玉米杂种优势育种——自交系群体循环相向选择的原理及途径

Heterosis Breeding in Maize——The Principle and Approaches of Recycling Selection of Inbred Populations in Face-to-face Direction

杂种优势是一个复杂的生物学现象,由生理、生化和分子机制共同决定。在群体水平上,作物产量取决于作物与环境、个体与群体、个体各个器官之间的协调,杂交育种追求群体优势。在个体水平上追求在特定群体条件下有利于单株产量形成的性状集合,该集合由优势性状、零优势性状和负优势性状组成。杂交导致后代发生遗传变化的机制可分3类:亲本等位基因一致、亲本等位基因不同、亲本含有不同的非等位基因。杂种优势是上述3类基因协调组合和表达的结果,可称为"协调基因表达谱"。该基因表达谱的创建涉及3个阶段的基因重组,即创造自交系选育群体的杂交、自交系选择时的自交和亲本自交系选配的杂交。根据杂种优势的分子机制,具有高配合力的亲本自交系之间,不仅在基因组成上具有一定的互补性,还应有一定的一致性,通过亲本自交系群体的循环相向选择,可以实现这一育种目标。同时,还需要进行协调基因表达谱的特点、形成规律及其与表现型关系的基础研究。注意研究自交系性状优势与基因群组成的一致性和互补性的关系,筛选出能够用于杂种优势预测的分子标记,提出新的杂种优势形成理论和利用途径,为更长远的杂种优势利用奠定基础。

Heterosis, a complicated phenomenon, is jointly controlled by physiological, biochemical and molecular mechanisms. At population level, crop yield depends on the coordination between crop and its environment, individual plant and its population, different organs in an individual. Hybridization breeding pursues the heterosls in a population level. At individual level, the cross breeding intends to achieve the collection of the characters which are in favor of an individual yield formation in particular population condition. This collection consists of the characters of positive heterosis, negative heterosis and zero heterosis. The basis of genetic changes in hyrbids, caused by crossing, may be classified into three categories： the parents having the same alleles, the parents having different alleles, the parents having different non-allele genes. Heterosis is the result of combination and concord expression of these three categories of genes, which could be called the concord gene expression profile. The creation of this gene expression profile is involved in the following gene recombination of three stages： （1） crossing when establishing an inbed population; （2） self-pollination when screening the inbed population; （3） crossing when screening the combinations of inbred lines. According to the molecular mechanism of heterosis, not only the complementarity, but also the consistency in the genetic composition are necessary between the inbred lines of parent possessing high combining ability. These breeding objectives can be achieved by the recycling selection of the inbreds in face-to-face direction. Meanwhile it is necessary to investigate the characteristics and the establishment pattern of the concord gene expression profile, and to explore the relationship between the concord gene expression profile and the phenotype. Especially, we should pay more attention to the relation of complementarity and consistency in the genetic composition with the traits controlled by them, and screen out the molecular marks used to predict the heterosis. Consequently, these investigations can provide new approaches and theoretical guidance for heterosis which will lay a foundation for the further heterosis utilisation.