The International Board for Plant Genetic Resources is headquartered in the buildings of the Food and Agriculture Organization of the United Nations in Rome. A handful of crops are singled out as being of the highest priority globally:
Phaseolus (common) beans, cassava, sweet potato, coffee, and tomato.

More than fifty crops have been assigned IBPGR�s highest priority rating at the time of writing, in one or more regions:
amaranth, eggplant, quinoa, apple, finger millet, radish, avocado, foxtail millet, sorghum, barley, greengram (mung bean), soybean, bitter gourd, groundnut, spinach, black gram, kangkong, squash family, breadfruit and jackfruit, lentil, starchy banana (plantain), broad bean, maize (corn), sugar beet, cabbage family, mango, sugarcane, cassava, muskmelon, cantaloupe, sweet potato, chayote, oilseed brassicas, taro and aroids, citrus fruits, onion, wheat, cocoa, peach, palm, yam, pear and quince, and yardlong bean.

IBPGR�s list of crops being of the second highest priority in at least one region:
Almond, date, peach and nectarine, apricot, fig, potato, bambara groundnut, grain amaranth, rice bean, bottle gourd, moth bean, rubber, cashew, oil palm, walnut, cherry, papaya, winged bean, and cotton.

A third group contains a number of important crops like:
oats, olive, plum, rye, safflower, strawberry, pea, jute, grape, sunflower, pineapple, and others.

There is a fourth priority group, and then there are various crops not listed at all and under study, including many tree fruits and nuts, forage crops, and plants used for medicinal purposes.

The Rural Advancement Fund International (RAFI) completed a study and found that of 7,098 varieties of apple in use between 1804 and 1904 in the United States, 6,121 or 86.2 percent have been lost. Of 2,683 varieties of pears in use during those same years, 2,354 or 87.7 percent are now extinct. Included among these is the Ansault pear, of which one of the America�s premier fruit experts, U.P. Hedrick, once said, "In particular, the flesh is notable, and is described by the term buttery, so common in pear parlance, rather better than that of any other pear. The rich sweet flavor, and distinct but delicate perfume contribute to make the fruits of highest quality ... Ansault should find a place in every collection of pears for home use."
Hedrick, U.P., The Pears of New York, Report of the New York Agricultural Experiment Station, Albany: J.B. Lyon Co., 1921, p. 123.

These losses of fruit and vegetable varieties are staggering. And perhaps most frightening of all is the fact that while most of the crop diversity that once existed in the U.S. is now gone, the U.S. has never had the crop diversity that many other countries in centers of diversity have had. The U.S. lost a lot, but it had less to lose. If this study of the U.S. is any indication, extinction rates in other countries during the last century may be even more awesome. Yet day by day, the losses climb. More and more varieties become extinct, never to be seen again. With the people of the world dependent on thirty kinds of plants for the bulk of their sustenance, one does not have to be a nature-lover to be concerned about the extinction of traditional crop varieties and their wild relatives.
Taken from Fowler, C. & Mooney, P., Shattering: Food, Politics, and the Loss of Genetic Diversity, The University of Arizona Press, 1990; pp. 63-67 ff.