Complex sentence: Wholesale markets for fresh food products have tended to decline in importance in OECD countries as well as in Latin America and some Asian countries as a result of the growth of supermarkets, which procure directly from farmers or through preferred suppliers, rather than going through markets.
Split into simpler sentences: Wholesale markets for fresh food products have tended to decline in importance in OECD countries. This also occured in Latin America and some Asian countries as a result of the growth of supermarkets, which procure directly from farmers or through preferred suppliers, rather than going through markets.