Genetic Constraints on Photosynthesis and Yield in Wheat

Abstract

Since the turn of the twentieth century, when wheat breeding was established on a scientific footing, there have been substantial improvements in the yielding capacity of varieties grown in the UK. Their total dry matter production has shown no trend with year of introduction and yield increases have been associated with a ‘redistribution’ of dry matter from straw, particularly stem, to grain (Austin et al. 1980). There seems little scope for a continuation of this trend (Austin, 1982). If so, further genetic improvement in the yielding capacity of varieties will depend on breeding for greater total dry matter production, whilst maintaining a high grain:straw ratio. It is axiomatic that this would entail greater dry matter production during grain filling, and it may also require increased production of vegetative dry matter before flowering. Selection experiments (Innes et al. 1982, 1983) have shown that increased tiller production and more erect leaves can increase dry matter and grain yields. This paper is concerned with another attribute, light-saturated rate of photosynthesis (Pmax), genetic variation in which has been known for some years (Evans, Dunstone, 1970; Austin et al. 1982) which seems likely, in principle, to offer a means of increasing biomass and grain yield in wheat.