Open Access

‘Jones hybrid’ hickory: a case study in Carya curation

  • L. J. Grauke1Email author,
  • M. Azucena Mendoza-Herrera2, 3,
  • David M. Stelly4 and
  • Patricia E. Klein5
SpringerPlus20165:1860

https://doi.org/10.1186/s40064-016-3531-4

Received: 29 November 2015

Accepted: 13 October 2016

Published: 24 October 2016

Abstract

‘Jones Hybrid’ hickory is an accession in the National Collection of Genetic Resources for Pecans and Hickories for which information about origin, identity and characteristics is very incomplete. Phenotypic and genetic profiles, when examined in the context of historic literature, provide evidence that the accession in question is ‘Siers’ a cultivar of Carya × laneyi (an interspecific hybrid between C. ovata and C. cordiformis). The accession has traits that make it interesting in the pecan breeding program, with potential for both rootstock and scion development. The tall, slender tree form of ‘Jones Hybrid’ is a trait that could be valuable in commercial pecan cultivars, allowing increased tree densities and reducing the need for expensive hedging operations. Tree size reduction is a goal to be pursued in scion selection and rootstock development, with each goal requiring assessment of reproductive potential of the accession.

Keywords

Carya ovata Carya cordiformis Carya × laneyi Carya illinoinensis Microsatellite profilesMorphology

Background

The National Collection of Genetic Resources for Pecans and Hickories (NCGR Carya) is the name given to what was formerly the National Clonal Germplasm Repository for Pecans and Hickories, designated as part of the National Plant Germplasm System in 1984 (Postman et al. 2006). The foundation of the NCGR Carya was grafted trees of pecan [Carya illinoinensis (Wangenh.) K. Koch] amassed from 1933 until his retirement in 1968 by Louis D Romberg, the first pecan breeder in the United States Department of Agriculture, for use in breeding pecans. Other staff members at what was then the USDA Pecan Field Station in Brownwood, Texas, added to the collection by grafting pecans and other hickories. The name change from “Clonal Germplasm Repository” to “Collection of Genetic Resources” more accurately reflects the strategy adopted by the Carya Crop Germplasm Committee at their first meeting in 1984: to represent not only grafted accessions representing the pecan industry and named cultivars of hickory, but to represent native populations of all Carya species by growing seedlings on their own roots, grown from seed collected from broadly distributed indigenous populations. As a result, the current collection includes an ex situ assemblage of cultivars and wild relatives that represent this important native North American nut crop.

Information related to a living accession in a germplasm collection falls into several interconnected categories: passport descriptors; management descriptors; environment and site descriptors; characterization descriptors; and evaluation descriptors (Alercia et al. 2012; Thormann et al. 2013). The database of the US National Plant Germplasm System, known as the Germplasm Resources Information Network (GRIN-Global), organizes data as recommended by FAO/Biodiversity Multi-Crop Passport Descriptors (MCPD V.2) (Alercia et al. 2012). Whether the accession originated by collection from the wild, or was obtained from another source, critical information is necessary to associate an accession with its history.

Historical records of the Brownwood orchards dating from the early 1930s are maintained as paper files and are consulted for questions of identity or origin. Trees are maintained even when little information is available concerning them. When necessary, accessions have been transferred by grafting to new inventories when original trees are damaged or removed. By associating records of graftwood origin with previous inventories, the line of descent can be traced from the present collection, through the valid evaluation records obtained from previous inventories, back to the ortet, or founding source of the cultivar. By knowing where that original tree grew, the ex situ collection is connected back to the forest, and to a long history of climatic and edaphic adaptation.

Some of the accessions in the initial collections of the NCGR Carya had no information other than the name. The purpose of this paper is to describe such an accession phenotypically and genetically, to associate it with the historic cultivar name it is believed to represent, and to describe preliminary efforts to utilize this cultivar in crosses with pecan to produce segregating progeny of utility in the USDA ARS Pecan Breeding Program.

