Microsatellite DNA suggests regional structure in the fusiform rust fungus Cronartium quercuum f. sp fusiforme

This paper reports results obtained from microsatellite DNA analysis of genetic structure for populations of the native fungus Cronartium quercuum f. sp fusiforme infecting loblolly pine (Pinus taeda L.) over much of this host's natural range. Mostly all fusiform rust galls formed under field conditions are produced as a result of infection and colonization by haploid mycelium originating from a single basidiospore of C. quercuum fusiforme. If multiple infections do occur, then only a single haplotype must ultimately dominate and be responsible for gall formation. High levels of microsatellite variability exist in C. quercuum fusiforme and most of this variation occurs within local populations (average 88.4%). A statistically significant proportion, however, is found among populations, and the magnitude of this differentiation is closely associated with geographic distance between populations. Unweighted pair-group mean analysis and principal components analysis both indicate that at least four genetically distinct regional groups of C. quercuum fusiforme exist in the south Atlantic and Gulf coastal plains. In summary, the distribution of genetic variability in C. quercuum fusiforme is consistent with a hypothesis of at least four metapopulations with gene flow occurring less among regions than among populations within regions, and where overall levels of gene migration are related to geographic distance between populations.     

Genome size variation in the pine fusiform rust pathogen Cronartium quercuum f.sp. fusiforme as determined by flow cytometry

The genome size of the pine fusiform rust pathogen Cronartium quercuum f.sp. fusiforme (Cqf) was determined by flow cytometric analysis of propidium iodide-stained, intact haploid pycniospores with haploid spores of two genetically well characterized fungal species, Sclerotinia sclerotiorum and Puccinia graminis f.sp. tritici, as size standards. The Cqf haploid genome was estimated at ~90 Mb, similar to other Pucciniales species for which reference genome sequences are available. Twenty-three Cqf pycniospore samples were compared that comprised three samples obtained from naturally occurring pine galls and 20 samples obtained after artificial inoculation with parental isolates and their progeny. Significant variation in genome size (>10% of mean) was detected among unrelated as well as sibling Cqf samples. The unexpected plasticity in Cqf genome size observed among sibling samples is likely to be driven by meiosis between parental genomes that differ in size.     

A survival model for unthinned loblolly pine plantations that incorporates non-planted tree competition,site quality,and incidence of fusiform rust

Future biomass yields are functionally related to the number of trees surviving at a given age. A stand level survival model was developed that incorporates competition of non-planted trees, site quality, and the incidence of fusiform rust (Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme). The model consists of a system of two equations, one of which represents the number of surviving trees infected by fusiform rust while the other represents the number of trees not infected by fusiform rust. Data from unthinned loblolly pine (Pinus taeda L.) plantations in East Texas were used to fit and evaluate the survival model and illustrate its use. The model successfully predicted that the number of surviving loblolly pine trees decreased as the number of non-planted trees increased. The model also successfully predicted the transition of loblolly pine trees from an uninfected to an infected status by fusiform rust.     

A genomic map enriched for markers linked to Avr1 in Cronartium quercuum f.sp. fusiforme

A novel approach is presented to map avirulence gene Avr1 in the basidiomycete Cronartium quercuum f.sp. fusiforme, the causal agent of fusiform rust disease in pines. DNA markers tightly linked to resistance gene Fr1 in loblolly pine tree 10-5 were used to classify 10-5 seedling progeny as either resistant or susceptible. A single dikaryotic isolate (P2) heterozygous at the corresponding Avr1 gene was developed by crossing Fr1 avirulent isolate SC20-21 with Fr1 virulent isolate NC2-40. Bulk basidiospore inoculum derived from isolate P2 was used to challenge the pine progeny. The ability to unambiguously marker classify 10-5 progeny as resistant (selecting for virulence) or susceptible (non-selecting) permitted the genetic mapping of the corresponding Avr1 gene by bulked segregant analysis. Using this approach, 14 genetic markers significantly linked to Avr1 were identified and placed within the context of a genome-wide linkage map produced for isolate P2 using samples from susceptible seedlings.     

Cronartium orientale, sp. nov., segregation of the pine gall rust in eastern Asia fromCronartium quercuum

The Asian pine gall rust, which has hitherto been assigned toCronartium quercuum distributed in North America, is described asC. orientale, sp. nov. The spermogonial and aecial states occur on hard pines, and the uredinial and telial states occur on various oaks.Cronartium orientale has globose, almost hyaline basidiospores in contrast to the ellipsoid, yellow-orange ones of North AmericanC. quercuum s.l. Characteristics of the new rust species in morphology, DNA analysis, and host alternation are discussed.     

