besides backcrossing, you can also create a new strain by takeing two purebreed parents, one male and one female(P1 and P2). note: you may get different results depending on which parent is the male, so some trial and error may be nessary; ex. NL(m)xPH(f) or NL(f)xPH(m). all of the offsprong will be a 50/50 cross of P1 and P2 that will be the F1 generation. then, F1xF1=F2, which will have almost every genetic possability avalable; ex. 50%P1/50%P2,10%P1/90%P2,100%P1,100%P2, and any other variation. from there, instead of backcrossing, you can breed for the traits you like, ie. taste, smell, high, look, ect. keep in mind the F2 gen will have many traits completly different from either P1 or P2, and the same princple of mxf or fxm applies because male plants often give off different traits than females. keep breeding for what traits you want(best to best) until the strain has stableized(becomes consistantly what you want in a new strain), this usually takes at least 5 generations, ie. F2, F3, F4, F5.

ta da...you have a new strain completly different from either parents.