Evidence for the occurrence of induced resistance to pitch canker,caused by Gibberella circinata (anamorph Fusarium circinatum), in populations of Pinus radiata

Pitch canker, caused by Gibberella circinata, was discovered in California in 1986. Although initially quite damaging to Monterey pines (Pinus radiata), the severity of pitch canker has moderated in areas where the disease was first observed and some trees appear to have recovered completely. The absence of symptoms on trees that were once severely affected implies they have become more resistant to the disease. Experimental work has shown that P. radiata can manifest systemic induced resistance (SIR) in response to infection by the pitch canker pathogen and observations of disease remission may indicate that SIR is operative under natural conditions as well. As a test of this hypothesis, the susceptibility of trees in remission was assessed by inoculating them with G. circinata and recording the extent of lesion development. In addition, randomly selected trees in areas that differed in residence time of pitch canker were inoculated to determine if trees with a longer period of exposure to the pathogen were more resistant to the disease. The results of these tests showed that 89% of trees observed to be in remission sustained very limited lesion development, consistent with resistance to pitch canker. Furthermore, trees in areas where pitch canker was well established tended to be more resistant than trees in areas where the disease was of more recent occurrence. In sum, these findings support the view that SIR occurs in P. radiata and is contributing to a moderation of the impact of pitch canker under natural conditions.     

Variation in growth of Heterobasidion annosum among clones of Picea abies incubated for different periods of time

Thirty‐seven 4‐year‐old clones of Picea abies were inoculated with one isolate of the S intersterility group of Heterobasidion annosum in a greenhouse. The dehardened cuttings were organized in three different groups with four to six ramets in each group. All groups were inoculated on the same day shortly after shoot elongation. The groups were sampled for H. annosum growth after 34 (group 1), 83 (group 2) and 182 days (group 3), respectively. Measured parameters were cutting height and diameter, vigour index of the cuttings, infection incidence, mortality rate and fungal growth in the stem. The height of the cuttings was almost constant during the 6 months of incubation, whereas the diameter increased by about 10% during the same period. The proportion of living cuttings containing H. annosum decreased with time (99.5, 93 and 67% infection in groups 1, 2 and 3, respectively) and differed significantly among clones in group 3. Mortality rate increased with time (0.5, 22 and 37% mortality in groups 1, 2 and 3, respectively) and differed significantly among clones in groups 2 and 3; the same clones being most susceptible for both times. Mean fungal growth into the wood was significantly different among groups and among clones within each group. The ranking position for fungal growth was similar in the three groups. The results indicate that frequency of infection success, mortality rate and fungal growth are clone‐dependent factors. Broad sense heritability varied between 0.08 and 0.25 for fungal growth and lesion length at the three incubation periods. Infection success frequency was initially not different among clones but in the longer incubation periods there were significant differences among clones, indicating differences in resistance. Fungal growth in wood differed among separate host clones irrespectively of the length of inoculation period. The vigour of the cuttings seem to influence the length of fungal extension only in the initial stage of the infection.     

Variation in relative resistance to spread of Fomes annosus in four clones of Picea abies

The stems of 160 cuttings including 32 controls of four clones of Picea abies (L.) H. Karst., grown for two seasons in the nursery, were inoculated with Fomes annosus (Fr.) Cke. No differences in resistance to spread of the pathogen were observed after 5 weeks, but after 13 weeks the fungus had spread (P < 0.10) less in one of the clones.     

