[Show abstract][Hide abstract] ABSTRACT: Peach is a self-pollinated species with a high level of linkage disequilibrium (LD) conservation for North American and European commercial varieties, LD~13-15cM. The analysis of the University of Florida peach germplasm founding clones, previous releases, and present selections, constitutes the main objective of this report. A total of 198 peach genotypes were fingerprinted with 37 SSRs distributed across the genome (~15-25 cM). Peach germplasm samples included genotypes from the University of Florida, the USDA-UGA-UF moderate-chill breeding effort, North Carolina State University, primitive low chill germplasm, and related species P. dulcis (Mill.) D.A. Webb and P. kansuensis Rehder. Number of alleles per locus (A), effective number of alleles (Ae), observed heterozygosity (Ho), expected heterozygosity (He), Wright’s fixation index (F), power of discrimination (PD), the probability of confusion (C), and Nei’s genetic distance (GD) per locus were calculated. An unrooted Neighbor-Joining tree was constructed using Nei’s genetic distance. ‘Diamante cling’, ‘Non-melting’, ‘Melting’, ‘High-chill’, and two ‘Nectarine’ clades were identified in the peach germplasm. Genetic diversity values in the range of 0.5 were observed. Past and present peach selections and cultivars developed by the UF breeding program have been determined by breeding strategies, objectives and commercial trends that changed through the years. To detect potential changes in allele frequencies resulting from the breeding efforts, the genetic diversity of germplasm representing different decades was compared.
[Show abstract][Hide abstract] ABSTRACT: Prunus umbellata is a diploid plum species native to the Southern US with a wide geographic range and adaptation to different soils and environments. Other species native to the Southern US include P. americana Marsh., P. angustifolia Marsh., and P. geniculata Harper. The objective of this research was to evaluate P. umbellata as a model plant for the identification of genomic regions associated with dormancy response. A total of 48 genotypes: 42 of P. umbellata ranging from central Georgia to south Florida, 2 of P. americana, 2 of P. angustifolia, and 2 of P. geniculata, were fingerprinted using 41 SSRs distributed across the peach genome (~15-25 cM). Similarly, genotype-by-sequencing (GBS) was used to identify SNPs across the genome of 48 multiplexed genotypes using Illumina HiSeq® 2000 system. GBS produced up to 175 million reads in one flow cell lane, yielding approximately 40 Gb of data, with a filtered 101 million reads and an average of 2.1 million reads per genotype. SNP markers were detected using Stacks software and ranged from 30,411 markers (6x depth) for at least 33 genotypes (r=0.7 or 70% of genotypes required to process a locus) to 487 markers (6x depth) for all genotypes (r=1.0 or 100% of genotypes required to process a locus). Genetic diversity and population structure results based on SSR and SNP markers (using different depth coverage and r values) were comparable. SSR and SNPs markers allowed the identification of hybrid genotypes among species. Similarly, these markers were used to identify genomic regions associated with dormancy response.
[Show abstract][Hide abstract] ABSTRACT: Peach production acreage in Central Florida is steadily expanding with the availability of new, high-quality, and low-chill requirement peach cultivars adapted to the region’s subtropical climate. Florida’s well-drained sandy soils are ideal for peach production except that they are also inhabited by plant pathogenic nematodes. ‘Flordaguard’ peach rootstock is recommended for commercial utilization because it is well-adapted to Florida’s acidic soils and exhibits good resistance to the endemic peach root-knot nematode, Meloidogyne floridensis (Mf). Additional nematode-resistant rootstocks are being identified to diversify the panel of improved rootstocks for the expanding peach industry. Two new rootstocks, ‘MP-29’ and ‘P-22’ (T. G. Beckman, USDA-ARS Byron, GA) offer potential for peach production in Central Florida. ‘MP-29’ is “pleach”, a hybrid between a red-leafed peach rootstock breeding selection and ‘Edible Sloe’ plum. The rootstock selection ‘P-22’ is a hybrid of ‘Guardian’ and ‘Flordaguard’ peach and is under consideration for release. A rootstock trial was planted at Citra, FL during the Spring of 2012 to test horticultural performance of these rootstocks with ‘Flordaguard’ in the presence of Mf. ‘Okinawa’ peach and ‘Barton’ peach rootstocks were included as susceptible and resistant controls, respectively. A commercial quality, low-chill peach scion, ‘UFSun’ was budded on all rootstocks to evaluate fruit quality. ‘MP-29’ clonal and ‘Barton’ seedling rootstocks were field-budded in 2012. ‘P-22’ clonal, ‘Okinawa’ seedling, and ‘Flordaguard’ seedling rootstocks were budded a year prior to field-transplanting in 2012. Scion growth was monitored one year after budding and fruits were harvested in the second season after establishment. Preliminary data indicate that the two new clonal rootstocks ‘MP-29’ and ‘P-22’ are promising alternatives to ‘Flordaguard’. During the two growing seasons, stem circumferences (2 inches below and above graft union) were significantly greater in ‘Okinawa’ and ‘P-22’ rootstocks. The relative growth rates of the scion were higher on field-budded ‘Barton’ and ‘MP-29’ rootstocks than those budded the previous year. ‘MP-29’ produced trees with yield efficiency and fruit size comparable to other tested rootstocks despite its smaller tree size – a characteristic useful for high-density planting systems. ‘Barton’ rootstock also demonstrates significant promise in terms of vigor (pruning weight and tree size) in the initial years of orchard establishment. Further evaluation is required to validate the effect of rootstocks on yield efficiency and resistance to Mf.
