Flowering & Grain Filling
The flowers of wheat, triticale, barley, and oat are self-pollinated; most of the pollen is shed before the anthers emerge from the florets. Flowering (anthesis, or pollen shed) usually occurs within 2 to 4 days after spikes have completely emerged from the boot (barley often flowers prior to emerging from the boot). If emergence occurs during hot weather, flowering may occur while spikes are still in the boot. Most cells of the grain endosperm are formed during a period of rapid cell division following pollination. These cells enlarge and accumulate starch during grain filling. Most of the carbohydrate used for grain filling comes from the photo- synthetic output of the flag leaf. Developing spikelets compete for limited supplies of photosynthate and nitrogen. The smallest, slow- est-growing florets, which occur at the tip of the barley spike and at the tip of each wheat spikelet, are often unable to obtain enough nutrients to keep growing. Some spikelets at the base of the wheat or barley spike also may fail to develop.
The stages of grain ripening are called milk, soft dough, hard dough, hard kernel, and harvest ripe (for wheat, see fig. 2).Drymatter begins accumulating in the kerneldurGrowth & Development
ing the milk stage. During early milk stage, a clear fluid can be squeezed from the ker- nel. During late milk stage, milky fluid can be squeezed from the kernel. Most of the dry matter accumulates during the soft dough stage. Loss of water gives the kernel a doughy or mealy consistency. At the end of the hard dough stage the kernel reaches physiologi- cal maturity, water content drops to about 30 percent, and the plant loses most of its green color. The kernel contents can be divided with a thumbnail. At the hard kernel stage the plant is completely yellow and water content of the kernel is 20 to 25 percent. The contents of the kernel are difficult to divide with a thumbnail, but its surface can be dented. When kernel moisture content has dropped to 13 to 14 percent, the grain is har- vest ripe. The surface of the kernel cannot be dented with a thumbnail.