Solanum acroscopicum

Description

Solanum acroscopicum distribution map
Solanum acroscopicum distribution map

Solanum acroscopicum is a Peruvian diploid species.  Plants range mostly 1 to 2 feet tall with long, narrow leaves.  Stolons grow as long as 32 inches (80 cm).  Tubers are white to tan, long and narrow, reaching as much as three inches in length, but usually much less.  Unlike most species in clade 3, which have moniliform tubers, this species has terminal tubers.  Flowers are light blue to purple.  This is a high elevation species that typically ranges from about 9800 to 12800 feet.  The specific epithet, acroscopicum, refers to the tendency of the leaflets to point toward the terminal leaflet or apex.

A tetraploid accession of this species differs in having short stolons, short day tuberization, larger leaves and flowers, and shorter internodes.  White flowers also appear occasionally in the tetraploids.  More information is reported below.

Jarvis (2008) predicts that this species will lose 95% of its present range by 2055 due to climate change, most likely entailing a critical loss of genetic diversity.

Resistances

Vega (1995) found that this species is about as frost tolerant as domesticated potato.  Hijmans (2003) found that about 50% of plants of this species survived a frost of -5 C and Luthra (2007) found a similar rate of survival for a frost of unspecified temperature.

MacKinnon (1962) found that survival of aphids on this species was low and that potato leafroll virus was not transmitted by infected aphids.

Condition Type Level of Resistance Source
Alternaria solani (Early Blight) Fungus Resistant Prasad 1980
Leptinotarsa decemlineata (Colorado Potato Beetle) Invertebrate Resistant Kiru 2008
Meloidogyne spp. (Root Knot Nematode) Invertebrate Somewhat Resistant Nirula 1967
Pectobacterium carotovorum (Blackleg/Soft Rot) Bacterium Low resistance Lojkowska 1989
Phytophthora infestans (Late Blight) Fungus Somewhat Resistant de Galarreta 1998
Phytophthora infestans (Late Blight) Fungus Not Resistant Tiwari 2015
Potato Leafroll Virus (PLRV) Virus Resistant de Galarreta 1998
Potato Virus M (PVM) Virus Not Resistant de Galarreta 1998
Potato Virus S (PVS) Virus Not Resistant de Galarreta 1998
Potato Virus Y (PVY) Virus Not Resistant de Galarreta 1998
Potato Virus Y (PVY), C Strain Virus Resistant Takacs 1999
Potato Virus Y (PVY), NTN Strain Virus Resistant Takacs 2001
Synchytrium endobioticum (Wart) Fungus Some with immunity Nagaich 1980
Tobacco Mosaic Virus (TMV) Virus Not Resistant Horvath 1985

Glykoalkaloid content

I have found no accounts of glycoalkaloid content for this species, other than a brief mention that glycoalkaloids are low (Kiru 2008).  I tasted freshly harvested tubers and found them pleasant and indistinguishable from domesticated potato.  This is true of both the diploid accessions and the tetraploid accession that may be a hybrid.  This is probably good evidence that the TGA content is at least close to the safety zone, but there is no guarantee that this species does not contain other toxic components.  I was surprised to find that even tubers that were partly exposed and greened had no detectable bitterness.  I have now eaten several large portions of my selections from this species with no apparent ill effects.

Images

Solanum acroscopicum plant
Solanum acroscopicum plant (4x)
Solanum acroscopicum plant
Solanum acroscopicum plant (4x)
Solanum acroscopicum berry
Solanum acroscopicum berry (4x)
Solanum acroscopicum plant
Solanum acroscopicum plant (4x)
Solanum acroscopicum flower
Solanum acroscopicum flower (4x)
Solanum acroscopicum flowers
Solanum acroscopicum flowers (4x)
Solanum acroscopicum tubers
Solanum acroscopicum tubers (4x)
Root ball of the wild potato species Solanum acroscopicum
Solanum acroscopicum root ball (4x)
Tubers of two plants of the wild potato species Solanum acroscopicum
Solanum acroscopicum tubers (4x)
Large tuber of the wild potato species Solanum acroscopicum
Solanum acroscopicum tuber (4x)
Solanum acroscopicum flowers, diploid center, tetraploid outside
Diploid (center) and tetraploid S. acroscopicum flowers
Solanum acroscopicum foliage, diploid left, tetraploid right
Diploid (left) and tetraploid (right) S. acroscopicum foliage
Tetraploid plant of the wild potato species Solanum acroscopicum
Solanum acroscopicum plant (tetraploid)
Solanum acroscopicum PI 607891 seedling
Diploid Solanum acroscopicum
Aerial plant of the wild potato species Solanum acroscopicum (diploid)
S. acroscopicum plant (2x)
 
