Exploration of a rare population of Chinese chestnut in North America: stand dynamics, health and genetic relationships

With the transport of plants around the globe, exotic species can readily spread disease to their native relatives; however, they can also provide genetic resistance to those relatives through hybrid breeding programmes. American chestnut (Castanea dentata) was an abundant tree species in North America until its decimation by introduced chestnut blight. To restore chestnut in North America, efforts are ongoing to test putative blight-resistant hybrids of Castanea dentata and Chinese chestnut (Castanea mollissima), but little is known about the ecology of C. mollissima. In a forest in northeastern USA in which C. mollissima has become established, we explored questions of stand dynamics, health and genetic relationships of C. mollissima offspring to an adjacent parent orchard. We found that C. mollissima was adapted and randomly distributed among native species in this relatively young forest. The genetics of the C. mollissima population compared with its parents indicated little effect of selection pressure as each of the parent trees contributed at least one offspring. The ease with which this exotic species proliferated calls to question why C. mollissima is rare elsewhere in forests of North America. It is likely that a time window of low animal predation allowed seedlings to establish, and the shallow soil at this site limited the maximum forest canopy height, permitting the characteristically short-statured C. mollissima to avoid suppression. Our results indicate that because C. mollissima exhibited pioneer species characteristics, hybrids between C. mollissima and C. dentata have the potential to be successful pioneer species of future forests in North America, and we challenge the paradigm that exotic tree species are wholly detrimental to native biodiversity. We contend that exotic tree species should be assessed not only by their level of threat to native species, but also by their potential positive impacts on ecosystems via hybrid breeding programmes.

Human-impacted landscapes facilitate hybridization between a native and an introduced tree

Spatial and temporal dynamics of hybridization, in particular the influence of local environmental conditions, are well studied for sympatric species but less is known for native-introduced systems, especially for long-lived species. We used microsatellite and chloroplast DNA markers to characterize the influence of anthropogenic landscapes on the extent, direction, and spatial distribution of hybridization between a native North American tree Juglans cinerea (butternut) and an introduced tree Juglans ailantifolia (Japanese walnut) for 1363 trees at 48 locations across the native range of butternut. Remarkably, admixture in anthropogenic sites reached nearly 70%, while fragmented and continuous forests showed minimal admixture (<8%). Furthermore, more hybrids in anthropogenic sites had J. ailantifolia seed parents (95%) than hybrids in fragmented and continuous forests (69% and 59%, respectively). Our results show a strong influence of landscape type on rate and direction of realized gene flow. While hybrids are common in anthropogenic landscapes, our results suggest that even small forested landscapes serve as substantial barriers to hybrid establishment, a key consideration for butternut conservation planning, a species already exhibiting severe decline, and for other North American forest trees that hybridize with introduced congeners.

Chestnut Breeding in the United States for Disease and Insect Resistance

The genus Castanea (family Fagaceae) is found in north temperate climates around the world, and is highly prized in many different cultures for its nutritious nuts and valuable timber. Selection for larger, better-tasting nuts has been ongoing in Asia and Europe for centuries. Early trade routes moved European chestnut trees (C. sativa) west of their native range (in the Caucasus mountains), and the Romans then moved them across their empire to provide support posts for grapevines, as well as for the nuts. Cultivar selection in Turkey, Italy, Spain, and Portugal has been extensive, and regional favorites developed. The many uses of the wood of American chestnut made this "all purpose" tree extremely valuable in its native range in North America. Nut production was important as a food source for rural families and many species of birds and animals. The other American species in the genus Castanea are classed as chinquapins, and may be divided into several or lumped as a single species. The small nuts from these trees and bushes serve primarily as mast for wildlife. Two serious diseases of chestnut trees changed the direction of chestnut research in the United States. Ink disease, caused by the root pathogen Phytophthora cinnamomi, was discovered to be the cause of widespread death of chestnuts and chinquapins in the southern United States, which had been observed since about 1850. This imported pathogen probably came into the southern United States before 1824. The second chestnut disaster was the introduction of chestnut blight disease, which was first found in the United States in 1904. The pathogen causing the lethal cankers is an Ascomycete now known as Cryphonectria parasitica. The longest continuing chestnut breeding program in the United States is in Connecticut.

