Number Of Cankers Research Articles

A novel Xanthomonas citri subsp. citri NADPH quinone reductase involved in salt stress response and virulence

BackgroundXanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker is maintained as an epiphyte on citrus leaves until entering the plant tissue. During epiphytic survival, bacteria may encounter low water availability that challenges the infection process. Proteomics analyses of Xcc under saline stress, mimicking the conditions found during epiphytic survival, showed increased abundance of a putative NAD(P)H dehydrogenase encoded by XAC2229. MethodsExpression levels of XAC2229 and a Xcc mutant in XAC2229 were analyzed in salt and oxidative stress and during plant-pathogen interaction. An Escherichia coli expressing XAC2229 was obtained, and the role of this protein in oxidative stress resistance and in reactive oxygen species production was studied. Finally, Xac2229 protein was purified, spectrophotometric and cofactor analyses were done and enzymatic activities determined. ResultsXAC2229 was expressed under salt stress and during plant-pathogen interaction. ΔXAC2229 mutant showed less number of cankers and impaired epiphytic survival than the wild type strain. ΔXAC2229 survived less in the presence of H2O2 and produced more reactive oxygen species and thiobarbituric acid-reactive substances than the wild type strain. Similar results were observed for E. coli expressing XAC2229. Xac2229 is a FAD containing flavoprotein, displays diaphorase activity with an optimum at pH 6.0 and has quinone reductase activity using NADPH as an electron donor. ConclusionsA FAD containing flavoprotein from Xcc is a new NADPH quinone reductase required for bacterial virulence, particularly in Xcc epiphytic survival on citrus leaves. General significanceA novel protein involved in the worldwide disease citrus canker was characterized.

Butternut (Juglans cinerea) health, hybridization, and recruitment in the northeastern United States

Butternut (Juglans cinerea L.) trees are being extirpated from their natural range by an epidemic caused by a fungal pathogen. Widespread mortality is reminiscent of past epidemics on American chestnut (Castanea dentata (Marsh.) Borkh.) and American elm (Ulmus americana L.). Butternut has remained relatively understudied, resulting in unsampled areas and gaps in our understanding of this forest epidemic and the future outlook of this species in North America. The previously unsampled area consisting of the northeastern United States was surveyed for the presence of J. cinerea, and several population health metrics were recorded, including recruitment, disease pressure, and hybridization. A total of 252 butternut trees were sampled. Analysis indicates that there is insufficient J. cinerea recruitment to maintain population sizes. Further compounding low recruitment, butternut saplings demonstrate elevated levels of disease impact from the fungal pathogen Ophiognomonia clavigignenti-juglandacearum Broders & Boland. Natural hybridization of butternut with introduced congenics such as Juglans ailantifolia Carrière is strongly associated with lower disease impact. Hybrid trees displayed an average of 2.4 cankers per tree compared with 4.5 cankers for nonhybrid butternut. Further niche and resistance studies are required to assess whether butternut hybrids can replace butternut in a natural setting. It still remains uncertain whether tree size or habitat affect disease impact; however, smaller trees, often residing in riparian habitats, were found to have a greater number of cankers. The data presented here, combined with past studies, provide critical information for use in butternut management strategy plans.

Incidence of Gremmeniella abietina in planted seedlings of Picea abies and Pinus sylvestris in northern Finland

SummaryThe ascomycete Gremmeniella abietina causes a disease (scleroderris canker) on conifers. The pathogen kills terminal shoots and branches of Pinus sylvestris and Picea abies, sporulates on host shoots and causes leader changes (i.e. dieback). Damage caused by G. abietina was investigated in young P. abies and P. sylvestris plantations in northern Finland. Side branches from seedlings of both species and the main stems of P. sylvestris were collected from three sites in two locations (Poksa 1 and 2, Kivalo) in northern Finland. The number of cankers and leader changes was counted in branches of each age (i.e. year) in a total of ca. 6300 shoots of P. abies and 1200 shoots of P. sylvestris. Cankers were common on both P. abies and P. sylvestris in Poksa 1 (2002–2008) and on P. abies in Poksa 2 (1998–2001). In Kivalo, cankers occurred only sporadically on P. sylvestris. Leader changes were most frequent in 1999–2009 in Poksa 1, in 2001–2009 in Poksa 2 and in 2003 in Kivalo. Cankers and other symptoms of infection were more obscure on P. abies than on P. sylvestris. According to both conidial morphology and molecular analysis, the strain of G. abietina infecting both P. abies and P. sylvestris was small‐tree type (STT). This is the first report of G. abietina, STT or B type, injuring P. abies in plantations.

