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Ockert Greyvenstein, Terri Starman, Brent Pemberton, Genhua Niu, and David Byrne

The decline of garden rose sales over the past 20 years can be partially attributed to the lack of material adapted to a wide range of landscapes, which includes adaptation to high temperature stress. Current methods for evaluating high temperature susceptibility in garden roses are based on field observations, which are time consuming and subjected to ever-changing environmental conditions. A series of experiments were conducted to optimize protocols and compare the use of chlorophyll fluorescence (CFL) and cell membrane thermostability (MTS) by way of electrolyte leakage as methods to screen for high temperature susceptibility. Immature leaves proved better than mature leaves for both CFL and MTS measurements, using either detached leaf or whole plant stress assays. MTS measured on immature leaves stressed in a water bath at 50 °C for 45 minutes proved most consistent in separating rose clones based on high temperature susceptibility. Stressing actively growing plants with flower buds of 2 mm in diameter in a heat chamber at 44 °C for 3 hours resulted in increased flower abscission and leaf necrotic lesions on more susceptible clones when compared with those that were heat tolerant. Combining MTS measurements from immature leaves stressed in a water bath with the flower abscission and leaf necrosis responses 10 days after stress in a heat chamber could be the first step to screen and select against the more susceptible clones in a garden rose breeding program. Power analyses suggest that the proposed MTS protocol would be efficient in detecting differences between clones when the difference in electrolyte leakage is greater than 10%.

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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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Bhimanagouda S. Patil, Kevin Crosby, David Byrne, and Kendal Hirschi

In recent years, concerns about global, sustainable, and nutritional security have gained substantial momentum propelled by rapid increases in global population and food insecurity. Historically, plant breeding has played a key role in improving crop yield to keep pace with the rising global population; however, current plant breeding efforts focusing on increasing yield may need to be realigned toward nutritional security issues. Although traits affecting yield and disease resistance remain essential, emerging research highlights the importance of nutrition, flavor, quality, and enhanced health-promoting properties in reducing food and nutritional impoverishment. We review plant breeding efforts to address nutritional impoverishment and the importance of consumer perception of flavor, nutrition, and quality. The Vegetable and Fruit Improvement Center (VFIC)’s interdisciplinary research related to “Foods for Health” in pepper, cantaloupe, citrus, carrot, peach, and plum provides specific examples of improvements in vegetable and fruit quality and health-promoting properties. We discuss historical perspectives, case studies, current programs, and a future outlook on the role of plant breeding in nutritional security. Our work focuses on the nexus of plant breeding, human health, and nutritional security as a foundation for future plant improvement strategies.

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William A. Black, David H. Byrne, and H. Brent Pemberton

Five commercial cultivars and one species of rose were evaluated in a field trial for resistance to blackspot caused by Marssonina rosae. The trial was set up as a split-plot with two treatments. Each subplot was either protected on a weekly basis with a fungicide application to control blackspot or left to progress naturally with the disease. The trial was evaluated for blackspot resistance and for growth characteristics. Only the one species, Rosa roxburghii, was disease-free in both situations. Two cultivars, Peace and Sunflare, were the least resistant. They averaged 65% defoliation and a 50% infection rating. This corresponded to a 50% reduction in height and a 90% reduction in fresh weight of the plant. `Red Radiance' had ≈20% less defoliation than the two above cultivars, which was reflected by a 20% increase in growth. `Old Blush' had a higher resistance rating, but its propensity to quickly drop its foliage upon infection left it with a similar growth reduction as `Red Radiance'. `Carefree Wonder' was the most-resistant commercial cultivar. It had only a 43% decrease in fresh weight. `Red Radiance' and `Carefree Wonder' both displayed much greater defoliation during December, whereas the other susceptible cultivars showed the same degree of defoliation as earlier in the season.

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Yan Ma, David H. Byrne, and Katrina G. Porter

Several colchicine-induced amphidiploids of blackspot-resistant, wild diploid rose species were produced for interbreeding with tetraploid garden roses. Shoot-tip chromosome counts confirmed that 86-7 (Rosa wichuraiana Crep. × R. rugosa rubra Hort.) and 86-3 (R. laevigata Michx. × R. banksiae Aiton) are amphidiploids (2n = 4x = 28), and that 84-1000 (R. roxburghii Tratt. × R. laevigata Michx.) is a mixoploid with diploid (2n = 2x = 14) and hypotetraploid (2n = 4x-1 = 27) sectors. The measured volume of pollen grains and guard cells was higher in the tetraploids. Pollen stainability was higher in amphidiploids 86-3 and 86-7 than in mixoploid 84-1000. The amphidiploid 86-7 has greater pollen fertility as determined by crossing with a range of commercial tetraploid roses than 86-3 and 84-1000, but is less fertile than its parental diploid species. Leaflets of the amphidiploids are larger and more crinkled along the midrib than in their diploid parents. These three amphidiploids provide new additions to tetraploid rose germplasm.

