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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.
Nineteen peach [Prunus persica (L.) Batsch] genotypes and 45 plum (Prunus salicina Erhr. and hybrids) genotypes with different flesh and skin color were analyzed for their antioxidant content and activity. Anthocyanin content, phenolic content, and antioxidant activity were higher in red-flesh than in light-colored flesh peaches. Carotenoid content was higher in yellow-flesh peaches than in light-colored ones. Red-flesh plums generally had higher anthocyanin and phenolic contents than the other plums but not necessarily greater antioxidant capacity. The total phenolic content had the most consistent and highest correlation with antioxidant activity, indicating that it is more important in determining the antioxidant activity of peaches and plums than are the anthocyanin or carotenoid contents. In general, the wide range of phytochemical content and antioxidant activity found indicates that the genetic variability present can be used to develop cultivars with enhanced health benefits.
Fifteen genetically diverse roses were evaluated for the ability to undergo somatic embryogenesis. Over the two media (MS and B5), two sugars (glucose and sucrose), and two explants (filaments and petiole) used, 20 to 30% of the `Tournament of Roses' callus was embryogenic whereas only crystalline callus was produced in cultures of `Baby Love', `Ingrid Bergman', `Perfume Delight', `Prominent', `Sunflare', and 90-202. Cultures of `Tournament of Roses' consistently produced somatic embryos whereas `Baby Love' produced no embryos. An F1 progeny of `Tournament of Roses' × `Baby Love' was chosen to test whether the ability to undergo embryogenesis in Rosa hybrida L. is heritable. Data collected from tests on F1 progeny between these genotypes suggest that the ability to undergo embryogenesis is indeed heritable in an additive fashion.
The influence of medium formulation, methods of ovule support, and ovule perforation on in vitro growth of immature peach [Prunus persica (L.) Batsch] embryos (4.0 to 8.7 mm long) was investigated. Maximum embryo dry weights were attained with vermiculite support, ovule perforation, and 10% sucrose in the medium. At high sucrose levels, all three tested media (Monnier, modified Murashige and Skoog, or modified Stewart and Hsu medium) performed similarly. Adding IAA and kinetin to culture media did not enhance embryo growth. Using the vermiculite support system, small embryos of early maturing peach cultivars, obtained at fruit maturity, were cultured successfully and used as maternal parents in breeding programs. Chemical name used: indole acetic acid (IAA).
Seedlings of 108 families from crosses among 42 peach [Prunus persica (L.) Batsch] cultivars and selections were evaluated for six plant characteristics in 1993, 1994, and 1995. The data were analyzed by using a mixed linear model, with years treated as fixed and additive genotypes as random factors. Best linear unbiased prediction (BLUP) was used to estimate fixed effects. Restricted maximum likelihood (REML) was used to estimate variance components, and a multiple trait model was used to estimate genetic and phenotypic covariances among traits. The narrow-sense heritability estimates were 0.41, 0.29, 0.48, 0.47, 0.43, and 0.23 for flower density, flowers per node, node density, fruit density, fruit set, and blind node propensity, respectively. Most genetic correlations among pairs of traits were ≥0.30 and were, in general, much higher than the corresponding phenotypic correlations. Flower density and flowers per node (ra = 0.95), fruit density and fruit set (ra = 0.84) and flower density and fruit density (ra = 0.71) were the combinations of traits that had the highest genetic correlation estimates. Direct selection practiced solely for flower density (either direction) is expected to have a greater effect on fruit density than direct selection for fruit density.