Biological control of chestnut blight

After 77 years of being attacked by the chestnut blight fungus, American chestnut trees continue to sprout from gradually declining root systems. The blight fungus in Italy is now associated with virus-like agents that limit its pathogenicity, and attempts have been made to introduce these controlling agents into the blight fungus in the United States. If a way can be found to help the spread here of strains of the fungus with controlling agents, it may be possible to save the American chestnut trees in our eastern forests.

Chestnut Blight: Biological Control by Transmissible Hypovirulence in Endothia parasitica

Hypovirulence in Endothia parasitica is caused by a cytoplasmic determinant that is transferred by hyphal anastomosis in host tissue and in culture. Transmission of this determinant affects the virulence of the fungus to the extent that host invasion by previously virulent isolates is limited.

Genetic Analyses of ENDOTHIA PARASITICA: Linkage Data for Four Single Genes and Three Vegetative Compatibility Types

The loci cre, met and ts segregate independently in Endothia parasitica. The phenotype brown (br) seems to be determined by an allele at or very near the cre locus. The vegetative compatibility types (v-c) 5 and 39 are determined by different alleles at a locus that is not linked to cre, met or ts. Analysis of two crosses of v-c 5 strains by v-c 10 strains provides evidence that these two v-c groups are different at 5 or more v-c loci.

Diaporthe eres (Phomopsis oblonga) as a Pathogen of Butternut (Juglans cinerea) in Connecticut

Butternut seedlings from North Carolina (S. Schlarbaum, University of Tennessee) were planted during the spring of 2005 in an open space at the edge of the Mattatuck State Forest in Plymouth, CT. There were mature butternuts with visible cankers that were at the forest edge and out of reach. In May 2006, some seedlings had died and many small, dark lesions were found on the twigs and stems of living seedlings. Stems with lesions were surface sterilized with 10% bleach, rinsed with sterile water, the epidermis peeled away, and slices of the wood were placed on the surface of 2% water agar plates. From these, we consistently isolated a Phomopsis sp. that grew well on potato dextrose agar (PDA) at 28°C and produced alpha and beta spores (average 8 × 2 μm and 25 × 1 μm, respectively). A mixture of six such isolates on autoclaved pieces of butternut stem supported by water agar produced perithecia after 6 months with ascospores that matched the description of Diaporthe eres (two-celled, slightly constricted at the septum, and averaged 12 × 3 μm). Two of our isolates of Diaporthe eres, both of which were weakly pathogenic and recovered from the lesions, were inoculated into cut, dormant stems of butternut 'Buckley' in the laboratory, This ascomycete was reported to be a pathogen of Juglans ailantifolia and J. regia var. orientes in Japan (1) but has not been reported on J. cinerea. There is a rather vague report of Diaporthe spiculosa on other species of Juglans and Phomopsis juglandina on twigs (with a question mark) of J. regia (with a question mark) in California (2). These were not reported by T. Kobayashi. References: (1) T. Kobayashi. Bull. Gov. For. Exp. Stn. No. 226, 1970. (2) U.S. Dep. Agric. Index of Plant Diseases in the United States. Agric. Handb. No. 165, 1960.

Hypovirus Transmission to Ascospore Progeny by Field-Released Transgenic Hypovirulent Strains of Cryphonectria parasitica

