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American Chestnut Trees (american + chestnut_tree)

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Life Sciences	100%

Selected Abstracts

Importance of Cryphonectria parasitica stromata production and intermediate-pigmented isolates in spread of Cryphonectria hypovirus 1 on grafted American chestnut trees

FOREST PATHOLOGY, Issue 5 2008
E. P. Hogan
Summary Large, surviving American chestnut trees, grafted in 1980, were inoculated in 1982 and 1983 with four ,white' European (French and Italian) hypovirulent strains of Cryphonectria parasitica infected with Cryphonectria hypovirus 1 (CHV1). Spread of Italian CHV1-Euro7, indicated by nucleotide sequence analysis of CHV1 isolates, and a high level of blight control, occurred on these trees for over 20 years. However, the means by which CHV1 spreads and the possible role of stromata production in that spread are unknown. In this study, 249 C. parasitica isolates were recovered from stromata excised from natural cankers on the grafted trees and plated on an agar medium; 5.2% of the stromata yielded white phenotype isolates, 9.2% yielded intermediate-pigmented isolates (30,70% pigmentation) and the remainder were normal-pigmented isolates. For comparison, cankers artificially established on blight-free, forest-clear-cut American chestnut trees, following inoculation with three Italian white hypovirulent strains, were evaluated in a similar manner. Of 241 C. parasitica isolates recovered from stromata, 66.4% had a white colony phenotype, 19.1% had an intermediate-pigmented phenotype and the remainder were normal-pigmented isolates. For single conidia collected from stromata and plated, nearly equal frequencies of only white and intermediate-pigmented colony phenotypes were obtained. Following dsRNA extraction and electrophoresis, 21 of 33 intermediate-pigmented isolates were positive for CHV1. Some normal pigmented isolates also were positive for CHV1. Single-sporing a CHV1-positve, normal-pigmented, natural-canker, stroma isolate (Str 1) from the grafts resulted in several deeply red-orange pigmented (JR) isolates as well as some white isolates. The dsRNA in the JR isolate was extracted and cDNAs made by reverse transcriptase-polymerase chain reaction (RT-PCR) for part of a region (p29) in ORF A. Nucleotide sequencing indicated 100% identity to CHV1 present in the inoculated Italian white strain, Ep 47. The results indicate that stromata production on the grafted trees may contribute to CHV1 spread, and the presence of CHV1 in intermediate-pigmented isolates and some normal pigmented isolates indicates these isolates, often overlooked, may be important in CHV1 spread and the high level of blight control on the grafted trees. [source]

Incomplete movement of Cryphonectria hypovirus 1 within a vegetative compatibility type of Cryphonectria parasitica in natural cankers on grafted American chestnut trees

