title: Plant breeding can be made more efficient by having fewer, better crosses.
abstract: BACKGROUND
  Crop 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.
  
  
  RESULTS
  We 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.
  
  
  CONCLUSIONS
  The 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.
authors: Centre for Advanced Research in International Agricultural Development (CARIAD), Bangor University, Bangor, Gwynedd, United Kingdom. j.r.witcombe@bangor.ac.uk
authors: John R
authors: JR
authors: Witcombe
authors: Sanjaya
authors: S
authors: Gyawali
authors: Madhu
authors: M
authors: Subedi
authors: Daljit S
authors: DS
authors: Virk
authors: Krishna D
authors: KD
authors: Joshi
mesh_terms: D001947:Breeding; D018556:Crops, Agricultural / Q000502:physiology*; D003433:Crosses, Genetic