Methods

The USDA ARS Pecan Breeding and Genetics program maintains two locations where collections of the NCGR Carya are held: the original home of the Pecan Breeding Program in Brownwood, Texas; and land in Burleson County, Texas made available through cooperation with Texas A&M University in College Station, Texas.

Molecular profiles have been developed for many accessions in the collection using 14 nuclear microsatellite markers and 3 plastid markers (Grauke et al. 2003, 2010, 2015). Immature leaflets are harvested from specific inventories and frozen at −80 °C until DNA extraction. Molecular profiles were also obtained from samples taken from in situ populations, but not maintained in ex situ collections. Particularly valuable samples were provided by Dr. Donald Stone, Duke University, from collections he made in Mexico in 2001. Those samples were stored at room temperature in silica gel desiccant and sample numbers correspond to the voucher specimens maintained at Duke Herbarium.

Total genomic DNA was extracted as reported in Grauke et al. (2010). Frozen tissue was ground in extraction buffer [0.35 M glucose, 0.1 M Tris–HCl pH = 8, 0.005 M Na2EDTA pH = 8, 2% (w/v) polyvinylpyrolidone (PVP-40)] at pH = 7.5 and a lysis buffer [0.1 M Tris–HCl pH = 8, 1.4 M NaCl, 0.02 M Na2EDTA pH = 8, 2% (w/v) CTAB, and 2% PVP-40]. During DNA extraction, 1% (w/v) of ascorbic acid and 0.2% (v/v) of β-mercaptoethanol was added to both buffers. DNA was cleaned with chloroform:isoamyl alcohol (24:1) and precipitated with salt and isopropanol or ethanol. PCR reactions were performed as reported in Grauke et al. (2015). PCR fragments were labeled with a fluorescent forward primer at the 5′-end using either 6-FAM (blue color) or HEX (green color). To load the samples on the ABI Prism Genetic Analyzer 3130 (Applied Biosystems, Foster City, Calif. USA), 0.5 μl of the PCR was mixed with 5 μl of 400-ROX internal size standard in deionized formamide at 2.5%. The relative size of the allele was determined using GeneScan and Genotyper software v 3.7 (Applied Biosystems). Alleles were called as a whole number in bp after a binning process with the FlexibinV2 software (Amos et al. 2007). Interpretation of molecular profiles is by visual analysis of allelic patterns within species and hybrids, by geographic regions.

Pollen of ‘Jones Hybrid’ BRW 9-7 was collected on 15, 16 April 2015 for use in making controlled crosses using standard procedures of the breeding program (Grauke and Thompson 1996). Pollen was applied to 80 bagged clusters of 88-FLA-FL-1.1 (Carya floridana) on 21 April 2015, and to 170 bagged clusters of ‘Mandan’ pecan on 23 April, 2015. Pollen was stained with 1.5% acetocarmine and photographed under 10X magnification on 28 April 2015.

Pistillate flowers on both Brownwood inventories of ‘Jones Hybrid’ were bagged on 16 April 2015 and pollen of ‘Mandan’ pecan was applied on 23 April 2015. Number of nuts set on all controlled crosses was monitored through the season, and nuts that were set were harvested on 17 September 2015.