Topographic influences on the distribution of white pine blister rust in Pinus albicaulis treeline communities

The exotic disease white pine blister rust (caused by Cronartium ribicola) damages and kills whitebark pine (Pinus albicaulis), even in the extreme environments of alpine treeline communities. We surveyed P. albicaulis trees and tree islands for blister rust in 2 distinct alpine treeline communities in Montana, USA, and examined meso- and microtopographic factors potentially related to the climatic requirements for blister rust infection. For each of 60 sampling plots, we created high-resolution digital elevation models, derived microtopography variables, and compared these and distance to water feature variables with blister rust occurrence and intensity (number of cankers per infected tree) for every sampled P. albicaulis tree. Infection rates were 19% (of 328 sampled trees) and 24% (of 585 sampled trees) at the 2 sites. Tree island P. albicaulis had higher infection percentages than solitary trees. Using Bayesian analysis and a zero-inflated Poisson regression model, we determined that solar radiation and moisture-related variables correlated with both presence and number of blister rust cankers on P. albicaulis. Site factors that influence moisture, such as local topography, hydrology, and climate, differed between the 2 treeline study areas, which may account for the model variability.

Effects of Pruning in Monterrey Pine Plantations Affected by Fusarium circinatum.

Fusarium circinatum Nirenberg and O’Donnell (1998) is the causal agent of Pitch Canker Disease (PCD) in Pinus species, producing damage to the main trunk and lateral branches as well as causing branch dieback. The disease has been detected recently in northern Spain in Pinus spp. seedlings at nurseries and in Pinus radiata D. Don adult trees in plantations. Fusarium circinatum seems to require a wound to enter the tree, not only that as caused by insects but also that resulting from damage by humans, i.e. mechanical wounds. However, the effects of pruning on the infection process have yet to be studied. The aim of the present study was to know how the presence of mechanical damage caused by pruning affects PCD occurrence and severity in P. radiata plantations. Fifty P. radiata plots (pruned and unpruned) distributed throughout 16 sites affected by F. circinatum in the Cantabria region (northern Spain) were studied. Symptoms of PCD presence, such as dieback, oozing cankers and trunk deformation were evaluated in 25 trees per plot and related to pruning effect. A significant relationship between pruning and the number of cankers per tree was observed, concluding that wounds caused by pruning increase the chance of pathogen infection. Other trunk symptoms, such as the presence of resin outside the cankers, were also higher in pruned plots. These results should be taken into account for future management of Monterrey Pine plantations.

Antifungal activity of a Pinus monticola antimicrobial peptide 1 (Pm-AMP1) and its accumulation in western white pine infected with Cronartium ribicola

