Host range and pathogenicity studies of Marssonina castagnei to poplars

Laboratory studies investigating the host range and pathogenicity of Marssonina castagnei (Desm. + Mont.)Magn. to poplars established that this species was not specifically pathogenic to P. alba but also to cultivars of the Sections Aigeiros, Tacamahaca, and inter sectional hybrids Aigciros × Tacamahaca, Leuce × Aigeiros and Lcucc × Tacamahaca. The potential threat of this pathogen could be reduced by routine screening of new selections for resistance.     

Melampsora and Marssonina pathogens of poplars and willows in New Zealand

New Zealand has hosted three Melampsora species attacking poplars (Populus spp.), namely, Melampsora larici-populina, Melampsora medusae and for a single season, Melampsora medusae-populina, a unique interspecific hybrid. The predominant species, M. larici-populina, over-winters via larch and each year new races appear causing defoliation of previously rust-resistant cultivars. Melampsora medusae also occurs in some seasons following over-wintering on certain hosts or by aerial transport from Australia. Willows (Salix spp.) host four Melampsora species, Melampsora coleosporioides, Melampsora epitea var. epitea and two unidentified species attacking Salix viminalis and Salix daphnoides/Salix incana× open pollinated hybrids, respectively. The host range and pathogenicity of these species have remained static as no breakdown in host resistance has been observed. The anthracnose fungi, Marssonina brunnea and Marssonina castagnei on poplar, and Marssonina salicicola on tree willows occur throughout New Zealand. All three species can cause severe defoliation of susceptible cultivars in moist districts where annual rainfall exceeds 1000 mm. Although all form abundant microconidia during autumn, the Drepanopeziza states have never been observed in New Zealand. During an unusually wet summer (199–93), a new strain of Marssonina salicicoa appeared which defoliated the previously resistant cultivar, salix matsudana × salix alba cv. 1002 The importance of monitoring the morphological (conidial dimensions, DNA fingerprints) and physiological (host range and pathogenicity) attributes of local populations of Melampsora and Marssonina species is discussed.     

Captive sentinel hosts efficiently measure the establishment,seasonality and dispersal of a parasitoid biological control agent

Introduced biological control agents are used to suppress populations and reduce the damage caused by many exotic herbivorous insects in New Zealand pasture. Understanding the dispersal behaviour of a recently introduced biocontrol agent in its new environment is important as it helps biocontrol practitioners make decisions on the number and location of future releases. In this study, a monitoring device which contained sentinel hosts was developed to monitor the establishment and dispersal of the Irish strain of Microctonus aethiopoides (Hymenoptera, Braconidae) into areas of the South Island of New Zealand where the clover pest Sitona obsoletus Gmelin (Coleoptera, Curculionidae) had recently become established. Field tests of the monitoring device at five sites in Marlborough confirmed that M. aethiopoides would enter the device through a 900 µm mesh and parasitise the sentinel weevils within. In a further trial conducted over 4 years at four sites in North Canterbury, monitoring devices successfully tracked the dispersal and establishment of M. aethiopoides at sites up to 27 km from the original release site. Monitoring devices containing sentinel hosts may help reduce the cost of classical biological control programmes as they enable rapid sampling of numerous sites and largely eliminate the time consuming practice of dissecting field collected hosts to determine the presence of the parasitoid.

     

Ultrastructural study of the pathogenesis of Marssonina species to poplars

Studies on the pathogenesis of Marssonina brunnea, M. castagnei and M. populi to susceptible poplars showed that germtubes penetrated poplar leaves directly by enzymatic activity and indirectly through stomata. Six days following inoculation, hyphae had ramified throughout palisade and mesophyll tissues causing penetrated cells to become moribund. Acervuli were formed within seven days of inoculation and conidia were released by rupture of the cuticle and upper epidermal wall.     

