Leaf trait dissimilarities between Dutch elm hybrids with a contrasting tolerance to Dutch elm disease

Background and Aims

Previous studies have shown that Ophiostoma novo-ulmi, the causative agent of Dutch elm disease (DED), is able to colonize remote areas in infected plants of Ulmus such as the leaf midrib and secondary veins. The objective of this study was to compare the performances in leaf traits between two Dutch elm hybrids ‘Groeneveld’ and ‘Dodoens’ which possess a contrasting tolerance to DED. Trait linkages were also tested with leaf mass per area (LMA) and with the reduced Young''s modulus of elasticity (MOE) as a result of structural, developmental or functional linkages.

Methods

Measurements and comparisons were made of leaf growth traits, primary xylem density components, gas exchange variables and chlorophyll a fluorescence yields between mature plants of ‘Groeneveld’ and ‘Dodoens’ grown under field conditions. A recently developed atomic force microscopy technique, PeakForce quantitative nanomechanical mapping, was used to reveal nanomechanical properties of the cell walls of tracheary elements such as MOE, adhesion and dissipation.

Key Results

‘Dodoens’ had significantly higher values for LMA, leaf tissue thickness variables, tracheary element lumen area (A), relative hydraulic conductivity (RC), gas exchange variables and chlorophyll a fluorescence yields. ‘Groeneveld’ had stiffer cell walls of tracheary elements, and higher values for water-use efficiency and leaf water potential. Leaves with a large carbon and nutrient investment in LMA tended to have a greater leaf thickness and a higher net photosynthetic rate, but LMA was independent of RC. Significant linkages were also found between the MOE and some vascular traits such as RC, A and the number of tracheary elements per unit area.

Conclusions

Strong dissimilarities in leaf trait performances were observed between the examined Dutch elm hybrids. Both hybrids were clearly separated from each other in the multivariate leaf trait space. Leaf growth, vascular and gas exchange traits in the infected plants of ‘Dodoens’ were unaffected by the DED fungus. ‘Dodoens’ proved to be a valuable elm germplasm for further breeding strategies.     

Transgenic American elm shows reduced Dutch elm disease symptoms and normal mycorrhizal colonization

The American elm (Ulmus americana L.) was once one of the most common urban trees in eastern North America until Dutch-elm disease (DED), caused by the fungus Ophiostoma novo-ulmi, eliminated most of the mature trees. To enhance DED resistance, Agrobacterium was used to transform American elm with a transgene encoding the synthetic antimicrobial peptide ESF39A, driven by a vascular promoter from American chestnut. Four unique, single-copy transgenic lines were produced and regenerated into whole plants. These lines showed less wilting and significantly less sapwood staining than non-transformed controls after O. novo-ulmi inoculation. Preliminary observations indicated that mycorrhizal colonization was not significantly different between transgenic and wild-type trees. Although the trees tested were too young to ensure stable resistance was achieved, these results indicate that transgenes encoding antimicrobial peptides reduce DED symptoms and therefore hold promise for enhancing pathogen resistance in American elm.     

Seasonal changes in wood formation of Ulmus pumila and U. minor and its relation with Dutch elm disease

Elms containing narrow and scattered vessels have been reported to be more resistant to Ophiostoma novo-ulmi (Dutch elm disease pathogen) than elms with large and contiguous vessels. However, recent measurements in Ulmus pumila and U. minor showed a contrary trend. The pin method was applied to 4-yr-old branches of eight clones planted in Madrid. During 2002, radial growth increments and vessel diameters were measured monthly, and beetle trapping was undertaken weekly. U. minor formed larger vessels at the beginning of the season, coinciding with a peak of captured beetles, but, up to June 15, vessels were larger for U. pumila. The number of vessels per group, the transversal area per vessel group, and the mean theoretical hydraulic conductances were significantly higher for U. minor on most dates. Researchers should take into consideration the seasonal changes in vessel size. The results highlight that seasonal variation of vessel diameters and hydraulic parameters, in combination with beetle abundance, are the main factors that could explain the different susceptibility of both elm species to O. novo-ulmi.     

