Genetic variation is the raw material for the plant breeder, who must often select from primitive and wild plants, including wild species, in search of new genes. The appearance of new diseases, new pests, or new virulent forms of disease causing organisms makes it imperative that the plant be preserved, because it offers a potential for the presence of disease resistant genes not present in cultivated varieties. Also, there are demands for new characters-- for example, high protein, improved nutritional factors, and fertility restoration. ....