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- Author or Editor: William R. Okie x
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.
Response to chilling temperatures is a critical factor in the suitability of peach [Prunus persica (L.) Batsch] cultivars to moderate climates such as in the southeastern United States. Time of bloom depends on the innate chilling requirement of the cultivar as well as the timing and duration of cold and warm temperatures experienced by the buds. Most current chilling models have considered dormancy break a sequential process: after appropriate chilling is received, a fixed amount of heat accumulation will produce bloom. This research shows that as chilling exposure increases, the time and heat accumulation required for peach floral budbreak decreases in an exponential relationship. When chilling is ample, a sequential, two-part dormancy model is adequate to describe budbreak, and increased chilling has little effect on heat requirement. In lower-chilling situations relative to a particular cultivar, the curvilinear relationship between chilling and heat requirement results in more heat being required for budbreak. This relationship, in conjunction with the range of chilling requirement found among the buds on a tree, results in an extended, asymmetrical budbreak.
Timing of budbreak in response to winter chilling is a critical factor in the suitability of peach [Prunus persica (L.) Batsch] cultivars to moderate climates such as that in the southeastern United States. Much of the research on chilling and dormancy has used excised cuttings or potted trees exposed to various treatments and forced under controlled conditions. Light is not generally considered an important factor in such experiments, and the effect of light during forcing has been little studied. The objective of this research was to compare light versus dark conditions during forcing as well as the effects of different colors of light during forcing. Our results showed that after chilling had been minimally satisfied, peach floral and vegetative budbreak occurred faster when forced in the presence of light than when forced in darkness. Light increased budbreak rate as well as the total percentage of budbreak. Red, yellow, and fluorescent light were more promotive in increasing budbreak than blue, green, infrared, or incandescent light, suggesting a role for phytochrome. Promotive effects of light were less when buds had received enough natural chill and heat to break within a week of forcing at 18 °C. In conclusion, light during forcing can have a significant effect of budbreak and needs to be considered when doing research on chilling and dormancy.
Peach (Prunus persica) cultivars maintained at the U.S. Department of Agriculture program at Byron, GA, have never been characterized with any molecular markers. In this study, 20 microsatellite markers were used to genotype 112 cultivars and the data were analyzed to discern their population structure and phylogenetic relationships. STRUCTURE simulations revealed four K clusters and broad genetic admixture among the cultivars. Principal coordinate analysis (PCoA) showed the cultivar groups from western, northeastern, and southeastern U.S. states were adjacent to each other except cultivars from Michigan (close to most southeastern state groups) and Florida (most distant from the other groups). Principal component analysis (PCA) showed that these cultivars had no obvious PCA partitioning boundaries. The intertwined distribution in both PCoA and PCA partitions suggested many of them were genetically closely related to each other largely because most shared same ancestral parentages. Most pairwise distance means within and between the cultivar groups were relatively low, suggesting close phylogenetic relations among those cultivars, as were demonstrated in the phylogenetic tree. Limiting factors and perspectives relevant to peach breeding are discussed.
Several new peach (Prunus persica) flower types were discovered in an F2 segregating population from an open-pollinated, non-showy-flowered F1 seedling of ‘Helen Borchers’, a double-flowered ornamental cultivar. The novel flower types were white and red single-flowered, non-showy blooms, as well as double-flowered, non-showy red, pink, white, and yellow phenotypes. The double, non-showy flowers were very attractive, and resembled pom-pom chrysanthemums. Yellow flower color is unknown in peach. Flower type in the F2 family segregated ≈3:1 for non-showy (Sh_) vs. showy (shsh), for anthocyanin-present vs. anthocyanin-absent, and for pink (R_) vs. red (rr), independently. Flower petal number segregated at about 9:3:4 for classes single:semi-double:double. Although both parents were late flowering, the F1 was not. The F2 seedlings showed a wide range in time of flowering. Higher petal number was correlated with later bloom, although it is unclear whether this is due to linkage or developmental differences in the flowers with extra petals. These novel flower types might be useful as ornamentals, and for use in genetics and breeding studies. Microsatellite analysis of possible pollen donors revealed that ‘Oldmixon Free’, a non-showy-flowered peach cultivar, was likely the pollen parent of the F1.
Several available Prunus chloroplast genomes have not been exploited to develop polymorphic chloroplast microsatellites that could be useful in Prunus phylogenetic analysis and maternal lineage group (MLG) categorization. In this study, using available bioinformatics tools, 80, 75, and 78 microsatellites were identified from the chloroplast genome of P. persica (CPpe), P. kansuensis (CPka), and P. mume (CPmu), respectively. The genome features and polymorphism status of these microsatellites were characterized. The genomic locations and motif types of most chloroplast microsatellites were conserved in CPpe, CPka, and CPmu. Of the 67 microsatellites with primer sequences and names, 57 were polymorphic for their in silico motif, amplicon lengths, or both among the three genomes. Based on the genotyping data of eight most polymorphic microsatellites, eight unique MLGs were found among the 736 peach materials in a breeding program. Most peach cultivars (111 of 161 genotyped) belong to MLG-1, the Chinese Cling-derived group reflecting the heavy use of this germplasm in early peach development. Forty-one cultivars belong to MLG-2, the European-derived group of peaches. MLG-3 consists of ornamental accessions. MLG-4 and MLG-5 contain only ‘Flordaking’ and ‘Reliance’, respectively. MLG-6 to MLG-8 consists of selections derived from P. tangutica, P. davidiana, and P. mira, respectively. These amplicons from the representative material for each MLG were sequenced, revealing additional single nucleotide polymorphisms (SNPs) within the amplicons. With the polymorphism status and amplification reliability validated, these new polymorphic chloroplast microsatellite markers may be useful in Prunus phylogenetic analysis.
Peach fruit set is affected by cumulative chill and spring frost. A spring frost occurred on 29 Mar. 2015 at the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Byron station after 3 weeks of bloom, reducing fruit set and resulting in many buttons (abnormally small fruit with dead embryos). Fruit set was rated in 2014, 2015, and 2016 and button set rated in 2015 using the same scale (0 = no fruit/button to 9 = 1–2 fruit/button at every node). The overall fruit set rating was substantially different in the 3 years, averaging 5.61 in 2014, 2.61 in 2015, and 6.04 in 2016. Buttons and skin-damaged fruit in 2015 varied among peach genotypes. Comparison of fruit and button set ratings showed that there was no difference between cultivars and selections, but some significant differences in fruit set for four ripening months, among the 3 years, and among the nine chilling classes, respectively. Among the cultivars, the most common button set rating was 0–3. For example, ‘Sunprince’, ‘Loring’, and ‘Carored’ trees had a high button set rating, whereas ‘Flameprince’, ‘Julyprince’, and ‘Contender’ trees were low. As for peach selections, BY04P1690n was among those with the highest button set rating. In the population derived from a cross of button-prone BY04P1690n and button-free BY99P3866w, fruit and button counts from 10 long fruiting shoots ranged from 4 to 53 fruit (21.63 on average) and 2 to 27 buttons (10.39 on average). The peach button rate ranged from 5.36% to 87.10% (30.70% on average). The range, distribution, and percentage of the button counts suggested that, if buttoning was genetically controlled, it appeared quantitative. Further assessment is needed.