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Unaroj Boonprakob and D.H. Byrne

Blind nodes in peach, the condition in which a node has no obvious vegetative or reproductive buds, is a problem in peach production in low and medium chill regions. Observations were made at 3 locations in Texas on peach cultivars which range in chilling requirement from 150 to 850 chill units. Four types of growing shoots (terminal or lateral shoot and east or west side) from peripheral canopy about 150-200 cm were sampled twice a month to determine the phonological development. Blind bud development was most frequent during the period of highest daily temperature and did not correspond with the position of the sample on a tree. High chilling cultivars showed greater susceptibility to the symptoms than low chilling cultivars. The anatomical differences between normal and blind nodes are described.

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Yan Shi and D. H. Byrne

A standardized screening procedure for tolerance to bicarbonate-induced Fe chlorosis using a commercial fertilizer mix (Plantex) as the nutrient source, high solution pH (8.5) and 1.5 m m bicarbonate to simulate a calcareous soil situation was used with a 1 vermiculite:1 perlite (v/v) support media, small pots and topping (pinching back the tops of shoots). The tolerance level of peach [Prunus persica (L.) Batsch] rootstock could be assessed by leaf visual-chlorosis ratings and Spad-502 chlorophyll readings instead of extractable leaf-chlorophyll concentration or plant Fe concentration. Although most of the tolerant genotypes had almond [P. amygdalus (Mill.) D.A. Webb] in their parentage, a few peaches (`Swat', NJ672281007) showed high to moderate levels of tolerance.

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Sudahono, D.H. Byrne, and R.E. Rouse

Eighteen citrus rootstock seedling lines were tested for their tolerance to Fe chlorosis using sand culture. Potassium carbonate was used to induce Fe-deficiency chlorosis. Chlorosis was quantified by 1) visual ratings, 2) SPAD-502 chlorophyll meter readings, 3) leaf chlorophyll concentration, 4) leaf active Fe, and 5) leaf total Fe. The first four criteria were well correlated among each other but not with leaf total Fe. Although any of the first four measurements could be used to quantify chlorosis, visual ratings and SPAD-502 readings were more convenient. The rootstock that have been reported to be tolerant or very susceptible to Fe chlorosis in calcareous soils were rated similarly for tolerance to bicarbonate-induced Fe chlorosis. Nontrifoliate types such as Texas sour orange (C. aurantium L.), Cleopatra mandarin (C. reticulata Blanco), Vangasay lemon (C. limon Burro.), and Ridge pineapple x Milam 1578-201 (C. sinensis L. Osbeck x C. jambhiri) were tolerant to moderately tolerant. Although most of the trifoliate hybrids tested were moderately susceptible to very susceptible, Smooth Seville x Argentine trifoliate {[C. grands (L.) Osbeck x C. aurantium] x Poncirus trifoliata (L.) Raf.} and F-81-12 citrange (C. sinensis x P. trifoliata) exhibited relatively high tolerance to lime-induced Fe chlorosis.

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T.A. Bacon and D.H. Byrne

A study was conducted on various peach [Prunus persica (L.) Batsch.] cultivars to determine the relationships among seed germination, seedling survival, seedling rosetting, fruit development period (FDP), and percent dry weight of the ovule (PDO). Germination and survival increased rapidly between 80 and 100 days of FDP, corresponding to an increase in mean PDO from 16% to 50%. Germination and survival leveled off after 105 days of FDP at >85%, corresponding to a mean PDO of 64%. Rosetting was high among seedlings for cultivars with FDP <110 days, but dropped rapidly as FDP increased. PDO was found to be a better indicator of seed germinability and seedling survival than FDP.

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C.H. Jan, D.H. Byrne, J. Manhart, and H. Wilson

The genus Rosa consists of more than 100 species classified into four subgenera, Eurosa, Platyrhodon, Hesperhodos, and Hulthemia, and distributed widely throughout the northern hemisphere. The subgenus Eurosa includes 11 sections. The other subgenera are monotypic. One hundred and nineteen accessions and 213 markers of 36 rose species that include eight sections of the subgenus Eurosa and one species each from the subgenera Hesperhodos and Platyrhodon were used to calculate a similarity matrix, which was clustered with the unweighted pair group method using arithmetic means (UPGMA). The RAPD markers distinguished between all the rose accessions, and species grouped into their respective sections. Therefore, classification of Rosa using RAPD data generally supports traditional classification. The Asian rose sections (Laevigatae, Banksianae, Bracteatae, Pimpinellifoliae, Chinenses, and Synstylae) were consistently separated from the primarily North American sections (Cassiorhodon and Carolinae). The Cassiorhodon and Carolinae sections were grouped together with the subgenera Hesperhodos and Platyrhodon. Both subgenera separated out at the same level as sections within the subgenus Eurosa, suggesting that they are more appropriately classified as sections within the subgenus Eurosa. Sections Cassiorhodon and Carolinae overlapped, and are probably best grouped as one section as previously suggested.

