Claudia B. Cáceres  Svetka Kuljich  Ahmed Koubaa 《Wood material science & engineering》2018,13(1):28-35

Fifteen stems of jack pine (Pinus banksiana Lamb.) of 3 commercial thinned plots (control, moderate, and intensive thinning) and 15 stems of black spruce (Picea mariana (Mill.) B.S.P), both coming from the Abitibi-Témiscamingue region – Canada, were cross-cut into three 2.4?m length sections: bottom, middle, and top logs. Logs were processed with a chipper-canter at three cutting widths (12.7, 19.1, and 25.4?mm), producing chips and a three-faced cant. The middle section of the cant was used to evaluate surface quality across the grain on each face. Roughness and waviness parameters and depth of torn grain were recorded. Knot characteristics were assessed in the three cant faces. Poorer surface quality was found in the lower part compared to the upper part of the cant for both species. At larger cutting widths, jack pine logs coming from a natural stand showed lower surface quality compared to logs from thinned stands. Black spruce waviness increased with the cutting width and stem height. These results were attributed to the increase of forces and vibration when cutting at larger cutting widths, which was worsened by the presence of bigger, more numerous knots at the control plot and in the top logs. Black spruce had deeper torn grain compared to jack pine. Their differences in knot characteristics resulted in a maximum torn grain depth favored by the presence of more knots rather than by bigger knot size. Other knot characteristics, such as the position of the knots in the cant face, the insertion angle of the branch and the distribution of the knots around the log, should be studied to better understand the relationship between torn grain formation and knottiness.  相似文献   

  总被引：2，自引：0，他引：2  

Pinkard  E. A.  Beadle  C. L. 《New Forests》1998,15(2):107-126

An experiment was established in two high quality Eucalyptus nitens Deane and Maiden (Maiden) plantations in Tasmania. At the start of the experiment the trees were three years old and the plantations were on the point of canopy closure. Selected trees were pruned to remove 0, 50% or 70% of the lower green crown length, and each was surrounded by eight unpruned trees. The 50% treatment had no impact on height or diameter increment in the two years following treatment, but removal of 70% of the lower crown length resulted in significant decreases in both height and diameter increment. There were no changes in the height of 50%-pruned trees relative to the height of surrounding unpruned trees (relative height), and it was concluded that dominance would not be affected by this treatment. The relative height of 70%-pruned trees was less at one site, and this treatment may result in loss of dominance. Stem taper was generally unaffected by either pruning treatment. Changes in stem form were restricted to trees in the 70% pruning treatment and were only transient. It was concluded that removal of 50% of the lower green crown length is an appropriate level of pruning for the species provided that growth rates are rapid and pruning is timed to coincide with canopy closure. Since dominance was unaffected by this level of pruning, thinning at the time of pruning is unnecessary. It may be possible to minimise the impact on growth of higher levels of pruning by thinning at the time of pruning.  相似文献   

  总被引：1，自引：0，他引：1  

Rubeena  P. W. J. Taylor    P. K. Ades    R. Ford 《Plant Breeding》2006,125(5):506-512

Quantitative trait locus (QTL) analysis of ascochyta blight resistance in lentil was conducted using genomic maps developed from two F₂ populations, viz. ILL5588/ILL7537 and ILL7537/ILL6002. Five QTLs for ascochyta blight resistance were identified by composite interval mapping (CIM) across four linkage groups (LG) in population ILL5588/ILL7537. Three QTLs were identified by CIM in population ILL7537/ILL6002 (two in close proximity on LGI and one on LGII). Two of these coincided with regions identified using multiple interval mapping (MIM) and were shown to be conditioned by dominant and partial dominant gene action. Together, they accounted for approximately 50% of the phenotypic variance of disease severity. Comparison between the two populations revealed a potentially common QTL and several common regions that contained markers significantly associated with resistance. This study demonstrated the transferability of QTLs among populations and identified markers closely linked to the major QTL that may be useful for future marker‐assisted selection for disease resistance.  相似文献   

    

Buan Payandeh  Yonghe Wang 《New Forests》1995,9(2):147-155

A site index model based on the Weibull cumulative distribution function was fitted to three stem analysis data sets of black spruce (Picea mariana (Mill) BSP), white spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx.). The resulting equations were compared with those based on the modified Richards' (1959) biological growth function (Ek 1971; Payandeh 1977, 1978). The Weibull-type model performed as well as or better than the biological growth function for white spruce and aspen, respectively, but it performed less accurately in the case of black spruce. The Weibull-type model appears to behave better, i.e., it produces more realistic height growth patterns, than the Richards function upon extrapolation particularly at young ages.  相似文献   

    

《Plant Production Science》2013,16(2):186-191

Abstract

Anatomical observations were conducted to clarify some characteristics of the crown root primordia (CRP) formation in wheat stems. Unelongated portions of main stems were sampled from the plant at 3.2 and 7.2 plant age in leaf number, which were adopted as indexes because of the similarity to rice plants. Then, serial cross sections were made to investigate the position of CRP in the unelongated stem taking into consideration the running of vascular bundles in the stem. CRP were formed just outside tissues of the peripheral cylinder of longitudinal vascular bundles. The positions of CRP were not successive along the stem axis. They showed no definite relation to the running of vascular bundles. Diameters of CRP at the upper portion of the stems were larger than those at the lower portion. The positions of CRP along the stem axis were not distinguishable into nodal and internodal position. CRP and emerged CRs were not classified by the well-known ‘nodal root’ or ‘shoot unit root’, or the ‘unit’, which have been applied recently to rice plants. Further studies are necessary to clarify the factors controlling CRP formation anatomically and quantitatively.  相似文献   

