You can answer this question by reading in Chapter 5. It is answered most clearly in Table 5.1 in that chapter. There, we can see that Diamond says the earliest plants to be domesticated were wheat, peas, and olives. Diamond says that these plants were domesticated (along with sheep and goats) in Southwest Asia, which is also called the "Fertile Crescent." These crops were domesticated by 8500 BC. According to this table, the next crops to be domesticated were rice and millet which were domesticated (along with pigs) in China by 7500 BC. The table gives you more crops and their dates of domestication if you need to go further than this.
Grains, or cereal crops, are generally thought to be the first domesticated food, in around 9000 BC in the Fertile Crecent. However, there is new evidence that it may have been figs that were first about 11, 400 years ago, or 1,000 years before the grains (Science Daily). Still others think tubers were first. All claims list the Fertile Crecent or Middle East as the starting point.