Results and discussion

Historical records include individual tree cards showing the date a seedling was planted, and providing information concerning seedling source, grafting dates, scion identities and sources. Information concerning origin of the scion was not provided for ‘Jones Hybrid’ and no other reference has been found to a hickory tree of this name. The tree labeled as ‘Jones Hybrid’ was established in USDA ARS collections by grafting in 1975. The scion was grafted onto an interstock of B53-16-15 (a ‘McCallister’ seedling) which had been grafted in 1966 onto a pecan seedling rootstock growing in the USDA Brownwood Orchard (BRW) at Row 148, tree 17. ‘McCallister’ is an interspecific hybrid between Carya laciniosa and pecan, a hybrid family known as Carya × nussbaumeri. Records do not indicate a specific cultivar source of pollen for the B53-16 cross series. Open pollinated seedlings would most likely be back-crosses to pecan. The seedling rootstock onto which B53-16-15 was grafted was a controlled cross seedling of the 56-23 series (the 23rd combination of selected pecan parents made in 1956), which had been planted at that location in 1960. The progeny 56-23 was made using pollen of ‘Cherokee’ (‘Schley’ × ‘Evers’) to pollinate flowers of 1944-15-0030 (‘Odom’ × ‘Evers’). The compound tree at BRW 148-17 was removed in 1991, and graftwood of ‘Jones Hybrid’ was collected and grafted to open-pollinated ‘Apache’ seedling rootstocks growing in the newly established Brownwood Variety Orchard (BWV) 5-31 and BWV 9-7. Scions of BWV 5-31 were used to establish a tree at the College Station site, with grafts made to an ‘Apache’ seedling rootstock at CSV 15-20 in 2006.

Trees of ‘Jones Hybrid’ are noteworthy for their columnar growth habit (Fig. 1a). Dormant winter buds are plump, with imbricate scales (Fig. 1b). Outer bud scales shed in a pattern similar to C. tomentosa, but terminal buds are smaller, to 1 cm only. Bark is tight and gray, as is typical of both C. cordiformis and C. tomentosa and young trees of C. ovata prior to bark exfoliation (Grauke 2003).
Fig. 1

‘Jones Hybrid’ inventory BWV 5-31 of the National Collection of Genetic Resources for Pecans and Hickories; a Tree form on 17 Apr 2012 showing columnar habit; b bud structure on 3 Mar 2015; c nut shape, 2009 crop

First fruit was obtained from BWV 9-7 in 2001, the eleventh leaf after grafting, and from BWV 5-31 in 2008 (18th leaf). The involucre or ‘shuck’ of the fruit separates at sutures, or ‘splits’, in late October or early November. Nut samples have been collected, measured and photographed over many seasons (Table 1; Figs. 1c, 2). Nuts are orbicular with a length to height ratio of 1.1; have a prominent apical stipe, and are laterally compressed with a height to width ratio of 1.4 (Grauke and Thompson 2001a, b). Kernels are ruminated with a prominent basal cleft formed by the high secondary septum of the nut, similar to nuts of C. cordiformis (Fig. 2). Nuts are borne in shucks with wings on the sutures from the apex to the middle of the nut, typical of C. cordiformis (Fig. 3). Leaves are dark green and leathery, with 5-7 oblanceolate leaflets like those of C. ovata, but lacking the tufted hairs at the tips of leaf serrations typical of that species. Leaflets are densely pubescent on the lower surface with simple hairs. This trait might suggest a relationship with C. tomentosa, although the hairs are mostly single and not the tufted hairs more typical of that species. Leaves are also characterized by short petioles (Fig. 3).
Table 1

Nut dimensions of ‘Jones Hybrid’, by inventory and year. Each value is the mean of 5 nuts (except for BWV 9 7 in 2001 and 2009, which had 2 and 4 nuts respectively)

Orchard

Row

Tree

Year

Lng mm

Wd mm

Ht mm

Lng:ht

ht:wd

Nut g

Ker g

Ker pct

BWV

9

7

2001

35

21

30

1.2

1.4

9.3

4.1

44.8

BWV

9

7

2002

33

21

29

1.1

1.4

8.4

4.4

52.4

BWV

9

7

2003

30

20

29

1.1

1.4

8.3

4.1

49.5

BWV

9

7

2005

32

20

28

1.2

1.4

7.6

3.2

42.0

BWV

5

31

2008

30

21

29

1.1

1.4

8.3

4.0

48.6

BWV

9

7

2008

27

19

26

1.0

1.4

6.5

3.3

51.0

BWV

5

31

2009

31

21

30

1.0

1.4

8.4

4.2

49.6

BWV

9

7

2009

30

21

28

1.1

1.4

7.6

  
 

Mean

  

