Abstract:

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.