Thirteen peach [Prunus persica (L.) Batsch] fruit characteristics were investigated for 3 years, 1993, 1994, and 1995, in College Station, Texas, to determine heritability, genetic and phenotypic correlations, and predicted response to selection. Seedlings of 108 families resulting from crosses among 42 peach cultivars and selections were used in the evaluations. A mixed linear model, with years treated as fixed and additive genotypes as random factors, was employed to analyze the data. Best linear unbiased prediction (BLUP) was used to estimate fixed effects. Restricted maximum likelihood (REML) was used to estimate variance components, and a multiple trait model was used to estimate genetic and phenotypic covariances between traits. Genetic and phenotypic correlations ≥0.65 and <0.30 were considered strong or very strong and weak, respectively. Date of ripening, fruit development period (FDP) and date of full bloom had the highest heritability (h2) estimates, 0.94, 0.91, and 0.78, respectively. Fruit cheek diameter and titratable acidity (h2 = 0.31) were the traits with the lowest estimates. Fruit development period, fruit blush, and date of ripening had the highest predicted selection responses, whereas fruit suture, fruit cheek, L/W12 (ratio fruit length to average fruit diameters), and fruit tip had the lowest values. Most genetic correlations were ≥0.30 and were, in general, much higher than the corresponding phenotypic correlations. All four measures of fruit size were genetically and phenotypically very strongly correlated. Important genetic correlation estimates were also observed for date of ripening with FDP (ra = 0.93), date of ripening and FDP with fruit blush (ra = -0.77, ra = -0.72), SS (percent soluble solids) (ra = 0.63, ra = 0.62) and TA (ra = 0.55, ra = 0.64), and SS with TA (ra = -0.56). Direct selection practiced solely for early ripening and short FDP is expected to have a greater effect on correlated traits than direct selection for early bloom and large fruit mass.
Breeding values (BVs) for four plant (bloom date, fruit development period, fruit density, and blind node propensity) and five fruit (weight, blush, shape, soluble solids, and titratable acidity) traits of 28 peach [Prunus persica (L.) Batsch (Peach Group)] genotypes used as parents in the Texas A&M University peach breeding program were predicted using best linear unbiased prediction (BLUP). Data from seedlings of 108 families developed from 42 peach parents were analyzed by using a mixed linear model, with years treated as fixed and additive genotypes as random factors. The precision of the predictions was high for most parental genotypes, as indicated by the correlations (rTI) between predicted and true BVs and the standard error of the predictions (SEP). In most cases, the higher the number of progeny, the better the agreement between predicted and true BVs for that parent. Parents with observations from more than 30 seedlings had a rTI ≥ 0.90 and smaller SEPs. For all traits analyzed, the lowest precision (low rTI and high SEP) was observed for `Flordaking', whose predicted BVs was based only on pedigree information.
Blind nodes in peach is widely observed in the mid summer growth in the southern of the U.S.A. This condition is characterized by the apparent absence of axillary buds. The developmental anatomy of blind nodes was investigated by sampling peach shoots every two weeks throughout the season. Although the bud initiation was observed in both blind and normal nodes, the differentiation in the blind nodes was limited such that no prophyll development was observed. Furthermore, it appeared that the initiated meristems in the blind nodes may have degenerated to form blank leaf axils.
SH and MS media, sucrose concentrations (6% and 10%) and types of support (0.25% Gelrite, vermiculite and filter paper bridge) were compared in a factorial experiment to determine the effects on growth of immature embryos from peach cultivar B611505. Embryos were measured at the beginning of the experiment (control) and all treatments were kept in the dark at room temperature, for 40 days. Although gelrite, over all media treatments, increased embryos wet weight by 66%, the embryos were soft and succulent and their dry weight increased only 37%. Vermiculite support, on the other hand, increased wet and dry weights by 63% and 79%, respectively. Less embryo growth occurred with MS medium and filter paper bridge. Except for vermiculite and SH medium, 10% sucrose was more effective than 6% in increasing embryo growth.
Sixty-one cultivars of geraniums, including zonal, regal, ivy, and scented, were tested for susceptibility to three strains of Ralstonia solanacearum: a race 1, biovar 1 (R1B1) strain P597 isolated from tomato in Florida, a R1B1 strain P673 obtained from pothos originated from Costa Rica, and a race 3, biovar 2 (R3B2) strain UW551 isolated from geranium imported from Kenya. These three strains represent populations of R. solanacearum found in the United States or imported with infected plant propagative material. A genomic comparison of the geranium cultivars was also done using amplified fragment length polymorphisms. Both R1B1 strains were more virulent than the R3B2 strain, producing wilt symptoms on most cultivars of zonal, regal, and ivy types. Variation in susceptibility of geranium cultivars to the two R1B1 strains was observed. The R3B2 strain UW551 had a much more restricted host range and was not able to infect most regal geranium cultivars when applied as a soil drench. Many of the scented cultivars were found to be resistant to all three strains of R. solanacearum when tested using the drench inoculation method. However, most scented cultivars were found to be susceptible when plants were wound-inoculated. The greatest variation in type of resistance was observed between the scented geranium cultivars and specific strains of R. solanacearum.