31

20

28

1.1

1.4

7.9

3.9

48.6

Lng nut length, Wd nut width, Ht nut height, Lng:ht nut length to height ratio, ht:wd nut height to width rato, Nut g individual nut mass in grams, Ker g individual nut kernel mass in grams, Ker pct percentage of nut comprised of kernel, Mean mean of values across years of measurement

Fig. 2

Orbicular nuts of ‘Jones Hybrid’, showing apical stipe and ruminated kernels with prominent basal cleft, traits reminiscent of C. cordiformis

Fig. 3

‘Jones Hybrid’ inventory BWV 9-7 fruit, showing wings on shuck sutures from apex to mid-nut. 7 Sep 2011

Molecular profiles from the CSV 15-20 inventory of ‘Jones Hybrid’ are shown (Table 2) with those of representatives of other species. The profile of ‘Jones Hybrid’ is typical of those from diploid species: diploid species of Carya typically have only two alleles at each nuclear locus, while tetraploids often have as many as four. All profiles observed for the tetraploid species C. tomentosa, C. texana, C. floridana and C. glabra have multiple loci with greater than two alleles (all data not shown, but see Table 2, profiles of Scarit C. tomentosa and Scarit C. texana). The type specimen of C. × collina (Laughlin 1968)(an interspecific hybrid of those two tetraploid species collected from the Scarit Point, MO population and obtained from Don Stone) has only two alleles at each locus, showing no evidence of polyploidy. Some accessions of C. ovata (e.g. ‘Grainger’ and Stone 4160) have more than two alleles at locus cin4.
Table 2

Nuclear microsatellite alleles in base pairs, alleles arranged vertically by locus for Carya species from diverse geographic regions, presented by species within Section and hybrid group

Sample

Section

Spp

State

Accession

cin22

cin13

cin20

cin4

cin23

ca10

ga38

ga39

ga41

wga242

wga118

wga321

wga4

A05

LJ06-49

apo

cor

LA

02-COR-LA-BF-1

117

126

141

99

83

133

111

112

122

207

177

221

248

110

     

117

126

141

99

83

139

111

126

132

211

223

221

270

115

LJ06-50

apo

cor

LA

02-COR-LA-BF-2

117

126

141

90

74

133

111

110

100

209

165

223

258

115

     

117

126

141

138

74

139

111

132

100

211

181

223

268

120

LJ06-181

apo

cor

NY

06-COR-NY-1

117

126

141

105

74

139

111

106

207

181

221

254

110

     

117

126

141

138

83

139

111

120

211

193

221

254

115

LJ98-33

apo

cor

KS

90-COR-KS-2

117

126

141

99

74

133

111

112

90

209

173

221

256

105

     

117

126

141

99

74

133

111

112

108

223

183

223

260

105

LJ09-903

apo

cor

NY

Schreiner/Stone COR

117

141

105

74

139

111

110

90

209

177

221

268

115

     

117

141

105

83

139

111

110

94

217

177

221

274

115

LJ06-18

apo

ill

TX

Western

114

120

138

93

83

115

117

86

104

213

171

235

242

160

     

114

135

138

108

83

115

123

86

104

219

189

259

244

165

LJ06-62

apo/apo

xbr

IL

Abbott Thinshell

114

132

138

93

83

115

109

82

106

207

173

211

242

115

     

117

132

141

99

89

133

111

82

106

219

185

257

270

160

LJ06-105

apo/apo

xbr

OK

Pleas

114

132

138

114

83

115

111

96

104

203

175

221

244

115

     

117

132

141

144

83

139

129

96

118

209

191

237

244

160

LJ10-4160

apo/car

xio

MX

Stone 4160

108

132

138

93

80

85

111

86

94

217

177

247

228

105

     

114

132

138

108

80

115

115

96

104

233

179

247

240

160

        

114

          

LJ06-55

apo/car

xio

TX

89-XIO-RDM-1

108

120

138

108

80

85

111

86

92

205

175

225

230

105

     

114

120

138

108

83

115

117

94

104

219

189

259

242

160

LJ06-115

apo/car

xla

KY

Jones Hybrid

108

132

138

108

80

85

111

98

94

217

175

219

234

105

     