ABSTRACT Strains of the chestnut blight fungus, Cryphonectria parasitica, have been genetically engineered to contain an integrated full-length cDNA copy of the prototypic virulence-attenuating hypovirus CHV1-EP713. Unlike natural hypovirulent C. parasitica strains, these transgenic hypovirulent strains are able to transmit virus to ascospore progeny under laboratory conditions. This ability provides the potential to circumvent barriers to cytoplasmic virus transmission imposed by the fungal vegetative incompatibility system. During July 1994, transgenic hypovirulent strains were introduced into a Connecticut forest site (Biotechnology Permit 94-010-01). Subsequent analysis of the release site confirmed hypovirus transmission from transgenic hypovirulent strains to ascospore progeny under field conditions. Additionally, it was possible to recover transgenic hypovirulent strains from the test site as long as 2 years after the limited, single-season release. Evidence also was obtained for cytoplasmic transmission of transgenic cDNA-derived hypovirus RNA, including transmission to mycelia of a virulent C. parasitica canker after treatment with conidia of a transgenic strain. Finally, a transgenic hypovirulent strain was recovered from a superficial canker formed on an untreated chestnut tree. Genetic characteristics of the recovered strain suggested that the canker was initiated by an ascospore progeny derived from a cross involving an input transgenic hypovirulent strain. The durability of a molecular marker for field-released cDNA-derived hypovirus RNA is discussed.

Isolation of Nectria galligena from Cankers on Sweet Birch

The fungus Nectria galligena infects many species of hardwood trees, causing "perennial canker," "European canker," or "target canker." Cultures from ascospores produced in stromata on the cankers have confirmed the pathogen species, but the fungus has rarely been successfully isolated from inside the cankers. Concern for the sweet birch trees affected by this disease in Connecticut prompted us to try isolations, using a method successful in isolating chestnut tree pathogens. Small pieces of cankered bark were stabbed into Granny Smith apples and, after incubation in boxes in the laboratory, pure cultures of N. galligena were easily removed as the pathogen slowly grew out, unchallenged, into the tissue of the apples. This technique will now be used to sample the N. galligena population in the birch populations being studied.

Molecular mapping of resistance to blight in an interspecific cross in the genus castanea

ABSTRACT A three-generation American chestnut x Chinese chestnut pedigree was used to construct a genetic linkage map for chestnut and to investigate the control of resistance to Endothia parasitica (chestnut blight fungus). DNA genotypes for 241 polymorphic markers (eight isozymes, 17 restriction fragment length polymorphisms [RFLPs], and 216 random amplified polymorphic DNAs [RAPDs]) were assayed on an F(2) family consisting of 102 individuals. Of these markers, 196 were segregating as expected and, subsequently, used for primary linkage mapping. Two isozymes, 12 RFLPs, and 170 RAPDs were mapped to 12 linkage groups spanning a total genetic distance of 530.1 Kosambi centimorgans. F(2) plants were evaluated for a response to E. parasitica infection by directly inoculating them with two unique fungal isolates and measuring canker expansion over a period of 3.5 months. Results were compared with the marker genotype data, thereby identifying genomic regions significantly associated with a resistance response. Single-marker or nonsimultaneous analyses of variance identified seven genomic regions that appear to have an effect on host response. Multiple-marker or simultaneous models suggest that three of these regions have a significant effect on host response, together explaining as much as 42.2% of the total variation for canker size. At each of the three putative resistance loci, alleles derived from the Chinese chestnut grandparent were associated with smaller canker size, or higher levels of resistance.

Isolation and characterization of a virus-resistant mutant of Cryphonectria parasitica

Hypovirulent strain NB58 of Cryphonectria parasitica contains a dsRNA virus with a genome size of approximately 12.5 kb. Although NB58 is very stable in culture, a phenotypically-distinct sector arose which was found to be dsRNA-free. Attempts to infect the mutant strain, termed NB58F, by pairing with the parent strain (NB58) or other conversion-compatible, virus-containing strains have been unsuccessful. DNA fingerprint analysis showed that NB58, NB58F, and a representative dsRNA-free single-conidial isolate of NB58 termed NB58-19, were isogenic. The mutant culture was phenotypically stable, and all single-conidial progeny had the NB58F morphology. NB58F was intermediate between NB58 and NB58-19 in laccase production and virulence. Pigmentation and sporulation of NB58F, however, were reduced to near the level of NB58. In mating studies, NB58F functioned only as the male in sexual crosses. The mutant phenotype (F) predominated by a ratio of 5:2 among the ascospore progeny of F-type x wild-type crosses. These data suggest the lesion is nuclear and may be associated with a chromosomal abnormality. Attempts to infect the NB58F-type ascospore progeny failed, whereas the wild-type progeny were successfully infected with strains compatible with one or the other parent at a frequency of about 34%. Hyphal anastomosis and movement of cytoplasmic material occurred when NB58F was paired with a compatible strain, suggesting that the lesion is involved in viral maintenance as opposed to initial virus infection. NB58F represents the first virus-resistant isolate of C. parasitica to be described.

