shuidaoshizihuashoufenzuowu
，pinzhongyichuanxingbijiaowending，danyigeyouliangpinzhongjingguoduoniantuiguangzhongzhihou，youyuwaijieyurenweiyinsuyingxiang，qiyouliangzhengqidequntihuifashengbianhua，congershipinzhongyouchunbianza，pinzhongyouyoubianlie，kangnixingjiangdi
，chanliangxiajiang
，qizhuyaohunzayuanyinruxia：

1
、機械混雜。在水稻浸種催芽、播種、移栽
、收獲
、脫粒、曬種、貯藏、yunshudengyixilieshengchanliutongguochengzhong
，renweishuhu，meiyourenzhenzhixingcaozuoguicheng，dourongyizaochengpinzhongjianshenzhizhongjiandehunza。qiciqianzuohezacaozhongzidezirantuoluo
，huozheshiyonghunyouzuowuhezacaozhongzideweijingchongfenfushudeyoujifeiliaodoukezaochengjixiehunza，zhijiejiangdilepinzhongdechundu，yingxiangdaopinzhongshengchangzhengqiduhefengchanxing。

2
、生物學混雜。一般情況下
，水稻的自然雜交率一般在4%zuoyou，yincishuidaoyouliangpinzhongduonianzhongzhibujinxingtichunfuzhuang，youyuyuqitapinzhongjinxingdeziranzajiaodengziranyinsudoukeshiyouliangpinzhongxiadaizhizhuxingzhuangfashengfenli
，zazhuzengduo，pinzhongtuihua。

3、環huan境jing條tiao件jian不bu良liang與yu栽zai培pei管guan理li不bu當dang。一yi個ge水shui稻dao優you良liang品pin種zhong的de優you良liang性xing狀zhuang都dou是shi在zai一yi定ding的de自zi然ran環huan境jing和he栽zai培pei條tiao件jian下xia形xing成cheng的de，即ji良liang種zhong與yu良liang法fa要yao配pei套tao，良liang種zhong才cai能neng充chong分fen發fa揮hui其qi增zeng產chan潛qian力li。如ru果guo不bu能neng保bao證zheng一yi定ding的de環huan境jing條tiao件jian
，優you良liang品pin種zhong由you於yu自zi然ran選xuan擇ze使shi品pin種zhong產chan生sheng適shi應ying性xing變bian異yi，適shi應ying性xing強qiang的de個ge體ti往wang往wang豐feng產chan性xing較jiao低di
，年nian複fu一yi年nian
，適shi應ying性xing強qiang的de個ge體ti增zeng加jia

，就jiu會hui導dao致zhi品pin種zhong逐zhu步bu退tui化hua
、變劣。