British Columbia requires all seed orchard seedlots to be registered. Part of this registration is the calculation of genetic diversity (Ne, effective population size) which is based on weighted estimates of contribution from seed-cone (measured volume) and pollen-cone production (visual estimates of volume).
Seed orchard seedlots are the result of outcrossing (wind-pollinating) among a relatively few selected parents with certain levels of outside pollen contamination entering the orchard pollen pool. This type of mating system of conifers captures high levels of genetic diversity present in the general population (i.e.=1-1/2N, thus 10 randomly mating clones would capture 95% of the population genetic diversity). However, orchard seedlots can suffer losses in genetic diversity by disproportional gamete contributions of orchard clones (non-panmixia) and nursery practices (thinning and culling) can further reduce family representation in the final seedling crop. This has been shown in Douglas-fir (El-Kassaby and Thomson 1990, 1996) and interior spruce orchard seedlots (Stoehr and El-Kassaby 1997). For example, El-Kassaby and Thomson (1992) found that germination, thinning and culling contributed to 66, 20 and 14%, respectively in the variability of the final seedling production of Douglas-fir and to maintain diversity, it was recommended that single seed or family sowing be used for nursery production.
We do not have this information for lodgepole pine but we expect a certain level of diversity will be lost at the orchard level (where parents do not contribute gametes equally) and at the nursery level (where only bulk orchard lots are used at a sowing rate of 1.25 seeds per cavity). Furthermore, in the previous studies (El-Kassaby and Thomson 1992) only losses of the female contribution were studied. Now with molecular techniques, paternity analyses of both seed and seedling crops, we can study the loss of diversity of both the female (we know the parent from which seed was collected) and male (paternity analyses).
In the early stages of lodgepole pine seed orchard production, the number of contributing parents was high (>70 parents). However, as high breeding value parents are identified from the breeding program and new orchard establishment focuses on maximizing the genetic worth of seed crops, fewer parents (<40) are used. It is now important to challenge the basic assumptions we use to calculate genetic diversity.
A reduction in genetic diversity is associated in losses in ecological resilience of plantations, an important trait in view of uncertainties of climate change effects. Currently, lodgepole pine (Pl) is at the forefront of the battle caused by early signs and consequences of climate change. As such, it is prudent that we evaluate and determine potential forces that can reduce genetic diversity in orchard crops by evaluating steps from seed production in the orchard to the final crop emerging from the nursery. If critical stages in the production of orchard seedlings can be identified, possible remedies (orchard and nursery practices) can be formulated that may increase genetic diversity.
Webber, Joe E., Stoehr, Michael U.. 2009. The ecological resilience of lodgepole pine seed orchard crops. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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