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David H. Byrne

Despite the hundreds of existing stone fruit (Prunus spp.) cultivars used for fresh market, there is a continuing need to develop new stone fruit cultivars as the requirements of the industry change. Over the last 20 years there has been a shift toward private breeding as the public sector decreases its support of these long-range programs. As a result there are fewer public breeding programs and many of those still operating protect their releases and partially fund their programs with royalty payments. Other trends that are shaping the development of new stone fruit cultivars are a need for smaller or more easily managed tree architecture, a trend toward the use of fewer agricultural chemicals, the expansion of production zones into the milder winter zones to allow year-round availability of stone fruit, a general diversification of fruit types being marketed, the increased awareness of the health benefits of fruit consumption, the need for better and more consistent quality, and given the global marketing of these fruit the increased need for enhanced postharvest qualities. The breeding programs of the world are responding to these trends and working toward developing the cultivars for the world markets of the future.

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David H. Byrne and Natalie Anderson

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David H. Byrne and Natalie Anderson

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David H. Byrne and Natalie Anderson

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David H. Byrne and Natalie Anderson

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Unaroj Boonprakob and David H. Byrne

Diploid plums such as Prunus salicina, P. simonii, P. cerasifera, P. americana, P. angustifolia, P. mexicana, and their hybrids have a high level of RAPD polymorphisms. Of 71 successfully used primers, there are 417 reproducible RAPD markers and only 55 (13%) markers are not polymorphic. Genetic relationships of these diploid plums based on RAPD data is estimated using genetic distance (GD) defined as GDij = 1 – Sij, where Sij is similarity coefficient. Two similarity coefficients, Jaccard's and simple matching coefficient, are compared. Simple matching always yields higher similarity coefficients. Genetic distance within and between each gene pool: California, southeastern U.S., foreign, is estimated. Genetic distances of these diploid plums ranged from 0.32 to 0.68, and agreed well with the natural geographic distribution of the species. The cluster analysis using unweighted pair-group methods using arithmetic averages (UPGMA) was used to construct phenograms to summarize the relationships among these cultivated diploid plums and plum species.

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Unaroj Boonprakob and David H. Byrne

Six controlled crosses of cultivated and advanced selection Japanese-type plums adapted to southeast and southwest regions of the United States were made in 1990 and 1991. Over 800 seedlings from these crosses along with open pollinated seedlings of the parents were established in Suiting nurseries. The long range objective of this study is to determine linkage relationships between RAPD markers and commercially important traits (soluble solid, resistance to bacterial leaf spot, chilling requirement, fruit development period). The first step in the projects to characterize RAPD genotypes in the progenies. Eighty oligodecamers have been screened and 57 yielded successful reactions with an average of two to three bands per primer. The variability and inheritance of the RAPD markers in these plum populations will be described.

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Terry Bacon and David H. Byrne

Mild winter weather conditions reduce fruit yield and quality of many peach cultivars grown in the Medium Chill Region of the United States. Peach fruit shape instability limits marketing options for growers in this region. The Stonefruit Breeding Program at Texas A&M University evaluated a wide range of peach cultivars and breeder selections from throughout the world during the mild winters of 1988-198 9 and 1989-1990. Fruit shape response was highly variable among genotypes with similar chilling requirements. The implication of this is that the potential is high for eliminating fruit shape instability due to highly variable winter conditions in the Medium Chill Peach Production Region.

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David H. Byrne and Natalie Anderson