Stomatal characteristics of Eucalyptus grandis clonal hybrids in response to water stress

This study describes the stomatal response occurring during water stress and subsequent recovery of three Eucalyptus grandis clonal hybrids. The aim was to investigate the degree to which stomatal conductance (g _s) and stomatal density differ between the clonal hybrids across seasons and in response to water stress. Plants from one E. grandis × E. camaldulensis (GC) and two E. grandis × E. urophylla (GU1 and GU2) clones were grown for 18 months in 80 l planting bags. Plants were subjected to three watering treatments: control (100% field capacity), chronic water stress (maintained at 15% of field capacity) and acute water stress (cyclic water stress, where water was withheld until leaf wilting point, and a subsequent period of recovery followed). Stomatal conductance was measured after 6, 12 and 18 months growth. At 12 months of age, the recovery of g _s 1, 2 and 7 d after rewatering (following acute water stress) was further investigated. The GC hybrid showed consistently higher g _s than the GU clones at each measurement period. Stomatal conductance was 24–66% higher during winter (after 12 months growth) than during summer. The recovery of stomatal conductance from acute water stress was more rapid in the GC clone than the GU clones. Chronic water stress was shown to decrease g _s in GU clones by up to 70%, but not in the GC clone. Water stress did not affect stomatal density or size. Remarkably, stomata were absent from the adaxial leaf surface of clone GU1 leaves, but not from the leaves of the other E. urophylla hybrid cross (GU2). Total biomass of the GC clone was significantly greater at 9 months growth, but after 18 months growth the GU1 clone had attained greater biomass accumulation (although not significantly). Measurement of g _s, transpiration, stomatal density and total biomass in the GU1 clone indicated stomatal sensitivity to water stress, a favourable trait during periods of drought. The differing growth strategies of the GU and GC clones could be partially explained by their differences in stomatal sensitivity in response to water stress.     

Screening for resistant clones of Casuarina equisetifolia to bacterial wilt and the analysis of AFLP markers in resistant clones

Bacteria wilt (BW) of Casuarina equisetifolia L. Johnson, caused by Ralstonia solanacearum (E. F. Smith) Yabuuchi, is one of the most important diseases of C. equisetifolia L. Johnson, the main coastal protective forest tree in southeast China. The resistance of 33 C. equisetifolia L. Johnson clones to BW was determined by means of hydroponic and pot inoculation methods with the suspension of R  solanacearum (E. F. Smith) Yabuuchi as inocula in the two‐step procedure. The results showed that clones FJ11 and FJ13 were highly resistant to BW with the lowest disease incidences of 10.8 and 15.8%, respectively, whereas clones FJ9 and GD15 were the most susceptible ones with the highest disease incidences of 100.0%. The analysis of AFLP markers was performed on clones FJ11, FJ13, FJ9 and GD15, and the results indicated that three DNA fragments E‐AAA/M‐CCG, E‐AAG/M‐CGC and E‐AGG/M‐CAA were found to be linked to the BW resistance. BLAST searches revealed that the first two fragments (GenBank accession numbers: KC111411 and KC135871) had no identities to any sequences, and the third one showed a high similarity to some sequences which code for heat shock protein. Taken together, the two resistant clones screened in our research were undoubtedly the valuable resistant resources of C. equisetifolia L. Johnson, and the three AFLP markers could be used in marker‐assisted selection of C. equisetifolia L. Johnson in the future.     