Ophiostoma novo-ulmi sp. nov., causative agent of current Dutch elm disease pandemics

The aggressive subgroup of the Dutch elm disease pathogen Ophiostoma ulmi (Buism.) Nannf. syn. Ceratocystis ulmi (Buism.) Moreau is named as a new species, O. novo-ulmi, and is thereby separated from the old non-aggressive subgroup, which is retained as O. ulmi. O. novo-ulmi differs from O. ulmi in colony morphology, growth rate, optimum temperature for growth, perithecial neck length, pathogenicity to elm, bark colonising ability, cerato-ulmin protein production, synnemetal and protoperithecial production, mating type frequency, protein and isozyme polymorphisms, mitochondrial DNA and nuclear DNA polymorphisms, and mitochondrial DNA size. In addition, a strong unidirectional fertility barrier operates between the two species, while their hybrids show remarkable variation, poor fitness, and many are infertile. These aspects are summarised. New information on perithecial dimensions is presented. O. ulmi is redefined and a neotype designated. The status of the Eurasian and North American races of O. novo-ulmi is currently under investigation.Abbreviations EAN Eurasian race - NAN North American race     

Learning from history, predicting the future: the UK Dutch elm disease outbreak in relation to contemporary tree disease threats

Expanding international trade and increased transportation are heavily implicated in the growing threat posed by invasive pathogens to biodiversity and landscapes. With trees and woodland in the UK now facing threats from a number of disease systems, this paper looks to historical experience with the Dutch elm disease (DED) epidemic of the 1970s to see what can be learned about an outbreak and attempts to prevent, manage and control it. The paper draws on an interdisciplinary investigation into the history, biology and policy of the epidemic. It presents a reconstruction based on a spatial modelling exercise underpinned by archival research and interviews with individuals involved in the attempted management of the epidemic at the time. The paper explores what, if anything, might have been done to contain the outbreak and discusses the wider lessons for plant protection. Reading across to present-day biosecurity concerns, the paper looks at the current outbreak of ramorum blight in the UK and presents an analysis of the unfolding epidemiology and policy of this more recent, and potentially very serious, disease outbreak. The paper concludes by reflecting on the continuing contemporary relevance of the DED experience at an important juncture in the evolution of plant protection policy.     

Metabolic distinction of Ulmus minor xylem tissues after inoculation with Ophiostoma novo-ulmi

Dutch elm disease (DED) is the most devastating and widespread disease of elms. The pathogen, Ophiostoma novo-ulmi, spreads systemically causing xylem vessels blocking and cavitation, and ultimately resulting in the development of a wilt syndrome. Twig samples from susceptible and resistant Ulmus minor trees were harvested at 0, 5, 15, 30, 60, and 120 days post-inoculation (dpi) with O. novo-ulmi. Fourier transform-infrared (FT-IR) spectroscopy, in tandem with chemometrics, was used to monitor changes in wood chemistry as consequence of infection. Principal component analysis distinguished between spectra from inoculated and control elms, and from susceptible- and resistant-inoculated elms. By 30 dpi, infected xylem showed reduced relative levels of carbohydrates and enhanced relative levels of phenolic compounds, probably due to the degradation of cell wall polysaccharides by fungal enzymes and the synthesis of host defence compounds. On 15 dpi, samples from resistant-inoculated elms showed higher levels of starch than samples from susceptible-inoculated elms, suggesting that availability of starch reserves could affect the tree's capacity for defensive responses. The results showed the power of FT-IR spectroscopy for analysing changes in the major components of elm xylem as consequence of infection by DED, and its potential for detecting metabolic profiles related to host resistance.     

Accumulation of mansonones E and F in seedlings of Ulmus americana in response to inoculation with Ophiostoma ulmi

Summary The accumulation of mansonones E and F was investigated in Ulmus americana L. seedlings 5 weeks after inoculation with three aggressive and three non-aggressive isolates of Ophiostoma ulmi (Buism.) Nannf. The three non-aggressive isolates stimulated significantly more mansonone E and F accumulation than the three aggressive isolates of O. ulmi. Mansonone induction also varied within both the aggressive and the non-aggressive groups. Aggressive and non-aggressive isolates were recovered in equal frequencies from the inoculation wounds, whereas the aggressive isolates were recovered more frequently than the non-aggressive isolates 15 cm and 25 cm up the seedlings' stem. Vascular browning in the outer xylem of the seedlings correlated with mansonone E and F accumulation. Mansonone accumulation in U. americana seedlings is therefore associated with vascular browning and a reduction in fungal spread.     