108

132

138

117

80

115

111

100

100

243

191

219

240

105

LJ06-180

apo/car

xla

NY

C– × laneyi type

108

120

138

99

89

85

111

108

120

207

169

223

238

110

     

117

126

138

138

89

139

111

114

120

209

169

225

280

110

LJ06-42

apo/car

xnu

IN

McCallister

114

132

138

102

80

85

111

88

104

203

165

233

228

105

     

114

132

138

102

83

115

115

104

114

231

177

239

250

160

LJ06-114

apo/car

xnu

MO

Wilson

114

129

138

105

80

85

111

104

106

227

169

229

228

105

     

114

129

138

108

83

115

111

110

114

231

175

255

242

150

LJ01-453

car

lac

KY

Stevens (LAC)

114

132

138

105

83

85

111

94

94

227

171

229

226

100

     

114

132

141

120

83

85

115

104

102

245

177

235

228

110

LJ98-36

car

lac

IN

Stephens(LAC)

114

123

138

96

80

85

111

96

94

227

171

229

226

100

     

114

129

141

99

80

115

111

104

102

245

177

235

228

105

LJ06-43

car

lac

Nieman

108

132

138

93

80

85

111

102

92

213

179

229

228

105

     

114

132

144

93

80

85

111

104

94

215

179

233

228

110

LJ06-44

car

lac

IL

Lindauer

114

132

138

93

80

85

109

94

92

225

183

229

228

105

     

114

132

138

93

80

115

111

94

102

225

191

233

228

105

LJ09-905

car

ovt

NY

Schreiner/Stone OVT

108

129

138

114

80

85

111

94

90

233

163

219

226

100

     

108

129

138

120

80

85

111

96

94

235

173

251

226

105

LJ10-103

car

ovt

TX

10OVT-6

108

129

138

123

80

85

111

94

94

225

163

219

226

105

     

111

129

138

123

80

117

111

94

94

225

175

229

226

105

LJ10-104

car

ovt

TX

10OVT-W1

108

129

138

123

80

85

111

94

94

225

163

219

226

105

     

111

129

138

123

80

117

111

94

94

225

175

229

226

105

LJ06-89

car

ovt

LA

01-OVT-LA-2–1

108

129

138

108

80

85

111

94

94

213

173

219

226

105

     

108

129

138

117

80

139

111

96

124

213

175

221

234

110

LJ98-38

car

ovt

LA

91-OVT-LA-1

108

129

138

93

80

85

111

94

92

225

163

219

230

105

     

108

132

138

120

80

115

111

96

92

225

183

239

230

105

LJ06-67

car

ovt

PA

Seas

108

120

138

93

80

85

111

96

94

221

175

219

226

105

     

114

120

138

93

80

85

111

104

94

221

179

235

234

110

LJ10-4131

car

ovt

MX

Stone 4131

108

129

138

99

80

85

111

94

94

223

169

225

228

105

     

108

129

138

114

80

85

111

96

134

225

187

233

228

110

LJ10-4161

car

ovt

MX

Stone 4161

108

126

138

114

80

85

111

96

94

217

169

225

226

105

     

111

132

138

123

80

139

111

96

94

219

173

241

228

105

LJ06-102

car

ovt

TN

Grainger

108

126

138

105

80

85

109

94

94

209

183

225

226

105

     

114

129

138

114

80

85

111

102

106

227

191

231

244

105

        

117

          
        

120

          

LJ06-113

car

ovt

OH

Yoder 1

108

120

138

108

80

115

109

102

94

229

171

235

226

105

     

114

132

138

108

80

115

111

102

94

229

185

245

234

105

LJ06-100

car

ovt

IL

01-OVT-IL-8–3

108

129

138

117

80

85

109

100

96

219

163

223

228

105

     

114

129

138

117

80

85

111

100

106

225

177

223

228

105

LJ09-1816

car

tom

MO

Scarit 1816 TOM

108

120

138

108

80

85

111

104

94

169

225

238

110

     