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David H. Byrne, Aleksander N. Nikolic, and Edward E. Burns

A wide range of color, sugar, and acid composition was found among 12 peach [Prunuspersica (L.) Batsch] genotypes. Among the high-acid genotypes, a trend of increasing Hunter `a' values, fructose, soluble solids concentration (SSC): titratable acidity (TA) ratio, and decreasing TA and citric acid levels was noted with decreasing mesocarp firmness. Mesocarp firmness was correlated with both skin and flesh `a' values within all genotypes. Among genotypes, the Hunter `a'/firmness relationship varied. `Elberta', a cultivar known to retain a greenish ground color, had a lower Hunter `a' value when soft than did more recent releases such as `Dixiland', `Redhaven', and `Suwanee'. `Sam Houston', a low-acid cultivar, had lower TA and malic, citric, and quinic acid levels than the other cultivars. The dominant acid for all genotypes was malic (50% to 60% of total) with about equal amounts of citric and quinic. Soluble sugars included sucrose (54% of total), fructose (31%), and glucose (15%). `Sam Houston' had lower SSC, a higher percentage of sucrose, lower levels of glucose and fructose, but the same relative sweetness values as the high-acid cultivars.

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David H. Byrne, Natalie Anderson, Jonathan Sinclair, and A. Millie Burrell

Embryo culture techniques are employed in early ripening peach and nectarine cultivars. Generally, the embryos in these varieties are not mature by the time the fruit matures, thus rendering normal stratification procedures ineffective. In 1998 and 1999, immature embryos from multiple peach genotypes were cultured in an embryo rescue media (WPM, 3% Sucrose) at 5 °C for 45 days in the dark. Embryos were then placed under lights at either a cool temperature (18 °C in 1999 and 20 °C in 1998) or a warm temperature (30 °C in 1999 and 28 °C in 1998) treatment with a photoperiod of 12 h for germination and initial growth. After 2 to 4 weeks embryos were rated for germination, root number, and top growth. The embryos incubated at the cool temperature regime not only had better germination, but also had a higher rate of greenhouse survival.

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Qianni Dong, Xinwang Wang, David H. Byrne, and Kevin Ong

Black spot disease, caused by the fungus Diplocarpon rosae Wolf, is one of the most serious diseases of garden roses. Both complete (vertical) resistance conditioned by dominant Rdr genes and partial (horizontal) resistance conditioned by multiple genes have been described. The use of resistant rose cultivars would reduce the demand of agrochemical applications. The characterization of 16 genotypes for resistance to black spot using two laboratory assays, the detached leaf assay (DLA) and the whole plant inoculation (WPI) approach, indicated that these techniques were well correlated. Thus, either method could be used to assess the resistance of the plants to black spot. Fifteen diploid hybrid populations from 10 parents segregating for partial (horizontal) resistance to black spot derived from Rosa wichuraiana ‘Basye’s Thornless’ (RW) were assessed for black spot resistance by quantifying the percentage of the leaf area with symptoms (LAS) and lesion length (LL) measured by the diameter of the largest lesion per leaf in DLAs. The narrow-sense heritability of partial resistance to black spot as measured by LAS and LL data of DLA was estimated to be from 0.28 to 0.43 when calculated with a genetic variance analysis and from 0.74 to 0.86 when generated from offspring–midparent regression. This suggests that the development of rose cultivars with high levels of stable partial resistance to black spot is a feasible approach for the rose industry.

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William A. Black, David H. Byrne, and H. Brent Pemberton

Forty-five rose genotypes including modem cultivars and rose species were evaluated in a field trial for resistance to black spot caused by Marssonina rosae. The trial was designed as a randomized block with four replications at two sites. The plots were planted at College Station (East Central Texas) and Overton (Northeast Texas). Ratings were done for the percentage of leatlets with black spot lesions and for leaf defoliation. These ratings were taken four times during the growing season from May to October 1993. Preliminary results indicate a high degree of resistance in the ten species studied, Modem cultivars were equally divided into moderate resistance, low resistance, and susceptible with only four showing high resistance. Disease pressure was higher and occurred earlier in the season at the Overton site. Disease pressure was highest at both sites in late spring and again in fall. Pressure was lowest in August after a prolonged period without rain. Introduction during the growing season of a previously unseen race of the pathogen was observed by the performance of the cultivar Sunbright.

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Bruce D. Mowrey, Dennis J. Werner, and David H. Byrne

Eighteen isozyme systems were surveyed in the peach [Prunus persica (L.) Batsch.] plant introduction collection. Seven systems were polymorphic. Three previously unreported isocitrate dehydrogenase (IDH; EC 1.1.1.41), three malate dehydrogenase (MDH; EC 1.1.1.37) and two shikimate dehydrogenase (SDH; EC 1.1.1.25) banding patterns were detected in the clones. Isocitrate dehydrogenase was dimeric in structure, with two alleles present at a single locus. Malate dehydrogenase was dimeric in structure, with three alleles present at the fast locus, while a second locus was monomorphic. Shikimate dehydrogenase was monomeric, with one allele present in most clones, while PI 113452, PI 113650, and PI 117679 were heterozygous for a slow SDH allele. Electrophoretic evidence suggests PI 113452, PI 113650, and PI 117679 are peach × almond (P. dulcis Webb) hybrids, since they were heterozygous for alleles previously reported only in almond.