Fourth cycle breeding and testing strategy for Pinus taeda in the NC State University Cooperative Tree Improvement Program

Abstract

The Cooperative Tree Improvement Program at North Carolina State University used the differential evolution algorithm developed for animal breeding (Kinghorn, Genet Sel Evol 43(1):4, Kinghorn 2011) to design the mating in the 4th cycle of loblolly pine (Pinus taeda L.) breeding. The mate selection algorithm optimizes genetic gain while putting constraints on progeny inbreeding and coancestry level. The final mating list (4th cycle population) is expected to produce an index breeding value 63% higher than the candidate population mated at random. The average inbreeding coefficient in the candidate population was 0.000146. It increased to 0.000285 in the 4th cycle progeny. Only eight crosses out of 748 with progeny inbreeding value greater than zero were included in the mating list. One parent with a high index breeding value was used in 13 matings. A high majority of 421 individuals (75%) were mated two or more times; the remaining were mated once. The Cooperative also made significant changes in experimental design protocols to increase the efficiency of progeny testing by implementing an alpha-cyclic incomplete row-column design. Progeny test series across years were connected with a rolling front testing strategy by overlapping genetic entries across years. The Cooperative is expected to complete the 4th cycle in about 14 years, a significant reduction compared to previous cycles. With availability of high-throughput genotyping platforms, the Cooperative is moving toward implementation of genomic selection in the 5th cycle and beyond.