Black canker and leaf spot of Salix in New Zealand caused by Glomerella miyabeana (Colletotrichum gloeosporioides)

Two new diseases have been observed attacking willows in New Zealand. In the first instance black stem cankers formed on S. matsudana × S. alba × S. alba cultivars, eventually killing them. In the second instance foliage of S. gooddingii and S. amygdaloides was attacked and premature defoliation occurred. Morphological studies and host inoculations established that Glomerella miyabeana (Colletotrichum gloeosporioides anamorph) was the causal agent of both diseases. Foliage of cultivars exhibiting stem cankering was not attacked nor were stems of cultivars with foliar lesions. Electron microscope studies showed that conidia of Colletotrichum gloeosporioides formed phialidically within acervuli and comdial dimensions varied significantly with host.     

Impact of weather variables and season on sporulation of Phytophthora pluvialis and Phytophthora kernoviae

Phytophthora pluvialis and Phytophthora kernoviae are the causal agents of important needle diseases on Pinus radiata in New Zealand. Little is known about the epidemiology of the diseases, making the development of control strategies challenging. To investigate the seasonality and climatic drivers of sporulation, inoculum traps, consisting of pine fascicles floating on water in plastic containers, were exchanged fortnightly at five sites in P. radiata plantations between February 2012 and December 2014. Sections of needle baits were plated onto selective media and growth of Phytophthora pluvialis and P. kernoviae recorded. To explore the generalizability of these data, they were compared to detection data for both pathogens from the New Zealand Forest Health Database (NZFHDB). Further, equivalent analyses on infection of Rhododendron ponticum by P. kernoviae in Cornwall, UK allowed the comparison of the epidemiology of P. kernoviae across different host systems and environments. In New Zealand, inoculum of P. pluvialis and P. kernoviae was detected between January–December and March–November, respectively. Inoculum of both species peaked in abundance in late winter. The probability of detecting P. pluvialis and P. kernoviae was greater at lower temperatures, while the probability of detecting P. pluvialis also increased during periods of wet weather. Similar patterns were observed in NZFHDB data. However, the seasonal pattern of infection by P. kernoviae in the UK was the opposite of that seen for sporulation in New Zealand. Phytophthora kernoviae was likely limited by warmer and drier summers in New Zealand, but by colder winter weather in the UK. These results emphasize the importance of considering both environmental drivers and thresholds in improving our understanding of pathogen epidemiology.     

Canker disease of willow and poplar caused by Cryptosphaeria pullmanensis recorded in China

A new canker disease of Salix alba and Populus alba has been observed in Xinjiang, China. Black circular spots on dead branches and stems are the symptoms of the disease. Sixty‐seven isolates recovered from Salix matsudana, S. alba and Populus alba were identified as Cryptosphaeria pullmanensis based on morphological features and multigene phylogeny. Pathogenicity tests were performed on S. alba and P. alba stems using the C. pullmanensis isolates. Cankers on and Cryptosphaeria pullmanensis of C. pullmanensis from the stems fulfilled Koch's postulates and confirmed C. pullmanensis as the causal agent of the canker disease. C. pullmanensis is characterized by its yellow stromatic tissue surrounded by a black conceptacle with regularly arranged multiple locules sharing common walls and hyaline, allantoid, aseptate conidia (mean size 7.42 × 1.72 μm). This is the first report of C. pullmanensis causing Cryptosphaeria canker in China, and S. alba and P. alba are new host records for C. pullmanensis.     