Genetic dissection of fusiform rust and pitch canker disease traits in loblolly pine

Loblolly pine (Pinus taeda L.) exhibits genetic resistance to fusiform rust disease (incited by the biotrophic fungus, Cronartium quercuum f. sp. fusiforme) and pitch canker disease (incited by the necrotrophic fungus, Fusarium circinatum). In this study, a total of 14,015 loblolly pine cuttings from 1,065 clones were screened in controlled greenhouse conditions to identify phenotypes of clones, families, and parents that guide a genetic dissection of disease traits associated with pitch canker and fusiform rust. A total of 23,373 phenotypic data points were collected for lesion length (pitch canker) and gall score, gall length, and gall width (fusiform rust). We verified heritable fusiform rust and pitch canker traits and calculated parental, clonal, and full-sib family rankings for both diseases. Genetic correlations revealed that traits associated with fusiform rust are genetically distinct from one another, and that the genetic mechanisms underlying pitch canker and fusiform rust resistance are independent. The disease phenotyping described here is a critical step towards identifying specific loci and alleles associated with fusiform rust and pitch canker resistance.     

Qualitative and Quantitative Evaluation of Gall Induced by <Emphasis Type="Italic">Pseudophacopteron alstonium</Emphasis> Yang et Li 1983 (Hemiptera: Psyllidae: Phacopteronidae) as Plant Parasite,in <Emphasis Type="Italic">Alstonia scholaris</Emphasis> Leaves

Alstonia scholaris (Dr C. Alston, 1685–1760) (Family Apocynaceae) (Chattim tree), commonly known as devil tree, is an evergreen tropical tree. The tree is native to India and also found in Sri Lanka, Southern China, throughout Malaysia to northern Australia. This plant is seriously damaged by formation of tumor like galls across the Kolkata city,West Bengal which affects its ornamental and medicinal value. Gall is formed by ovipositing adults of Pseudophacopteron alstonium Yang et Li 1983 (Hemiptera: Psyllidae: Phacopteronidae) and results in destruction of host plant. The nymphal stage undergoes moulting through first instar to third instar to reach the adult within galls. It is observed that highly infested leaves can bear 60–80 galls. The gallmaker Pseudophacopteron sp. stresses the host organ, and the host counters it with physiological activities supplemented by newly differentiated tissues. In infested leaves, chlorophyll and carbohydrate contents decreased sequentially with the age of the gall. There were no significant changes in protein and total amino acid content in gall tissue. But total lipid content was highest in mature galled leaves. Increased phenolic content after psylloid herbivory, which exerted oxidative stress on the host plants, was observed in gall infested leaves as compared to fresh ungalled leaves of Alstonia scholaris. Moisture content was highest in ungalled healthy leaves than the young galled, mature galled and perforated galled leaves.     

Pine genes regulated by the necrotrophic pathogen <Emphasis Type="Italic">Fusarium circinatum</Emphasis>

A targeted genomics approach was used to construct a cDNA array of potential pathogen-regulated genes for investigating host–pathogen interactions in pine trees (Pinus species). This array, containing a nonredundant set of 311 cDNAs, was assembled by combining smaller sets of cDNAs generated by differential display or suppression subtraction hybridization using a variety of pathogen treatments and elicitors. The array was probed to identify host genes regulated by Fusarium circinatum, a necrotrophic fungus that incites pitch canker disease on pine stems. A set of 29 cDNAs were induced during the disease state. Notably, cDNAs on the array that were derived from experiments with fusiform rust, incited by Cronartium quercuum f. sp. fusiforme (a biotrophic fungus) were unregulated by Fusarium. The results imply distinct genetic responses in pine to diseases incited by necrotrophs and biotrophs. This cDNA collection expands the genomics toolkit for understanding interactions between conifers and their microbial associates in forest ecosystems.     

The chemical composition of plant galls: are levels of nutrients and secondary compounds controlled by the gall-former?