Individual resistance of Fraxinus angustifolia clones to ash dieback

The presumed resistance of individual ash trees to ash dieback caused by invasive pathogen Hymenoscyphus fraxineus is an important issue for the maintenance of ash in European forests. All known studies regarding the resistance of ash trees to ash dieback were conducted in plantations and stands of F. excelsior; however, no such data exist for F. angustifolia. Crown damage assessments were performed over four consecutive years between 2009 and 2012 at a F. angustifolia clonal plantation in Hra??ica, Slovenia. Inoculation of H. fraxineus into the branches of the most and least damaged clones of F. angustifolia and leaf phenology assessments was performed to verify the presence of defence mechanisms that limit fungal growth or promote disease escape. Additionally, root collars of selected clones were inspected for fungal infections. The crown damage assessments showed considerable differences among F. angustifolia clones, indicating genetic variability in susceptibility to ash dieback. Crown dieback progressed significantly over the 4‐year time period; the mean crown damage of individual clones in 2012 varied between 16.7% and 83.8%. Significant differences among F. angustifolia clones were found in the inoculation trials and leaf phenology assessments. However, defence mechanisms such as early leaf flushing, early leaf shedding and the ability to inhibit pathogen growth in host tissues were not confirmed. High frequency of Armillaria spp. and H. fraxineus root collar infection demonstrated the need for whole tree inspection to determine causal agent of damages on individual ash trees. Armillaria spp. may be highly associated with ash decline epidemiology.     

四川阿坝辐射松引种长期森林健康风险初步评估

Pinus radiata was introduced to the summer rainfall environments of Sichuan Province, China in the 1990s as a part of an afforestation pmgram for soil and water conservation in the arid and semi-arid river valley area of Aba Prefecture. Within this region a total area of 26 000 ha have been identified through climate matching as suitable and a further 63 000 ha potentially suitable for environmental plantings of P. radiata. The plantations are being established in widely separated small patches on steep and degraded slopes along the dry river valley The newly introduced P. radiata are exposed to two kinds of forest health risks： they may be attacked by （a） indigenous pathogens and pests against which they may not possess any resistance or （b） by inadvertently introduced foreign pests or pathogens. This paper presents a survey of the potential damaging pests and a preliminary assessment of forest health risks facing the P. radiata plantations over a much longer timeframe than the initial phase of introduction and early plantation establishment. An empirical appmach was adopted to evaluate forest health risks by a combination of literature review, examination of historical records of pest and disease outbreaks in the surrounding conifemus forests, field surveys and inspections, specimen collection and identification, and most importantly, expert analysis of the likelihood of attack by specific pests and pathogens and the subsequent impact of such attacks. The assessment identified some specific forest health risks to the long-term success of P. radiata introduction in this area. These risks are closely associated with the indigenous pests and pathogens of the two native pine species, P. tabulaeformis and P. armondii since these pests and pathogens are considered more likely to establish on P. radiata over time. Exotic pests and pathogens are of a quarantine concern at present. Based on the results of assessment, recommendations are pmvided to improve forest vigour and to reduce the forest health risks pos     

Differential responses of Central American and Mexican pine species and Pinus radiata to infection by the pitch canker fungus

Seedlings from a wide array of 23 species, varieties,and geographic races were screened for resistance topitch canker using artificial inoculation in agreenhouse. Seed to represent these taxa weregenerally collected in natural stands. In addition,seedlings from 79 families of P. radiata fromcommercial populations from Chile and New Zealand werescreened in a separate experiment. There was littlevariation in resistance among the commercial P.radiata families, with over 98% mortality. Similarresults were obtained with native P. radiatapopulations. All close relatives of P. radiata(sub-section Patula) were very susceptible. However,a number of closed-cone pine species (specifically,from sub-section Oocarpa) were generally veryresistant, with survival approaching 100%. Inaddition, in P. oocarpa, P. jaliscana, and P. tecunumanii from low elevation provenances anextremely high frequency of trees suffered no apparentdamage from the pathogen (92%, 85% and 80%,respectively).     

