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.
Jules Janick, Christiane Cabral Velho and Anna Whipkey
Farrell C. Wise and Rodney O. Jones
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.
Wei Qiang Yang, Amy K. Dunbar and Mary A. Topa
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.
Anthony V. LeBude*, Barry Goldfarb and Frank A. Blazich
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.
Sven E. Svenson, Fred T. Davies Jr. and Calvin E. Meier
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.
B. Tisserat and S.F. Vaughn
The growth (fresh weight), morphogenesis (number of needles and roots and shoot length) and monoterpene (α- and β-pinene) levels were determined in Pinus taeda L. (loblolly pine) seedlings exposed to 350, 1,500, 3,000, 10,000, or 30,000 μmol·mol-1 CO2 for 30 days under greenhouse conditions. Seedlings exposed to ultra-high levels (i.e., ≥3000 μmol·mol-1 CO2) had significantly higher (P = 0.05) fresh weight, needle number, root number, and shoot lengths compared to seedlings grown under ambient air (350 μmol·mol-1 CO2). Seedling fresh weights, number of roots, shoot length, and number of needles from pine seedlings supplemented with 10,000 μmol·mol-1 CO2 increased 341%, 200%, 74%, and 75 %, respectively, when compared to seedlings grown without any CO2 enrichment. In addition, α- and β-pinene levels in seedlings increased under ultra-high CO2 levels. The dominant monoterpene, α-pinene, increased 57% in seedlings grown under 10,000 μmol·mol-1 CO2 compared to levels obtained under 350 μmol·mol-1 CO2.
D.B. Rowe, F.A. Blazich, D.M. Pharr and F.C. Wise
Containerized, 2.5-year-old, hedged stock plants of four, full-sib families of loblolly pine (Pinus taeda L.) were fertilized daily with a complete nutrient solution containing 10, 25, 40, 55, or 70 ppm N, which resulted in a range of stock plant soluble carbohydrate (SCHO) and tissue N levels. SCHOs included myo-inositol, glucose, fructose, sucrose, and raffinose. Nitrogen concentrations and SCHO: N ratios ranged from 1.23% to 2.24% and 16:1 to 29:1, respectively. Softwood cuttings were taken in May and July 1995 and placed under intermittent mist. May cuttings rooted at significantly greater percentages than July cuttings (60% vs. 34%). Averaged over all N treatments, the best rooting family (56%) contained the highest tissue concentration of SCHOs (465 mg·g–1 dry weight) and had the highest SCHO: N ratio (26:1), whereas, the poorest rooting family (39%), exhibited the lowest level of SCHOs (357 mg·g–1 dry weight) and the lowest SCHO: N ratio (21:1). Rooting exhibited a quadratic response in regards to N fertilization levels and tissue SCHO concentrations. For both rooting trials, maximum rooting (83%) was noted for May cuttings taken from stock plants of one family fertilized with 40 ppm N, which corresponded to a tissue N concentration of 1.95% and a SCHO: N ratio of 22:1.
D.B. Rowe, F.A. Blazich, F.C. Wise and S.L. Warren
Containerized, 1.5-year-old, hedged stock plants of four full-sib families of loblolly pine (Pinus taeda L.) were fertilized daily with a complete nutrient solution containing 9 ppm P, 38 ppm K, and either 0, 5, 10, 20, or 40 ppm N. Softwood cuttings were removed in May and July 1994, and placed under intermittent mist at two locations: Raleigh and Summerville. Overall rooting was significantly greater at Summerville (49%) than in Raleigh (37%). Cuttings taken in May rooted at significantly greater percentages than the July cuttings (57% vs. 29%). Overall rooting (56%) and root area (12 cm2) were greatest at 40 ppm N, whereas root number (two), root dry weight (66 mg), and total root length (108 cm) were maximized at 20 ppm N. Although family was not significant, a family × nitrogen interaction occurred. For both rooting trials, maximum rooting (83%) was noted for May cuttings rooted in Summerville, which were taken from stock plants of one family fertilized with 20 ppm N.
Anthony V. LeBude, Barry Goldfarb, Frank A. Blazich, John Frampton and Farrell C. Wise
Two experiments were conducted during which juvenile hardwood or softwood stem cuttings of loblolly pine (Pinus taeda L.) were rooted under six mist regimes in a polyethylene-covered greenhouse to investigate the effect of mist level on vapor pressure deficit (VPD) and cutting water potential (Ψcut), and to determine the relationships between these variables and rooting percentage. In addition, net photosynthesis at ambient conditions (Aambient) and stomatal conductance (gs) were measured in stem cuttings during adventitious root formation to determine their relationship to rooting percentage. Hardwood stem cuttings rooted ≥80% when mean daily VPD between 1000 and 1800 hr ranged from 0.60 to 0.85 kPa. Although rooting percentage was related to Ψcut, and Aambient was related to Ψcut, rooting percentage of softwood stem cuttings was not related to Aambient of stem cuttings. Using VPD as a control mechanism for mist application during adventitious rooting of stem cuttings of loblolly pine might increase rooting percentages across a variety of rooting environments.
Farrell C. Wise, Laura L. Greenwood and D. Bradley Rowe
Clonal propagation of recalcitrant conifers like loblolly pine depends on producing juvenile cuttings on hedges sheared several times annually. Although dormant cuttings root well, it will be economically important to also root softwood shoots produced between shearings. Several variables were therefore evaluated in a factorial experiment to enhance rooting and handling of summer cuttings. Rooting percentages were equivalent for 3 media after a 5-week hardening period (56% overall), but open flats of 1 perlite:1 vermiculite induced larger root systems at the end of rooting and hardening phases. Extending the rooting period from 10 to 14 weeks increased rooting from about 45% to 58% by the end of hardening. Primary root length per cutting increased 12-63% during hardening, depending on medium. After transplanting, overwintering survival was 98%. Foam rooting wedges produced smallest root systems, and resulting plants were consistently shortest through the following growing season. Weekly applications of soluble fertilizer during the last 6 weeks of rooting did not improve rooting or subsequent growth