The chemical composition of galled and ungalled plant tissue was compared in a series of experiments. Gall and adjacent plant tissue was analysed for 20 species of gall-former on 11 different plant species. There were clear differences between galled and ungalled tissue in levels of nutrients and secondary compounds. Gall tissue generally contained lower levels of nitrogen and higher levels of phenolic compounds than ungalled plant tissue. The gall tissue produced by the same plant in response to different species of gall-former differed in chemical composition, as did the gall-tissue from young and mature galls of the same species. The chemical differences between gall and plant tissues were studied in more detail in two field manipulations. Firstly, the seasonal changes in phenolic biosynthesis in Pontania proxima and P. pedunculi (Hymenoptera: Tenthredinidae) gall tissue were compared to those of their host plants, Salix alba and S. caprea. In both types of gall tissue, phenolic levels declined as the season progressed, but levels in the surrounding plant tissue increased. When the gall insects were killed with insecticide, phenolic levels in the galled tissue dropped to the same level as those in adjacent plant tissue. Secondly, the density of Cynips divisa (Hymenoptera: Cynipidae) galls on Quercus robur leaves was reduced by removing half the galls present, either those from the central region of the leaf or those from the edge. Decreasing gall density increased the size of the remaining galls and the weight of the insects, but these effects were most marked when the galls remaining were growing centrally on the leaf, i.e. when the galls from the edge had been removed. Decreasing gall density increased the nitrogen content of the remaining galls, again to a greater extent in galls growing centrally on the leaf. The results of these studies suggest that the levels of nutrients and secondary compounds in gall tissue are usually markedly different to those of surrounding plant tissue, and that gall-formers may produce species-specific and temporally variable changes in the chemical composition of gall tissue. Received: 7 July 1997 / Accepted: 29 September 1997     

Arthropod-induced neoplastic formations on trees change photosynthetic pigment levels and oxidative enzyme activities

Abstract

In order to test the hypothesis that arthropod-induced neoplastic formations on trees affect biochemical characteristics of both the newly formed galls and host plant tissues, biochemical characteristics with a possible adaptive role were determined in nine gall-former–host tree combinations. Photosynthetic pigments, extractable protein content, and oxidative enzyme activities were determined in gall tissues, leaf tissues of galled leaves, and leaves on ungalled tree branches. Neoplastic tissues were characterized by a low content of photosynthetic pigments, decreased chlorophyll a/b ratio, lower extractable protein content, and decreased activities of peroxidase and polyphenol oxidase as compared with ungalled host leaf tissues. In galled leaves or in leaves adjacent to galls, increased level of peroxidase activity was found. In several gall-inducer–host plant combinations, galled host plant tissues contained increased activity of polyphenol oxidase as well. The presented data reflect long-term systemic effects of neoplastic formation on host tree physiology suggesting that gall inducers affect potential adaptive responses of host plants.     

一种花瘿蚊(双翅目:瘿蚊科)与其寄主植物对萼猕猴桃Actinidia valvata的相互关系(英文)

猕猴桃属植物Actinidia spp,自然分布于中国的亚热带地区。对萼猕猴桃A.valvata的花芽受Pseudasphond ylia 瘿蚊属一未知种的寄生而形成花芽虫瘿,这种花芽瘿由于近年来在制药工业上的应用而受到重视。在中国中南地区研究对萼猕猴桃—瘿蚊的相互关系过程中,我们的记载表明该造瘿昆虫在一定情形下可能改变其寄主植物的雌雄异株之生殖模式。野外调查与实验证明寄主植物受寄生而形成虫瘿的比例很高。但虫瘿密度却于不同沟谷间,或同一沟谷内不同植株间有异。在二条沟谷内,92％和75％植株分别被寄生,而在第3条沟谷内没有植株受寄生。受寄生的雄性植株只产生虫瘿,而受寄生的雌性植株则产生正常果与虫瘿。有迹象显示当寄主植株有虫瘿形成时其正常果数量也更多。作者认为这可能是昆虫诱导功能上雌雄异株植物形成雄性异株雌雄同株之生殖模式的少数例子     

Sexually dimorphic gall structures correspond to differential phytohormone contents in male and female wasp larvae