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D.H. Byrne, Y. Ma, W. Black, and H.B. Pemberton

Extensive field screening of rose (Rosa spp.) germplasm at two sites in Texas has determined that most modern roses are susceptible to blackspot [Diplocarpon rosae (Lib.) Wolf]. Fortunately, there is a high level of resistance in a number of diploid rose species, such as Rosa laevigata, R. ganksiae, R. rugosa, R. wichuraiana, and R. roxburghii. These species were used to create three amphidiploids: 84-1000 (R. roxburghii x R. laevigata), 86-3 (R. banksiae x R. laevigata), and 86-7 (R. wichuraiana x R. rugosa rubra). These were examined for fertility to determine their usefulness in a breeding program. 86-7 had the most abundant pollen production and the greatest pollen fertility, as measured by hip set (38%), followed by 86-3 (19%), and 84-1000 (13%). The female fertility of 86-3 and 84-1000 is low, and 86-7 is female-sterile. Although 86-7 showed poor female fertility, F1 hybrids exhibited a wide range of fertility, indicating that the fertility of this germplasm can be quickly increased in subsequent generations.

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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.

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L.H. Zhang, D.H. Byrne, R.E. Ballard, and S. Rajapakse

Microsatellite or simple sequence repeat (SSR) markers were developed from Rosa wichurana Crépin to combine two previously constructed tetraploid rose (Rosa hybrida L.) genetic maps. To isolate SSR-containing sequences from rose a small-insert genomic library was constructed from diploid Rosa wichurana and screened with several SSR probes. Specific primers were designed for 43 unique SSR regions, of which 30 primer pairs gave rise to clear PCR products. Seventeen SSR primer pairs (57%) produced polymorphism in the tetraploid rose 90-69 mapping family. These markers were incorporated into existing maps of the parents 86-7 and 82-1134, which were constructed primarily with AFLP markers. The current map of the male parent, amphidiploid 86-7, consists of 286 markers assigned to 14 linkage groups and covering 770 cm. The map of the female tetraploid parent, 82-1134, consists of 256 markers assigned to 20 linkage groups and covering 920 cm. Nineteen rose SSR loci were mapped on the 86-7 map and 11 on the 82-1134 map. Several homeologous linkage groups within maps were identified based on SSR markers. In addition, some of the SSR markers provided anchoring points between the two parental maps. SSR markers were also useful for joining small linkage groups. Based on shared SSR markers, consensus orders for four rose linkage groups between parental maps were generated. Microsatellite markers developed in this study will provide valuable tools for many aspects of rose research including future consolidation of diploid and tetraploid rose genetic linkage maps, genetic, phylogenetic and population analyses, cultivar identification, and marker-assisted selection.

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C.K. Kim, J.Y. Oh, J.D. Chung, A.M. Burrell, and D.H. Byrne

Somatic embryogenesis was initiated from in vitro-grown leaf explants of rose using an induction period of 4 weeks on MS basal medium supplemented with auxin followed by several subcultures on MS basal medium with cytokinin. `4th of July' showed the highest regeneration frequency (24.4%) on 5.3 μm NAA followed by culture on medium containing 18.2 μm zeatin. `Tournament of Roses' produced somatic embryos when cultured for 4 weeks on medium containing dicamba, 2.3 μm followed by three subcultures on medium containing 18.2 μm zeatin. Embryogenic callus matured on MS media containing 0.5 μm NAA, 6.8 μm zeatin, and 2.9 μm GA3. Long-term cultures were established for both cultivars. Somatic embryos germinated on MS medium containing IBA and BA. Silver nitrate (58.8 μm) enhanced shoot formation and germination of somatic embryos. Plants derived from somatic embryos were acclimatized and successfully established in the greenhouse.