Dennis J. Werner

Targeted mapping and linkage analysis of morphological isozyme, and RAPD markers in peach

Nine different F2 families of peach [Prunus persica (L.) Batsch] were analyzed for linkage relationships between 14 morphological and two isozyme loci. Linkage was detected between weeping (We) and white flower (W), 33 cM; double flower (Dl) and pillar (Br), 10 cM; and flesh color (Y) and malate dehydrogenase (Mdh1), 26 cM. A leaf variant phenotypically distinct from the previously reported wavy-leaf (Wa) mutant in peach was found in progeny of ‘Davie II’. The new willow-leaf character (designated Wa2) was closely linked (0.4 cM) to a new dwarf phenotype (designated Dw3). Two families derived from the pollen-fertile cultivar ‘White Glory’ segregated for pollen sterility, but segregation did not follow a 3∶1 ratio. Evidence is presented suggesting that ‘White Glory’ possesses a pollen-sterility gene (designated Ps2) that is non-allelic to the previously reported pollen-sterility gene (Ps) in peach. Ps2 was linked to both weeping (We-Ps2, 15.5 cM) and white flower (Ps2-W, 25.3 cM). A genomic map of peach containing 83 RAPD, one isozyme, and four morphological markers was generated using an F2 family obtained by selfing an NC174RL x ‘Pillar’ F1. A total of 83 RAPD markers were assigned to 15 linkage groups. Various RAPD markers were linked to morphological traits. Bulked segregant analysis was used to identify RAPD markers flanking the red-leaf (Gr) and Mdh1 loci in the NC174RL x ‘Pillar’ and ‘Marsun’ x ‘White Glory’ F2 families, respectively. Three markers flanking Mdh1 and ten markers flanking Gr were identified. The combination of RAPD markers and bulked segregant analysis provides an efficient method of identifying markers flanking traits of interest. Markers linked to traits that can only be scored late in development are potentially useful for marker-aided selection in trees. Alternatives for obtaining additional map order information for repulsion-phase markers in large F2 populations are proposed.

Isozyme survey of various species of Prunus in the subgenus Amygdalus

Abstract Seventeen isozyme systems were surveyed in clones of almond ( Prunus dulcis Webb), P. davidiana (Carr.) Franch., P. kansuensis Rehd., P. mira Koehne, peach ( P. persica (L.) Batsch), and P. persica ssp. ferganensis , all members of the subgenus Amygdalus . Nine systems, representing 16 presumptive loci, stained consistently to characterize. Three of these presumptive loci were monomorphic, while the other 13 presumptive loci were polymorphic for 36 possible alleles. The significance of these results relative to the genetic mapping of peach is discussed.

Stability of bacterial leaf spot resistance in peach regenerants under in vitro, greenhouse and field conditions

SummaryPhenotypic stability of bacterial leaf spot resistance in peach (Prunus persica (L.) Batsch) regenerants, either selected at the cellular level for insensitivity to a toxic culture filtrate of Xanthomonas campestris pv. pruni or screened at the whole plant level for resistance to X. campestris pv. pruni, was investigated. A detached-leaf bioassay was used to evaluate the original regenerants again after three years in the greenhouse and also after a two to three year cycle of tissue culture propagation. Peach trees derived through micropropagation from the original regenerants were also evaluated after one to three years growth in the field. Although leaf spot resistance was retained in some regenerants over time in the greenhouse, following in vitro propagation, and under field conditions, resistance was either lost or not expressed in others. Regenerants # 19-1 and #156-6, derived from embryo callus of bacterial spot susceptible ‘Sunhigh’, were significantly more resistant than ‘Sunhigh’. High levels of resistance were exhibited in greenhouse plants and field-grown trees of regenerant #122-1, derived from embryo callus of moderately resistant ‘Redhaven’. This research provides additional evidence that selecting or screening for somaclonal variants with disease resistance is a feasible approach to obtaining peach trees with increased levels of bacterial spot resistance.

Genetic diversity in peach [Prunus persica (L.) Batsch] at the University of Florida: past, present and future

The University of Florida (UF) stone fruit breeding and genetics program was created in 1952 to develop early ripening stone fruit cultivars with high quality, adaptation to summer rainfall, low chilling requirements, and the ability to withstand high disease pressure. Diverse germplasm sources were used to introduce desirable traits in UF breeding pool. The main objective of this research was to determine the genetic diversity and population structure of the breeding germplasm, and to search for loci under selection. A total of 195 peach genotypes were used: UF cultivars and advanced selections (n = 168), cultivars and selections from the UF-UGA-USDA joint breeding effort (n = 13), landrace cultivars (n = 4), high-chilling cultivars released by NCSU (n = 5), and related Prunus (n = 5) species. A total of 36 SSR markers distributed across the peach genome amplified 423 alleles. An average of 18 genotypes were detected per marker: A (number of observed alleles) of 11.43, Ae (effective number of alleles) of 2.58, Ho (observed heterozygosity) of 0.4, He (expected heterozygosity) of 0.52, F (Wright’s fixation index) of 0.25, and PIC (polymorphism information content) of 0.48. UPGMA cluster analysis based on Nei’s genetic distance represented best the known pedigree information for the germplasm pools. Two major groups were observed across the germplasm corresponding to melting and non-melting flesh cultivars/selections. Population structure results supported these two major groups. Several loci closely located to genome regions where different phenotypic traits have been previously mapped were detected to be under selection.

Inheritance and allelism of morphological traits in eastern redbud (Cercis canadensis L.)