A survey of Ophiostoma species vectored by Hylastes ater to pine seedlings in New Zealand

Ecological studies in New Zealand require consideration of the impact of exotic (introduced) organisms from disparate environments. A survey of Ophiostoma species isolated and identified from Pinus radiata stumps, the bark beetle Hylastes ater collected from these stumps and from P. radiata seedlings following sublethal damage by H. ater, was undertaken in 10 reforestation sites in New Zealand. Nine Ophiostoma species were isolated and identified in this survey. Ophiostoma galeiformis and Ophiostoma huntii were isolated most frequently from all the substrates sampled. Ophiostoma floccosum, Ophiostoma setosum, Leptographium procerum and Leptographium truncatum were also isolated from stumps, damaged seedlings and beetles. Ophiostoma quercus was only isolated from stumps and beetles and Ophiostoma ips only from beetles. A strong relationship between the severity of H. ater feeding damage, and the presence and number of species of Ophiostoma was found. Eight Ophiostoma species were transmitted by H. ater to P. radiata seedlings in laboratory transmission experiments. From the results of this field survey and the laboratory experiments we confirm that H. ater is a vector of Ophiostoma species to P. radiata seedlings in New Zealand.     

Influence of environmental,host and cultural factors on conidium morphology of Marssonina species pathogenic to poplars

Laboratory studies investigating the influence of environmental, host and cultural factors on conidium morphology of isolates of Marssonina brunnea, M. castagnei and M. populi established that conidial features (length and breadth dimensions, shape, conidium ratios, L:B, LS:B and septum location) were remarkably stable. Significant differences in length and breadth dimensions and ratios were induced by culture media and host but not by media pH, incubation temperature, photoperiod, leaf age, leaf surface and infection severity. Significant differences in conidial dimensions and ratios of M. brunnea were observed following examination of monthly collections from a single field-grown tree. The variation in conidial features induced by environmental, host and cultural factors in no instance obscured taxonomic differences between species.     

Browse yield and nutritive value of two Salix species and Dorycnium rectum in New Zealand

The willows Salix matsudana x alba and S. kinuyanagi, and the leguminous shrub Dorycnium rectum, are used for soil conservation in New Zealand and have potential value as browse plants. Two experiments were conducted in the lower North Island to ascertain the effect of selected establishment and cutting practices on their browse yield and nutritive value. A hill site experiment determined the effect of rooted and unrooted stem cuttings on establishment and initial production of the Salix species. A flat site experiment determined the effect of cutting height (0.10–0.30 m, 0.80 m, and 1.20 m above ground) and cutting frequency (once or twice per year) on yield of the Salix species and D. rectum. The establishment and dry matter (DM) yields of the Salix species were unaffected by the type of stem cutting. S. matsudana x alba (1.2 kg DM/tree) plants yielded more edible DM than S. kinuyanagi (0.9 kg DM/tree) and D. rectum (0.4 kg DM/tree). Cutting height had no effect on edible DM yield but affected total DM yield of the Salix species. Nitrogen concentration in edible DM, of all species, was 18–22 g/kg DM. In vitro organic matter digestibility of S. matsudana x alba (648–691 g/kg DM) and D. rectum (664–666 g/kg DM) was greater than S. kinuyanagi (611–615 g/kg DM). The condensed tannin concentration in edible DM of S. kinuyanagi was four-fold higher than in S. matsudana x alba (255 vs. 59 g/kg DM). It was concluded that S. matsudana x alba had the greatest potential as a browse species and D. rectum the least.This revised version was published online in November 2005 with corrections to the Cover Date.     

Terpene response of Picea abies and Abies alba to infection with Heterobasidion s.l.

The monoterpene composition of Picea abies and Abies alba resin was analysed in relation to growth by Heterobasidion spp. Fifteen‐year‐old P. abies and A. alba trees were inoculated on branches with three species of Heterobasidion annosum s.l. After 4 months of incubation, each host was colonized to a significantly greater degree by the pathogen specific to that host (H. parviporum on P. abies, H. abietinum on A. alba) than by the other fungi. Analysis of the enantiomeric monoterpene profiles in the spruce and fir showed that the response in terms of the relative proportions of the monoterpene compounds in the resin differed between tree species. Following challenge with Heterobasidion spp., A. alba trees did not show changes in monoterpene composition in addition to those in the wounding response (increase in (−)‐α‐pinene and (−)‐camphene, and decrease in β‐phellandrene). In P.abies, (−)‐α‐pinene, (+)‐α‐pinene and δ‐3‐carene increased following Heterobasidion attack but not after wounding alone.     

