seed corn
noun [ U ] uk/ˈsiːd ˌkɔːn/ us/ˈsiːd ˌkɔːrn/
谷种;（尤指）玉米种
grain, especially corn, that is kept for planting to produce new plants
希望之种;前景光明之物
something that is important because it is the starting point for future development
Investment is the seed corn of economic progress. 投资是经济发展的希望之种。