USDA-ARS-AFRS 2217 Wiltshire Road Kearneysville, WV 25430 Voice: (304) 725-3451 x353
2217 Wiltshire Road
Kearneysville, WV 25430
Voice: (304) 725-3451 x353
Professional Biographical Information:
Ph.D. in Plant Breeding and Genetics (1978), Department of Horticulture,
M.S. in Plant Breeding and Genetics (1975), Department of Horticulture,
B.A. in Biology (1969),
1980-present: Research Horticulturist, USDA-ARS, Appalachian Fruit Research Station,
1978-1980: Associate Horticulturist, Department of Horticulture,
1974-1978: Graduate Research Assistant, Department of Horticulture,
Description of Research Projects:
The long-term objective of the USDA pear improvement program is the development of genetic solutions to the major problems affecting pear production and consumer acceptance. The program seeks to develop new and improved pear cultivars which combine excellent fruit quality, high productivity, precocious fruit bearing, and long postharvest storage life, and which have improved levels of resistance to the major diseases and insect pests. Current research and breeding focuses on resistance to fire blight, resistance to pear psylla, and development of productive dwarf pear trees. Projected impacts include (1) enhancing the economic returns to commercial orchardists by providing a high quality product and reducing production costs due to pesticide usage, (2) providing home orchardists with high quality pear cultivars which can be grown with fewer or no pesticides, and (3) providing consumers with high quality fruit with improved quality and ripening characteristics. The breeding program seeks to utilize the broad genetic resources of pear available worldwide. The research program characterizes these genetic resources for important traits and determines their genetic control in order to more effectively develop new cultivars. Traditional breeding, molecular genetic mapping, as well as genetic transformation is utilized for appropriate traits.
Current research and breeding goals include:
Breeding new fire blight resistant pear cultivars
Goal: Develop new cultivars and germplasm of pear with resistance to fire blight.
Background: The major varieties of pear grown in the
Approach: Hybridizations utilizing new and diverse germplasm will be incorporated into the program. European-type buttery flesh pears for the fresh market are the primary focus of the breeding program. A broad range in seasons of maturity and flavor types are being sought, but with added emphasis on dual-purpose cultivars with '
Collaborators: Jay Freer, Cornell University;
Breeding for host resistance to pear psylla
Goal: Develop new cultivars and germplasm of pear with resistance to pear psylla.
Background: The pear psylla (Cacopsylla spp.) is a major pest of European pear (Pyrus communis) in orchards in most temperate regions where the crop is grown. In
Host plant resistance has been characterized in the East Asian pear species, P. ussuriensis and P. xbretschneideri. and in P. ussuriensis x P. communis hybrids. Within P. communis, we have previously identified 15 old European cultivars with high levels of resistance. Ovipositional antixenosis, nymphal antibiosis, and feeding antixenosis have been identified as modes of host plant.
Approach: The two breeding populations currently utilized consist of (1) second and third generation backcross hybrids between P. communis and the Chinese species P. ussuriensis (primarily Illinois 65 and Illinois 76), as well as (2) first generation hybrids between east and west European P. communis germplasm. Additional third and fourth generation modified Asian x European backcrosses (to non-recurrent P. communis parents) and intercrosses have been made. Resistance to pear psylla in seedling selections will be verified using bioassays for nymphal feeding antixenosis, ovipositional antixenosis, and antibiosis. The general breeding strategy is based upon a combination of modified "backcrosses" to unrelated parents with high fruit quality and intercrosses to increase recombination.
Genetics of Host Resistance to Pear Psylla
Goal: Determine the mode of inheritance of host resistance to pear psylla in pear seedling populations
Background: Resistance in P. ussuriensis x P. communis populations has been characterized as quantitative, polygenic, and moderately heritable, and positively correlated with large fruit size. Preliminary data on nymphal feeding from our program with P. ussuriensis-derived populations confirms the polygenic nature. The mode of inheritance of resistance derived from East European pear cultivars (P. communis) has not been characterized. Knowledge of whether the inheritance is due largely to one (monogenic) or a few major genes (oligogenic), or to many genes (polygenic), and the nature of gene action is important in designing an appropriate breeding strategy.
Approach: Psylla-resistant east European pear cultivars have been hybridized in most combinations with susceptible parents. Nymphal feeding antixenosis of seedlings from each cross will be assayed, and the data analyzed to determine heritability and general and specific combining ability of the parents. In addition, association of molecular genetic markers to genes determining resistance will be investigated. Such markers could then be used to estimate the number and relative importance of the genes, and used as indirect selection criterion for resistance, that is, in marker-assisted selection.
Genetic transformation for fire blight resistance
Goal: Determine their efficacy of selected lytic peptide genes in enhancing resistance to fire blight in major pear cultivars.
Background: Lytic peptide genes exhibit antimicrobial activity by disrupting the cell membranes of bacteria and fungi, causing cell lysis and death. Various lytic peptides occur in plants, insects, and higher animals, and synthetic peptides have also been designed. Naturally occurring peptides such as attacin and cecropin, as well as synthetic cecropins have been shown to confer moderate enhancement of resistance to fire blight in apple and resistance of other crops to some of their most serious diseases.
Approach: Transgenic clones of the fire blight-susceptible '
Development of Transgenic Dwarfing of Pear
Goal: Determine the potential of growth regulating genes to produce dwarfed, but precocious and productive, pear trees, either as the scion or as the rootstock.
Background: Efficient production of pears is limited by large tree size and the long period of time necessary for newly planted trees to produce economically rewarding yield. Genetically dwarfed scion cultivars have not been commercially introduced. Pear rootstocks that would result in the degree of tree size control and precocious, high fruit yields in a manner similar to that achieved in apples have not been widely introduced from breeding programs. Various genes have been found to have an effect on plant growth habit. Genes from Agrobacterium rhizogenes, rolA, and rolC, have each shown effects on growth habit in woody and herbaceous plants, primarily reduced internode length. We have previously transformed 'Beurre Bosc' pear with the rolC gene and produced transgenic plants which display an extreme dwarf phenotype. Research in
Approach: Pear cultivars expressing the rolC gene and other growth regulating genes will be produced in order to evaluate more fully the effect of this gene on pear tree growth. Transgenic pears will be evaluated on their own roots, as scions budded onto clonal pear rootstock, and as rootstocks with 'Beurre Bosc' as the scion. Growth measurements in the greenhouse will include shoot length, lateral branch production, internode length, leaf size, leaf number, stem diameter and timing of active growth periods.