苗期低温是制约东北水稻生产的一个重要逆境因子,培育苗期耐低温的水稻品种是解决这一问题最有效的途径之一。以粳型恢复系C418为轮回亲本与7个来自不同地域的供体杂交和回交培育BC2F2群体，利用沈阳春季田间自然低温进行耐冷筛选，并对入选的177个苗期耐冷导入系后代在自然和人工气候室两种不同强度的低温胁迫条件下的苗期表现进行评价。结果表明，虽然供体亲本均为苗期耐冷性弱的品种，但在全部回交后代中均出现耐冷的超亲分离，表明这些供体亲本均携带对耐冷性有利的“隐蔽基因”, 不过组合间的耐冷性选择效率存在较大差异。以人工气候室低温胁迫后的存活率为耐冷性鉴定指标，导入系之间出现广泛分离，田间筛选入选比例高的BG300和中413导入系群体中出现存活率高的导入系后代比例较其它群体高，说明在同一轮回亲本遗传背景下回交后代的耐冷水平取决于供体。在室内严格低温条件下表现为强耐冷性的导入系在相对温和的自然低温胁迫下表现为苗高、苗干重较非胁迫条件生长抑制不明显，且能够促进根系生长。结果表明，大量的耐冷有利基因以“隐蔽”的形式存于水稻种质资源中。通过利用来源广泛的种质资源作为供体进行回交育种，对回交后代进行严格耐冷筛选，可有效选育高产耐冷水稻品种和有价值的育种材料。
Low temperature at the seedling stage has been an important factor limiting rice production in Northeast China. Developing rice cultivars with good seedling cold tolerance (CT) is the most effective approach to solve the problem. To efficiently discover and utilize useful genes from rice germplasm resources is the key to achieve new breakthroughs in rice improvement. In this study, C418, an elite japonica restorer (Oryza sativa L.), was used as the recurrent parent and 7 varieties of diverse origins (6 are indica lines) were used as donors to obtain BC2F2 bulks by crossing and continued backcrossing. Initial screening for CT under the low temperature of the field conditions resulted in 177 CT BC2F2 introgression lines (ILs). Replicated experiments under both normal (non-stress) and natural low-temperature (stress) conditions indicated that all donors had poor CT but there were transgressive segregations in all BC populations for CT, indicating the presence of ‘hidden genetic variation’ for improved CT in apparently cold-susceptible donors. Performances of BC2F6 ILs selected from 7 BC populations for traits related to seedling CT in replicated progeny testing under the controlled phytotron low-temperature conditions showed that a total of 93 promising ILs from the BC populations which had higher survival rates than C418. The BC populations involving donors BG300 and Zhong413 produced the highest number of CT progeny, including 28 ILs with a high level of CT, expressed as less affected seedling height and dry weight, and stronger root vigor under the low temperature of both the phytotron and field conditions. Our results indicate that backcross breeding coupled with efficient screening is a powerful way to exploit this hidden diversity and that using diverse indica germplasm as donors in BC breeding program can effectively improve CT of japonica rice varieties in Northeast China without loosing their high yield potential.
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