Genetic evaluation of Prosopis alba (algarrobo) in Argentina for cloning elite trees

Algarrobo (Prosopis alba) is an important nitrogen-fixing tree adapted to the semiarid regions of northwestern Argentina. The tree provides fuelwood and dimensionally stable lumber for flooring and furniture; its pods that have a high sugar content are consumed by livestock and humans. P. alba has been one of the most heavily harvested species. This paper reports on the evaluation of a nine-year-old Prosopis alba progeny trial containing 57 half-sibling families of eight provenances in northwestern Argentina (of the 1,596 trees planted, 1,289 survived in 1999). Considering the multiple uses of P. alba, the selection criteria included: total biomass production (from basal diameter using regression equations), height, rate of pod production, and pod sensory characteristics. The family-narrow-sense-heritability was 0.487 for height. 0.548 for biomass production, and 0.244 for pod production. In 1998, 12 of the 1,289 trees were more than 4 m tall and had more than 1.75 kg pods per tree; and their pods had a sweet or very sweet non-astringent taste. Scions from these 12 trees were successfully grafted onto unselected P. alba rootstock. These are currently being used to produce rooted cuttings. The pod production, biomass, and height of the 12 clones ranged from 6.55 to 14.4, 1.57 to 13.5, and 1.29 to 1.70 times the respective population means. The genetic gains of 13.5%, 77%, and 147% for height, biomass, and pod production respectively are greater than genetic gains for other tree species and are probably due to the great genetic variability in the local population and the lack of any prior genetic improvement program.This revised version was published online in November 2005 with corrections to the Cover Date.     

Detection of phytoplasma infections in declining Populus nigra ‘Italica’ trees and molecular differentiation of the aster yellows phytoplasmas identified in various Populus species

A disease of Populus nigra‘Italica’ associated with foliar yellowing, sparse foliage, stunting, dieback, and decline was observed in south-western Germany; a witches’ broom disease of Populus alba that is known in other countries was also detected in Hungary and Germany. The aetiology of the diseases was studied by fluorescence microscopy and polymerase chain reaction (PCR) amplification. Using fluorescence microscopy, phytoplasmas could be detected only in P. alba. However, most diseased trees of P. nigra‘Italica’ tested phytoplasma-positive by PCR. In some of the trees the phytoplasma numbers were so low that nested PCR was required to detect the infection. Very low phytoplasma numbers were also observed in diseased Populus tremula. The identity of phytoplasmas from P. nigra‘Italica’ sampled in Germany and France, P. alba and also P. tremula was examined by restriction fragment length polymorphism (RFLP) analysis of PCR-amplified ribosomal DNA. In all poplars, phytoplasmas of the aster yellows group were detected. However, three different RFLP groups were identified that consisted of (1) French strains from P. nigra‘Italica’, (2) German strains from P. nigra‘Italica’ and (3) strains from P. alba and P. tremula. The profile observed in the last group was probably the result of sequence heterogeneity in the two 16S RNA genes.     

Nitrogen accretion in soil and biomass production by three Prosopis species

Trunk circumferences and canopy diameters of Prosopis glandulosa, P. chilensis and P. alba, and soil nitrogen under and between the trees were measured in a seven-year-old plantation at the University of California, Riverside. P. glandulosa had the smallest biomass of the three species. However, the nitrogen concentration of the soil under P. glandulosa was higher than under the other two species. Presumably more nitrogen is cycled through the leaves of this species rather than invested in wood production, where it would be sequestered. The soil nitrogen accumulation under P. glandulosa was significantly higher (total and subsurface) than that measured in soil taken between trees. The soil nitrogen content under P. chilensis and P. alba was not significantly different than that between the trees. These results indicate that the choice of woody legume in an agroforestry system will depend on its intended use. The most efficient nutrient cycling is not necessarily associated with the best biomass production.     

