2. 1 The whole growth period of rice includes two stages: vegetative growth and reproductive growth. Generally speaking, the beginning of young spike differentiation is the sign of reproductive growth. 2. 1 The whole growth period of rice includes two stages: vegetative growth and reproductive growth. Generally speaking, the beginning of young spike differentiation is the sign of reproductive growth. 2. 1. 1 vegetative growth period is the growth of rice vegetative body, which is divided into seedling stage and tillering stage. Production is divided into seedling stage and big (original) field stage (from transplanting to greening to jointing). 2. 1.2 Reproductive growth period is the growth of fruiting organs, from young panicle differentiation to flowering and fruiting, and it is divided into long panicle period and flowering and fruiting period. The differentiation from young panicle to heading is the same period of vegetative growth and reproductive growth, and the reproductive growth period is basically after heading. The long panicle stage starts from young panicle differentiation to heading stage, generally about 30 days. The fruiting period, from heading to flowering to grain maturity, varies with climate and varieties, generally 25? /FONT & gt； Between 50 days. 2. 1.3 rice growth type (relationship between young panicle differentiation and jointing) Early, middle and late rice varieties are different, and early rice varieties are called overlapping growth type after young panicle differentiation; Mid-season rice varieties, jointing and young panicle differentiation at the same time, are called continuous type; Late rice varieties differentiate young panicles at intervals after jointing stage, which is called separated growth type. 2.2 Stability and variability of rice varieties in growth period. The growth period of rice varieties is controlled by their own genetic characteristics and influenced by environmental conditions. 2.2. 1 Stability of growth period of rice varieties The same variety is cultivated in the same area, the same season and different years, and its growth period is relatively stable due to similar ecological conditions between years. Early-maturing varieties always show early maturity, and late-maturing varieties always show late maturity. This stability is mainly controlled by genetic factors. Therefore, in production practice, it can be divided into early rice according to the length of growth period, and the whole growth period is 100? /FONT & gt； 125 days, mid-season rice 130? /FONT & gt； 150 days, late troubles of continuous cropping 120? /FONT & gt； 140 days, one-season late rice 150? /FONT & gt； 170 days, the difference of growth period of early, middle and late-maturing rice can also be divided into early, middle and late-maturing varieties to meet the needs of natural conditions and farming systems in different regions, thus ensuring the relative stability and continuity of agricultural production in a certain period. 2.2.2 The variability of rice varieties in growth period varies with different ecological environment and cultivation conditions. When the same variety is cultivated in different areas, the growth period is prolonged with the increase of latitude and altitude, and conversely, it is shortened with the decrease of latitude and altitude. The cultivation of the same variety in different seasons shows that the growth period is shortened with the delay of sowing date and extended with the advance of sowing date. Early rice varieties are cultivated as continuous cropping late rice, and the growth period is shortened; Introduced from the south to the north, the growth period is prolonged. 2.3 The "three characteristics" of rice varieties are the genetic characteristics of light sensitivity, temperature sensitivity and basic nutritional growth. In different regions and different cultivation seasons, the growth period of rice varieties (from sowing to heading) is basically determined by the comprehensive effect of the "three characteristics" of the varieties. Therefore, the three characteristics of rice varieties are the essence of determining the growth period and change of rice varieties. The three characteristics of rice are formed under the influence of climatic conditions and cultivation seasons. For any specific variety, these three characteristics are an interrelated whole. 2.3. 1 The photosensitivity of rice varieties is characterized by the change of growth period due to the length of sunshine in the temperature range suitable for rice growth, which is called the photosensitivity of rice. For photosensitive varieties, short sunshine can accelerate their development and change and lead to early heading differentiation, that is, heading earlier than a certain day; When it is longer than a certain day, the heading is obviously delayed, also known as "the temporary day length of delayed heading", which is the upper limit of the day length to induce the differentiation of young panicles. Different rice varieties and different planting areas have different temporary days to postpone heading. In the northern and southern rice areas of China, the growth period of rice is mostly in 1 1? /FONT & gt； Between 65438 and 06 hours. 2.3.2 The temperature sensitivity of rice varieties is within the temperature range suitable for rice growth. High temperature will shorten the growth period of rice, while low temperature will prolong the growth period. This characteristic that the growth period changes due to high and low temperatures is called the temperature sensitivity of rice varieties. The growth period of rice varieties will be shortened at high temperature, but the degree of shortening varies with the characteristics of rice varieties. The temperature sensitivity of late rice varieties is stronger than that of early rice, but the development and transformation of late rice varieties are mainly controlled by the conditions of day length. When the day can't meet the requirements, the effect of high temperature can't be shown. Mid-season rice varieties are between early rice and late rice. 2.3.3 Basic vegetative growth of rice varieties The vegetative growth period of rice that cannot be shortened under the influence of high temperature and short sunshine before it enters reproductive growth is called the basic vegetative growth period of rice. Not affected by environmental factors, also known as the basic nutritional growth of varieties. The part where the vegetative growth period is shortened by short-day high temperature is called digestible vegetative growth period. The "three characteristics" of rice are formed under the influence of climatic conditions and cultivation seasons. For any variety, these three attributes are an interrelated whole. According to the light and temperature sensitivity of varieties and the length of basic vegetative growth period, the types of light and temperature response were divided. In fact, it is to combine the three characteristics of different ecological types of rice seeds. Most early rice varieties have weak photosensitivity, short to medium basic vegetative growth period, medium sensitivity to temperature, no strong photosensitivity and long basic vegetative growth period; Most mid-season rice varieties have long basic vegetative growth period, medium strong temperature sensitivity and weak light sensitivity; Late rice varieties have strong photosensitivity, short to medium basic vegetative growth period and strong to medium temperature sensitivity. The basic vegetative growth period of late rice in China is short, and there is no weak or moderate photosensitivity. The temperature sensitivity of late rice can only be reflected in short sunshine. Early rice varieties planted in temperate high latitudes can be heading normally under the condition of long sunshine in summer and mature before the arrival of low temperature, while in the middle and lower reaches of the Yangtze River, 5? /FONT & gt； In June, under the condition of long sunshine, young panicles began to differentiate and completed development and transformation; The late rice type is swollen, which is not suitable for planting in temperate high latitudes, but it can be planted as single-season late rice and double-season late rice in the middle and lower reaches of the Yangtze River. Among the mid-season rice varieties, the early-maturing mid-season rice is biased towards early rice, while the late-maturing mid-season rice is biased towards late rice. When cultivated in early season, the heading date was obviously delayed compared with early rice, and when cultivated in late season, it was delayed compared with late rice.