Sexually dimorphic galls are rare among gall‐inducing insects and the reason for their occurrence is unknown. The pteromalid wasp Trichilogaster acaciaelongifoliae, which induces galls on Acacia longifolia, is one such species. In the present study, the anatomical and physiological attributes of male and female galls of T. acaciaelongifoliae are examined and compared. Histological preparations are used to characterize anatomical differences between male and female gall chambers. Bioassays, high‐performance liquid chromatography‐mass spectrometry and an enzyme immunoassay are used to measure concentrations of auxin and cytokinin in normal buds, galled tissues, and larvae of both sexes. Female chambers are found to be 3.3‐fold larger, and are associated with 1.5‐fold more storage tissue and 3.5‐fold more vascular tissues than male chambers. Tissues from female chambers induce stronger cytokinin‐like bioactivity than tissues from male chambers. Female larvae have considerably higher concentrations of cytokinin free bases, ribosides, glucosides and monophosphates than male larvae; higher auxin‐like bioactivity than in normal or galled plant tissues; and almost twice the concentration of auxin than male larvae. Both male and female larvae contain much higher auxin concentrations than either galled or normal plant tissues. These findings suggest that differing levels of phytohormones are involved in the development of sexual dimorphism of gall structures in this species.     

Plant organ abscission and the green island effect caused by gallmidges (Cecidomyiidae) on tropical trees

Plants exhibit a wide array of inert and induced responses in defense against herbivore attack. Among these the abscission of organs has been argued to be a highly effective mechanism, depending, however, on the herbivore’s feeding mode. While consisting of plant tissues, insect induced galls are seen as the extended phenotype of the gall inducer which might circumvent many or most of the plant defenses. There is very little information whether and how far beyond the gall tissue gall inducers might affect plant tissues. A localized impact is likely to leave the abscission of galled organs as a viable defense although at a cost. Here, we report on an instance where the host plant, Neea madeirana (Nyctaginaceae) abscises leaves galled by two species of Bruggmannia (Diptera: Cecidomyiidae), more frequently than ungalled leaves in a rain forest in Amazonia, Brazil. Once on the forest floor the leaves decay quickly, while both gall types show signs of localized maintenance of healthy tissues for a while (the green island effect). However, on the forest floor galls are exposed to a new set of potential natural enemies. Both gall types show a minimum of a five-fold increase in mortality due to pathogens (fungi and bacteria) compared to galls that were retained on the host tree. We discuss the adaptive nature of plant organ abscission as a plant defense against gallers and as a gall inducer adaptive trait. Handling editor: Graham Stone.     

Alteration of free amino acid concentrations in insect galls induced by Andricus mukaigawae (Hymenoptera; Cynipidae)

1. Insect galls are abnormal plant growths that develop in response to a stimulus provided by a galling insect. The nutrition hypothesis suggests that the concentrations of nutritive compounds in galls are changed to provide optimum nutrition for the larvae and adults of galling insects. 2. To test the nutrition hypothesis, we determined the concentrations of 20 free amino acids in galls and in galled and ungalled twigs of Quercus fabri during the larval and adult stages of Andricus mukaigawae using high-performance liquid chromatography with ultraviolet–visible detection. 3. At the larval stage, the concentrations of 12 out of 20 amino acids in A. mukaigawae galls were significantly higher than those in galled and ungalled twigs. Asparagine and tryptophan were the most abundant nonessential and essential amino acids, respectively, in A. mukaigawae galls. 4. At the adult stage, the concentrations of most amino acids, except proline, were significantly lower in A. mukaigawae galls than in galled and ungalled twigs. The A. mukaigawae adults may not manipulate amino acid levels because the adults do not feed on galls. The decrease of amino acid levels in adult galls may be viewed as a depletion. 5. The composition of free amino acids in A. mukaigawae galls was significantly different from the composition in galled and ungalled twigs in both the larval and adult stages. 6. Our results may support the nutrition hypothesis. We suggest that a high concentration of proline in A. mukaigawae galls may protect larvae and adults from plant defense responses.     

Three loblolly pine CesA genes expressed in developing xylem are orthologous to secondary cell wall CesA genes of angiosperms

Specific plant cellulose synthases (CesA), encoded by a multigene family, are necessary for secondary wall synthesis in vascular tissues and are critical to wood production. We obtained full-length clones for the three CesAs that are highly expressed in developing xylem and examined their phylogenetic relationships and expression patterns in loblolly pine tissues. Full-length CesA clones were isolated from cDNA of developing loblolly pine (Pinus taeda) xylem and phylogenetic inferences made from plant CesA protein sequences. Expression of the three genes was examined by Northern blot analysis and semiquantitative RT-PCR. Each of three PtCesA genes is orthologous to one of the three angiosperm secondary cell wall CesAs. The PtCesAs are coexpressed in tissues of loblolly pine with tissues undergoing secondary cell wall biosynthesis showing the highest levels of expression. Phylogenetic and expression analyses suggest that functional roles for these loblolly pine CesAs are analogous to those of orthologs in angiosperm taxa. Based upon evidence from this and other studies, we suggest division of seed plant CesA genes into six major paralogous groups, each containing orthologs from various taxa. Available evidence suggests that paralogous CesA genes and their distinct functional roles evolved before the divergence of gymnosperm and angiosperm lineages.     

