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J. H. Aldrich and W. J. French

Trees budded on the Brazilian rootstock `A-82' have a lower feeding preference by the primary vector of Phony peach disease over trees on `Nemaguard'; the southeastern industry standard rootstock. `A-82' budded trees have lower levels of infection of the xylem-limited bacteria Xylella fastidios a compared to `Nemaguard' budded trees.

The feasibility of using `A-82' in the industry was evaluated by budding `Flordaking' and `Flordaglobe' peach and `Sungem' and `Armking' nectarine to `A-82' and `Nemaguard'. Vegetative and fruiting responses of these trees will be discussed.

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Paul E. Hansche

The heritability of fall leaf abscission and spring bloom date were estimated in a peach breeding stock recently infused with genes of divergent evolutionary origin. One of the two recent progenitors of this breeding stock was evergreen. The other had a high chilling requirement. The heritability of full-bloom date in this breeding stock was estimated to be 0.60 ± 0.08 SD, under the assumption of no outcrossing, and 0.67 ± 0.08 s d, under the assumption of 30% random mating. The heritability of the percentage of leaves abscised by 18 Nov. 1988 was estimated to be 0.33 ± 0.08, under the assumption of no outcrossing, and 0.47 ± 0.08, under the assumption of 30% random mating. The heritability of the percentage of leaves abscised, estimated from data collected on 14 Nov. 1989, was 0.49 ± 0.08, under the assumption of no outcrossing, and 0.55 ± 0.08, under the assumption of 30% random mating. The phenotypic correlation between date of full bloom and percentage of leaves abscised in the following November was estimated to be 0.21; 0.18 t(0.05) > 0.21 > 0.26 t(oo.1). Apparently, these traits readily could be genetically manipulated to circumvent the freeze damage that leads to susceptibility to Cytospora and related disease organisms.

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Vance Baird, L. Belthoff, R. Ballard, R. Scorza, A. Callahan, R. Monet, and A. Abbott

Flow cytometric analysis, of leaf nuclei from three cultivars, was used to estimate the DNA content of peach (∼0.61 pg or ∼0.59 × 109 bp/diploid nucleus; 2x=16), and ndicated that the peach genome is only slightly larger than that of Arabidopsis. This value was indirectly confirmed by measurements of nuclei from haploid, triploid and “tetraploid” (cytochimera) peach accessions. cDNA and genomic clones have been used to determine the level of polymorphism among various peach cultivars and related species. Overall, ∼33% of the clones detected polymorphic loci. As expected, the highest level of polymorphism was found in interspecific hybrids (∼50%); whereas in intraspecific populations, only 1 in 5 genomic clones, and 1 in 3 cDNA clones were able to detect polymorphisms (RFLPs). These clones, as well as RAPD primers, are being used to construct a genetic linkage map by analyzing their segregation in 3 intraspecific peach populations (an Fl from France and two F2s from the U.S.). Taken together, these populations are segregating for 12 Mendelian traits and a number of quantitative traits. Our results have enabled us to identify a number of linkage groups, some composed of both molecular and phenotypic markers. The current structure of the peach map is reported.

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Bryon Sosinski, W.V. Baird, S. Rajapakse, R.E. Ballard, and A.G. Abbott

We have developed a highly saturated genetic linkage map in peach (diploid, 2n = 16) using two separate crosses. The first population consists of 48 randomly selected F2 individuals which were generated by selfing an F1 from the cross of `New Jersey Pillar' x KV 77119. This progeny set exhibits segregation for gross morphological traits including: canopy shape, fruit flesh color, and flower petal color, size, and number. The second population contains 48 F2 progeny derived from the cross of `Suncrest' x `Bailey'. These progeny segregate for quality traits such as fruit diameter, weight, flesh color, cling vs. free stone, soluble solids, pH of juice extract, and fruit developmental period. Nine linkage groups were identified in the first cross, which cover 590 cM of the genome. In the second cross, eight linkage groups were found that contain several significant chromosomal intervals contributing to fruit quality characteristics by QTL analysis. Anchor loci present in both maps were used to join the linkage groups to create a single combined map of the peach genome. Physical mapping is currently underway to assign the each linkage group to the appropriate chromosome.

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Michael Wisniewski, Carole Bassett, Timothy Artlip, Jenny Renaut, and Robert Farrell

We have characterized the seasonal accumulation of transcripts and proteins in peach (Prunuspersica), particularly a 60 kDa dehydrin (PCA60; PpDhn1). Recently, we have isolated another dehydrin gene (PpDhn2). The present report compares the structural organization of the two dehydrin genes, their promoters, and the response of the genes to temperature, photoperiod, and water deficit. Trees were exposed for 3 or 5 weeks to either short day (SD) or long day (LD) photoperiods at either 25 or 5 °C. Additional experiments exposed trees to a period of water deficit followed by recovery. Transcript abundance of both genes, as assessed by RT-PCR, was determined, in response to the different photoperiods and temperatures as well as a prolonged SD/5 °C regime, from monthly-collected field samples, and trees subjected to water deficit. Results indicated that water deficit increased transcript abundance of both genes, but their abundance differed dramatically in response to low temperature and seasonal cues. Surprisingly, neither gene exhibited a significant elevation in transcript abundance in response to SD conditions. The lack of response of PpDhn1to SD is problematical given the observation that transcript levels in field-collected samples begin to increase substantially in September, prior to the onset of cold temperatures. Analysis of the promoter regions and cis-acting elements suggest that ABA may play an important role in seasonal expression, interacting with photoperiod in field conditions. Two CRT/DRE elements are present in the promoter region of PpDhn1, but absent in the promoter of PpDhn2.

