Answer:
Over the ages the tendency of crop improvement efforts has been to select varieties with traits that give the highest return, largely by concentrating on genetic strains that combine the most desirable traits. The resulting homogeneity and uniformity can offer substantial advantages in both the quantity and quality of crop harvested, but this same genetic homogeneity can also reflect greater susceptibility or pathogens. Thus it appears the more that agricultural selection disturbs the natural balance in favor of variety uniformity over large areas, the more vulnerable such varieties are to losses from epidemics. The increased risks presented by genetic selection and the increased cultivation of only a few selected cultivars are easily perceived. Chapters 1 and 2 of this reports focus on crop vulnerability, because it is a broadly recognized problem. The issue of genetic vulnerability, however, is only one of several important problems affecting the management of global genetic resources.