Growing economic decay in sub-Saharan Africa, where the number of people living in poverty rose from 42 percent to 47 percent between 1981 and 2001, is the biggest development challenge the world faces, the U.N. Industrial Development Organization said today in a report. Fostering macroeconomic management and good governance and increasing agricultural output will be key to improving the lot of sub-Saharan Africans, the report said. Creating institutional and social capabilities and diversifying their economies will also be important, it added.