Genetic variation in basal area increment phenology and its correlation with growth rate in loblolly and slash pine families and clones

Abstract

We quantified basal area increment phenology over a 2-year period in one loblolly pine (Pinus taeda L.) and four slash pine (Pinus elliottii Engelm. var. elliottii) full-sib families propagated as rooting cuttings. In 2002, basal area growth started in March and stopped in October for both species, while in 2003, initiation and cessation occurred 2 weeks earlier for all families. In both years, peaks in basal area increment occurred in short (2–3 week) periods in the early spring for all families, followed by linear basal area growth until cessation. While there were significant size differences among taxa (species and families) at age 6 and 7 years, genetic differences in basal area growth rate were only expressed during short, discrete time periods primarily in the spring and fall. Basal area growth rate increased during periods when water soil availability increased (up to 300 mm), but an excess in water availability in the soil had a negative impact on growth. Within-family individual-tree broad-sense heritabilities ranged from 0.01 to 0.37 for all traits. In general, heritabilities were higher for growth traits than for phenological traits for all families. Both the strength and direction of correlation estimates of phenological traits with growth rate varied across families and years.

Growth Rhythm Parameters as Components of Hybrid Vigour in Young Seedlings of Hybrid Larch (Larix decidua x L. kaempferi)

“…For several Larix species, BALTUNIS and GREENWOOD (1999) found that total height was positively correlated with the date of cessation of shoot growth and the total duration of growth but not with the time of shoot initiation and with the rate of elongation. In some other studies (MCCRADY and JOKELA, 1996;EMHART et al, 2006), no significant differences could be found for these growth phenology parameters among families or even among species probably due to a more restricted origin of their genetic material.…”

“…hybrids and their related parents in this study) and thus ways by which heterosis is built up over the growing season. Indeed as shown by EMHART et al (2006), the significant differences observed in basal area size among two pine species (Pinus taeda and P. elliottii) were explained by differential growth rates expressed only during short, discrete time periods. In fact, a more detailed look on growth rhythms in our study (such as plotted in Figure 2) revealed contrasting situations for expression of hybrid vigour over the growing season.…”

Phenotypic analysis of first-year traits in a pseudo-backcross {(slash x loblolly) x slash} and the open-pollinated families of the pure-species progenitors

“…The date of initiation and cessation determine the duration of growth, and those factors together with the daily rate of growth determine the total growth for the season (Emhart et al 2006). BC1 started growth earlier than was estimated from the initial measurement.…”

“…Initiation differed by more than 20 days, whereas cessation only differed by 8 days. These differences could have been caused by siteto-site variation (Parisi 2006) or year-to-year variation (Jayawickrama et al 1998;Emhart et al 2006). BC1 demonstrated positive and negative heterosis for several traits and no heterosis for others.…”

“…For each height measurement, a graduated pole was used to measure the distance from the ground to the tip of the highest bud. The phenological traits initiation day, 50% growth day (AG50) and cessation day for height growth were estimated using a linear interpolation to determine when the plants reached 5%, 50% and 95% of their annual growth, respectively (Mirov et al 1952;Hanover 1963;Jayawickrama et al 1998;Emhart et al 2006). The other traits considered were: duration of the growing season (D, days) estimated as the difference between the initiation and the cessation day; TG (cm) as the difference in height between initiation and cessation date and ASRE (cm/day) as the ratio of TG to D. Evaluation of pest incidence was part of the measurement protocol; however, tip moth was the only pest present.…”