[Show abstract][Hide abstract] ABSTRACT: The primary focus of the USDA-ARS stone fruit rootstock program at Byron, Georgia has been the development of disease resistant rootstocks for peach. Historically peach tree short life (PTSL), aka ‘Bacterial Canker Complex’, and Armillaria root rot (ARR) have been the two most important causes of premature mortality of commercial peach trees in the southeastern United States. Several root-knot nematode species are of concern in this region as well. In addition to these disease issues the horticultural performance of trees on the new materials developed in this program is also of parmount importance. We have screened a broad range of Prunus germplasm and, in addition to useful differences in disease resistance, have found that these materials also have an impact on a number of important plant performance traits. Data will be presented on rootstock influence on tree vigor, anchorage, yield, fruit size, suckering and tree survival on disease prone sites.
[Show abstract][Hide abstract] ABSTRACT: Peach trees in the Southeastern United States are damaged by fungal gummosis (incited by Botryosphaeria dothidea [(Moug.:Fr.) Ces. & De Not.] with a fruit yield reduction up to 40% per tree in severe cases. Previous studies indicated a high level of susceptibility in commercially recommended rootstocks and cultivars. The climatic conditions in the Southeastern United States are conducive to the development of the disease and currently, there are no proven effective cultural or chemical controls for peach fungal gummosis. Our group has evaluated peach germplasm for over 2 decades, searching for sources of resistance to peach fungal gummosis. Preliminary research in our lab indicates that almond, a species closely related and sexually compatible with peach, may provide a new source of genes for resistance to peach fungal gummosis. Preliminary tests comparing commercial quality peach cultivars with peach x almond F1 hybrids indicated the existence of a novel source of resistance to gummosis. Parental genotypes and segregating backcross populations of peach, peach X almond F1 hybrids, and peach X (peach X almond) progeny were evaluated for 3 consecutive years using a previously established rating system based on gumming severity. Selected peach x almond F1 hybrids presented the lowest mean for gummosis susceptibility. Pearson chi-square analysis of the disease rating data suggested a dependent segregation of the populations for gummosis. Further analysis of the standardized residuals deviations identified differences in backcross population 8 (UFSharp x (Flordaguard x almond)). The phenotypic segregation ratio for fungal gummosis resistance is consistent with the presence of a single dominant locus. Backcross population 8 has been genotyped for SSR markers sourced from the Prunus reference genome map and Quantitative Trait Locus (QTL) analysis will be performed.
