The genetic control of sexual reproduction in Eucalyptus globulus

While clonal propagation is used to establish some plantations of Eucalyptus globulus in countries such as Chile and Portugal, the majority of plantations worldwide are established from seed (Tibbits et al. 1997; Griffin 2001). The genetically improved seed used in industrial plantations is usually derived from open pollinated seed orchards (seedling or grafted), but with the advent of single-visit (Williams et al. 1999) and one-stop (Harbard et al. 1999) pollination procedures an increasing component is now derived from large-scale controlled pollination programs producing elite polymix or full-sib families. Regardless of the system, seed production varies markedly between trees and in most cases the choice of female can strongly influence the profitability of seed production (Leal and Cotterill 1997). In addition, as E. globulus has a mixed mating system (Griffin et al. 1987; Eldridge et al. 1993) and selfing results in severe inbreeding depression for growth traits (Hardner and Potts 1995), outcrossing rate is a key factor. Outcrossing rate will affect the genetic quality of seeds obtained from seed orchards and whether predicted additive genetic gains will be realised. One of the main drivers of the outcrossing rate is the level of self-incompatibility of the female tree (Patterson et al. 2001), which varies widely in the species (Potts and Savva 1988; Pound et al. 2002a,b, 2003). This paper reports the results of two studies aimed at determining whether there is a genetic basis to variation in traits affecting sexual reproduction in E. globulus. The first study examined the genetic basis of variation in the quantity and quality of open pollinated seed from over 800 seed orchard trees of E. globulus. The second study examined the genetic basis of the large variation in self-incompatibility observed within the species.