DOI: 10.5061/dryad.prr4xgxm5
title: Hybridizations and fruit geography of Solanum jamesii

description: Premise: Plant domestication can be detected when transport, use and
 manipulation of propagules impact reproductive functionality, especially
 in species with self-incompatible breeding systems. Methods: Evidence for
 human-caused founder effect in the Four Corners potato (Solanum jamesii
 Torr.) was examined by conducting 526 controlled matings between
 archaeological and non-archaeological populations from field-collected
 tubers grown in a greenhouse.  Specimens from 24 major herbaria,
 along with collection records from &gt;160 populations were examined
 to determine which produced fruits. Results: Archaeological populations
 did not produce any fruits when self-crossed or out-crossed between
 individuals from the same source.  A weak ability to self- or
 out-cross within populations was observed in non-archaeological
 populations.  Out-crossing between archaeological and
 non-archaeological populations, however, produced fully formed,
 seed-containing fruits, especially with a non-archaeological pollen
 source.  Fruit formation was observed in 51 of 162 occurrences,
 with minimal evidence of constraint by monsoonal drought, lack of
 pollinators, or spatial separation of suitable partners.  Some
 archaeological populations (especially those along ancient trade routes)
 had records of fruit production (Chaco Canyon) while others (those in
 northern Arizona, western Colorado, and southern Utah) did not. 
 Conclusions: The present study suggests that archaeological populations
 could have different origins at different times – some descending directly
 from large genepools to the south and others derived from gardens already
 established around occupations.  The latter experienced a chain
 of founder events, which presumably would further reduce genetic diversity
 and mating capability.  Consequently, some archaeological
 populations lack the genetic ability to sexually reproduce, likely as the
 result of human-caused founder effect.
description: <strong>Breeding Experiment:</strong>
 <br> <em>Propagation of Source Populations</em>
 – Tubers from five archaeological (A) and five non-archaeological (N)
 source populations were obtained directly from 2013-2019 field collections
 or from accessions stored at the U.S. Potato Genebank, Sturgeon Bay,
 Wisconsin.  Populations varied greatly in size based on the number of
 above-ground shoots observed during late summer and early fall.  In all
 cases, attempts were made to maximize distance between collections within
 a population to avoid sampling from the same clones.  Tubers were stored
 at 5°C until grown under optimal greenhouse conditions in April 2020. 
 Propagation began with 82 tubers from 10 populations (5 A and 5 N) that
 averaged 71% sprouted (72% and 69%, respectively). Each sprouted tuber was
 planted in potting soil in a one gallon container and watered with
 nutrient solution every three days, thus removing any resource constraints
 to growth, flowering, and fruiting. Flowering began in early July and
 crosses began on 13 July 2020.    
 <em>Crosses</em> – Given that we could not be certain
 that tubers from a single source population came from different clones,
 only source populations were considered independent replicates for each
 type of cross.  Each source was designated a source symbol (e.g. Anc =
 North Creek Shelter source). Multiple plants (e.g. Anc1, Anc2, etc.) and
 pollen transfers between flowers within each source population were
 treated as repeated attempts at each type of cross (self, outcross within
 a population (W), outcross between populations (B)). Repeated attempts
 ensured that a particular cross would not fail because of inadequate
 pollen load on the stigma, indelicate handling of flowers or other
 uncontrolled factors that inhibited seed and fruit formation. <br>
 We began the breeding experiments with the following types of
 crosses:<br> 1)    Self – pollen transfers among flowers on the same
 individual plant of a source population (e.g. Anc1 X Anc1, Nsr1 X
 Nsr1)<br> 2)    Outcross W – pollen transfers between flowers on
 different individual plants from within the same source population (e.g.
 Anc1 X Anc2)<br> 3)    Outcross B – pollen transfers between flowers
 on individuals from different source populations (e.g. Anc1 X Nsr1). 
  <br> Newly opened or unopened flowers receiving pollen were
 emasculated by removing the stamens and petals, exposing the pistils.
 Pollen was released from stamens using a mid-C tuning fork onto a piece of
 clean paper. The paper was then spread evenly over the receiving stigma. A
 labeled, fine-mesh bag was placed over the pollinated stigma and all tools
 were then cleaned and sanitized. These were performed between 13 July and
 5 August 2020, interspersing cross types among the flowers available at
 any point in time.  Consequently, the number of replicates and repeats
 (plant or flowers) could vary as the floral season progressed and the
 number of available flowers fluctuated.   <br> Fruits were left to
 mature and collected when the peduncle senesced and could be easily
 removed or fell off on its own. All fruits were dried in paper bags at
 room temperature. <strong>Geography of Fruit
 Production:</strong> <br>
 <em>Population database </em>– Field surveys and collections
 of S. jamesii began in 1992 (U.S. Potato Genebank) and have extended
 through 2020 (U.S. Potato Genebank and University of Utah).  The current
 U.S. Potato Genebank database for S. jamesii records the species at 162
 geo-referenced locations and includes observations of habitat, population
 size and condition, tuber collections, and the presence of flowers and/or
 fruit.  Repeated visits to these locations have resulted in 243
 population-specific observations, especially at archaeological sites
 throughout the range. Sites were subsequently sorted into archaeological
 vs. non-archaeological and fruit observed or not observed during the
 surveys. <br> <em>Herbaria
 Survey</em> – Seven major herbaria within and beyond the Four
 Corners region were visited between 2014 and 2020 to examine every
 available specimen of S. jamesii.  These included: Garrett (UT-Botany);
 Intermountain (USU-UTC); Deaver (ASC); University of New Mexico
 (UNM-Vascular Plants); Brigham Young University, S.L. Welsh (BRY-V); Royal
 Botanic Gardens Kew (KEW); British Museum of Natural History (NHM).  This
 resulted in 250 specimens examined, with one fruit occurrence added to the
 population database.<br> We also examined records and photographs
 (if available) of specimens of S. jamesii for occurrences of fruit
 available on the Consortium of Intermountain Herbaria
 (https://intermountainbiota.org/portal/collections/index.php), which
 included 17 institutions: ARIZ; ASU-CCH; ASU-Seeds; BLM-BLMGJFO; BLM-NM;
 COCO; COLO-V; CS; ENMU; FLD; GCNP; Harvard; KAIB; MABA-Plants; MESA; MNA;
 NAVA; NHI; NMC; NMNHI; NPS-MEVE; NPS-PISP; SJNM; SNM; SUU; SWRS; USFS-COC;
 USFS-GILA; USFS-SWRH; USFS-TEUI; UVSC; WSCO; YU; ZNP.  This search
 resulted in an additional 206 specimens, adding three fruit occurrences to
 the database.  <br> On average, 86% of all collection records were
 made during the phenoperiod for fruiting (August through October) and
 geo-referenced occurrences of flowering and fruiting were mapped in ArcGIS
 (ESRI, Redlands, California) using U.S. Geological Survey topographic
 basemap.
description: See ReadMe file.