114

132

141

120

89

115

111

110

104

179

233

240

115

        

126

       

237

244

120

                

253

  

LJ09-1814

car

tex

MO

Scarit 1814 TEX

108

141

98

80

85

107

100

94

167

225

226

110

     

108

144

108

80

115

111

100

104

169

233

254

115

        

129

  

113

   

171

237

  
               

179

   

LJ09-828

car

flo

FL

09FLA-ABS1

108

120

138

99

77

115

111

98

94

217

171

225

234

     

108

132

141

99

80

139

111

102

112

223

181

227

238

      

138

144

      

227

185

 

248

 
              

233

  

290

 

LJ09-1812

car/car

xco

MO

Scarit 1812 XCO

108

120

138

102

77

85

111

90

175

226

105

     

114

132

138

114

80

115

119

104

175

228

115

Profiles for Stone 4131, 4160 and 4161, are matched by herbarium vouchers with those numbers in the Duke Herbarium

Profiles for Scarit 1812, 1814 and 1816 are matched by herbarium vouchers with those numbers in the Duke Herbarium

Section Apocarya = apo; Section Carya = car; hybrids by Sections = apo/apo, apo/car, or car/car; Species: C. aquatica = aqu; C. cordiformis = cor; C. illinoinensis = ill, C. floridana = flo; C. laciniosa = lac; C. ovata = ovt; C. texana = tex; C. tomentosa = tom; C. × brownii = xbr (ill × cor); C. × collina = xco (tom × tex), C. illinoinensis × C. ovata = xio, C. × nussbaumeri = xnu (lac × ill), C. × laneyi = xla (cor × ovt)

All accessions of C. cordiformis examined have the 117 bp allele at the cin22 locus and the 141 bp allele at the cin20 locus, while previously examined interspecific hybrids have those two alleles plus a second allele from the other parent (Table 2). Note that the profile from the type tree of C. × laneyi (C. cordiformis × C. ovata)(LJ06-180) from Riverside Cemetery in Rochester NY has the 117 bp allele from C. cordiformis (Table 2). None of the typical C. cordiformis alleles are found in ‘Jones Hybrid’. However, there is clear morphological evidence of hybridity with C. cordiformis in the nut, kernel and shuck characteristics. The 108 bp allele of cin22 has been found in all C. ovata examined and is present in ‘Jones Hybrid’, which is consistent with parentage by that species. However, that allele is also found commonly in the tetraploids C. texana and C. floridana and in some accessions of C. tomentosa (Table 2).

Chloroplasts are maternally inherited, and allele sizes at ccmp2, ntcp40 and ntcp9 are presented in Grauke et al. (2010). ‘Jones Hybrid’ has alleles sizes 209, 196 and 351 bp at these three loci, which is a haplotype that has not been observed in C. cordiformis. That pattern is among the most common plastid haplotypes found in Carya, and has been observed in C. aquatica, C. illinoinensis, C. palmeri, C. glabra, C. myristiciformis, C. laciniosa, C. ovata, C. texana, and C. tomentosa (Grauke et al. 2010). That haplotype has not been observed in C. cordiformis. If ‘Jones Hybrid’ is an interspecific hybrid between C. ovata and C. cordiformis, this suggests that the maternal parent was C. ovata. By contrast, the plastid haplotype of the C. × laneyi type tree (LJ06-180) in Rochester (208/197/350 bp) is shared by a local C. cordiformis (06-COR-NY-1, Sample LJ06-181) (data not shown).

‘Jones Hybrid’ pollen dehisced prior to pistillate receptivity, inferring that the accession is protandrous. No nuts were set on trees of ‘Jones Hybrid’ pollinated using ‘Mandan’ pollen. No nuts were set on the tetraploid Carya floridana tree pollinated using ‘Jones Hybrid’ pollen. Of 33 nuts initially set on ‘Mandan’ trees pollinated using ‘Jones Hybrid’ pollen, only three remained at harvest.