Dissimilar stem and leaf hydraulic traits suggest varying drought tolerance among co-occurring Eucalyptus grandis × E. urophylla clones

In South Africa, there is currently a phenomenon where a Eucalyptus grandis × E. urophylla clone is dying on a large scale, whereas co-occurring clones in the same plantation area remain healthy. No primary biotic pathogen has been isolated from these dying trees. However, the plantation region has endured severe drought conditions. We hypothesised that the specific E. grandis × E. urophylla clone dieback is due in part to the affected trees having an elevated drought vulnerability. We tested this hypothesis retrospectively by examining how the dying (branch dieback started) as compared with two healthy and co-occurring E. grandis × E. urophylla clones vary in branch xylem anatomy (water transport) and leaf stable carbon isotopes (gas exchange) across two levels of mean annual precipitation in the planted landscape. There was significant intra-hybrid variation in the range of studied hydraulic traits. It appeared that the dying clone is maladapted to drier field conditions relative to the two healthy growing clones. Individuals of the drought-susceptible clone had increased hydraulic conductivity, having both wider vessel lumens and larger lumen fractions, and also did not regulate leaf-level transpiration in the drier landscape as efficiently as the two unaffected clones (lower δ¹³C ratios). In turn, one of the healthy growing clones had a completely different hydraulic strategy, having higher wood density, lower lumen fractions, and higher δ¹³C ratios that are widely considered as hydraulically resilient during water stress. The other clone appeared to also gain drought tolerance via higher leaf-level water-use efficiency, although drought tolerance was less clear regarding xylem anatomy. We highlight how variation in relative drought vulnerability can be highly significant even between clones within a single hybrid group. Knowledge of this variation in plant hydraulics between commercially planted and closely related Eucalyptus trees would complement clone deployment programmes in a target landscape.     

Biomass production and potential water stress increase with planting density in four highly productive clonal Eucalyptus genotypes§

The choice of planting density and tree genotype are basic decisions when establishing a forest stand. Understanding the interaction between planting density and genotype, and their relationship with biomass production and potential water stress, is crucial as forest managers are faced with a changing climate. However, few studies have investigated this relationship, especially in areas with highly productive forests. This study aimed to determine the interaction between biomass production and leaf water potential, as a surrogate of potential water stress, in different clonal Eucalyptus genotypes across a range of planting densities. Four clones (two clones of E. urophylla × E. grandis, one clone of E. urophylla, and one clone of E. grandis × E. camaldulensis) and four planting densities (ranging from 591 to 2 949 trees ha^?1) were evaluated in an experimental stand in south-eastern Brazil. Biomass production was estimated 2.5 years after planting and predawn (ψ_pd) and midday (ψ_md) leaf water potential were measured 2 and 2.5 years after planting, in February (wet season) and August (dry season) in 2014. For all clones, total stand stemwood biomass production increased and leaf water potential decreased with planting density, and their interaction was significant. Thus, wood biomass at tighter spacings was higher but exhibited lower leaf water potentials, resulting in a trade-off between productivity and potential water stress. These are preliminary findings and still need to be supported by more experimental evidence and repetitions. However, in light of the increased frequency of extreme climate events, silvicultural practices that are tailored to the potential productivity of each region and that result in low potential water stress should be considered.     

Early growth results of three Eucalyptus grandis × Eucalyptus nitens hybrid clonal trials and their response to snow events

Eucalyptus grandis × Eucalyptus nitens (G×N) hybrid clones are selected to combine complimentary characteristics of E. nitens and E. grandis. G×N hybrid clones also have the potential to increase growth rates and provide adaptability to a changing climate. A series of three trials planted across a range of high-productivity, mid-altitude sites in the KwaZulu-Natal midlands was established to test the suitability of a suite of G×N hybrid clones. Seven commercially available G×N clones together with two widely planted pure species controls, Eucalyptus dunnii and Eucalyptus smithii, were chosen for this study. The trials were set out in random complete block designs with nine treatments and four replications set out in square plots of 25 trees. The trials were measured for diameter at breast height at 23 months and monitored for snow damage over two winter seasons. Snow was noted at the Baynesfield site and subsequent snow damage assessments were performed. Basal area per hectare was calculated for each plot as a function of diameter at breast height and survival. Significant differences were observed between G×N hybrid clones in both growth and snow tolerance. The top-performing clones significantly outperformed both pure species controls in terms of growth and snow tolerance. Early results indicate that G×N hybrids may be better suited to high-potential, mid-altitude sites exposed to light snow risk than the currently recommended pure species.     

