plant pathology

1-2 page (single-spaced) answer for the question. 

For wheat stem rust in North America, we are worried about an invasion of the Ug99 lineage from Africa or Asia. The three major strategies for durable rust resistance are: 1) quantitative (minor) gene resistance, 2) combinations (pyramids) of qualitative (major) resistance genes, and 3) increasing the diversity of resistance through cultivar mixtures, regional gene deployment, etc. For each of these three strategies, explain exactly how they could slow or stop pathogen evolution. Think about probabilities of developing virulence and the relative fitness of any new variants. After your analysis of the strategies, what is your best recommendation to breeders in North America for how to protect our crop from exotic races of wheat stem rust? Why do you prefer that strategy?