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美国的水稻分布在南部各州中,也就是在北纬以南35°的所谓水稻地区。所有品种根据生长期长短、籽粒大小和形态及胚乳的化学成分等三个性状分类。按品种的早熟性可分成四个类型:极早熟(生育期为100～115天)、早熟(116～130天)、晚熟(131～149天)及极晚熟(150天及150天以上)。依水稻籽粒类型则分为短粒——粒长5.5毫米以下,长宽比在2.1以下;中等——粒长5.51～6.6毫米,长宽比在2.1～3;长粒——6.61～7.5毫米,长宽比在3以上。就籽粒化学成分可以分为两类:含大量淀粉的——胚乳内既含直链淀粉又含枝链
Rice in the United States is distributed in the southern states, the so-called paddy region, 35 ° south of latitude. All varieties were classified according to the three traits of growth period, grain size and morphology, and the chemical composition of endosperm. Premature varieties by species can be divided into four types: very early maturity (growth period of 100 to 115 days), early maturity (116 to 130 days), late maturing (131 to 149 days) and very late maturing (150 days and more than 150 days). According to the type of rice grain is divided into short-grain length of 5.5 mm below the aspect ratio of 2.1 or less; medium - grain length 5.51 ~ 6.6 mm, aspect ratio of 2.1 to 3; long grain - 6.61 ~ 7.5 mm , Aspect ratio of 3 or more. The chemical composition of the grain can be divided into two categories: with a lot of starch - endosperm contains both amylose and branched