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David H. Byrne and Terry A. Bacon

A computer program was developed to calculate the percent contribution of the founding parents for any given peach or nectarine (Prunus persica) cultivar. The founding parents used most frequently for three low-chill (0 to 500 chill units) peach and nectarine breeding programs (Florida and Pelotas and Campinas, Brazil) were determined. The Florida program used several low-chill honey type peaches (`Hawaiian', `Okinawa') as a source of low chilling and then did extensive crossing with higher quality cultivars developed mainly in the northeastern United States. About 50% of the background of the Brazilian peach releases consists of local selections that were originally brought by the Portuguese explorers. Although each of the Brazilian programs used local peach materials, the local peaches used by each program are different. In addition, the program at Pelotas used germplasm from the Georgia–Florida and New Jersey breeding programs and the Campinas program used `Jewel' (honey peach) and several Florida nectarines (`Sunlite', `Sunred') in their development work. The founding parents among these three programs, although there is some common parentage, are different, and the intercrossing of materials from the various programs would be a useful approach to create more diversity in this germplasm.

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Yan Ma, David H. Byrne and Jing Chen

An objective of our rose breeding research is to transfer resistance to blackspot and other diseases from wild diploid species to modern rose cultivars. Interspecific hybrids among blackspot-resistant diploid species were chosen for chromosome doubling to produce fertile amphidiploids that could be hybridized to the tetraploid commercial germplasm. Five such F1 interspecific hybrids were treated with colchicine. The study included two different application procedures (shake in colchicine solution or colchicine in media), four colchicine concentrations (0.05%, 0.1%, 0.15%, and 0.20%), and five treatment periods (1, 3, 5, 8, and 10 days). After colchicine treatment, all the materials were cultured in vitro. One thousand-thirty-seven surviving explants were selected for typical “gigas” characteristics of doubled diploids. Chromosome counts on shoot tips of these selected genotypes confirmed 15 amphidiploids. The best colchicine treatment varied among the interspecific hybrids. Higher colchicine concentrations or duration reduced growth rating, rooting, and percent survival. The recognition of amphiploids and ploidy chimeras from young seedlings will also be discussed.

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Jonathan W. Sinclair and David H. Byrne

Carbohydrate energy source of various tissue culture media has an effect on growth and survival of the explants. Sucrose is the standard carbohydrate used in most tissue culture systems. The objective of the study was to determine the effect of five carbohydrate sources (fructose, glucose, maltose, sorbitol, and sucrose) at two levels (2% and 3%) on germination, growth, and survival of immature peach embryos (9.7 to 14.7mm) in vitro. Five cultivars were used. Overall, fructose, maltose, and sucrose each stimulated germination and growth as the primary carbohydrate energy source of peach embryo culture to the same degree; glucose and sorbitol were inferior. However, fructose was superior to sucrose in one cultivar. In general, sugar level did not affect survival, although cultivars did vary somewhat. Survival was found to be highly dependent upon embryo maturity.

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Yan Ma, David H. Byrne and Jing Chen

A high priority in rose (Rosa spp.) breeding research is the transfer of disease resistance, especially to black spot (Diplocarpon rosae Lib.), from wild diploid Rosa species to modern rose cultivars. To this end, amphidiploids (2n = 4x = 28) were induced with colchicine from five interspecific diploid (2n = 2x = 14) hybrids involving the black spot resistant diploid species R. wichuraiana Crép, R. roxburghii Thratt., R. banksiae Ait., R. rugosa rubra Hort., and R. setigera Michaux. Two application procedures (agitation of excised nodes in colchicine solution or tissue culture of shoots on medium with colchicine), five colchicine concentrations (0.0, 1.25, 2.50, 3.76, and 5.01 mmol), and five durations (2, 3, 5, 8, and 10 d) were used. After colchicine treatment, the materials were cultured in vitro and the surviving explants were examined for the “gigas” characteristics typical of doubled diploids. Chromosome counts of morphologically suspect genotypes confirmed 15 amphidiploids among 1109 plants that survived colchicine treatment. Although the effect of colchicine treatment varied some among interspecific hybrids, 2.50 mmol for 48 h of node agitation or 1.25 mmol for at least 5 d of shoot culture were optimal.