Pollen grains from ‘Jones Hybrid’ BWV 9-7 were variable in stain absorption and size (Fig. 4). Grains lacking stain are inferably non-viable and nonfunctional, whereas stainable ones would potentially be viable and functional. Strong variation in size suggests variation or inconsistency in numerical patterns of meiotic chromosome disjunction. Presence of “micro” pollen suggests formation of meiotic products with just one or a few chromosomes, also an indication of perturbed meiosis. Among stained grains, the range in diameters was wide enough (ca. 1.29-fold) to possibly indicate presence of haploid (n), diploid (2n) pollen and/or related aneuploid grains, where 2n grains would be unreduced (diploid) and potentially fertile, along with haploid grains (Fig. 4).
Fig. 4

Pollen from ‘Jones Hybrid’ BWV 9-7, collected 15 Apr 2015, stained with acetocarmine 28 Apr 2015, imaged using a ×10 objective lens, showing diversity of pollen size and viability, including the presence of “micro” (tiniest) and small unstained pollen, and a wide range of sizes among stained pollen grains

The association of morphological traits linking C. cordiformis, C. tomentosa and C. ovata suggested comparison of the ‘Jones Hybrid’ with the ‘Siers’ hybrid, reported to be a cross between C. cordiformis and C. tomentosa in some references and C. ovata × C. cordiformis in others (Grauke 1988). The oldest reference to ‘Siers’ described it as “a hybrid pecan” entered in a nut contest conducted by the Northern Nut Growers Association in 1915 (Deming 1929). ‘Siers’ was thoroughly described by Reed (1944) who provided pictures of the tree, buds, nuts and shucks (Fig. 5). Comparison of Reed’s (1944) figures (Fig. 5) to Fig. 1 in this report shows striking similarity. Cross sections of nuts in Reed’s (1944) figure have nut height to width ratios averaging 1.36, close to the value (1.39) for ‘Jones Hybrid’ (Table 1). Reed (1944) noted that the tree had “dark and rather rough” leaves, and “the petiole below the lowermost leaflets is not more than 3 inches in length.” Kernels were described as deeply divided, pink to reddish, and often astringent. All descriptions are consistent with current and previous observations on ‘Jones Hybrid.’
Fig. 5

Reproduction of Figs. 25, 26, and 27 from Reed (1944) showing pictures of the columnar tree form, plump buds with shed outer bud scales, and characteristic apiculate, laterally compressed nuts with shucks

The original ‘Siers’ tree was found around 1905 by Dr. I. T. Siers of Lawrenceburg, KY, who estimated its age in 1916 to be 25 years (germinating around 1891). Trees were first propagated in 1916 by the J. F. Jones Nursery, Lancaster, PA. Reed (1944) noted that “propagation by nurserymen appears to have ceased by 1930”, due to kernel astringency. Wyman (1942) reported that trees of ‘Siers’ (C. cordiformis × C. tomentosa) were offered for sale by E. A. Riehl Nursery of Godfrey, IL, but not by J. F. Jones Nursery who had other pecan, hickory and hybrid cultivars listed. Among the listed hazelnut and filbert cultivars being sold by J. F. Jones Nursery was one named “Jones Hybrid.”

‘Siers’ was listed as a “shagbark-bitternut” (=C. ovata × C. cordiformis) hybrid by L. H. MacDaniels (1969, 1979), describing it in both places as a “tall slender ornamental; low quality nut. Formerly, and probably erroneously, called a mockernut-bitternut hybrid” [sic] (=C. tomentosa × C. cordiformis).

Evidence indicates that ‘Jones Hybrid’ in our collection is ‘Siers.’ Adding ‘Siers’ as a synonym to the record will associate the history of that cultivar with our accession, and provide a geographic point of origin for evaluation in further testing. It is more interesting that several other prominent interspecific hickory hybrids originate in that geographic region: ‘McCallister,’ among the most prominent cultivars of C. × nussbaumeri, originated just north of the Ohio River near Mount Vernon, IN; ‘Major,’ a pecan that has contributed to several cultivars released by the USDA ARS Pecan Breeding Program, originated in the Henderson, KY area on the Green River and carries alleles from C. cordiformis and possibly C. ovata (Grauke et al. 2015). Hybridity occurs in areas of sympatry, and that region has the highest concentration of sympatric Carya species (Grauke and Mendoza-Herrera 2012).

