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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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Shuyin Liang, Xuan Wu and David Byrne

This project examined rose (Rosa ×hybrida) performance by measuring flower size and flower numbers per inflorescence in spring, summer, and fall seasons (mean temperatures 21.7, 30.0, and 18.1 °C, respectively) in interrelated rose populations. Populations and progeny differed in flower size as expected. Heat stress in the summer season decreased flower diameter (18%), petal number (17% to 20%), and flower dry weight (32%). Analysis of variance (ANOVA) showed a significant population/progeny × heat stress interaction for flower diameter indicating that rose genotypes responded differentially to heat stress. Flower size traits had moderate low to moderate narrow-sense (0.38, 0.26–0.33, and 0.53 for flower diameter, petal number, and flower dry weight, respectively) and moderately high to high broad-sense (0.70, 0.85–0.91, and 0.88 for flower diameter, petal number, and flower dry weight, respectively) heritability. Genotype × environment (G × E) variance (population/progeny × heat stress) for flower diameter accounted for ≈35% of the total variance in the field experiment indicating that heat stress had moderate differential genotypic effects. However, the genetic variance was several fold greater than the G × E variance indicating selection for flower size would be effective in any season but for the selection of a stable flower size (heat tolerant) rose genotype, selection would be required in both the cool and warm seasons. Seasonal differences in flower productivity of new shoots did not appear related to heat stress but rather to the severity of pruning conducted in the different seasons. The number of flowers produced on the inflorescence had moderate narrow-sense (h 2 = 0.43) and high broad-sense (H 2 = 0.75) heritability with a moderate genotype × pruning effect that explained about 36% of the variance.

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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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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.