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Xuan Wu, Shuyin Liang and David H. Byrne

Plant architecture is a crucial trait in plant breeding because it is linked to crop yield. For ornamental crops such as roses, plant architecture is key for their aesthetic and economic value. In 2015, six rose plant architectural traits were evaluated on 2- to 3-year-old plants of F1 rose populations in May and December in College Station, TX, to estimate variability and heritability. The traits included plant height, the number of primary shoots, the length of primary shoots, the number of nodes on the primary shoot, the number of secondary shoots per primary shoot, and the number of tertiary shoots per primary shoot. Among these traits, plant height, the number of primary shoots, and the length of primary shoots showed a substantial amount of variability, whereas the number of secondary and tertiary shoots per primary shoot were skewed toward zero. Using a random effects model restricted maximum likelihood (REML) analysis, the architectural traits demonstrated low to moderate narrow-sense heritability (0.12–0.50) and low to high broad-sense heritability (0.34–0.92). Plant height and the number of primary shoots changed little after the first growth phase, whereas the other four traits were affected greatly by the genotype-by-environment (growth phase) interaction.

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Terry A. Bacon and David H. Byrne

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Young-ju Kim and David H. Byrne

Isozyme analysis has been used for cultivar identification, but little has been done with the genus Rosa. One hundred and sixty rose accessions (species, cultivars, and hybrids) were characterized for isozyme phenotypes using starch gel electrophoresis. Six enzyme systems were stained on three electrode buffer systems. ACP, MDH, and 6PGD were run on morpholine citrate (pH 6.1) and histidine (pH 5.7), PGI and PGM were run on histidine (pH 5.7) and lithium borate (pH 8.3), and SKDH was run on morpholine citrate (PH 6.1) and lithium borate (PH 8.3). The most variable isozymes were MDH and 6PGD. MDH and 6PGD revealed 10 and 9 bands, respectively. This study showed that isozyme variability exists in roses and can be useful in their classification into species groups.

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Xuan Wu, Shuyin Liang and David H. Byrne

Criteria to determine the horticultural quality of ornamental plants include plant architecture, flower characteristics, and resistance to biotic and abiotic stresses. The architecture of a rose (Rosa sp.) bush is linked to flower yield and ornamental value. The Texas A&M University (TAMU) Rose Breeding and Genetics program has the objective of developing garden rose cultivars that flower heavily and exhibit a compact full shape. To determine which architectural traits are key for the development of this desired shape, five rose seedlings with a desirable compact growth habit and five with an undesirable growth habit were selected from TAMU diploid rose breeding germplasm. This comparison indicated that the key traits for the selection of compact growth habit are the number of primary shoots followed by the number of secondary and tertiary shoots produced.

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David Shupert, David H. Byrne and H. Brent Pemberton

Research with the Basye Rose Breeding and Genetic Program at Texas A&M University has developed rose populations to use to study the genetic nature of leaf, stem, and several other rose traits. The rose populations are from the backcross of Rosachinensis`Old Blush' to WOB (interspecific hybridization of the diploid parents Rosawichuariana `Basye's Thornless' and `Old Blush'). The qualitative trait of presence of stem prickles and the quantitative traits of stem prickle density and leaflet number were observed in three field locations. Two locations are in College Station, Texas, and one location in Overton, Texas. The qualitative trait of presence of stem prickles supports the reported monogenic modes of inheritance. The presence of stem prickles (dominant) had a segregation ratio of 1:1 for prickles: no prickles. Prickle density and leaflet number demonstrated a quantitative mode of inheritance. For prickle density the genotype was significant and environment was nonsignificant. For leaflet number the genotype/generation was significant and environment was nonsignificant. This shows that genotype influences prickle density and leaflet number expression. The genotype by environment interaction was nonsignificant for all traits.

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Yan Ma, David H. Byrne and David M. Stelly

Mitotic chromosome numbers and measurements were determined from enzymatically digested shoot tips for 14 species of Rosa, subgenus Hulthemia, Platyrhodon, and Rosa (the latter represented by sections Pimpinellifoliae, Cinnamoneae, Synstylae, Banksianae, Laevigatae, and Bracteatae). All were 2n = 14 or 2n = 28, as expected from previously published chromosome counts in Rosa. Arm lengths of chromosome pairs measured from digitized images were analyzed for similarity using a least-squares algorithm. On this basis, tetraploid species were compared to their diploid relatives. This study demonstrates the value of karyotypic data in combination with morphological and ecological information for examining the evolution of Rosa.