Newly recognized bacteria involved in trunk scab and canker of white and hybrid poplars

In a 4‐year‐old collection of native Italian Populus alba, growing in the eastern Po valley, many trunks showed severe symptoms characterized by brown spots, similar to trunk scab and/or by cankers. Canker‐like growths, often with gall‐like‐formations in the earlier developmental phases were also found on some clones of P. trichocarpa and their hybrids, as well as on P. deltoides growing in several Northern Italian nurseries. Bacteria and fungi present in the affected tissues and potentially involved in the disease were examined. No fungi were detected, however, several species of bacteria were isolated and identified: Pseudomonas mendocina and Erwinia herbicola group, from the brown spots; Erwinia carotovora sub sp. carotovora and, occasionally, E. herbicola group, from cankers. Only E. carotovora sub sp. carotovora produced clear symptoms of canker when artificially inoculated on young plants of different poplar species. This is the first time this symptomology on poplar species has been clearly related to E. carotovora sub sp. carotovora.     

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.     

Infection of Populus alba var. hickeliana by Melampsora medusae Thüm.

The first record of infection of Populus alba var. hickeliana by the American rust, Melampsora medusae Thum. is reported. The morphology of uredospores of rust on P. alba is compared with that of other Melampsora spp. infecting white poplars. The implications of these observations for the widespread establishment in the future of white × black hybrid poplars are discussed.     

Testing of selected South African <Emphasis Type="Italic">Pinus</Emphasis> hybrids and families for tolerance to the pitch canker pathogen, <Emphasis Type="Italic">Fusarium circinatum</Emphasis>

Plantations of Pinus spp. constitute approximately 50% of the South African forestry industry. The first aim of this study was to develop a reliable inoculation technique to screen Pinus spp., for tolerance to infection by F. circinatum, which threatens pine forestry in South Africa. Inoculation of branches was compared with stem inoculations and we considered the number of branches or trees required to obtain statistically significant results. Furthermore, variation in the susceptibility of some Pinus families, clones and hybrids was considered. Results showed that branch inoculations were closely correlated with those from stem inoculations, and that it is important to consider branch and stem diameters when assessing susceptibility of trees. Subsequent trials using branch inoculations showed significant differences in F. circinatum tolerance amongst a range of pine species and hybrids of potential interest to forestry in South Africa. Significant differences in susceptibility were also found among clones of two P. radiata families. The most tolerant trees were P. elliottii × caribaea and P. patula × oocarpa hybrids, while the most susceptible species were P. patula, P. greggii and hybrids of these two. This is the first trial considering the susceptibility of Pinus hybrids, Pinus clones and some P. patula provenances, and the results indicate excellent potential for breeding for tolerance to pitch canker in South Africa. Application The accurate selection of disease tolerant planting stock for the South African forestry industry is crucially important for the continued sustainability of this important industry. The work described here provides valuable information on an artificial inoculation technique that will assist the industry in screening trees for tolerance to the pitch canker fungus, F. circinatum. It also provides some indication of the relative susceptibility of a number of Pinus spp., hybrids and families currently being evaluated in the country.     

Impact and control of dothistroma blight of pines

The incidence of dothistroma blight [Dothistroma septospora (Doroguin) Morelet] throughout the world during the last fifteen years is reviewed with particular reference to its economic effects. Impact of the disease has been generally slight in the northern hemisphere, with most severe effects localised in nursery and ornamental stocks in parts of the USA and Canada. In Central and East Africa and New Zealand chronic defoliation has caused serious loss of increment in young Pinus radiata; in Chile outbreaks have been acute and of short duration, causing only slight yield loss. Economic control has been obtained by a well organised copper fungicide spray programme in New Zealand, but this means has proved impracticable in Africa. Experience gained in New Zealand will be valuable when similar problems arise in industrial forest plantations in the future.