Clonal stability in <Emphasis Type="Italic">Pinus radiata</Emphasis> across New Zealand and Australia. I. Growth and form traits

To investigate genotype by environment interaction (G×E) for clones of radiata pine (Pinus radiata), clonal stability was evaluated for growth and form traits from three trials in New Zealand and three trials in Australia. There were 215–245 clones in common between pairs of New Zealand trials, 17–26 clones in common among Australian trials, while 32–52 clones were in common between New Zealand and Australian sites. Clonal repeatability ( [^(H)]² ) \left( {\hat{H}^{2} } \right) and type-B genetic correlations were estimated. The general trend across the six trials for clonal repeatability was that [^(H)]² \hat{H}^{2} was greatest for height (HGT) followed by diameter at breast height (DBH), stem straightness (STR), and branch quality score (BRQ). Within New Zealand trials, there was little evidence of G×E for growth traits, but more for form traits. For DBH the average type-B genetic correlation within New Zealand was 0.82; and for HGT, the average type-B genetic correlation within New Zealand was 0.76. Within Australia, there was only one statistically significant type-B genetic correlation for DBH and this estimate was high indicating that clonal ranks were similar on these two trials. Additionally, within Australia and between regions type-B genetic correlations were generally high for form traits, at least for STR. One Australian trial (Trial 5) showed relatively high clonal stability with the three trials in New Zealand indicating that the ranks of these clones were relatively stable in both regions. From a clonal testing standpoint, these results suggest that stable clones can be identified that perform well in both New Zealand and Australia. Improvements in both growth and form traits can be expected when radiata pine clones are transferred between Australia and New Zealand within regions similar to those sampled in this trial series.     

Water relations of Eucalyptus nitens × Eucalyptus grandis: is there interclonal variation in response to experimentally imposed water stress?

This study tested the hypothesis that water stress increases the hydraulic efficiency of Eucalyptus nitens × E. grandis saplings as a result of osmotic and elastic adjustments. Eucalyptus nitens × E. grandis clones (NH00, NH58, NH69 and NH70) were potted in coarse river sand supplemented with a slow-release fertiliser, drip-irrigated four times daily and exposed to full sunlight for eight months. Thereafter, irrigation was withheld twice for seven consecutive days from half of the saplings of each clone, with a seven-day recovery period (regular irrigation) in-between. Relative soil moisture content did not correlate with stomatal conductance (g_s) at pre-dawn and at midday. Leaves of plants subjected to the water-stress treatment wilted in 7 d, and the reduction in g_s was significant at midday with no significant differences between clones. Stomatal conductance and all traits derived from pressure-volume graphs (e.g. osmotic potential at full turgor) were constant in the control treatment. There were no clear patterns in osmotic and elastic adjustments in both treatments. Root hydraulic conductance was constant between treatments and clones. However, water stress reduced shoot hydraulic conductance and stem hydraulic conductivity with significant interclonal effects. Plant biomass, leaf area and leaf weight ratio were significantly lower in the water-stressed plants, but there were no differences between the clones. In conclusion, the water-stress treatment did not introduce significant differences in stomatal conductance and tissue-water relations of Eucalyptus nitens × E. grandis clones. Interclonal variation in water-stress response was found in shoot hydraulic traits, and clone NH58 may be more suitable for planting across sites prone to moderate water stress.     

Effect of environment on the response of Eucalyptus clones to inoculation with Cryphonectria cubensis

The ascomycete Cryphonectria cubensis causes severe losses in Eucalyptus plantations in South Africa and selection programmes for disease tolerance are necessary. The aim of this study was to use two C. cubensis inoculation trials, planted at different locations to assess the disease susceptibility of the clones and the effect of the environment on disease development. These two trials consisted each of 21 Eucalyptus clones (E. grandis, E. grandis × camaldulensis and E. grandis × urophylla). All trees were inoculated with a single virulent strain of C. cubensis and lesion widths measured 6 and 12 months after inoculation. Clones differed significantly in their tolerance to C. cubensis. Further, disease severity differed depending on the geographical location of the trial. A significant clone × locality (genotype × environment) interaction was observed. Therefore, screening for disease resistance should take place only in areas where clones will be commercially grown.     