[Show abstract][Hide abstract] ABSTRACT: North America is a center of diversity for Prunus L. species. The University of Florida Stone Fruit Breeding and Genetics Program in collaboration with the National Germplasm Repository and USDA–ARS (Project No. 5306-21000-018-00D) collected and identified ~400 genotypes of approx. 30 taxa native to the United States. A core collection of 13 species was used to compare the utility of selectively neutral sequences and sequences believed to be under selection pressure in the elucidation of phylogenetic relationships of North American plums. The core collection represented the major clades within subgenus Prunus section Prunocerasus. The American clade was represented by P. americana Marsh., P. hortulana L.H. Bailey, and P. mexicana S. Watson; the Chickasaw clade included P. angustifolia Marsh., P. munsoniana W. Wight & Hedrick, and P. umbellata Elliot; and the Beach clade was represented by P. geniculata Harper and P. maritima Marsh. Outgroups included: P. pumila L. (subgenus Cerasus section Microcerasus), P. persica (L.) Batsch cv. Okinawa, AP05-18ws (UF peach haploid), 02-01c (UF peach haploid) (subgenus Amygdalyus section Amygdalus), and P. fasciculata (Torr.) A. Gray (subgenus Emplectocladus). A total of 41 simple sequence repeat (SSR) markers distributed across the peach genome (~15–25 cM), 7 chloroplast genome regions, nuclear ribosomal repeat ITS, and 55 candidate genes believed to be associated with flowering and plant architecture were used. A Neighbor Joining (NJ) analysis of the SSR markers yielded different species relationships than the results obtained using chloroplast DNA (cpDNA) regions, internal transcribed spacer region (ITS), and nuclear genes Maximum Parsimony (MP) and Maximum Likelihood (ML) analyses. Phylogenetic analyses using cpDNA regions, ITS and nuclear genes yielded some of the previously known species relationships. A total of 27,278 bp of sequence per species was used. The observed polymorphism rates were 3.67%, 10.82%, and 7.27% for the cpDNA sequences, ITS, and nuclear genes, respectively. Sequence variation in exon and intron regions of nuclear genes was 4% and 11%, respectively. Several highly informative regions were identified that will be used for larger phylogenetic analysis within Prunus.
[Show abstract][Hide abstract] ABSTRACT: North America is an important center of diversity for plum species. The North American plums grow in diverse climatic and geographic regions. High levels of variation for plant architecture, fruit size, flesh texture, flesh color, disease resistance, chilling requirement, and other traits, have been reported. The survival of several of these species is being negatively impacted by urban sprawl and agriculture. Similarly, climate change threatens their habitats. The objective of this research was to collect and identify plant specimens from the wild, create a herbarium and living collection that could be used to preserve the species and to clarify the phylogenetic relationships of the North American plums. The University of Florida Stone Fruit Breeding and Genetics Program in collaboration with the National Germplasm Repository and USDA–ARS (Project No. 5306-21000-018-00D) collected, identified and archived ~400 genotypes of approximately 30 taxa across the United States. Geographic coordinates, location descriptors, and plant characteristics were recorded for all these genotypes. Vouchers for each genotype were submitted and are available at the Florida Museum of Natural History, Gainesville, FL (http://www.flmnh.ufl.edu/herbarium/). Seed collected from the germplasm accessions were submitted to John E. Preece at the National Clonal Germplasm Repository for Fruit and Nut Crops, Davis, CA, for future use by the scientific community. These collections will allow us to preserve and conserve these species as important genetic resources of unique traits and information that could be used for breeding plum scions and rootstocks in the future. Additional information about this collection will be reported.
[Show abstract][Hide abstract] ABSTRACT: Dormancy is a condition that delays or inhibits growth in seed, vegetative buds, and floral buds. In peach, seed germination occurs when seed accumulate sufficient stratification and growing degree hours to break dormancy and begin growing. Correlations have been reported between mean seed stratification requirements and mean bud chilling requirements among Prunus families, but an individual seed’s germination date and subsequent vegetative and floral bud break date are not correlated. Prior to this study, the genetic factors involved in regulating seed dormancy and their location on the peach genomic map were unknown. Segregating F2 seed were collected from a high × low chill F1 peach hybrid in 2005, 2006, and 2008. Germination date and growth habit was measured after the stratification requirement of the 2005 seed was fully met. The seed collected in 2006 and 2008 received varying amounts of stratification, which enabled data on stratification requirement, heat requirement, and growth habit to be collected. Genomic DNA was extracted from seedling leaf tissue and screened with SSR markers selected from the Prunus reference map at an average resolution of 20 cM. Seed dormancy quantitative trait loci (QTLs) were detected on G1, G4, G6/8, and G7. The QTLs detected on G6/8 and G7 were discovered in the same region as QTLs associated with floral bud chilling requirement and bloom time in peach.