Pinus monticola antimicrobial peptide 1 (Pm-AMP1) was expressed and purified from bacterial cell lysate and its identity and purity confirmed by Western blot analysis using the Pm-AMP1 antibody. Application of Pm-AMP1 resulted in visible hyphal growth inhibition of Cronartium ribicola , Phellinus sulphurascens , Ophiostoma montium , and Ophiostoma clavigerum 3-12 days post-treatment. Pm-AMP1 also inhibited spore germination of several other phytopathogenic fungi by 32%-84% 5days post-treatment. Microscopic examination of C. ribicola hyphae in contact with Pm-AMP1 showed distinct morphological changes. Seven western white pine ( Pinus monticola Douglas ex D. Don) families (Nos. 1, 2, 5, 6, 7, 8, 10) showing partial resistance to C.ribicola in the form of bark reaction (BR) were assessed by Western immunoblot for associations between Pm-AMP1 accumulation and family, phenotype, canker number, and virulence of C. ribicola. There was a significant difference (p< 0.001) in mean Pm-AMP1 protein accumulation between families, with higher levels detected in the full-sib BR families (Nos. 1, 2, 5) than the half-sib BR families (Nos. 6, 7). Family 8, previously described as a Mechanism 'X' BR family, had the highest number of BR seedlings and displayed high Pm-AMP1 levels, whereas the susceptible family (No. 10) showed the lowest levels (p< 0.05). Family 1 showed a significant association between Pm-AMP1 accumulation and overall seedling health (p< 0.01, R= 0.533), with higher protein levels observed in healthy versus severely infected seedlings. In general, low Pm-AMP1 levels were observed with an increase in the number of cankers per seedling (p< 0.05), and seedlings inoculated with the avirulent source of C. ribicola showed significantly higher Pm-AMP1 levels (p< 0.05) in the majority of BR families. Cis-acting regulatory elements, such as CCAAT binding factors, and an AG-motif binding protein were identified in the Pm-AMP1 promoter region. Multiple polymorphic sites were identified within the 5' untranslated region and promoter regions. Our results suggest that Pm-AMP1 is involved in the western white pine defense response to fungal infection, as observed by its antifungal activity on C. ribicola and a range of phytopathogens as well as through its association with different indicators of resistance to C.ribicola.

Ecological status of American chestnut (Castanea dentata) in its native range in Canada

American chestnut (Castanea dentata (Marsh.) Borkh.) was once a dominant tree in eastern deciduous forests of North America and is now endangered in Canada, primarily because of the introduction of a fungal pathogen (Cryphonectria parasitica (Murrill) Barr) causing chestnut blight. A recovery plan is being developed, and more accurate information on the status of this species in its native range in southern Ontario is needed to assist in the restoration and management of this species. We conducted a 2-year inventory of the distribution and size of trees throughout southern Ontario, and characterized the habitat and incidence of blight. In total, 682 trees were sampled, 601 of which were not planted. Individuals were statistically most likely to occur in deciduous forest habitats with high canopy cover (&gt;50%), gentle slopes (0°–10°), and acidic (pH 4–6), sandy (&gt;75%) soils. Most trees were small (80% were &lt;20 cm diameter at breast height (DBH)) and nonreproductive (86%). Blight cankers were visible on only 25% of trees. Of six habitat variables measured, canopy cover was positively related to tree size (height, DBH) and incidence of blight. Litter depth was also a good predictor of cankers and virulent cankers in particular, but not healing and (or) healed cankers. The presence of Acer and Quercus spp. in the canopy was associated with reduced incidence and number of cankers per tree but increased frequencies of healing and (or) healed cankers, while Carya was correlated with increased incidence and number of cankers per tree. The abundance of American chestnut and the number of blight-free trees in southern Ontario is higher than previously known. The importance of canopy density and associated species in the habitat for tree health will contribute to the development of further research programs and management strategies for the restoration of this endangered species.

Relationship between early family-selection traits and natural blister rust cankering in western white pine families

Blister rust (Cronartium ribicola) cankering incidence was compared among half-sib families of both artificially and naturally inoculated western white pine (Pinus monticola). In the first test, artificially inoculated seedlings of six families had their individual infection spots tallied and any infected needles were removed before cankers developed. These healthy seedlings were classified as high or low spotters and were planted in row plots with four high spotters paired with four low spotters. After 7 years, 2 pairs had equal cankers, 12 had more rust on the high spotters, and 12 had more rust on the low spotters. The mean number of cankers per tree was 22 and 23 for high and low spotters, respectively. In the second test, 203 artificially inoculated western white pine families were ranked for their relative susceptibility to blister rust based on (i) family mean counts of individual infection spots per seedling (spotting) and (ii) the presence of only small cankers (slow canker growth resistance). These results were compared with the natural cankering incidence of the same families in eight plantations. There were few significant differences in spotting incidence among inoculated families. The range in field cankering in the test plantations (15–63 families each) was 22–88%. Seven plantations, including two with families significantly different in infection-spotting incidence, lacked a significant correlation (Spearman, P < 0.05) between percentage field cankering and spotting incidence from inoculations. Although one plantation had a significant correlation (r s = 0.64; P < 0.005) between spotting incidence from inoculation and cankering in a plantation, there was no overall trend across plantations. Incidence of slow canker growth resistance from artificial inoculation ranged from 0 to 18%. There was a significant positive correlation between field cankering and slow canker growth resistance, as determined by inoculation only in three of eight plantations. However, when the families were placed into slow canker growth classes, there was a trend of reduced cankering with increasing class of slow canker growth resistance (mean Spearman's r s value = 0.87 (P < 0.01) across all plantations). These studies indicate that selection on the basis of slow canker growth resistance resulted in less cankering in plantations than selection on the basis of reduced infection spotting.