Target Host Finding by Steinernema feltiae and Heterorhabditis bacteriophora in the Presence of a Non-Target Insect Host

The ability of Steinernema feltiae or Heterorhabditis bacteriophora infective juveniles (IJ), when applied to the soil surface, to infect a Galleria mellonella larva at the base of a soil-filled cup (276 cm³) was evaluated in the presence and absence of 100 larvae of a non-target insect, the aphid midge Aphidoletes aphidimyza, near the soil surface. In all four trials with either S. feltiae or H. bacteriophora, A. aphidimyza presence did not affect the number of IJ finding and infecting a G. mellonella larva. Steinernema feltiae and H. bacteriophora IJ movement (as measured by the percentage of IJ aggregating on either side of an experimental arena) in the presence of one or many A. aphidimyza larvae was evaluated in agar- and soil-filled petri dishes, respectively. Infective juvenile movement in the presence of A. aphidimyza did not differ from random, indicating that IJ were not attracted to A. aphidimyza. It is suggested, therefore, that A. aphidimyza does not reduce IJ efficacy when these two forms of biological control agent are present together in a field situation even though it is known that A. aphidimyza is susceptible to IJ of these species.     

Host persistence or extinction from emerging infectious disease: insights from white-nose syndrome in endemic and invading regions

Predicting species'' fates following the introduction of a novel pathogen is a significant and growing problem in conservation. Comparing disease dynamics between introduced and endemic regions can offer insight into which naive hosts will persist or go extinct, with disease acting as a filter on host communities. We examined four hypothesized mechanisms for host–pathogen persistence by comparing host infection patterns and environmental reservoirs for Pseudogymnoascus destructans (the causative agent of white-nose syndrome) in Asia, an endemic region, and North America, where the pathogen has recently invaded. Although colony sizes of bats and hibernacula temperatures were very similar, both infection prevalence and fungal loads were much lower on bats and in the environment in Asia than North America. These results indicate that transmission intensity and pathogen growth are lower in Asia, likely due to higher host resistance to pathogen growth in this endemic region, and not due to host tolerance, lower transmission due to smaller populations, or lower environmentally driven pathogen growth rate. Disease filtering also appears to be favouring initially resistant species in North America. More broadly, determining the mechanisms allowing species persistence in endemic regions can help identify species at greater risk of extinction in introduced regions, and determine the consequences for disease dynamics and host–pathogen coevolution.     

Expression profiles of hydrophobic surfactant proteins in children with diffuse chronic lung disease

Background

Abnormalities of the intracellular metabolism of the hydrophobic surfactant proteins SP-B and SP-C and their precursors may be causally linked to chronic childhood diffuse lung diseases. The profile of these proteins in the alveolar space is unknown in such subjects.

Methods

We analyzed bronchoalveolar lavage fluid by Western blotting for SP-B, SP-C and their proforms in children with pulmonary alveolar proteinosis (PAP, n = 15), children with no SP-B (n = 6), children with chronic respiratory distress of unknown cause (cRD, n = 7), in comparison to children without lung disease (n = 15) or chronic obstructive bronchitis (n = 19).

Results

Pro-SP-B of 25–26 kD was commonly abundant in all groups of subjects, suggesting that their presence is not of diagnostic value for processing defects. In contrast, pro-SP-B peptides cleaved off during intracellular processing of SP-B and smaller than 19–21 kD, were exclusively found in PAP and cRD. In 4 of 6 children with no SP-B, mutations of SFTPB or SPTPC genes were found. Pro-SP-C forms were identified at very low frequency. Their presence was clearly, but not exclusively associated with mutations of the SFTPB and SPTPC genes, impeding their usage as candidates for diagnostic screening.

Conclusion

Immuno-analysis of the hydrophobic surfactant proteins and their precursor forms in bronchoalveolar lavage is minimally invasive and can give valuable clues for the involvement of processing abnormalities in pediatric pulmonary disorders.     