Molecular Discrimination of Eucalypt Clones Using the ISSR Marker System

Clonal forestry captures genetic gain generated by skillful selection and is now well recognized as a method for mass production of desired trees to obtain increased economic benefits. In Eucalyptus, clonal plantations have enhanced the productivity twofold, compared to plantations of unimproved seed origin. The present investigation was carried out to assess the genetic relationship of 41 eucalypt clones using the intersimple sequence repeat (ISSR) marker system. The ISSR-derived dendrogram and principal coordinate analysis (PCA) clustered 39 clones into two groups of E. camaldulensis and E. tereticornis in agreement with their taxonomic classification. Further, a total of three clone specific diagnostic markers and five unique profiles were identified using five ISSR primers. The eucalypt clones analyzed in the present investigations are derived from the breeding populations of both the species and are presently being used for large-scale plantation and hybridization studies. The molecular marker based clonal discrimination can be used to avoid duplication of clones and quality control of planting stock.

[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Sustainable Forestry for the following free supplemental resource(s): ISSR Profiles of Eucalyptus Clones]     

Botryosphaeriaceae associated with Eucalyptus canker diseases in Colombia

The identities of Botryosphaeriaceae causing cankers on Eucalyptus in Colombia were investigated using morphological and DNA sequence comparisons. The pathogenicity of the species was also assessed on 42 Eucalyptus grandis clones planted at four different sites. Two species of the Botryosphaeriaceae were found to occur on E. grandis in Colombia. Neofusicoccum ribis was the more common species, and also the most pathogenic. Botryosphaeria dothidea was found only in one zone of Colombia, and was also less pathogenic than N. ribis. These two species could be distinguished easily based on DNA sequences of the ITS1/ITS2 rDNA region and EF1‐α, in addition to conidial sizes. Significant differences in resistance of clones to these pathogens were also evident from the various trials.     

不同桉树无性系造林对比试验

通过7个桉树无性系在3个不同立地条件的造林对比试验研究,结果表明:7个桉树无性系在本区表现良好,不同桉树无性系间在胸径、树高、蓄积量生长方面均存在显著差异;适宜本区发展的桉树无性系首选为尾赤桉201-2,其次为尾巨桉3229和尾圆桉184-1;海拔在300 m以下的适宜种尾赤桉201-2、尾圆桉184-1、尾巨桉3229等,海拔在300~460 m的适合种尾赤桉201-2和巨桉。     

Development of Eucalyptus clones for a summer rainfall environment with periodic severe frosts

Eucalyptus grandis, E. grandis hybrid, and E. saligna hybrid trees, developed through as many as four generations of selection in southern Florida, were naturally exposed to exceptionally low winter temperatures. In a genetic base population and related field studies, 100 phenotypically superior cloning candidates were selected after an 8-h freeze with a low of –11 °C. Following propagation as rooted cuttings, 55 clones (typically 11–42 ramets per clone) were outplanted in a single-tree plot design and evaluated for 3.8 years which included two additional severe freezes. Significant clonal variation was observed in frost resilience, vigor, and quality. After composite evaluation for frost resilience, size, and form, only three clones were considered suitable for operational planting. Selection of further clones for outplanting requires major commitments to locate candidates and to test them. Field testing for frost resilience requires considerable investment, much beyond the requirements for developing fast-growing clones alone. Clones identified by testing will not be resistant to freezing conditions but will be resilient and greatly reduce the risks now associated with plantation culture in southern Florida.(requests for offprints)     

桉树无性系主要性状差异分析与评价

对12个桉树无性系进行了生长、分枝、通直度、树皮厚度及抗风性进行研究,表明无性系间的性状指标均达到极显著或显著差异,E11和E7号无性系的单株材积分列第1、2位并显著高于其它10个参试无性系;用聚类分析方法将12个参试无性系分成6类,可根据实际情况需要进行选择.以产量、形质指标为选择目标,可选择E7、E11、E2、E8、E3号5个无性系;以抗风性强作为首选指标,则可选择抗风性强、产量中等至较好、形质中等的E12、E5、E1、E10、E6号无性系.     