    

Hans Pretzsch  Michael Heym  Samuel Pinna  Robert Schneider 《Scandinavian Journal of Forest Research》2014,29(3):222-233

Silviculture heading for structural heterogeneity creates many single trees standing at stand margins, inner edges or in remnant tree groups. As they played just a minor role in the age class forest, the growth behaviour of strongly released trees is rather unexplored. Here we show how retention cutting, presently spreading in the boreal of Québec province, affects stem and coarse root growth of remained single black spruce [Picea mariana (Mill.) Britton]. Increment cores from roots and stems of 125 trees show that retention cutting triggers coarse root growth of the remaining trees. Compared with reference trees retention trees accelerate root in relation to stem growth. Mean and variability of the root–stem allometry significantly rise after retention cutting. The found acceleration of root in relation to stem growth means mechanical stabilisation of the retention trees and corroborates the retention cutting method. Evaluation of silvicultural treatments can be incomplete and misleading as long as they are just based on aboveground reactions and neglect root growth.  相似文献   

  总被引：3，自引：0，他引：3  

H. S. Bariana  R. A. McIntosh 《Euphytica》1994,76(1-2):53-61

Summary The expression of rust resistances conferred by closely linked genes derived from VPM1 varied with environmental conditions and with genetic backgrounds. Under low light and low temperature conditions seedlings carrying Yr17 showed susceptible responses. Stem rust and leaf rust resistance genes Sr38 and Lr37 tended to confer more resistance at 17±2° C than at normal temperatures above > 20° C. These studies supported the hypothesis that Yr17, Lr37 and Sr38 were derived from Aegilops ventricosa, whereas Pm4b was probably derived from T. persicum. Studies on certain addition lines and parental stocks indicated that wheat cytoplasm may enhance the expression of Sr38.  相似文献   

    

R. J. Chynoweth  D. J. Moot 《Grass and Forage Science》2017,72(2):271-280

First‐year crops of diploid perennial ryegrass (cvs. Meridian, Bronsyn and Grasslands Impact) were sown on 1 April and 14 May 2008. Applications of trinexapac ethyl (TE) plant growth regulator at 0, 200 and 400 g a.i. ha^?1 were used to shorten stems to examine the impact of seed growth. Seed filling followed a consistent sigmoidal growth pattern with a lag phase of 127°C days, and linear duration of 390°C days. Time to 95% of final seed weight was 517°C days. Seed yield increases from TE were from higher numbers of first‐grade seeds m^?2, achieved by a higher rate of seed filling during the linear phase of 0·115 mg per °C day per spike. For all cultivars, the maximum stem dry weight occurred at 310–400°C days post‐anthesis, which suggest the stem was a strong sink. As seeds developed, their demand for assimilate increased and they drew more from the stem. At harvest, stem weights from TE treatments were 25% heavier than at anthesis, while untreated ‘Bronsyn’ and ‘Grasslands Impact’ stems were similar to those at anthesis. Thus, stems treated with TE contributed assimilates to increase seed yield but were still a net sink with assimilates in the stem at harvest. Trinexapac ethyl rate induced an inverse relationship between seed yield and stem height. This showed that competition for assimilate between stems and growing seeds limited the seed yield. Management or genetic factors that reduce stem height are likely to increase seed yields of perennial ryegrass.  相似文献   

    

H.D. Bertero  R.A. Ruiz 《Field Crops Research》2010

The proportion of growth allocated to reproductive organs can be an important determinant of yield variation between cultivars and environments. The main aim of this paper was to evaluate the adequacy of a model assuming constancy in partitioning coefficients (PC, the slope of organ weight to total weight relationship) within periods whose limits are associated with phenological phases to describe variation in reproductive growth (including seeds when present) in the Andean seed crop quinoa. A second objective was to analyze the dynamics of panicle and stem growth to advance our understanding of factors determining yield in this species. To do this, we used data from two experiments conducted in 2 years under field conditions in the Argentinean pampas, using four cultivars belonging to the Sea Level Type and adapted to temperate environments, under three densities. Reproductive partitioning followed a bi-phasic pattern; panicle biomass increased gradually until reaching a total biomass value, and then there was an increase in the slope of panicle vs. total aerial biomass relationship. Partitioning coefficients for the initial stage varied between some cultivars and densities in the first year, but not in the second. No significant differences were detected when PCs for the second stage were considered. The start of panicle growth was associated with thermal time to first anthesis (R² = 0.62) while thermal time to change in partitioning from low to high PC and that to end of flowering were strongly related (R² = 0.93). Combining data across cultivars, years and densities gave a PC of 0.15 for the initial stage and 0.90 for the second stage. Using these relationships and parameters dynamics of panicle biomass accumulation was predicted satisfactorily in an independent data set for a different environment, confirming the usefulness of a single model approach to describe partitioning across cvs. and environments in this crop. Besides, crop yield estimations improved when compared to those obtained by a seed number estimation model, predictions were only 7.25% lower than observed values compared to −24.5% using a seed number approach. There is a trade-off between final partitioning to reproductive structures (higher in short-cycle cvs.) and total crop biomass, one of the factors contributing to this trade-off being a negative association between the panicle–stem relationship at harvest and duration in thermal time units of stem growth; so, selection for high partitioning rate should be targeted at long duration cvs. within this germplasm.  相似文献   

Commercial Cell-based Therapies for Musculoskeletal Injuries in Horses     

Santiago D. Gutierrez-Nibeyro DVM  MS 《Veterinary Clinics of North America: Equine Practice》2011,27(2):363-371

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