Screening wild cherry (Prunus avium) for resistance to bacterial canker by laboratory and field tests

Currently, bacterial canker caused by Pseudomonas syringae is a major cause of dieback and tree death in wild cherry (Prunus avium) plantations. The evaluation of breeding collections is needed to produce less susceptible clones or cultivars. Resistance tests were performed using excised shoots (1 and 2 years old) from 79 clones in the laboratory. A subset of 10 clones was also tested in the field. The clones were inoculated with four to seven isolates of a set of 15 isolates of P. s. pv. morsprunorum, P. s. pv. syringae, P. s. pv. persicae, P. syringae pv. avii and P. fluorescens. In the laboratory tests, older and larger shoots were more susceptible. In the field test, size and age of the shoots were not related to girdling by the bacterial canker. Two‐year‐old shoots were best for clonal discrimination. Correlations between 1 and 2‐year‐old shoots were significant but not high. The isolates varied a lot between experiments, but as the clone × isolate interactions were always low, breeding could thus be facilitated. The ranking of clones was conserved quite well between two laboratory tests, but not between two others. Good agreement was found for the best clones in the laboratory tests and in the field test. However, the two worst clones in the latter were among the best in one laboratory test. At least two independent tests in the laboratory are needed to evaluate resistance/susceptibility of clones. Broad sense heritability for resistance varied from 0.27 to 0.51. Although moderate, such heritability clearly encourages a breeding approach to reduce the problem of bacterial canker.     

Indole-3-butyric acid accelerates adventitious root formation and impedes shoot growth of Pinus elliottii var. elliottii?×?P. caribaea var. hondurensis cuttings

Many plantation tree species are cloned to achieve the growth, disease resistance and wood quality characteristics required for a successful economic venture. However, clonal propagation is limited by declines in adventitious root formation with increasing stock plant age. We examined the effects of immediate or delayed IBA application on adventitious root formation and subsequent root and shoot development of cuttings harvested from 8-year-old clonal hedge plants of Pinus elliottii var. elliottii × P. caribaea var. hondurensis. IBA applied at the time of setting accelerated root formation, elevating the percentage of cuttings with roots at 13 weeks post-setting from 45 to 78% and from 83 to 93% for a low- and a high-rooting clone, respectively. Final rooting percentages for the same treatments and clones (78 and 85%, and 88 and 100%, respectively, at 20 weeks post-setting) were not significantly affected by IBA application. IBA increased the root:shoot ratio of rooted cuttings by decreasing shoot weight compared with untreated cuttings, without affecting root weight, root length, root surface area or root volume. IBA was only effective when applied at the time of setting. A simple IBA treatment for cuttings from 8-year-old clonal hedges, by accelerating root production, has potential for reducing nursery costs and increasing the root system quality of containerised pine cuttings.     

Clonal selection for resistance to Dothistroma needle blight in Pinus radiata

Fifty-two clones in twenty-two full-sib families were represented in a field trial. All cuttings were taken from hedged ortets which were four years from seed, but had been cut back periodically to one metre high since age two. One-year-old seedlings, from a seed orchard, where most of the parents of the clones were represented, were used as controls. The trial was assessed for Dothistroma needle blight infection six years after planting. The mean infection level of all the cuttings was 21.1%, compared to 29.8% for the seedlings. This difference was attributed to the greater maturation age of the cuttings. It was calculated that if the best 10% of the clones were selected, infection could have been further reduced to 12%, a level where other disease control measures would be considered unnecessary.     

Pine weevil (Hylobius abietis) damage to cuttings and seedlings of Norway spruce

Damage caused by pine weevil (Hylobius abietus L.) to planted seedlings and cuttings of Norway spruce (Picea abies (L.) Karst.) was studied at five clearcut sites in south-eastern Sweden. The main objective was to compare the two types of stock in terms of attack frequency and mortality due to pine weevil feeding. Cuttings and seedlings with the same initial stem-base diameter (4 mm) were compared. Two sites were harvested and scarified shortly before planting, two were harvested shortly before planting, but were not scarified, and one was harvested 2 years before and scarified the autumn before planting. The total mortality 5 years after planting was highest, greater than 90%, at the new, non-scarified sites, and lowest, 23%, at the old, scarified site. More than 90% of the mortality was caused by pine weevil feeding. Attack frequency and pine weevil induced mortality were significantly higher among seedlings than among cuttings. Mortality due to pine weevil damage was 4–43% higher in seedlings than in cuttings after the fifth year. Of the cuttings and seedlings that were attacked in the first year, a significantly higher frequency of the seedlings were girdled. The higher resistance of cuttings to pine weevil damage may partly explain the more rapid growth of cuttings reported in other studies. However, the causes of their higher resistance need to be further investigated. The thicker bark and needles on the stem base of the cuttings could be important in this respect.     