THE ORIGIN OF ASCOGENOUS NUCLEI IN ENDOTHIA PARASITICA

Two conidia can fertilize a single protoperithecium of Endothia parasitica, and reassortment can occur between genes in the male nuclei early in the perithecium development.

Stomatal Response to Light of Solanum pennellii, Lycopersicon esculentum, and a Graft-induced Chimera

To learn how species differences in stomatal behavior are regulated, the response of epidermal and leaf diffusive resistance to light was investigated in Lycopersicon esculentum Mill., Solanum pennellii Corr., and a periclinal chimera having an S. pennellii epidermis and an L. esculentum mesophyll that was produced from a graft of the two species. S. pennellii has about 23% fewer stomata per square millimeter than does L. esculentum, and the two species have contrasting stomatal sensitivities to light. The abaxial stomata of L. esculentum open in dimmer light and to a greater extent than the adaxial stomata. The abaxial and adaxial stomata of S. pennellii respond similarly to light incident on the adaxial epidermis and are less open at all quantum flux densities than comparable stomata of L. esculentum. The patterns of response to light of the abaxial and adaxial stomata of the chimera were practically identical to those of L. esculentum, and quite unlike those of S. pennellii. Thus, the pattern of stomatal light response in the chimera was regulated by the L. esculentum mesophyll. The reduction in stomatal frequency of the chimera, which was regulated by the epidermis of S. pennellii, contributed to the 40% difference in leaf diffusive resistance between the plants in moderate light.

Solid media containing carboxymethylcellulose to detect CX cellulose activity of micro-organisms

Solid media containing carboxymethyl cellulose (CMC) were developed to detect CX cellulose-producing micro-organisms. Hydrolysis of CMC was seen as a clear zone around colonies after flooding plates with 1% aqueous hexadecyltrimethyl-ammonium bromide. Tests with ten bacterial and four fungal species showed that the degree of substitution (DS) of the CMC affects both growth and enzyme production. Most of the organisms produced more CX cellulase on CMC with a DS of 0-9, but CMC with a DS of 0-4 was better for one fungus. A qualitative measure of cellulase production may be obtained by calculating the ratio of zone size to colony diameter. Solid media containing CMC provided a more rapid assay of CX cellulose production than a medium containing native cellulose.

Microorganisms from composting leaves: Ability to produce extracellular degradative enzymes

Mixed populations of bacteria, fungi, and actinomycetes in a leaf compost pile were examined over a 100-day test period for their ability to produce extracellular proteolytic, lipolytic, amylolytic, cellulolytic, pectolytic, and ureolytic enzymes and ability to utilize alkanes. Urea was added to the leaves to adjust the carbon to nitrogen ratio but was of little value in maintaining the proper ratio since it was degraded within the first few days. The degradative enzymes excreted by microorganisms was dependent on the temperature of the pile. In many cases organisms able to produce specific extracellular enzymes at medium temperatures were able to grow at high temperatures, but either did not excrete the specific enzymes or the enzymes were inactivated by the high temperature.

Haploid plants from anthers of tobacco - Enhancement with charcoal

Haploid plants of Nicotiana tabacum L. were produced in greater numbers from anthers on agar medium containing activated charcoal than on the same medium without charcoal.

Pathogenicity resulting from mutation at the b locus of Ustilago maydis

This paper explores the genetic basis of the ability of the fungus, Ustilago maydis, to induce neoplastic galls in the corn plant (Zea mays). Pathogenic mutants of U. maydis were produced by ultraviolet irradiation of cultures of nonpathogenic diploids homozygous at the b locus. The mutants formed smaller neoplasms, produced fewer teliospores, and showed higher frequencies of meiotic failure and lower rates of basidiospore survival than did the wild-type fungus.