[Show abstract][Hide abstract] ABSTRACT: The Prunus L. genus belongs to the subfamily Amygdaloideae (=Prunoideae) of the Rosaceae family. It is distributed around the world, with approximately 200 species. Species native to southeastern United States include P. americana Marsh., P. angustifolia Marsh., P. geniculata Harper, and P. umbellata Elliot. The existence of several wild plum species in Florida creates a unique opportunity for the study of allelic variation associated with important economic traits that can then be targeted and rapidly transferred to domesticated plum using molecular markers. The main objective of this research is to analyze the genetic diversity and population structure of P. umbellata in Florida. A total of ~70 genotypes of P. umbellata ranging from North to South Florida were fingerprinted using 41 SSRs distributed across the peach genome (~15–25 cM). Number of alleles per locus (A), effective number of alleles (Ae), observed heterozygosity (Ho), expected heterozygosity (He), Wright’s fixation index (F), polymorphism information content (PIC), and Nei’s genetic distance (GD) per locus were calculated. An unrooted Neighbor–Joining tree was constructed using Nei’s genetic distance. Population structure was analyzed. Prunus umbellata represents an underutilized resource for association genetic studies of adaptive and commercial traits in plums.
[Show abstract][Hide abstract] ABSTRACT: The genus Prunus L. is economically important source of fruit such as plums, cherries, almonds, apricots and peaches. Grafting techniques are commonly used to propagate superior commercial cultivars. The desired scion genotype is grafted onto a rootstock. Native wild Prunus species have been previously used as rootstocks for grafting commercial cultivars. However, the use of grafting techniques for conservation, restoration, and maintenance of native wild Prunus species has been not previously reported. North America is a center of diversity for plum species. Several plum species are listed as endangered with seeds being the primary means of propagation. The use of different grafting techniques for the nondestructive sampling, preservation and propagation of wild native Prunus species was the main objective of this study. A total of 94 P. geniculata, 20 P. umbellata Elliot, 14 P. angustifolia Marsh., and 5 P. americana Marsh. genotypes, native to southeastern US, were grafted using a modified-veneer and T-budding techniques. Two rootstocks, ‘Sharpe’ plum and P. cerasifera plum previously grafted onto Okinawa peach, were used and evaluated. Percentage bud take was measured for each genotype. ‘Sharpe’ rootstock had 36.71% and 27.96% bud take on average for modified-veneer and T-budding, respectively. P. cerasifera / Okinawa rootstock had 3.70% and 3.57% bud take on average for modified-veneer and T-budding, respectively. Grafting proved to be a feasible method for propagation and maintenance of wild Prunus species, particularly of P. geniculata, a federally endangered species with low seedling recruitment.
[Show abstract][Hide abstract] ABSTRACT: White flower color is controlled by a recessive allele w in peach. To map the W locus, open pollinated seed were collected from two different F1 hybrids. The first hybrid was an F1 between ‘White English’ ww (white flower) and ‘UFSun’ WW (pink flower). The second a hybrid was an F1 between ‘Brooks’ ww (white flower) and ‘UFBeauty’ WW (pink flower). Open pollinated seed were collected from both F1 hybrids to produce a segregating F2 population. ‘Brooks’ × ‘UFBeauty’ and ‘White English’ x ‘UFSun’ F2 populations consisted of 37 and 110 individuals, respectively. The F2 populations did not deviate significantly from a 3:1 pink to white phenotypic segregation ratio (c2 ≤ 0.01). White flower phenotypes were identified to be homozygous recessive, as previously described. Bulked samples of white and pink flower phenotypes from ‘White English’ × ‘UFSun’ F2 population were used to identify the genomic region linked with white flower ww locus using a total of 41 simple sequence repeat (SSR) markers. A linkage map was created with the SSR markers closely linked with white flower ww in peach and the locus placed on the Prunus reference genome map.
[Show abstract][Hide abstract] ABSTRACT: The genetic variation in commercial peach germplasm is low. Closely related species such as Prunus dulcis (almond), P. kansuensis (kansu peach) and P. davidiana (davids peach) represent valuable sources of genetic variation. These species have been used to a limited extent in rootstock breeding but have been largely ignored in scion breeding. The reluctance to use related species in peach scion breeding results from the high penalty in fruit quality of early generation crosses and the number of generations required to produce selections with commercial fruit size and quality. Large population sizes are needed to reduce linkage drag. The generation of large populations from controlled crosses is very laborious in peach due to the low seed content of fruit and the low fruit set of hand pollinations. In this work we present a breeding scheme that uses male sterility to enhance outcrossing in peach, facilitating the generation of large segregating populations for recurrent selection.