266 Response of Winter-injured Peach Trees to Pruning

When temperatures reach -26 °C and lower, even for brief periods of time, damage to fruit buds and woody tissue of the peach tree is common. Low temperature injury on peach can lead to bark damage, gummosis, increased incidence of perennial canker, partial or complete crop losses, reduced shoot growth and/or tree death. In Jan. 1994 the Eastern Panhandle of West Virginia and surrounding states experienced three successive nights of temperatures at -28 °C or lower. Beginning in Apr. 1994, 7-year-old `Blake'/Lovell peach trees were subjected to four pruning levels (none, light, heavy, and dehorned) each at three times (April, May, and June) in a replicated factorial arrangement. Specific pruning treatments were applied only in 1994; a local commercially recommended level and time of pruning were applied to all trees from 1995 through 1998. Treatments had a significant effect on canopy volume and fruit yields. Trees receiving no pruning or dehorned trees and trees pruned in June had lower yields in 1995 than trees pruned in April or May or trees receiving a light or heavy pruning. These treatments also produced fewer large fruit at harvest. Lower yields and smaller fruit led to reduced dollar returns per hectare in 1995. Yields from 1996 through 1998 were lower for trees that were dehorned pruned in 1994 although there were little or no differences in fruit sizes between treatments. Time and/or level of pruning had effects on the number of cankers and number of large (&gt;5.1 cm) cankers.

Analysis of Resistance to Eastern Filbert Blight in Corylus avellana.

Inheritance of resistance to eastern filbert blight, caused by Anisogramma anomala, in European hazelnut (Corylus avellana) was evaluated in the progeny of seven cultivars crossed in 12 combinations. The progeny were subjected to inoculation with A. anomala in the greenhouse and in the field. Three disease responses were measured: disease incidence, number of cankers, and proportion of wood diseased. In both the greenhouse and the field, progeny produced by crossing VR6-28 with three susceptible cultivars segregated 1:1 for complete resistance to eastern filbert blight, confirming a previous report that VR6-28 is heterozygous for a single, dominant resistance gene. Histograms of disease responses in progeny of the remaining six parents showed continuous distributions for all crosses examined. Consequently, these parents were analyzed for general and specific combining abilities for each disease response. In the field, general and specific combining ability were both significant (P < 0.05) for all disease responses, with general combining ability having twice the magnitude of specific combining ability. These results suggest these disease responses are controlled by additive gene action in the cultivars examined, with nonadditive gene action being of some importance. Based on general combining ability values, high levels of partial resistance were transmitted by the pollen parents, Gem and Tonda di Giffoni, and the seed parent, Willamette. Heritability of disease incidence, number of cankers, and proportion of wood diseased were calculated to be 0.21, 0.39, and 0.47, respectively, for this set of nine crosses after the first exposure period in the field. This suggests that it will be possible to use partially resistant parents to breed for hazelnuts exhibiting fewer and smaller cankers.

