Some Elements to Improve and Explore Genetic Drought Resistance.

Drought is a random environmental and ecologically adverse factor that affects the most the crop yield in the world. Fifty years ago we started drought resistance research and its reliability and continuity are highlighted by the challenges related with environmental change. Some fundamental elements introduced or developed are a) to consider drought as a period without rainfall within an ecological context and b) to evaluate drought resistance (DR) as a conceptual variable representing the energy stored by the plant against drought, making appropriate adjustments when another variable such as yield is used. To evaluate the contribution of a variable or characteristic to DR we developed two mathematical models. Model 1 has three terms: G, the variation among genotypes; D, the variation of levels of drought; and the interaction G*D. Model 2 has also three terms: R_O, the variation of DR among ontogenetic stages; RF, the variation among phylogenetic groups; and the interaction R_O*R_F. The use of Model 2 and the study of the genetic diversity within micro-regions, allow us to discoverthe varietal patterns that are systems of varieties, species and genus, generated through domestication. These patterns respond initially to variations of available moisture, matching rainfall and temperature patterns. México is "mega-diverse" , and consists of a mosaic of micro-regions, in which the most critical factor that our ancestors encountered was the variation of humidity in terms of DR for food production. The Drought Resistance Assessment and the use of hydrological modeling highlight its use to evaluate the impact of climate and land-use changes on crop yield and water resources. At the same time, it can be applied to generate strategies to mitigate drought effects at scales from microregional to global.