FOREST PATHOLOGY, Issue 6 2002
E. P. Hogan
Summary American chestnut trees, grafted in 1980 from large survivors, were inoculated in 1982 and 1983 with four white (European) hypovirulent strains of Cryphonectria parasitica, infected with C. hypovirus 1 (CHV1); this hypovirus has been shown to be capable of moving rapidly within the mycelium of a vegetative compatibility (vc) type of C. parasitica in blight cankers. Using a 49-cell lattice plot, 17.8×17.8 cm, the spatial patterns and frequencies of white and pigmented isolates and white and pigmented vc types were investigated within superficial cankers on the grafts located outside the hypovirulent-strain-inoculated zone. Four of six cankers assayed contained white isolates, and three of the four had random spatial patterns of white isolates, based on join-count statistics. Vc tests, using pigmented isolates and pigmented single-spore colonies of white isolates, indicated that the majority of white and pigmented isolates recovered from each of two cankers assayed were in one vc type. White and pigmented lattice-plot cells of the same vc type were frequently in contact with each other, indicating incomplete movement of CHV1 within a vc type. Nine and 10 vc types were found in the two cankers; it is hypothesized that small, white vc type areas in each canker may be a source of CHV1 transmission to the major vc types. Based on join-count statistics, the spatial pattern of the single, major vc type in one canker was non-random (aggregated), whereas the other canker had a random major vc type pattern. White and pigmented in vitro variants (sectors) of C. parasitica, that resemble white and pigmented in vivo variants in spatial contact and vc compatibility, were intermediate hypovirulent and virulent on forest American chestnuts, and dsRNA positive and negative, respectively. Incomplete movement of CHV1 within a vc type could be a major cause of the prevalence of pigmented isolates in superficial cankers on chestnut trees. Résumé Des châtaigniers américains greffés en 1980 à partir de grands arbres survivants, ont été inoculés en 1982 et 1983 avec quatre souches blanches (européennes) hypovirulentes de Cryphonectria parasitica, infectées par l'hypovirus 1 (CHV 1). Cet hypovirus avait été montré capable de migrer rapidement dans le mycélium végétativement compatible (vc) de C. parasitica dans des chancres. Grâce un dispositif à 49 cellules (17,8×17,8 cm), la répartition spatiale et la fréquence des isolats blancs et pigmentés, et des GCV, ont étéétudiées dans des chancres superficiels chez les greffons, en dehors de la zone inoculée par les souches hypovirulentes. Quatre des six chancres étudiés contenaient des isolats blancs, dont la répartition spatiale était erratique chez trois d'entre eux. Les tests de compatibilité végétative, utilisant des isolats pigmentés et des colonies pigmentées mono-sporées d'isolats blancs, ont montré que la majorité des isolats blancs et des isolats colorés trouvés dans chacun des deux chancres analysés, était d'un seul type végétatif. Les cellules du dispositif, blanches ou pigmentées du même GCV, étaient fréquemment en contact, ce qui indique un mouvement incomplet de CHV1 dans un GCV. Neuf et dix GCV ont été trouvés dans les deux chancres et on avance l'hypothèse que de petites zones à GCV blancs dans chaque chancre peuvent être une source de transmission de CHV1 aux types végétatifs majoritaires. L'unique GCV majoritaire dans un des chancres n'était pas réparti au hasard (agrégé), mais il l'était dans l'autre chancre. Les variants blancs et pigmentés in vitro (secteurs) de C. parasitica, qui ressemblent aux variants blancs et pigmentés in vivo en contact spatial, étaient intermédiaires en hypovirulence et en virulence sur les châtaigniers américains, et respectivement positifs et négatifs pour le dsRNA. Un mouvement incomplet de CHV1 dans un GCV pourrait être la principale cause de la prévalence d'isolats pigmentés dans des chancres superficiels. Zusammenfassung Amerikanische Kastanien (Castanea dentata), die im Jahr 1980 von adulten überlebenden Exemplaren veredelt worden waren, wurden 1982 und 1983 mit vier unpigmentierten, hypovirulenten Stämmen von Cryphonectria parasitica aus Europa inokuliert, die mit dem Cryphonectria parasitica - hypovirus 1 (CHV 1) infiziert waren. Es war nachgewiesen, dass sich dieses Hypovirus rasch innerhalb des Myzels eines vc-Typs von C. parasitica in Krebsen ausbreiten konnte. Bei oberflächlichen Krebsen an veredelten Bäumen ausserhalb der mit dem hypovirulenten Stamm inokulierten Zone wurde auf einer 17,8×17,8 cm grossen Fläche (die in 49 Quadrate unterteilt wurde) die räumliche Verteilung und die Häufigkeit von unpigmentierten und pigmentierten Isolaten sowie der vc-Typen untersucht. Vier von sechs analysierten Krebsen enthielten weisse Isolate und drei davon zeigten zufällige Verteilungsmuster der Isolate (gemäss Joint-Count-Statistik). Vc-Tests mit pigmentierten Isolaten und pigmentierten Einzelsporkulturen von weissen Isolaten zeigten, dass die Mehrheit der weissen und der pigmentierten Isolate von zwei Krebsen zur gleichen vc-Gruppe gehörten. Weisse und pigmentierte Probepunkte mit dem gleichen vc-Typ waren häufig benachbart, was eine unvollständige Ausbreitung des CHV 1 innerhalb eines vc-Typs anzeigt. In den 2 Krebsen wurden 9 bzw. 10 vc-Typen nachgewiesen und es wird vermutet, dass kleine Bereiche mit weissem vc-Typ innerhalb eines Krebses als Reservoir für die Übertragung des Virus zu den dominanten vc-Typen fungieren können. Mit Hilfe der Joint-Count-Statistik wurde nachgewiesen, dass das räumliche Muster des einen, dominanten vc-Typs in einem Krebs nicht zufällig, sondern aggregiert war, während der andere Krebs ein zufälliges Verteilungsmuster der vc-Typen aufwies. Weisse und pigmentierte Varianten von C. parasitica, die in vitro auftraten (Sektoren), und die den weissen und pigmentierten Varianten sehr ähnlich sind, die in der Natur in räumlichem Kontakt zueinander auftreten, und die vegetativ kompatibel sind, zeigten in Feldversuchen auf C. sativa eine mittlere Hypovirulenz bzw. Virulenz. Ausserdem waren sie dsRNA positiv bzw. negativ. Die unvollständige Ausbreitung des CHV 1 innerhalb einer vc-Typs könnte das überwiegen pigmentierter Isolate in oberflächlichen Krebsen erklären. [source]