Early responses to cadmium of two poplar clones that differ in stress tolerance

Soil cadmium (Cd) contamination is becoming a matter of great global concern. The identification of plants differentially sensitive to Cd excess is of interest for the selection of genotype adaptive to grow and develop in polluted areas and capable of ameliorating or reducing the negative environmental effects of this toxic metal. The two poplar clones I-214 (Populus × canadensis) and Eridano (Populus deltoides × maximowiczii) are, respectively, tolerant and sensitive to ozone (O₃) exposure. Because stress tolerance is mediated by an array of overlapping defence mechanisms, we tested the hypothesis that these two clones differently sensitive to O₃ stress factor also exhibit different tolerance to Cd. With this purpose, an outdoor pot experiment was designed to study the responses of I-214 and Eridano to the distribution of different Cd solutions enriched with CdCl₂ (0, 50 and 150 μM) for 35 days. Changes in leaf area, biomass allocation and Cd uptake, photosynthesis, chlorophyll fluorescence, leaf concentration of nutrients and pigments, hydrogen peroxide (H₂O₂) and nitric oxide (NO) production and thiol compounds were investigated. The two poplar clones showed similar sensitivity to excess Cd in terms of biomass production, photosynthesis activity and Cd accumulation, though physiological and biochemical traits revealed different defence strategies. In particular, Eridano maintained in any Cd treatment the number of its constitutively wider blade leaves, while the number of I-214 leaves (with lower size) was reduced. H₂O₂ increased 4.5- and 13-fold in I-214 leaves after the lowest (L) and highest (H) Cd treatments, respectively, revealing the induction of oxidative burst. NO, constitutively higher in I-214 than Eridano, progressively increased in both clones with the enhancement of Cd concentration in the substrate. I-214 showed a more elevated antioxidative capacity (GSH/GSSG) and higher photochemical efficiency of PSII (F_v/F_m) and de-epoxidation degree of xantophylls-cycle (DEPS). The glutathione pool was not affected by Cd treatment in both clones, while non-protein thiols and phytochelatins were reduced at L Cd treatment in I-214. Overall, these two clones presented high adaptability to Cd stress and are both suitable to develop and growth in environments contaminated with this metal, thus being promising for their potential use in phytoremediation programmes.     

Molecular cloning of two novel peroxidases and their response to salt stress and salicylic acid in the living fossil Ginkgo biloba

Background and Aims

Peroxidase isoenzymes play diverse roles in plant physiology, such as lignification and defence against pathogens. The actions and regulation of many peroxidases are not known with much accuracy. A number of studies have reported direct involvement of peroxidase isoenzymes in the oxidation of monolignols, which constitutes the last step in the lignin biosynthesis pathway. However, most of the available data concern only peroxidases and lignins from angiosperms. This study describes the molecular cloning of two novel peroxidases from the ‘living fossil’ Ginkgo biloba and their regulation by salt stress and salicylic acid.

Methods

Suspension cell cultures were used to purify peroxidases and to obtain the cDNAs. Treatments with salicylic acid and sodium chloride were performed and peroxidase activity and gene expression were monitored.

Key Results

A novel peroxidase was purified, which preferentially used p-hydroxycinnamyl alcohols as substrates and was able to form dehydrogenation polymers in vitro from coniferyl and sinapyl alcohols. Two peroxidase full-length cDNAs, GbPrx09 and GbPrx10, were cloned. Both peroxidases showed high similarity to other basic peroxidases with a putative role in cell wall lignification. Both GbPrx09 and GbPrx10 were expressed in leaves and stems of the plant. Sodium chloride enhanced the gene expression of GbPrx09 but repressed GbPrx10, whereas salicylic acid strongly repressed both GbPrx09 and GbPrx10.

Conclusions

Taken together, the data suggest the participation of GbPrx09 and GbPrx10 in the developmental lignification programme of the cell wall. Both peroxidases possess the structural characteristics necessary for sinapyl alcohol oxidation. Moreover, GbPrx09 is also involved in lignification induced by salt stress, while salicylic acid-mediated lignification is not a result of GbPrx09 and GbPrx10 enzymatic activity.     

Comparison of inhibition of N2 fixation and ureide accumulation under water deficit in four common bean genotypes of contrasting drought tolerance

Background and Aims

Drought is the principal constraint on world production of legume crops. There is considerable variability among genotypes in sensitivity of nitrogen fixation to drought, which has been related to accumulation of ureides in soybean. The aim of this study was to search for genotypic differences in drought sensitivity and ureide accumulation in common bean (Phaseolus vulgaris) germplasm that may be useful in the improvement of tolerance to water deficit in common bean.

Methods

Changes in response to water deficit of nitrogen fixation rates, ureide content and the expression and activity of key enzymes for ureide metabolism were measured in four P. vulgaris genotypes differing in drought tolerance.

Key Results

A variable degree of drought-induced nitrogen fixation inhibition was found among the bean genotypes. In addition to inhibition of nitrogen fixation, there was accumulation of ureides in stems and leaves of sensitive and tolerant genotypes, although this was higher in the leaves of the most sensitive ones. In contrast, there was no accumulation of ureides in the nodules or roots of stressed plants. In addition, the level of ureides in the most sensitive genotype increased after inhibition of nitrogen fixation, suggesting that ureides originate in vegetative tissues as a response to water stress, probably mediated by the induction of allantoinase.