Principal component analysis to evaluate the relative performance of nine year old hybrid poplar clones

Previous studies have identified particular hybrid poplar parentage lines associated with a certain level of growth or disease resistance. This study used principal component analysis (PCA) to evaluate the relative performance of 54 hybrid poplar clones based on nine year old measures of growth and canker disease. Growth was characterized by percentage survival and total basal area per clone, while disease was characterized by the number of cankers per living tree and canker appearance. The first principal component which accounted for 85% of the variation in the data set was used to rank the clones. In general, clones which exhibited high growth and low disease measures were ranked at the top of the list. One exception, clone GA88 (ranked near the top), was uncankered and despite having low survival, produced a relatively high basal area. PCA provided an ordering of clones based upon growth and disease which can be used to select clones for larger scale testing. Future applications of multivariate techniques can incorporate additional variables considered important for biomass, wood pulp, or veneer production.

Susceptibility of European Hazelnut Clones to Eastern Filbert Blight

In the springs of 1989 and 1990, 2- to 3-yr-old hazelnut trees representing 19 cultivars were exposed to ascospores of Anisogramma anomala, which causes eastern filbert blight. The trees were potted and randomly arranged under wire mesh platforms elevated 1.8 m from the ground. Diseased hazelnut branches were placed on top of the platforms in low, medium, or high numbers to provide three levels of inoculum. During periods of rain, ascospores of the pathogen were released from the diseased branches and deposited on the potted trees. External disease symptoms developed at 16 and 28 mo after initial exposure to inoculum, at which times disease responses were evaluated. Cultivars differed significantly in disease incidence, mortality, number of cankers per tree, proportion of wood cankered, and proportion of dead wood (.)

White Pine Blister Rust in British Columbia II. Can Stands be Hazard Rated?

Twelve to 30-year-old western white pine (Pinus monticola Dougl.) in 23 stands in British Columbia were surveyed for blister rust (Cronartium ribicola J.C. Fisch. ex Rab.) cankers. Canker length, mid-point diameter, and height above ground were measured. The number of cankers per tree tended to increase with tree diameter, was variable within stands, and on 15 to 20 cm diameter trees ranged from a mean of one to 14 per stand and the overall mean was four cankers per tree. Large branches bore longer cankers and tended to be higher in the tree than small branches which bore short cankers. Incidence of cankers above 2.5 m tended to increase with increasing slope and they were on the side of the tree subject to evening breezes. Based on Idaho standards all sites in British Columbia were rated as low hazard, but trees growing on slopes had a higher risk than those on flat sites.Key words:Cronartium, Pinus monticola, hazard rating

The Effect of European Canker and Its Spatial Pattern on Four Apple Cultivars in British Columbia

SUMMARY (1) The density and distribution of European canker (Nectria galligena) on all combinations of four scion and interstock cultivars in an orchard of 10 yr old trees in the Lower Mainland of British Columbia were determined. (2) There was no effect of interstock cultivar upon tree mortality, but there were large scion cultivar effects. The numbers of cankers and degree of aggregation of cankers on surviving trees followed a pattern similar to that of tree mortality. Trees of the cultivars 'Summerland Red McIntosh' and 'Harrold's Delicious' were quite susceptible to buildup of canker and subsequent death, while 'Spartan' and 'Golden Delicious' proved relatively resistant. (3) Multiple regression analysis indicated that the number of cankers per tree was significantly related to the sum of the cankers on the eight surrounding neighbours of each tree. (4) Trunk cross-sectional area was significantly correlated with the number of cankers per tree on McIntosh and Spartan trees. However, it was shown that differences in tree size alone did not account for the differences in numbers of cankers on the four scion cultivars. (5) It was concluded generally that scion cultivar and European canker may act in conjunction and result in a heterogeneously stunted apple orchard.

Bacterial canker of stone‐fruits

SUMMARYMost leaf‐scar infections of cherry trees are caused by bacteria washed from the leaf surfaces in rain. In estimates made from three young orchards in four different seasons the numbers of Pseudomonas mors‐prunorum on the leaf surfaces of the cherry variety Napoleon during the autumn were consistently higher than those on the more resistant variety Roundel, the ratio on occasion exceeding three to one. The amount of leaf surface inoculum and the number of cankers on each variety increased progressively with the age of the trees, but both were unrelated to the severity of leaf‐spot infection, which fluctuated widely from year to year. The possibility of epiphytic growth by the pathogen and the relationship between inoculum potential and ‘field’ resistance of the varieties are discussed.