The Contribution of Pollen Germination Rates to Uneven Paternity Among Polycrosses of Cryptomeria japonica

Polycrossing is a very useful and cost-effective approach when designing mating trials. However, since the maternal general combining ability (GCA) in polycross designs is estimated on the assumption of equal contributions from paternal parents; any unequal paternal contribution leads to biased GCA estimates. Progeny from polycrossing Cryptomeria japonica, in which three mixtures from three paternal donors were crossed with each of three maternal parents, were analyzed using microsatellite markers to detect departures from equal paternal contribution. The deviations from equal paternal contribution were evaluated using a χ2 goodness of fit test. In this test, we examined the null hypothesis of equal paternal contribution for each mother tree. Two different methods were used to calculate paternal contribution: first, simply the number of seeds produced by each male parent, and second, the number of seeds produced by each male parent weighted according to the proportion of full seeds in single cross. The results of the χ2 test showed that the contribution to seed production by each paternal clone differed significantly in all polycrosses. The average pollen germination rate was significantly different between paternal clones. The contribution of each pollen donor in a polycross was related to their pollen germination rate.