Abstract
BackgroundCrop yields have to increase to provide food security for the world’s growing population. To achieve these yield increases there will have to be a significant contribution from genetic gains made by conventional plant breeding. However, the breeding process is not efficient because crosses made between parental combinations that fail to produce useful varieties consume over 99% of the resources.ResultsWe tested in a rice-breeding programme if its efficiency could be improved by using many fewer, but more judiciously chosen crosses than usual. In a 15-year programme in Nepal, with varietal testing also in India and Bangladesh, we made only six crosses that were stringently chosen on complementary parental performance. We evaluated their success by the adoption and official release of the varieties they produced. We then modelled optimum cross number using assumptions based on our experimental results.Four of the six crosses succeeded. This was a fifty-fold improvement over breeding programmes that employ many crosses where only about one, or fewer, crosses in 200 succeed. Based on these results, we modelled the optimum number of crosses by assuming there would be a decline in the reliability of the breeder’s prediction of the value of each cross as more crosses were made (because there is progressively less information on the traits of the parents). Fewer-cross programmes were more likely to succeed and did so using fewer resources. Making more crosses reduced the overall probability of success of the breeding programme.ConclusionsThe efficiency of national and international breeding programmes would be increased by making fewer crosses among more carefully chosen parents. This would increase the number of higher yielding varieties that are delivered to farmers and hence help to improve food security.
Highlights
Crop yields have to increase to provide food security for the world’s growing population
Every year, cereal breeders in international agricultural research centres that helped produce the Green Revolution make hundreds, or thousands, of crosses and derive only small populations from each one. This breeding strategy is perpetuated because high-volume crossing, despite the inevitable inefficiency of having many failed crosses, produced the iconic Green Revolution varieties that were successful in dramatically increasing yields from the 1960s to the present day, and because it continues to produce genetic gains in crop yield
Experimental data for breeding programmes with contrasting cross numbers have not been reported in the literature, which is unsurprising given the size of the experiments required
Summary
Crop yields have to increase to provide food security for the world’s growing population. Cereal breeders in international agricultural research centres that helped produce the Green Revolution make hundreds, or thousands, of crosses and derive only small populations from each one This breeding strategy is perpetuated because high-volume crossing, despite the inevitable inefficiency of having many failed crosses, produced the iconic Green Revolution varieties that were successful in dramatically increasing yields from the 1960s to the present day, and because it continues to produce genetic gains in crop yield. To test varying combinations of m (number of crosses) and n (population size derived from each cross), an ideal experiment is two breeding programmes having the same total number of plants (K), the same selection methods, but contrasting values for m and n This demands huge resources but will still only test one possible strategy for selecting the crosses in the low m set. Other experimental approaches such as combining ability tests (e.g., diallel crosses) do not resolve the problem; they can provide estimates of the relative values of different crosses they cannot predict the probabilities of favourable genotypes occurring as population size varies
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