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jointly by the industrial supporters of the North Carolina State University Loblolly and Slash Pine Rooted Cutting Program and by the North Carolina Agricultural Research Service (NCARS) Raleigh, NC 27695-7643. Use of trade names in this publication does

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Mature seed weight of loblolly pine (Pinus taeda L.) averaged 25 mg (dry weight), of which 55.0% was seedcoat, 38.5% megagametophyte, and 6.4% embryo. Fatty acid (FA) content (dry-weight basis) was 17.5% for whole seed, 0.4% for seedcoat, 36.2% for megagametophyte, and 51.2% for embryo. Distribution of FAs (16:0; 18:0; 18:1; 18:2; 18:3 Δ5,9,12; 18:3 Δ9,12,15; 20:0; and 20:3) differed in seedcoat, megagametophyte, and embryo, but 18:2 was the predominant FA in all tissues. Seed development was analyzed for 110 days from 25 July, the year following pollination. Embryos could be macroscopically observed on or about day 30. Embryo dry weight, length, and FA accumulation increased until about day 50 and then remained constant. Embryo density decreased from day 30 to 50 and then stabilized at ≈1.0366 g·ml-1 or 10% sucrose equivalent. Excised zygotic embryos did not germinate in vitro until after day 51; germination increased linearly after this date, reaching 80% by day 72.

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This research was funded by the North Carolina State Univ. Loblolly and Slash Pine Rooted Cutting Project, Dept. of Forestry, Raleigh, NC 27695-8002, and the North Carolina Agricultural Research Service (NCARS), Raleigh, NC 27695-7643. Use

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Abstract

Abnormal needle tip curling was induced by low humidity in 4 half-sib families of loblolly pine (Pinus taeda L.) grown in a growth chamber. The injury developed on new growth on both 12-week-old and 1-year old seedlings when plants were maintained under 30% ± 5% relative humidity with a 16-hour photoperiod, 23°C light period and 17° dark period. Very little injury developed on plants maintained at 70% ±5% relative humidity. Significantly more needle tip curling occurred on seedlings grown from seed collected in Texas than in seed collected from Virginia.

Open Access

Forest products companies would like to grow clonal plantations of superior loblolly pine (Pinus taeda L.) to improve fiber yields. Feasibility depends on developing efficient propagation techniques and finding superior clones. Horticultural stem-cutting propagation methods and micropropagation techniques are being coupled to test, preserve, multiply, and ultimately deploy clones. Outstanding clones are being found through a series of field tests; each beginning with a superior full-sibling cross from a 40-year-old breeding program. Clones are first screened for rooting ability, and the top 25% to 35% of clones are then established on four sites. Since maintenance of juvenile phase tissue is critical to perpetuating high rooting rates and fast subsequent growth, each clone is preserved as a set of serially propagated hedges and as cold-stored microshoots. As field tests age, better-performing clones are multiplied gradually. Large-production stock blocks of juvenile hedges consequently may be established from both rooted cuttings and microshoots as soon as field tests end. Clones producing large numbers of long branches have been noted for their potential value as fast-growing ornamentals. Since such characters are opposite those desirable for forestry, these clones would need to be preserved, multiplied, and marketed separately from clones for plantation forests.

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Abstract

In a field study comparing seedlings and tissue culture plantlets of loblolly pine (Pinus taeda L.) after two growing seasons, the plantlets had numerous growth and morphological characteristics of mature trees. The appearance of mature traits was surprising, since the plantlets originated from juvenile, embryonic tissues. Evidence from other studies with tissue culture propagation of pine species suggests that plantlets often express mature characteristics. Some of the characteristics of the loblolly pine plantlets, such as lower incidence of fusiform rust [Cronartium quercuum Berk. Miyabe ex Shirai f. sp. fusiforme (Cumm.) Burds. et Snow], fewer branches, and less taper, would be of great economic advantage if the growth rates remain similar to comparison seedlings.

