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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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Shuyin Liang, Xuan Wu, and David Byrne

The effect of heat on rose flowers was examined by measuring flower size in 10 diploid rose populations created by crossing the heat-tolerant Texas A&M University (TAMU) breeding lines (M4-4, J06-20-14-3) and sensitive (97/7-2, ‘Red Fairy’, ‘Sweet Chariot’, ‘Vineyard Song’, ‘Old Blush’, and ‘Little Chief’) diploid roses. As expected, the populations and individual seedlings differed in flower size. The heat-shock treatment (1 hour at 44 °C) decreased flower diameter (15.7%), petal number (23.3%), and flower dry weight (16.9%). Flower-size traits had moderately low narrow-sense (0.24, 0.12, and 0.34 for flower diameter, petal number, and flower dry weight, respectively) and moderately high broad-sense (0.62, 0.74, and 0.76 for flower diameter, petal number, and flower dry weight, respectively) heritability indicating important nonadditive genetic effects. If rose genotypes vary in floral heat tolerance, a differential response to heat among populations, seedlings, or both detected statistically by a significant interaction effect would be expected. Both the analysis of variance (ANOVA) and the restricted estimated maximum likelihood (REML) analyses showed a positive population × heat stress interaction effect for flower diameter. Although our data indicate differences in floral heat tolerance among the populations and genotypes, the effect was small as compared with the other sources of variation. Thus, using this 1-hour heat-shock approach would not be an effective strategy to select for floral heat tolerance in rose.

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Terry A. Bacon and David H. Byrne

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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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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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Jonathan W. Sinclair and David H. Byrne

Carbohydrate source of peach [Prunus persica (L.) Batsch] embryo culture media affects embryo growth and survival. The first objective of this study was to determine the effect of five carbohydrates (fructose, glucose, maltose, sorbitol, and sucrose) in Woody Plant Medium (WPM) on the germination and survival of peach embryos in vitro. Fructose, glucose, maltose, and sucrose in WPM resulted in better embryo germination and survival than sorbitol. Fructose (2% and 3%) produced greater survival than all other carbohydrates tested in smaller embryos (<10% ovule dry weight). However, sucrose was better than all other carbohydrates tested in the larger embryos (≥10% ovule dry weight). In addition, large embryos (>10% ovule dry weight) on fructose at 1% combined with glucose, maltose, sorbitol, or sucrose at 1% had equivalent or higher survival than did those on either 1% or 2% sucrose in conjunction with the same carbohydrates. Embryo survival on different carbohydrates varied with genotype. The second objective of this study was to determine the effect of three levels of MES buffer (0.0 mm, 4.5 mm, and 9.0 mm) on medium pH stability and embryo survival. MES buffer at 0.0 mm and 4.5 mm concentration produced significantly better embryo survival than 9.0 mm. The pH stability was better at MES 9.0 mm, however survival decreased significantly. Chemical name used: [2-(N-morpholino)-ethane sulphonic acid] (MES)

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David H. Byrne and Terry A. Bacon

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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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David H. Byrne and Terry A. Bacon

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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.