[Show abstract][Hide abstract] ABSTRACT: North America is a center of diversity for Prunus species. Tree architecture, endodormancy requirement, heat requirement, fruit development period, fruit size, fruit texture, fruit flesh, disease resistance, and adaptive changes to multiple environmental conditions, are a few examples of the tremendous genetic variability available in the plum germplasm. Wild native Prunus species constitutes an important source for genetic diversity for stone fruit breeding and selection. The study of genetic variability within the subgenus Prunus section Prunocerasus was the primary objective of this research. In addition, the transferability and polymorphism level of 41 simple sequence repeat (SSR) markers distributed across the peach genome (~15–25 cM) in section Prunocerasus was studied. A total of 11 North American plum species were used to determine the genetic diversity available in section Prunocerasus. One genotype per species for: P. americana Marsh., P. angustifolia Marsh., P. geniculata Harper, P. hortulana L.H. Bailey, P. maritima Marsh., P. mexicana S. Watson, P. munsoniana W. Wight & Hedrick, P. persica (L.) Batsch cv. Okinawa, P. pumila L., P. umbellata Elliot, and P. fasciculata (Torr.) A. Gray (outgroup) were used for the preliminary screen. The number of alleles per locus (A), effective number of alleles (Ae), observed heterozygosity (Ho), expected heterozygosity (He), Wright’s fixation index (F), polymorphism information content (PIC), and Nei’s genetic distance (GD) per locus were calculated. A rooted Neighbor-Joining tree was constructed using Nei’s genetic distance. An average of 10.7 A, 0.58 Ho, 0.31 F, and 0.82 PIC were observed. The peach SSR markers were found to be widely transferable and applicable to the study of wild Prunus species genetic diversity.
[Show abstract][Hide abstract] ABSTRACT: Homalodisca vitripennis (Germar), the glassy-winged sharpsnooter, is a primary vector of phony peach and plum leaf scald diseases caused by XyIeIIa fastidiosa Wells et al. A survey of H. vitripennis on peach [Prunus persica (L.) Batsch] varieties established that leafhopper abundances varied from 0-13 per tree. Prunus persica cvs. Flordaking and June Gold and Prunus salicina Lindl. (cvs. Methley and Santa Rosa) were then budded on each of 3 P. persica rootstocks (cvs. Aldrighi, Lovell and Nemaguard). Leafhopper abundance was monitored on each of the two scions budded on each rootstock and on non budded rootstocks over a 2-yr period. The genotypes were container-grown in Year 1 and were planted in the field in Year 2. For both years leafhopper abundance was greatest during early June and on Methley and Santa Rosa cultivars compared with the peach genotypes. The feeding rates of leafhoppers were substantially higher on plum scions than on peach scions, and nocturnal feeding rates were often higher than daytime feeding rates. Mean leafhopper feeding rates were correlated with leafhopper abundance on Prunus genotypes from 3-8 June in a quadratic manner (F = 53.8; df = 2,12; R2 = 0.90; P < 0.0001); the mean nighttime feeding rate was best correlated linearly to mean cumulative leafhopper abundance (F= 446.9; df = 1, 13; R2 = 0.972; P < 0.0001).
Journal of Entomological Science 10/2008; 43(4). · 0.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Advanced lines of 'Guardian' (i.e., SL2891 and SC 3-17-7) and 'Lovell' peach rootstocks were evaluated for their susceptibility and growth response to Meloidogyne incognita (GA-peach isolate) and M. javanica (NC-tobacco isolate) 23 months after inoculation in field microplots. Results indicate that there was a significant interaction between nematode and rootstock for above-ground tree growth. Growth suppression, as measured by trunk diameter and fresh shoot weight of SC 3-17-7 was greater (P<0.05) in the presence of M. javanica as compared to the presence of M. incognita or to the uninoculated plots. 'Guardian' line SL2891 growth was not affected by either nematode when compared to the uninoculated plots. Tree growth of 'Lovell' was suppressed by both M. incognita and M. javanica when compared to the uninoculated plots. Below-ground growth suppression, as measured by dry root weight, was greater in 'Lovell' than in either SC 3-17-7 or SL2891 regardless of nematode species. No difference in dry root weight was detected between the two 'Guardian' lines. Root galling occurred on all rootstocks tested with either M. incognita or M. javanica. Root galling was more abundant on 'Lovell', intermediate on SL2891 and least abundant on SC 3-17-7. Similar results were also detected for number of eggs per gram dry root weight regardless of nematode species. In another microplot study, M. floridensis and M. incognita did not suppress tree growth of SC 3-17-7, 'Nemaguard', or 'Flordaguard' rootstocks as compared to the uninoculated control. Meloidogyne floridensis reproduced on all 3 rootstocks, with greatest number of eggs per gram dry root being produced on 'Guardian' and 'Nemaguard'.