Induction of phenylalanine ammonia lyase activity and control of Sphaeropsis sapinea infection in Pinus radiata by 5-chlorosalicylic acid

Phenylalanine ammonia lyase (PAL) activity increased rapidly in Pinus radiata seedlings after treatment with 2 mm 5-chlorosalicylic acid (5CSA) and peaked after 48 h at four-times the level of the control. Elevation of PAF is often associated with the induction of host resistance mechanisms. Thus, effects of 5CSA on subsequent infection of P. radiata by Sphaeropsis sapinea was investigated. Only one out of 16 seedlings treated with 2 mm 5CSA, 4 days before inoculation, developed deadtop compared to 14 of the controls. The 5CSA was directly inhibitory at this concentration and reduced growth rate of S. sapinea on agar by 27%. However, antifungal activity does not fully account for the observed disease control afforded by 5CSA since 0.5 mm and 0.25 mm 5CSA, which did not inhibit growth of S. sapinea, significantly reduced the incidence of deadtop. Furthermore, 1 mm 5CSA protected seedlings against fresh inoculation challenge for up to 32 days after application. Such durable resistance is unlikely to be attributable to the direct effects of the applied compound and may suggest the involvement of inducible host resistance mechanisms.     

The commercial use of conifer rooted cuttings in forestry: a world overview

Conifer reforestation programs have traditionally been carried out using natural seeding, direct seeding or, more recently, planting with nursery-grown stock. Only within the past decade have rooted cuttings found use in large scale commercial operations. To assess the current status of this technology questionnaires were developed and mailed to 50 individuals and organizations around the world. The questionnaires were designed to collect information on: (1) annual production by region and species, (2) objectives of rooted cutting programs, (3) production procedures, (4) field performance of cuttings as compared to seedlings, and other topics.According to the 36 responses received more than 65 million conifer rooted cuttings are being produced around the world annually, with this number growing rapidly. Fully half the production is in Japan where valuable sugi (Cryptomeria japonica D. Don) cultivars have been vegetatively propagated for at least five centuries. Another 10 million or more cuttings of radiata pine (Pinus radiata D. Don) are being grown in Australia and New Zealand annually. Canada, Scandinavia, and the British Isles together produce about 21 million Norway Spruce (Picea abies [L.] Karst), Sitka spruce (P. sitchensis [Bong.] Carr) black spruce (P. mariana [Mill.] B.S.P.) and other species annually. Programs of one million or less exist in France, West Germany, Belgium, Eastern Europe, the United States and the USSR.Aside from the Japanese program and some European and Scandinavian programs, where cloning valuable genotypes is the main aim of vegetative propagation, the primary use of rooted cutting technology is for bulk production of genetically improved half or full-sib families. Other uses include production of air pollution-resistant clones in eastern Europe, and production of species which have high commercial value but are difficult to propagate from seed.Propagation methods have changed little during the past 15 years. Most cuttings are produced from hedges, stock plants, nursery seedlings or field grown trees, and rooted under mist in glass or plastic covered houses. Rooting hormones are often, but not always, used. Roughly half are grown in containers and half bareroot, generally reflecting the preferred method of seedling production in a given region. Although relatively few detailed studies have been reported, field performance of rooted cuttings appears similar to that of seedlings provided donor plants are juvenile. Key research needs are juvenility maintenance, stock plant culture, root system improvement, mechanization, and field testing.     

