reliance on a narrow portfolio of crops or crop varieties can jeopardize food production systems. This is illustrated by the Great Famine of Ireland. Potatoes were introduced into Ireland from the New World in about 1600 and they became the major food source of most Irish people. The wind-borne Potato blight fungus spread throughout the country In 1845-1847 and caused almost complete failure of the potato crop. It is estimated that 1 million people died of starvation, cholera and typhoid. Ecosystem services A wide range of biologically diverse populations in natural ecosystems and in / near agricultural ecosystems maintain essential ecological functions that are critical for the production of food. Such populations contribute positively to, for example, nutrient cycling, decomposition of organic matter, crusted or degraded soil rehabilitation, pest and disease regulation, water quality maintenance, and pollination. Maintaining species diversity, while building on and enhancing ecosystem functions, reduces external input requirements by increasing nutrient availability, improving water use and soil structure, and controlling pests. Traits Genetic diversity within food species is a source of useful genes with a variety of benefits. For example: Wild subspecies of tomatoes (Solanum lycopersicum chmielewskii) were crossbred with cultivated tomato species. After 10 generations, new tomato strains with larger fruits were produced. There was a marked increase in pigmentation. The content of soluble solid, mainly fructose, glucose and other sugars increased. A barley plant from Ethiopia provides a gene that protects the barley crop from the lethal yellow dwarf virus. Host resistance gene, Xa21, from Oryza longistaminata is integrated into the genome of Oryza sativa for a broad range resistance to rice blight disease caused by Xanthomonas oryzae pv. oryzae See also Biodiversity Agricultural biodiversity References External links Facilitating Mechanism of the Global Plan of Action for the Conservation and Sustainable Utilization of Plant Genetic Resources for Food and Agriculture Bioversity International Biodiversity Nutrition Food and drink