Indica rice and japonica rice are two subspecies of cultivated rice in Asia. In the long history, with the differentiation and spread of cultivated rice, the situation of planting indica rice in the south, Japonica Rice in the north, indica rice at low altitude and Japonica Rice at high altitude have been formed in China. This is mainly due to the different temperature conditions. In the high altitude areas of high latitude and low latitude, the temperature during the growth period of rice (especially in the early and late stages) is generally lower, and the cultivation of Japonica rice is the main; in the warm areas of low latitude and low altitude, the cultivated rice is mainly indica rice. Specifically, indica rice is mainly distributed in the South China tropics and the lowlands in the subtropics of Huaihe River, while japonica rice is more widely distributed, including the southern tropical and subtropical Highlands, the Taihu Lake Basin in East China, and the north, northeast and northwest regions .
On the origin of Indica and japonica rice, Chinese scientist Ding Ying put forward the academic viewpoint of basic type and variant type. Because many characteristics of indica rice are more similar to those of common wild rice, Mr. Ding thinks that indica rice is the basic type, while japonica rice is a variant type based on indica rice. This is the result of artificial selection and the influence of terrain or latitude on agricultural geography. Later, because it was found that wild rice had the potential to evolve into japonica rice, some people thought that wild rice could also evolve into japonica rice directly.
Indica rice and japonica rice have their own characteristics, and the difference of grain morphology and cold resistance is large. Generally speaking, indica rice has longer grain length and poor cold resistance, while japonica rice has shorter grain size and stronger drought resistance. Japan and China have done a lot of research on the identification of Indica and japonica rice. In summary, the representative methods of indica japonica identification mainly include morphological character classification, discriminant function method (combination of morphological and physiological characteristics), biochemical method (isozyme) and molecular marker. The identification of cross compatibility is also an important index to identify indica and japonica rice.
Because there are some genetic differences between Indica and japonica rice, scientists have not only bred excellent indica or japonica rice conventional varieties, but also used them as two parents of hybrid rice to breed inter subspecific hybrid rice with higher heterosis.