Prognosis for genetic improvement of yield potential and water-limited yield of major grain crops

Abstract

Genetic improvement of crop yields under potential (Yp) and water scarce conditions (Yw) will be an important avenue to improved food security over the next four decades, at the end of which projected demand for food, feed and biofuel feedstock is expected to level out. Current measured relative rates of improvement in Yp and Yw for the three main cereal crops (maize, wheat and rice) in many cropping systems in the world are mostly well below the 1.16–1.31% y−1 rates required to meet projected demand for cereals in 2050. These relative rates can be expected to fall further if the current absolute rates of yield improvement continue unchanged and/or the current indications of stagnation in yield improvement for some crops in some regions of the world become widespread. This review assesses the available evidence for unexploited opportunities for enhancing current rates of genetic improvement for Yp and Yw, and examines some substantive proposals for achieving the same end through genetic engineering of photosynthesis, above-ground ideotype design, and improvement of root capacity for water uptake. Because time is of the essence, special attention is paid to the time scales required to progress potentially useful traits through to proof of concept under field conditions, from there to farmer-ready cultivars, and for widespread adoption by farmers of the improved cultivars. The requirements of breeders for inclusion of potentially important traits into the conventional breeding process are outlined and the value of molecular breeding tools as aids to genetic improvement of simple and complex traits is considered. Intellectual property and regulatory requirements are taken as additional potential drags on the rates of adoption into the breeding process of useful traits and/or to the free flow of information between research teams. Main conclusions are: (a) there are some unexploited opportunities to improve Yp or Yw in some crops and/or cropping systems; (b) exploitation of these opportunities could be hastened by increasing funding for focussed research and by identifying and eliminating or reducing drags at various stages of the idea to farmer-ready cultivar chain; (c) the time-scales required for major improvements in yield in farmer-ready cultivars through genetic engineering or ideotype realisation are likely to be measured in decades rather than years; (d) current and expected future relative rates of progress in Yp and Yw are a matter of real concern and are insufficient to meet projected demand for cereals by 2050. Possible step changes in Yp or Yw powered by genetic improvements such as exploitation of hybrid vigour in rice or hypothetical successes in the genetic engineering of photosynthesis are unlikely to change this outlook. The pessimistic assessments embodied in the last two conclusions should not obscure the fact that without continued investment in the search for sources of genetic improvement and development of aids to breeding, the unmet demands for cereals in 2050 will be even greater.