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Myong-Dong Cho, Hee-Seung Park, and Yong-Koo Kim

`Yumyeong' is one of the most popular peach varieties in Korea. This study was conducted to monitor the developments of cells and tissues, and the changes in sugar contents during the whole fruit growth stages. At bloom, there were two rows of vascular tissues, and the number and the position of internal vascular bundles were consistent during the fruit growth; however, the number of vascular tissues increased and the distribution was irregular in the flesh tissues. The tissues between the inner integument and the internal vascular bundles showed different development characteristics from other parenchyma cells, which consisted of small and dense cells containing tannins. Therefore, it was found that the nucleus of peach consisted of inner epidermis and cells in the internal vascular tissues. The outer epidermis consisted of single layer cells at bloom and was changed into one to two layers by horizontal cell division 14 days after full bloom. At 30 days after full bloom, the epidermis consisted of five to six layers by vertical cell division. The cell layers of the outer epidermis gradually decreased to one to two layers at maturity. The observations on the changes in the epidermis confirmed that some of the cells of the hypodermis of peach fruit originated from the cells of outer epidermis. Tylosis was observed from 35 days after full bloom, and the size and number of tylosis increased until full fruit maturity. The sucrose content sharply increased from 50 days to 120 days after full bloom, then decreased slightly. After stone hardening ended, other solids showed a gradual decrease from 80 days after full bloom.

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Thomas G. Beckman and William R. Okie

Differences in chilling and post-rest heat requirements of various stonefruits were investigated through the use of cuttings collected from field grown trees. Materials studied included P. angustifolia Marsh, P. besseyi Bailey, P. maritima Marsh, P. persica (L.) Batsch (`Agua 6-4', `Flordaking', `Pi Tao', `Redhaven', `Redskin', and `Ta Tao'), P. umbellata Ell. and a Japanese type plum (`Byrongold'). Cuttings were collected after natural leaf fall and shortly after the onset of of chill hour accumulation. Cuttings were stored at 4°C. Groups of cuttings were removed from storage after various amounts of chilling and allowed to develop at 16, 21 or 27°C. Cuttings were observed for both vegetative and flower bud break. Magnitude of differences in chilling and post-rest heat requirements and their implications in the breeding of peaches for low and moderate chill areas will be discussed.

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U.L. Yadava

A planting of 48 trees of `Redhaven' scion on Lovell, Nemaguard, and Wildpeach rootstocks (RS) was established in 1990, with four replications in randomized complete-block design. Cultural practices common in Georgia were used to maintain the planting. Orchard performance for peach tree short life (PTSL) related tree survival, RS suckering, fungal gummosis, and tree stresses from cold injury and Pseudomonas canker, was investigated to examine RS potential of Wildpeach compared with Lovell and Nemaguard. Trees on all RS showed 100% survival for the first 5 years in the orchard. Although canker became more prevalent in later years, trees had significantly higher ratings on Nemaguard (2.88) and Lovell (2.50) RS than on Wildpeach (1.44). However, PTSL stress enraged by Pseudomonas killed one tree each on Lovell and Wildpeach RS during 1995. Trunk cambial browning that estimated cold injury was trivial due to mild winters; however, trees on Nemaguard had higher TCB ratings (1.25) than on other RS. Trees on Wildpeach had fewer suckers than on Nemaguard or Lovell. Gummosis ratings were higher on Nemaguard RS than on Lovell and Wildpeach. The results showed that Wildpeach has good potential for a peach RS.

Open access

Donald A. Lloyd II and Gary A. Couvillon

Abstract

Three-year-old peach trees were manually defoliated on 6 successive biweekly dates starting in mid July of 1972. Approximately 30 days after treatment, flowers were forced. Flowers produced on 7/8 and 8/1 treatment trees were atypical, whereas flowers forced on 9/12 and 9/26 treatment trees were apparently normal. Defoliation on 8/15 and 8/29 produced flowers both atypical and normal types. The number of forced flowers, adjusted with trunk diameter, increased with each successive defoliation date although the number of flowers forced on any date was small. Floral abnormalities consisted of large leaf-like sepals without petioles, flowers with poorly colored petals, and exerted stigmas. Some abnormal flowers set fruit.

Vegetative bud break decreased with each successive defoliation date. Neither vegetative nor flower buds were forced when individual shoots were defoliated rather than whole trees.