Inheritance of purple, gold, and variegated foliage types, weeping architecture, and double flower was explored in F1, F2, and backcross families resulting from controlled hybridization of eastern redbud (Cercis canadensis L.). Potential allelic relationships were explored when possible. Inheritance analysis in families derived from controlled hybridization of ‘Covey’ (green leaf) and ‘Forest Pansy’ (purple leaf) suggest that purple leaf color and weeping architecture are both controlled by single recessive genes, for which the symbols pl1 and wp1 are proposed, respectively. Inheritance of gold leaf was explored in families of ‘Covey’ (green leaf) × ‘Hearts of Gold’ (gold leaf). Interpretation of inheritance of gold leaf in these families was confounded by the recovery of a leaf color phenotype in the F2 family unlike either parent. However, data suggested the action of a single locus controlling gold leaf color in ‘Hearts of Gold’, and that instability of gold leaf expression may be based on transposable element activity. Segregation of gold leaf in the F2 families of ‘Texas White’ [green leaf (C. canadensis var. texensis)] × ‘JN2’ [gold leaf (The Rising Sun)] did not fit a Mendelian ratio. Analysis of progeny of ‘Silver Cloud’ and ‘Floating Clouds’ (both showing white/green leaf variegation) with non-variegated cultivars demonstrated that variegation in ‘Silver Cloud’ is controlled by a single recessive nuclear gene, while variegation in ‘Floating Clouds’ is controlled by cytoplasmic factors. The symbol var1 is proposed for the gene controlling variegation in ‘Silver Cloud’. Double flower in progeny derived from ‘Flame’ (double flower) suggested that double flower is dominant to single flower, and that ‘Flame’ is heterozygous at the double-flower locus, for which the symbol Df1 is proposed. Allelism studies showed that the gene controlling purple leaf in ‘Forest Pansy’ is allelic to the purple leaf gene in ‘Greswan’ and that the gene controlling weeping phenotype in ‘Traveller’ (C. canadensis var. texensis) is non-allelic to the weeping gene found in ‘Covey’. Allelism of the gold leaf trait in ‘Hearts of Gold’ and ‘JN2’ was investigated, but no clear conclusions regarding allelism could be made due to recovery of leaf color phenotypes unlike either parent.

Short-term growth analysis of ‘Lovell’ and ‘Nemaguard’ peach rootstocks

SummaryA 14-week study was conducted to investigate differences in growth characteristics between cvs Lovell and Nemaguard peach rootstocks. Nemaguard exhibited a higher absolute growth rate, and had significantly greater values for leaf weight ratio and leaf-root dry weight ratio as compared to Lovell. Significant differences were detected between the two cultivars for root-shoot ratio and fresh weight-dry weight ratio. Nemaguard had a significantly greater root-shoot ratio early in development but exhibited a lower ratio for the final four harvest dates. The fresh weight-dry weight ratio showed a similar pattern. No significant differences in relative growth rate, unit-leaf rate or leaf area ratio were detected.

Will the traditional horticultural breeding and genetics research be fairly valued in academia

I wrote the inaugural Editorial when Horticulture Research was launched in January 2014. This second Editorial was trigged by the manuscript that was submitted to Horticulture Research (HORTRES.2015.49, www.nature.com/articles/hortres201549), a summary of 17 years of traditional genetics on a woody ornamental tree called redbud. I have always been fascinated by the wealth of unique ornamental trees, mostly caused by genetic mutations. Since the redbud and dogwood are the two signature ornamental trees in eastern Tennessee, where University of Tennessee locates, I called Dr Dennis Werner and asked him to write a story behind this research and how he could continue and sustain this research for 17 years. In his story (see below), I see several important questions that are in need of open discussions. Over the past 25 years as a faculty in land-grant universities in the United States, I have seen eliminations or switching from the traditional breeding and genetics research programs to biotechnology, molecular biology and genomics, and alike. University administrators are shifting funds and changing evaluation matrixes, and have been placing more emphasis on publications, grants, and high impact factor journal articles. During the six years of my joint appointment at Nanjing Agricultural University, China, I have been struck by the “typhoon” of publishing high impact factor journal articles and changing evaluation matrix that swept through the Chinese research institutions. I have contacted many faculty members in the United States and China, and asked the following questions: “Will the traditional breeding and genetics (or similar programs) be fairly valued in academia, especially in land grant, or similar mission-oriented universities where horticultural research is primarily conducted?” “In the current academic environment, how can young scientists set long-term research goals without worrying about short-term pressures of publishing?” “How do we evaluate high impact research and does it equal to high impact factor journal articles?” As the Editor-in-Chief, I accepted Dr Werner’s article, which has taken 17 years to collect and aggregate the data, in Horticulture Research, to offer my view and support on this solid, traditional genetics research. I invite and encourage faculty and administrators to openly discuss these questions which may greatly impact research and service we perform to the horticultural science, horticultural industry, and ultimately our life in general.

The effect of indolebutyric acid and kinetin on shoot induction of cauliflower leaf cuttings

Abstract In 3 separate experiments, IBA at 2000 or 5000 mg l−1 stimulated shoot development on leaf cuttings. Success was higher during the summer months. Kinetin in the range of 10–1000 mg l−1 neither promoted nor inhibited shoot development. Hormones were prepared as aqueous solutions in 50% ethanol and applied to the basal portion of the cuttings. This technique provides a practical method for vegetative propagation of cauliflower for use in breeding programs in temperate regions.