昆明和玉溪直干桉、蓝桉无性系的生长测定

1994年在昆明、玉溪两试验点营造的直干桉和蓝桉无性系测定林,根据1999年的生长数据分析后看出两地的测定林都是直干桉比蓝桉生长好,玉溪两个树种的生长都比昆明好.在直干桉无性系中两试验点的生长性状差异均达显著或极显著水平,而蓝桉无性系在两试验点都不显著.在昆明试验点测定林保存完好的无性系中,直干桉有5个、蓝桉有3个无性系的材积超过对照(实生木),其中超过30%有6个(直干桉4个,蓝桉2个).玉溪试验点参试的7个直干桉无性系有6个的材积超过对照,其中材积显著大于对照的有两个;蓝桉3个无性系中没有1个超过对照.根据云南省目前的经济技术水平,走选优、建园的遗传改良途径更为积极稳妥.     

Assessment of salt tolerance in eucalypts using chlorophyll fluorescence attributes

Chlorophyll fluorescence attributes were investigated for their potential as rapid, non-invasive indices of salt stress in eucalypts. After representative clones of E. camaldulensis and E. urophylla×grandis were subjected to salinity treatments, dark-adapted and quenching attributes did not show consistent responses to salinity stress. The light-adapted attribute F _ds, when measured in a controlled environment, did decline, often before physical symptoms of stress were visible. This value is required for the derivation of the effective quantum yield, and each measurement can be acquired and automatically recorded in a few seconds, permitting the rapid survey of large groups in a propagation facility. Monitoring of plants, that were treated with increasing concentrations of NaCl over time, permitted overall ranking of the responses of groups of clones and seedlings. Usually the data were heteroscedastic, so non-parametric methods of statistical analysis were used, and P0.01 for ascribing significance to differences. Also, following the responses of individuals within clones and provenances showed the method should be useful for the early detection of particularly susceptible or resistant seedlings.     

Experimental testing of rust fungus‐mediated herbivory resistance in Betula pendula

Correlative evidence suggests that pathogenic leaf rust fungus, Melampsoridium betulinum, in late summer may negatively affect folivorous insects in the following summer. Correlative association does not necessarily, however, reveal causality. Alternatively, other interconnected plant characters may determine rust densities and herbivore performance. In this study, we used birch clones and rust fungus inoculations to manipulatively test the effects of birch rust and birch genotypes on the growth performance of folivorous moth larvae of Epirrita autumnata (Lep. Geometridae) in the subsequent year. The inoculation treatment increased rust densities (three‐ to 60‐fold) compared with natural infection levels. E. autumnata performance varied among birch clones and showed 4% lower growth performance on rust‐inoculated trees. However, the larval performance did not differ between rust‐treated shoots and untreated control shoots and the use of tree‐specific rust densities as a covariant in statistical analyses failed to reveal any negative association between rust fungus and larval performance. As the slight difference in larval growth performance also levelled until pupation, we propose that rust infection has biologically insignificant importance to the performance of E. autumnata.     