Open Access

Loblolly pine (Pinus taeda L.) is the most widely planted tree species in the Atlantic Coastal Plain. To maximize its aboveground yield, it is vital to understand how root production, particularly fine root production, affects root carbon allocation to its root systems under various environmental conditions. Over a 2-year period (1998-99), we conducted a field study using minirhizotron technology to investigate fine root production and turn over in four families of a 6-year-old loblolly pine stand in Scotland County, N.C. A total of 144 minirhizotron tubes were installed to examine potential genetic differences in fertilizer effects on fine root turnover. Data analyses indicated an interaction between these families and fertilizer treatments for total fine root length and total fine root number. The effect of treatment on total root length was less clear in the faster-growing families. However, fertilization increased total root length in a slow-growing family but decreased total root length in a faster-growing family. Total root number was decreased by fertilizer treatment in the two fastest-growing families, but increased in the two slowest-growing families. Because ectomycorrhizae are significant carbon sinks in pine root systems and more than 90% of short roots in these loblolly pine families were colonized, ectomycorrhizal short roots (clusters) were classified into nine different morphotypes. No treatment and family interactions were found. Fertilizer treatment decreased the number of mycorrhizal clusters per unit root length. Dark and brown morphotypes were dominant mycorrhizal morphotypes among all the families. Our results suggest possible genetic differences and treatment effects on root system carbon demands of loblolly pine.

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Abstract

Height, number of roots, root length, and shoot quality rating on loblolly pine (Pinus taeda L.) tissue culture plantlets were measured in the laboratory and related to subsequent nursery and field performance. Shoot quality rating was the most important characteristic and was most consistently correlated with nursery and field traits. These results imply that only plantlets with the best shoot quality rating should be used so that growth rates will be similar to seedlings.

Open Access

Producing high quality rooted stem cuttings on a large scale requires precise management of the rooting environment. This study was conducted to investigate the effect of the rooting environment on adventitious root formation of stem cuttings of loblolly pine (Pinus taeda L.). Hardwood stem cuttings of loblolly pine were collected in Feb. 2002 from hedged stock plants and stored at 4 °C until setting in Apr. 2002. One hundred stem cuttings per plot in each of two replications received 45, 61, 73, 102, 147, or 310 mL·m-2 of mist delivered intermittently by a traveling gantry (boom) system. Mist frequency was similar for all treatments and was related inversely to relative humidity (RH) within the polyethylene covered greenhouse. Rooting tubs in each plot were filled with a substrate of fine silica sand, and substrate water potential was held constant using soil tensiometers that activated a subirrigation system. Cutting water potential was measured destructively on two cuttings per plot beginning at 0500 hr every 3 hh until 2300 hr (seven measurements) 7, 14, 21, or 28 days after setting. During rooting, leaf temperature and RH were recorded in each plot to calculate vapor pressure deficit (VPD). Cutting water potential and VPD were strongly related to mist application. Cutting water potential was also related to VPD. Rooting percentage had a linear and quadratic relationship with mean cutting water potential and VPD averaged between 1000 and 1800 HR. Eighty percent rooting occurred within a range of values for VPD. Data suggest that VPD can be used to manage the water deficit of stem cuttings of loblolly pine to increase rooting percentage. These results may be applicable to other species and to other rooting environments.

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The influence of ectomycorrhizae on drought acclimation was studied in an open-pollinated family of loblolly pine (Pinus taeda L.). Seedlings inoculated with Pisolithus tinctorius (Pers.) Coker and Couch (Pt) maintained a higher shoot relative growth rate under high and low soil moisture regimes. However, fascicle area, shoot and root mass, and fascicle nutrient elemental content were similar for seedlings inoculated with Pt and noninoculated seedlings. Seedlings under low soil moisture were drought-acclimated by five 11-day drought cycles. During peak water deficit (cycle 6), drought-acclimated, Pt-inoculated seedlings had the lowest predawn fascicle water potential (ψ pd), conserved water with lowest bulk fascicle diffusive conductance (g), and maintained low g and transpiration (E) during recovery (cycle 6). Enhanced drought acclimation of Pt-inoculated seedlings was independent of plant size and fascicle nutrient content.

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