文章从玉米耐密性的遗传改良、影响因素以及高密度的不利影响等方面,对国外玉米耐密性的研究进展进行了综述,指出现代玉米杂交种的产量提高主要归功于耐密性的增强;耐密性是一个复杂的生理性状,受很多因素的影响;高产性和稳产性的统一是现代优良杂交种的必备条件.

The quantitative relationships between wheat factors and characters and researches were reviewed in this paper, in order to provide references to the theory research of wheat freezing injury and production practice of disaster mitigation.

[Objective] The research aimed at introducing the background and utilization of germplasm resources in maize.[Method] The research progress on genetic background and utilization of maize germplasm resources was comprehensively reviewed in this paper,including maize heterotic groups and heterotic patterns,their flexible application in breeding and the utilization of various types of original materials.[Result] The results show that germplasm resource is the premise and basis for maize breeding.In-depth understanding and a reasonable selection of germplasm resources can significantly improve the breeding efficiency and speed up the breeding process.At the same time,it is considered that the selection and construction of original materials in maize breeding can not be limited to the heterotic groups and heterotic patterns,but has to be used reasonablely according to different types of germplasm resources and individual breeding objective and idea as well.[Conclusion] This study had broadened the idea and provided inspiration for the maize breeding practice in China.