尾细桉等5种桉树无性系生物量和能量的比较研究

对广东廉江石岭林场尾细桉等5种7.5年生桉树无性系的生物量和能量进行了研究。结果表明:不同无性系各组分生物量的分布规律均以干的最大、叶的最小,枝、根、皮介于中间;5种桉树无性系各组分的生物量排序为:赤桉、尾细桉、巨尾桉为干根枝皮叶,雷林1号桉为干根皮枝叶,尾叶桉为干枝根皮叶。人工林生物量现存量的排列顺序为尾细桉(161.60 t.hm-2)巨尾桉(127.96 t.hm-2)尾叶桉(112.60 t.hm-2)赤桉(83.81 t.hm-2)雷林1号桉(71.36 t.hm-2)。各组分的灰分含量各不相同,以叶最高(4.08%~6.88%),干最低(0.17%~0.43%)。不同组分的干质量热值介于17.94~21.06 kJ.g-1间,去灰分热值介于18.57~22.12 kJ.g-1间,均以叶的值最高。植株体的平均干质量热值和去灰分热值分别为19.02~19.32、19.49~19.85 kJ.g-1,平均干质量热值的排序为雷林1号桉尾叶桉尾细桉赤桉巨尾桉,平均去灰分热值的排序为雷林1号桉赤桉尾叶桉尾细桉巨尾桉。5种桉树无性系林的能量现存量为1 360.73~3 067.47G J.hm-2,大小顺序为尾细桉巨尾桉尾叶桉赤桉雷林1号桉。综合生物量和能量现存量分析,尾细桉选作能源树种最为理想,巨尾桉和尾叶桉次之,赤桉与雷林1号桉最差。     

桉树无性系在湛江地区生长比较

对湛江地区引入的13个桉树无性系的2年生幼苗主要生长性状进行分析比较,结果表明：胸径、树高、单株材积、蓄积量及风折率等性状在不同桉树无性系间均存在极显著差异;适宜本地区发展的桉树无性系首选为广林9、DH184-1,其次是WC3,再次是DH201-2、D3、DH32—29、灵山优选27无性系;初选出的7个优良无性系2年生平均树高、胸径、单株材积、蓄积生长量、保存率、风折率分别为11．46m、8．20cm、0．033861m^3、80．46m^3／hm^3、96．1％、12．1％,达到速生丰产的要求。2年生U6无性系的组培苗无论生长量还是抗风能力均优于扦插苗。     

Response of ethylene and chlorophyll in two eucalyptus clones during drought

A study was conducted with seven-month-old plantlets, of the clone 2814 of Eucalyptus grandis × E. camaldulensis Dehnh. hybrid and of the clone 2798 of E. grandis × E. robusta Sm., subjected to sublethal water stress. During the imposed drought, leaf water potentials and transpiration rates decreased, while ethylene production and leaf chlorophyll concentration increased to a maximum during the onset of water stress, and then declined. Stomatal closure coincided with or preceded maximum ethylene production. A saturation type relationship between ethylene production and chlorophyll concentration was observed. Genotypic differences in the response to water stress occurred between clones with clone 2814 appearing to be a drought avoider and clone 2798 a drought tolerator.     

6年生11种桉树无性系生物量与炭化研究

对雷州半岛6年生11种桉树无性系的林分生长量、生物量、炭化量进行了研究。结果表明:11种桉树无性系林分蓄积量大小排序为:GL4>GL9>DH32-22>LH5>DH201-2>LH1>M1>EC34>柳桉1>UC184-1>SH7,林分蓄积量最大的GL4是最小的SH7的2.12倍。11种桉树无性系各组分生物量变化不一致,但都以树干的最大,叶片的最小。LH5和GL4的林分生物量最大,均高于180t·hm-2,SH7和UC184-1林分生物量较小,均低于130t·hm-2,其它几种较为平均,在140~170t·hm-2之间。11种桉树无性系炭化量受林分生物量和炭化率影响,林分生物量和炭化率越大,炭化量越大。LH5、DH201-2、LH1和GL4的炭化率较高,均大于20%,UC184-1和SH7的炭化率最低。11种桉树无性系中LH5林分生物量最大,炭化率最高,故炭化量最高;其次为GL4和LH1,其炭化量均高于60t·hm-2,EC34、GL9、柳桉1、M1和DH32-22均大于50 t·hm-2,UC184-1的炭化量低于40 t·hm-2为最低。综合生长量、生物量和炭化率分析,GL4、LH5、GL9和DH32-224个无性系为一类,可作为薪炭林品系发展;LH1、EC34、DH201-2和M14个无性系划分为一类,作为薪炭林发展潜力较低;柳桉1、UC184-1和SH73个无性系为一类,不适合作为薪炭林发展。