes and see what you come with. You’ll be both surprised and perplexed at the results!