THE RELATIONSHIP BETWEEN A FLOWER GALL MIDGE PSEUDAS-PHONDYLIA SP. (DIPTERA: CECIDOMYIIDAE) AND ITS HOST PLANT ACTINIDIA VALVATA*

Abstract Kiwifruit plants, Actinidia sp., are native to subtropical China. The flower-bud gall of A. valvata, which is induced by an undescribed gall midge in the genus Pseud as phond ylia, is valued by the pharmaceutical industry. When studying the biology of the Actinid ia/Pseud as phond ylia interaction in Central-south China we found evidence suggesting that under certain circumstances the gall insect modifies the reproductive mode of the dioecious host plant. Surveys and field experiments in the National Hupingshan Natural Reserve showed a high frequency of galled trees. The density of galled trees varied among valleys and among trees within the valleys. In two valleys, 92% and 75%, respectively, of all trees were attacked, while in a third valley no trees were attacked. When infested, staminate tree only produced galls, whereas pistillate plants produced normal fruits as well as galls. Gall shape differed between male and female trees. Trees with galls tended to produce more fruits than treea without galls. We speculate that this is one of a few documented examples of an insect that induces androdioecy in an otherwise functionally dioecious plant.     

The effects of host-plant properties on gall density,gall weight and clone size in the aphidAploneura lentisci (Pass.) (Aphididae: Fordinae) in Israel

Summary Samples of shoots ofPistacia lentiscus carrying galls of the aphid,Aploneura lentisci, were collected at three localities in Israel. Shoots growing near pruning scars carried more galls than elsewhere on the plant, but these galls weighed less and contained fewer aphids (smaller clones). The proportion of empty galls increased with gall density. Crowding of galls at such sites may be due to the early burst of buds at the time of aphid emergence from the overwintering eggs, and not to active search for preferred sites. Shoots bearing larger numbers of leaves carried heavier galls, which contained larger aphid clones. The position of the galled leaf on the shoot had no effect on gall weight nor on clone size. The physiological condition of the plant may be an important environmental (ecological) factor affecting the variation in clone-size and in aphid morphology among galls.     

Phenotypic plasticity and similarity among gall morphotypes on a superhost,Baccharis reticularia (Asteraceae)

Understanding factors that modulate plant development is still a challenging task in plant biology. Although research has highlighted the role of abiotic and biotic factors in determining final plant structure, we know little of how these factors combine to produce specific developmental patterns. Here, we studied patterns of cell and tissue organisation in galled and non‐galled organs of Baccharis reticularia, a Neotropical shrub that hosts over ten species of galling insects. We employed qualitative and quantitative approaches to understand patterns of growth and differentiation in its four most abundant gall morphotypes. We compared two leaf galls induced by sap‐sucking Hemiptera and stem galls induced by a Lepidopteran and a Dipteran, Cecidomyiidae. The hypotheses tested were: (i) the more complex the galls, the more distinct they are from their non‐galled host; (ii) galls induced on less plastic host organs, e.g. stems, develop under more morphogenetic constraints and, therefore, should be more similar among themselves than galls induced on more plastic organs. We also evaluated the plant sex preference of gall‐inducing insects for oviposition. Simple galls were qualitative and quantitatively more similar to non‐galled organs than complex galls, thereby supporting the first hypothesis. Unexpectedly, stem galls had more similarities between them than to their host organ, hence only partially supporting the second hypothesis. Similarity among stem galls may be caused by the restrictive pattern of host stems. The opposite trend was observed for host leaves, which generate either similar or distinct gall morphotypes due to their higher phenotypic plasticity. The Relative Distance of Plasticity Index for non‐galled stems and stem galls ranged from 0.02 to 0.42. Our results strongly suggest that both tissue plasticity and gall inducer identity interact to determine plant developmental patterns, and therefore, final gall structure.