Early progeny testing and evaluation of controlled crosses of black spruce

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Abstract
Known parent F1 crosses of black spruce (Picea mariana (Mill) B.S.P.) were ranked in field progeny tests at ages 7 to 13 years for height and stem volume growth. Nine crosses, including two selfs, were chosen for early juvenile progeny testing in a glasshouse environment. Performance of early seedling growth for the same nine families grown under both field and glasshouse conditions were thus compared in a retrospective study. Juvenile-mature correlations were established between a number of traits associated with tree growth and vigor. Within the nine families there was a ranking from "fast"- to "slow"-growing family groups. Monthly measurements of morphological characters at ages 3 to 6 months in the glasshouse showed highly significant family variation for total height, root collar diameter, lateral branch number, needle number, volume, branch length, and shoot, root, and total seedling dry weights. Weekly application of gibberellin A4/7(GA4/7) beginning at age 3 months influenced 5- and 6-month shoot volume and shoot height, and final dry weight measurements (age 6 months). Height growth of the four slowest growing families (two outcrossed, two selfed) was significantly (P .ltoreq. 0.05) increased by GA4/7 application, but the hormone had no significant effect on height growth of the five faster-growing families (all out-crossed). This may indicate that endogenous gibberellins are not limiting for height growth of faster growing families, but may be limiting for height growth of slower growing families. Simple correlations were highly significant between age 7 to 13 years for field height measurements, and 13-year field volume, versus glasshouse height, stem volume, and the several dry weight measurements at age 6 months. Similarly, Spearman rank order correlations were also significant. These strong correlations between early growth in the glasshouse environment and that of field growth (age 7 to 13 years) suggest that the poorest growing crosses can be identified in a juvenile growth progeny test under glasshouse conditions by at least age 6 months. Rogueing of the poorest performers as a result of glasshouse testing would thus be at least as reliable as rogueing based on 13 years of field assessment. Selected families for such tests should of course come from similar latitudes and elevations.

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