Conclusion

Until more convincing evidence is found linking the accession to C. tomentosa, the ‘Jones Hybrid’=’Siers’ will be considered a hybrid between C. ovata and C. cordiformis, the C. × laneyi family of hybrids. The facile hybridizations of C. ovata with other diploid Carya species, the genetic anomalies seen in pollen of this hybrid accession, and allelic associations between C. ovata and the tetraploid species suggest not only that C. ovata may be a progenitor of the tetraploid species of Carya, but that its hybrids may provide a bridge for valuable traits of tree shape and size control.

Preliminary efforts in constructing controlled cross progenies were unsuccessful. Whereas ‘Jones Hybrid’ pollen applied to diploid pecan led to a very limited amount of fruit, indicating fertility of haploid grains, pollen applied to tetraploid C. floridana did not. The pollination results would seem to suggest that the larger pollen grains were not diploid, or if so, that they were non-functional. Other possible explanations exist, however, e.g., the pistillate flowers may have been past receptivity (control pollinations were not made at the same time), or other issues precluded function. Additional efforts will be needed to fully determine if 2n pollen are produced and are functional.

The wild relatives of pecan provide abundant diversity for the future development of this valuable tree crop. Their exploitation will require improved genomic tools to facilitate strategic phenotypic selection. The tall, slender tree form of ‘Jones Hybrid’ could be valuable in commercial pecan cultivars, allowing increased tree densities and reducing the need for expensive hedging operations. Tree size reduction is a goal to be pursued not only in scion selection, but through rootstock development. Negative traits such as long juvenility, low productivity, poor kernel percentage and astringent kernel flavor all need to be avoided as positive aspects of columnar tree form and reduced tree size are pursued. Development of molecular genetic markers associated with traits will assist selection. Strategic use of the accessible diversity in collections of the NCGR Carya will provide the foundation for development of those tools for pecan, the most important native North American nut crop.

Declarations

Authors’ contributions

All authors contributed to the development and interpretation of data and preparation of this manuscript. LJG maintains living inventories and associated records and made tissue collections and crosses. MAM-H performed microsatellite analyses under supervision of PEK. DMS imaged and interpreted pollen morphology. All authors read and approved the final manuscript.

Acknowledgements

This research was supported by the United States Department of Agriculture, Agricultural Research Service CRIS project 3091-21000-036-00D “Management and Characterization of Pecan (Carya) Genetic Resources and Wild Populations; by USDA ARS CRIS project 3091-21000-035-00D “Pecan Improvement through Breeding and Genetics”; by Cooperative Agreement 3091-21000-036-01S “Developing Molecular Markers for Carya” with Texas A&M University; by Cooperative Agreement 3091-21000-036-02S “Genomic Analyses in Carya” with Texas A&M University. Research reported on plastid haplotypes was supported by a grant from the Salopek Foundation. The cooperation of Dr. Donald E. Stone (1930-2011), Duke University, and generous sharing of his Carya samples is gratefully acknowledged.

Competing interests

The authors declare that they have no competing interests.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors’ Affiliations

(1)
National Collection of Genetic Resources for Pecans and Hickories, USDA ARS Pecan Breeding and Genetics, Somerville, USA
(2)
Department of Entomology (formerly Post-Doc, Department of Horticultural Sciences), Texas A&M University, College Station, USA
(3)
Department of Horticultural Sciences, Texas A&M University, College Station, USA
(4)
Department of Soil and Crop Sciences, Texas A&M University, College Station, USA
(5)
Department of Horticultural Sciences, Texas A&M University, College Station, USA

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Copyright

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