Conclusions

Variability of drought-induced inhibition of nitrogen fixation among the P. vulgaris genotypes was accompanied by subsequent accumulation of ureides in stems and leaves, but not in nodules. The results indicate that shoot ureide accumulation after prolonged exposure to drought could not be the cause of inhibition of nitrogen fixation, as has been suggested in soybean. Instead, ureides seem to be produced as part of a general response to stress, and therefore higher accumulation might correspond to higher sensitivity to the stressful conditions.     

Host and pathogen ecology drive the seasonal dynamics of a fungal disease,white-nose syndrome

Seasonal patterns in pathogen transmission can influence the impact of disease on populations and the speed of spatial spread. Increases in host contact rates or births drive seasonal epidemics in some systems, but other factors may occasionally override these influences. White-nose syndrome, caused by the emerging fungal pathogen Pseudogymnoascus destructans, is spreading across North America and threatens several bat species with extinction. We examined patterns and drivers of seasonal transmission of P. destructans by measuring infection prevalence and pathogen loads in six bat species at 30 sites across the eastern United States. Bats became transiently infected in autumn, and transmission spiked in early winter when bats began hibernating. Nearly all bats in six species became infected by late winter when infection intensity peaked. In summer, despite high contact rates and a birth pulse, most bats cleared infections and prevalence dropped to zero. These data suggest the dominant driver of seasonal transmission dynamics was a change in host physiology, specifically hibernation. Our study is the first, to the best of our knowledge, to describe the seasonality of transmission in this emerging wildlife disease. The timing of infection and fungal growth resulted in maximal population impacts, but only moderate rates of spatial spread.     

Photobiont selectivity leads to ecological tolerance and evolutionary divergence in a polymorphic complex of lichenized fungi

Background and Aims

The integrity and evolution of lichen symbioses depend on a fine-tuned combination of algal and fungal genotypes. Geographically widespread species complexes of lichenized fungi can occur in habitats with slightly varying ecological conditions, and it remains unclear how this variation correlates with symbiont selectivity patterns in lichens. In an attempt to address this question, >300 samples were taken of the globally distributed and ecologically variable lichen-forming species complex Tephromela atra, together with closely allied species, in order to study genetic diversity and the selectivity patterns of their photobionts.

Methods

Lichen thalli of T. atra and of closely related species T. grumosa, T. nashii and T. atrocaesia were collected from six continents, across 24 countries and 62 localities representing a wide range of habitats. Analyses of genetic diversity and phylogenetic relationships were carried out both for photobionts amplified directly from the lichen thalli and from those isolated in axenic cultures. Morphological and anatomical traits were studied with light and transmission electron microscopy in the isolated algal strains.

Key Results

Tephromela fungal species were found to associate with 12 lineages of Trebouxia. Five new clades demonstrate the still-unrecognized genetic diversity of lichen algae. Culturable, undescribed lineages were also characterized by phenotypic traits. Strong selectivity of the mycobionts for the photobionts was observed in six monophyletic Tephromela clades. Seven Trebouxia lineages were detected in the poorly resolved lineage T. atra sensu lato, where co-occurrence of multiple photobiont lineages in single thalli was repeatedly observed.

Conclusions

Low selectivity apparently allows widespread lichen-forming fungi to establish successful symbioses with locally adapted photobionts in a broader range of habitats. This flexibility might correlate with both lower phylogenetic resolution and evolutionary divergence in species complexes of crustose lichen-forming fungi.     

Sex-specific responses to sexual familiarity,and the role of olfaction in Drosophila

Studies of mating preferences have largely neglected the potential effects of individuals encountering their previous mates (‘directly sexually familiar’), or new mates that share similarities to previous mates, e.g. from the same family and/or environment (‘phenotypically sexually familiar’). Here, we show that male and female Drosophila melanogaster respond to the direct and phenotypic sexual familiarity of potential mates in fundamentally different ways. We exposed a single focal male or female to two potential partners. In the first experiment, one potential partner was novel (not previously encountered) and one was directly familiar (their previous mate); in the second experiment, one potential partner was novel (unrelated, and from a different environment from the previous mate) and one was phenotypically familiar (from the same family and rearing environment as the previous mate). We found that males preferentially courted novel females over directly or phenotypically familiar females. By contrast, females displayed a weak preference for directly and phenotypically familiar males over novel males. Sex-specific responses to the familiarity of potential mates were significantly weaker or absent in Orco¹ mutants, which lack a co-receptor essential for olfaction, indicating a role for olfactory cues in mate choice over novelty. Collectively, our results show that direct and phenotypic sexual familiarity is detected through olfactory cues and play an important role in sex-specific sexual behaviour.     

