Polymix breeding with paternity analysis in Populus: a test for differential reproductive success (DRS) among pollen donors

Abstract

Polymix breeding with paternity analysis (PMX/ WPA) has been proposed as an alternative to traditional full-sib breeding and testing schemes. To fully capture the benefits of PMX/WPA, differential reproductive success (DRS) of pollen parents used in the polymix must be modest. DRS was evaluated in an operational test of PMX/ WPA for a hybrid poplar breeding program. A 16-parent pollen polymix (Populus nigra L.) was used to pollinate seven clones of Populus deltoides (Bartr. ex. Marshall) under greenhouse breeding conditions. Progeny were grown out briefly and randomly sampled (357) prior to out-planting in field trials. Twenty-eight simple sequence repeat (SSR) loci were evaluated and 15 were selected for genetic characterization in small populations of three Populus spp (P. nigra, P. deltoides, and P. balsamifera spp trichocarpa Torr. & Gray). Seven loci were ultimately selected for paternity analysis of progeny. The average exclusion probability of the seven loci in P. nigra was 0.604; combined, the theoretical exclusion probability was 0.9999. However, only 95% of sampled progeny were unambiguously assigned a single paternal parent. Missing data likely accounted for most of the ambiguity. DRS was statistically significant though not prohibitive for practical utility of PMX/WPA as a breeding system. Of the 112 potential crosses in this study, 92 were represented. Eight of the 16 pollen parents contributed 83% of the progeny. Good pollen vigor, as measured by germination percent, did not ensure paternal success, but poor vigor was associated with lack of paternal success. PMX/WPA appears to be logistically and economically attractive for hybrid poplar breeding and testing.

Impact of reconstructed pedigrees on progeny-test breeding values in red spruce

“…Progenies of polymix (PMX) and open-pollinated (OP) forest genetic tests are usually assumed to be related as half-sibs (relationship coefficient= r = 0.25) but in reality a more complex pedigree exists as the result of male differential reproductive success (Wheeler et al 2006;Doerksen and Herbinger 2008) and inbreeding (Squillace 1974;Sorensen and White 1988). The unidentified contributions of males to the pedigree can increase the genetic correlation among offspring, causing genetic variance and heritability to be overestimated (Squillace 1974).…”

Testing for unequal paternal contributions using nuclear and chloroplast SSR markers in polycross families of radiata pine

“…The paternal contributions in controlled polycross families were shown to be unequal for Populus spp. (Wheeler et al 2006), Picea mariana (Rogers and Boyle 1991), Pseudotsuga menziesii (Apsit et al 1989;Nakamura and Wheeler 1992), Picea abies (Schoen and Cheliak 1987;Skrøppa and Lindgren 1994), Picea glauca (Schoen and Stewart 1986) and P. radiata (Moran and Griffin 1985), but the equal mating hypothesis was verified for Pinus taeda (Wiselogel and van Buijtenen 1988). All of these studies used isozyme loci, but a few recent studies have used highly polymorphic nuclear microsatellites (nSSR) (Grattapaglia et al 2004) and chloroplast microsatellites (cpSSR) (Plomion et al 2001) for paternity analyses in polycross seed orchards.…”

“…All previous studies, except Wheeler et al 2006, have tested for unequal pollen contribution using seeds from polycross families. Parental GCA estimates are obtained from young offspring and thus this hypothesis should actually be tested using offspring that were planted in progeny trials.…”

With a little help from my friends: hybrid fertility of exotic Populus x canadensis enhanced by related native Populus nigra

“…Pollen germination rates of 10-55% are considered sufficient for adequate seed-set (Rajora and Zsuffa 1986) but it is unknown whether variation in pollen germination percentage might contribute to pollen competitiveness in polymix crosses of poplar (Wheeler et al 2006). In this study, seed-set of controlled crosses between two clones of P. x canadensis was extremely low and seeds were not viable.…”