How to maintain improved cultivars

Improved cultivars loose their identity and healthiness unless maintained properly. Contaminating and degrading forces, such as outcrossing, volunteer plants, mixing, natural selection, mutation and seed-borne diseases, are at the root of this. Maintenance selection can prevent this deterioration. How it is carried out depends on the reproduction system of the crop. Crops are therefore classified into four categories; typical cross-pollinating crops, self-pollinating crops with a substantial amount of outcrossing, typical self-pollinating crops with little outcrossing, and the vegetatively reproduced crops. Generally some of the “breeder seed” is used to plant a small plot with spaced plants. A fair number of healthy plants of the cultivar type is selected and the seed is harvested per plant. The progenies of the selected plants are grown in small plots. Non-uniform or deviating plots and plots with a seed-borne disease are removed. The seed of the progenies that are healthy, uniform and similar (and so of the cultivar type) are harvested per progeny to be tested next season on larger plots. The same selection is applied and only the seed of the progenies that are healthy, uniform and similar are harvested together to produce the “breeder seed”. The details of this maintenance selection vary with the reproduction system, the multiplication rate of the crop and the possibilities available to the breeder. Seven crops, potato, common bean, barley, wheat, faba bean, quinoa and maize are discussed here as they represent the different reproduction systems and multiplication rates, while being important Andean food crops.