Host Suitability of Soybean Cultivars and Breeding Lines to Reniform Nematode in Tests Conducted in 2001

Reproduction of reniform nematode Rotylenchulus reniformis on 139 soybean lines was evaluated in a greenhouse in the summer of 2001. Cultivars and lines (119 total) were new in the Arkansas and Mississippi Soybean Testing Programs, and an additional 20 were submitted by C. Overstreet, Louisiana State Extension Nematologist. A second test of 32 breeding lines and 2 cultivars from the Clemson University soybean breeding program was performed at the same time under the same conditions. Controls were the resistant cultivars Forrest and Hartwig, susceptible Braxton, and fallow infested soil. Five treatment replications were planted in sandy loam soil infested with 1,744 eggs and vermiform reniform nematodes, grown for 10 weeks in 10 cm-diam.- pots. Total reniform nematodes extracted from soil and roots was determined, and a reproductive factor (final population (Pf)/ initial inoculum level (Pi)) was calculated for each genotype. Reproduction on each genotype was compared to the reproduction on the resistant cultivar Forrest (RF), and the log ratio [log₁₀(RF + 1) is reported. Cultivars with reproduction not significantly different from Forrest (log ratio) were not suitable hosts, whereas those with greater reproductive indices were considered suitable hosts. These data will be useful in the selection of soybean cultivars to use in rotation with cotton or other susceptible crops to help control the reniform nematode and to select useful breeding lines as parent material for future development of reniform nematode resistant cultivars and lines.     

Determining mutations in G6PC and SLC37A4 genes in a sample of Brazilian patients with glycogen storage disease types Ia and Ib

Glycogen storage disease (GSD) comprises a group of autosomal recessive disorders characterized by deficiency of the enzymes that regulate the synthesis or degradation of glycogen. Types Ia and Ib are the most prevalent; while the former is caused by deficiency of glucose-6-phosphatase (G6Pase), the latter is associated with impaired glucose-6-phosphate transporter, where the catalytic unit of G6Pase is located. Over 85 mutations have been reported since the cloning of G6PC and SLC37A4 genes. In this study, twelve unrelated patients with clinical symptoms suggestive of GSDIa and Ib were investigated by using genetic sequencing of G6PC and SLC37A4 genes, being three confirmed as having GSD Ia, and two with GSD Ib. In seven of these patients no mutations were detected in any of the genes. Five changes were detected in G6PC, including three known point mutations (p.G68R, p.R83C and p.Q347X) and two neutral mutations (c.432G > A and c.1176T > C). Four changes were found in SLC37A4: a known point mutation (p.G149E), a novel frameshift insertion (c.1338_1339insT), and two neutral mutations (c.1287G > A and c.1076-28C > T). The frequency of mutations in our population was similar to that observed in the literature, in which the mutation p.R83C is also the most frequent one. Analysis of both genes should be considered in the investigation of this condition. An alternative explanation to the negative results in this molecular study is the possibility of a misdiagnosis. Even with a careful evaluation based on laboratory and clinical findings, overlap with other types of GSD is possible, and further molecular studies should be indicated.     

Tissue loss (white syndrome) in the coral Montipora capitata is a dynamic disease with multiple host responses and potential causes

Tissue loss diseases or white syndromes (WS) are some of the most important coral diseases because they result in significant colony mortality and morbidity, threatening dominant Acroporidae in the Caribbean and Pacific. The causes of WS remain elusive in part because few have examined affected corals at the cellular level. We studied the cellular changes associated with WS over time in a dominant Hawaiian coral, Montipora capitata, and showed that: (i) WS has rapidly progressing (acute) phases mainly associated with ciliates or slowly progressing (chronic) phases mainly associated with helminths or chimeric parasites; (ii) these phases interchanged and waxed and waned; (iii) WS could be a systemic disease associated with chimeric parasitism or a localized disease associated with helminths or ciliates; (iv) corals responded to ciliates mainly with necrosis and to helminths or chimeric parasites with wound repair; (v) mixed infections were uncommon; and (vi) other than cyanobacteria, prokaryotes associated with cell death were not seen. Recognizing potential agents associated with disease at the cellular level and the host response to those agents offers a logical deductive rationale to further explore the role of such agents in the pathogenesis of WS in M. capitata and helps explain manifestation of gross lesions. This approach has broad applicability to the study of the pathogenesis of coral diseases in the field and under experimental settings.