Demography of American chestnut populations: effects of a pathogen and a hyperparasite

JOURNAL OF ECOLOGY, Issue 4 2004
ANITA L. DAVELOS
Summary 1Matrix models were used to evaluate the effect of chestnut blight infection on transition probabilities and population growth rates for American chestnuts. Disease-free, epidemic and recovering (i.e. pathogen infected with a double-stranded (ds) RNA hypovirus) populations were compared. 2Population growth rates (,) did not differ significantly over time or with disease status. However, predicted stable stage distributions differed between population types, with disease-free and recovering populations more similar to each other than either was to epidemic populations. 3Survival had the highest proportional contribution to population growth rates as revealed by elasticity analyses. However, reductions in stasis of the largest trees contributed most to reductions in population growth rate when comparing diseased with disease-free populations using LTRE. 4The presence of hypovirus reduces pathogen virulence, allowing individual American chestnut trees to increase in size. Where dsRNA has spread, chestnut populations in Michigan have attained population dynamics similar to those found in disease-free populations. 5Matrix models and life table response experiments can be used to detect important pathogen-mediated changes in the dynamics of host populations. [source]

Limited Reintroduction Does Not Always Lead to Rapid Loss of Genetic Diversity: An Example from the American Chestnut (Castanea dentata; Fagaceae)

RESTORATION ECOLOGY, Issue 3 2007
Sarah A. M. Pierson
Abstract In restoring species, reasons for introducing limited numbers of individuals at different locations include costs of introduction and maintenance, limited founder supply, and risk "bet hedging." However, populations initiated from few founders may experience increased genetic drift, inbreeding, and diversity loss. We examined the genetic diversity of an isolated stand of more than 5,000 American chestnut trees relative to that of the 9 surviving stand founders (out of 10 total) planted in the 1880s. We used minisatellite DNA probes to reveal 84 genetic markers (circa 24 loci) among the nine founders, and their genetic diversity was compared with three separate plots of descendant trees, as well as with two natural stands. The descendants were circa 7.3% more heterozygous than the founders (mean estimated H= 0.556 vs. 0.518, respectively; p < 0.0001). Genetic differentiation was not pronounced (FST < 0.031), and no markers, including those at low frequency among the founders, were lost in the descendants. The founders and natural transects were not significantly different in H or similarity (mean proportion of bands shared). Special planting or mating protocols for establishment of a vigorous American chestnut population from a low number of founders may not be required to avoid strong effects of genetic drift and inbreeding. These results demonstrate that loss of genetic diversity following reintroduction of a limited number of founders is not always inevitable, such as this case where the species is highly outcrossing, expression of heterozygous advantage may occur, the original founders remain as gene contributors over generations, and the establishing population expands constantly and rapidly. [source]