Improvement Strategy for Mature Plant Breeding Programs

In mature plant breeding programs an elite core germplasm forms the backbone of the breeding effort, confronting the breeder with the challenge of maintaining germplasm diversity as genetic distance between the elite core germplasm and donor germplasm widens. This research assessed the effects on grain yield of transferring genes from two‐row barley ( Hordeum vulgare L.) cultivars to a six‐row gene pool. We conducted three cycles of recurrent‐type breeding, beginning with crosses involving five two‐row donor parents. The crossing scheme led to progenies with theoretical proportions of two‐row germplasm of 25 to 50% in Cycle 1, 12.5 to 25% in Cycle 2 and 6.25 to 12.5% in Cycle 3. In Cycle 1, yield of the six‐row progeny across the five populations ranged from 86 to 97% of the respective six‐row parent. Kernel weight of the six‐row progeny was also low in Cycle 1. In Cycle 2, grain yield improved to 99% of the check mean and kernel weight improved to 102% of the check mean. In Cycle 3, sets of lines representing three populations yielded from 112 to 119% of the check mean in 1997 and 1998 and individual lines surpassed ‘Stander’, the highest yielding check in both 1997 to 1998. The highest yielding lines in each cycle were derived from populations having the highest theoretical percentage of adapted recurrent parent germplasm, that is, when six‐row gene combinations were predominately left intact. Results from the three breeding cycles support the proposition that a strategy that maintains favorable gene combinations while introgressing relatively small amounts of donor germplasm can lead to incremental yield gains.