Early Selection in Pinus ponderosa: Compromises Between Growth Potential and Growth Rhythm in Developing Breeding Strategies

Author： Rehfeldt G. E.

Publisher： Society of American Foresters

ISSN： 0015-749X

Source： Forest Science, Vol.38, Iss.3, 1992-08, pp. : 661-677

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Abstract

Shoot elongation of seedlings from 13 wind-pollinated families in each of 3 natural populations was described in years 2 and 5 by a function that allowed calculation of the start, rate, duration, and cessation of elongation. Additive genetic variances for these variables and for height in year 5 were pronounced, heritabilities were high, and expected responses to selection were large. The age-age genetic correlation for each trait was strong, as were the genetic correlations for 5-year height with all traits except the start of shoot elongation. Expected responses to selection suggested that (1) genetic gains in growth can be pronounced; (2) strong selection for increased growth is accompanied by a change in growth rhythm to that typical of unselected populations from much milder environments; (3) selecting for the rate of shoot elongation tends to control the correlated responses in growth rhythm while providing about 70% of gains expected from direct selection on height; and (4) selecting in the greenhouse in year 2 is nearly as effective as selecting the field in year 5. While breeders might choose among strategies that either control correlated responses or optimize gains in growth potential, developing a program that is capable of realizing the expected gains requires an understanding of the system of genetic variability. For. Sci 38(3):661-677.