Susceptibility to Heterobasidion parviporum in Picea abies clones grown in different environments

Thirty-five Norway spruce, Picea abies, clones from Sweden were tested for resistance to Heterobasidion parviporum. Rooted cuttings of the clones were planted in Italy and Greece and cultivated for two growing seasons before inoculation with H. parviporum. Extent of infection was determined 6 weeks later. The results were compared to those of earlier inoculations in Sweden. Plant growth traits were under strong genetic control in all locations with broad sense heritability estimates between 0.14 and 0.54. Lesion and fungal extension heritabilities were moderate, H² ranged from 0.09 to 0.20, and exhibited rather large genetic variation. There was significant genotypic correlation between Italy and Greece with respect to both lesions and fungal extension. No such correlations were found between Sweden and the two other countries. The lack of repeatability in testing susceptibility is unsatisfactory. It could be explained by C-effects associated with propagation of the host plants. Height growth correlated significantly and positively among all countries.     

The influence of alternative plant propagation and stand establishment techniques on survival and growth of eastern cottonwood (Populus deltoides Bartr.) clones

Four eastern cottonwood clones, including standard operational clone ST66 and three advanced clonal selections were produced and included in a test utilizing five different plant propagation methods. Despite relatively large first-year growth differences among clones, all clones demonstrated similar responses to the treatments and clone × cutting treatment interactions were generally non-significant. The effects of changing cutting lengths are consistent with previous studies which indicated the potential for increased plant survival and growth with increased cutting lengths. Differences in stored carbohydrate reserves alone do not appear to completely control first-year growth and development of cuttings. First-year growth of 51 cm long cuttings planted 30.5 cm deep was greater than the same cuttings planted 48 cm deep. Stem form of plants derived from whip-tip propagation did not differ from plants derived from standard, unrooted cuttings. This propagation method offers the potential of far greater production capacity from a cutting orchard and rapid bulk-up of new or limited clones. Stand uniformity assessments suggest that surviving trees of each individual cutting treatment exhibit similar levels of growth variation. Optimization of plantation establishment techniques has the potential to increase growth of young Populus plantations.     

Rooting Success of Cuttings from Young Picea abies in Transition to Flowering Competent Phase

Abstract

Abundant flowering occurred in a central Swedish trial with 10-yr-old Picea abies L. (Karst.) cuttings, taken on 4-yr-old seedlings. Large deviations in cone-set between clones were assumed to reflect different stages in transition from juvenile to flowering competent phase. Rooting success and first-yr growth performance (leader length, leader origin and plagiotropic growth) were studied on cuttings originating from the upper and lower parts of the crown in 15 clones with heavy cone-set and 15 clones without cones. Twigs from the lower part of the crown had a significantly higher rooting percentage. Cone-set did not have an effect on any of the variables analysed. The results suggest that flowering ability and rooting capacity are independent age-related processes, implying that selection for high rooting capacity in clonal forestry does not reduce flowering competence. The results will have a great impact on breeding of P. abies, since both early flowering and high rooting ability are important traits for reducing the turnover time of the breeding cycle.     

Methods of inoculation and evaluation of Erwinia psidii in eucalypt

The dieback and wilting caused by Erwinia psidii are emerging eucalypt diseases that have been observed since 2014 in the south and central‐south regions of Brazil. Field observations have shown variability in disease severity resistance among Eucalyptus spp. clones and species. It is hypothesized that this variability is due to genetic resistance. To confirm this hypothesis, inoculations in genetically distinct eucalypt plants are necessary. However, lack of an inoculation method and disease assessment makes difficult to select resistant genotypes for use in commercial plantations or genetic breeding programmes. Three inoculation methods were tested on eight clones of Eucalyptus spp. Among them, inoculum deposition with bacteria‐impregnated toothpick on the axillary buds was the simplest and most effective, capable to reproduce the disease symptoms observed under conditions of natural infection. We also developed a rating scale for disease assessment. Among eight clones tested, only Clone 1 (Eucalyptus saligna) and Clone 2 (Eucalyptus urophylla) were resistant.     

Field performance of Salix clones propagated via shoot cultures in vitro

Survival, growth, plant structure and insect damage of in vitro‐derived cuttings from two Salix clones (5. schwerinii and 5. viminalis) were compared in a field trial with performance of conventional cuttings of the same clones. No obvious morphological abnormalities were induced by in vitro treatment. The survival rate of in vitro‐derived cuttings of the S. schwerinii clone was much higher than that of conventional cuttings. In the 5. viminalis clone, height growth was slightly but significantly reduced for in vitro‐derived cuttings compared with conventional cuttings although stem basal area and estimated plant dry weight were unaffected. The number of stems per cutting, the number of side shoots per stem and gall midge damage did not appear to be affected by the type of cutting. Electrophoretic analysis of 12 enzyme systems revealed identical isozyme patterns for m vitro‐derived and conventionally propagated plants.     

Variation in pitch canker resistance among provenances of <Emphasis Type="Italic">Pinus patula</Emphasis> and <Emphasis Type="Italic">Pinus tecunumanii</Emphasis> from Mexico and Central America

Pinus patula and high-elevation (HE) sources of P. tecunumanii exhibit intermediate levels of resistance to pitch canker (Fusarium circinatum), compared to extremely resistant species such as P. oocarpa, and extremely susceptible species such as P. radiata. Seedlings from 20 P. patula provenances and 15 HE P. tecunumanii provenances were artificially inoculated with the pitch canker fungus at 21 and 12 weeks of age, respectively, and assessed for resistance 12–20 weeks later. There was important provenance variation in pitch canker resistance for both species. The 20-week LiveStem percentage ranged from 70.3% to 43.6% among the P. patula provenances and 59.6% to 11.7% among HE P. tecunumanii provenances. There was a geographic pattern to the provenance variation, and in both species, low altitude sources demonstrated more resistance than those from high elevation. Provenance variation in pitch canker resistance could be useful when making selection and breeding decisions with these species.     

Mycelial growth and exclusion of Heterobasidion parviporum inoculated in branches of 15‐year‐old Picea abies clones

Twigs of 22 clones of 15‐year‐old Picea abies grafts were inoculated with Heterobasidion parviporum in July and in September 2003. Fungal growth varied between clones and exclusion of the pathogen varied significantly among clones inoculated in July. The results indicate that twigs exhibit the same infection pattern as cuttings when inoculated with H. parviporum and that exclusion of the pathogen in twigs is a clone‐dependent character that occurs during the vegetation period.     

Exposure to a pine pathogen enhances growth and disease resistance in Pinus radiata seedlings

Most studies of Fusarium circinatum, the cause of pitch canker in pines, have focused on its activity as a pathogen. However, recent findings indicate that this fungus can colonize roots of Pinus radiata without inducing symptoms. Contrary to expectations, this study revealed that seedlings grown in infested sand grew more rapidly than seedlings not exposed to F. circinatum, based on root and shoot biomass, with modifications to root system architecture, including increased mycorrhizal root development. These effects were dependent on inoculum density and duration following growth in infested rooting medium. Plants exposed to F. circinatum expressed elevated resistance to stem infections, which significantly decreased the incidence of mortality; as above, effects were dependent on inoculum density. Resistance to stem infections was also enhanced in seedlings that emerged through infested litter, as occurs in native stands. Beneficial to neutral interactions of F. circinatum with its host suggest that the life history of this fungus may be more complex than previously recognized, with activities similar to non‐pathogenic endophytes. The potential for non‐lethal infections by F. circinatum to induce resistance in seedlings may influence dynamics of stand establishment. Overall, these results indicate that pathogenic organisms with asymptomatic states may have cryptic ecological functions that extend beyond the impacts of disease.