Flower of the wild potato species Solanum acroscopicum
Diploid S. acroscopicum flower
Flower of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum flower (2x)
Flower of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum flower (2x)
Aerial plant of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum plant (2x)
Flower of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum flower (2x)
Flowers of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum flowers
Flower of the diploid wild potato species Solanum acroscopicum
S. acroscopicum flower (2x)
Flower of the diploid wild potato species Solanum acroscopicum
S. acroscopicum flower (2x)
Flowers of the wild potato species Solanum acroscopicum
Solanum acroscopicum (2x) flowers
Berry of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum berry (2x)
Berry of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum berry (2x)
Flowers of the diploid wild potato species Solanum acroscopicum
S. acroscopicum (2x) flowers
Multi locule berry on the wild potato species Solanum acroscopicum
Solanum acroscopicum berry
Berries of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum berries
Berries of the diploid wild potato species Solanum acroscopicum
Solanum acroscopicum (2x) berries
 
 

Cultivation

I have found seeds of this species easy to germinate using the standard conditions for S. tuberosum.  The USDA Potato Introduction Station found that an accession of this species stored at near freezing temperature for 17 years retained 100% germination (Towill 1982).

Tetraploid of this species (or at least those accessions that I have grown) tuberize under long day conditions and many of the tubers are clustered tightly around the base of the plant.  Spring sown plants began to senesce in August and yielded about 8 ounces of tubers per plant.

Tuber dormancy appears to last about six to eight weeks, so this species should be treated like low dormancy domesticated diploids in storage.

Accessions Evaluated

The following accessions were examined to prepare this profile.  I have evaluated 4/4 accessions currently available from the US Potato Genebank.

PI 230495

Excellent germination and strong seedling growth, greatly outpacing the diploid accessions.  Seedlings vary considerably in form, some with green stems, some with purple, some glabrous, some pubescent, some with lots of apex-directed leaflets, and some with fewer leaflets, appearing similar to domesticated potato seedlings.  Flowers are large, pink, light blue, or white.

This is the first accession of this species that I grew and it turned out to have a lot of unexpected traits.  I noticed, after growing it, that the USDA lists this accession as having 48 chromosomes, when it should be diploid with 24 chromosomes.  This was probably the wrong accession to choose to represent the species on this page.  Seedlings from this accession formed tubers under long day conditions, had very short stolons, and apparently very low glycoalkaloid content.  Beyond that, although the morphology is often roughly consistent with S. acroscopicum, the leaves are larger and broader, the internodes are shorter, and the flowers much larger when compared to the diploid accessions.  Most of the plants also appear to be self-compatible.  These sorts of changes are common with polyploidy and are similar to those seen between domesticated diploid and tetraploid potatoes.

The accession was collected by Carlos Ochoa in 1953 in Chivateria, Tacna, Peru and designated Ochoa 2043.  Ochoa 2043 is an isotype, a collection of the same plant from which the original species description was made.  That makes it highly unlikely that it was originally tetraploid, since the species has always been described as diploid. I contacted the gene bank to see if they knew anything more and learned that Hawkes reported it as tetraploid and off type in 1969 and recommended discarding the accession.  So, it has been tetraploid for at least 50 years.  I’m sure glad that they didn’t discard it, because it has produced some very interesting progeny.

The exact identity of this accession remains unknown, but I have come to suspect that it is most likely a hybrid between S. acroscopicum and domesticated Andean potato.

I considered five possibilities to explain the unusual combination of traits found in this accession:

1. The chromosome count is incorrect.

This seemed unlikely, but was easy to double check.  A guard cell chloroplast count was consistent with tetraploidy in domesticated potatoes.  Even if it were true, it would not explain any of the other traits.

2. This accession is misidentified and is not S. acroscopicum at all and perhaps just a domesticated potato.

I tend to discount this possibility because the plants differ very obviously in form from domesticated potatoes, however, domesticated potatoes have a lot of diversity in form.  I can’t rule out this possibility.  Two papers discussed below group this accession with S. acroscopicum and S. tuberosum.  If the seed lot used in the 1999 study ran out and was replaced before the 2006 study, that would open up the possibility that a mistake was made at the genebank.  On the other hand, as noted above, Hawkes noticed that it was off type 30 years before the 1999 study.  That doesn’t square with a more recent mistake.

3. This is a natural doubling of S. acroscopicum to tetraploidy.

I still don’t consider this possibility ruled out, but in two different studies of genetic markers, seedlings grown from this accession grouped with either S. acroscopicum diploids (Miller 1999) or Andean domesticated potatoes (Bryan 2006).  This suggests that there are genes from both groups in this accession, so it is less likely to be a pure S. acroscopicum tetraploid.  I have my doubts that simple polyploidization would be enough to explain the abundance of domesticated traits in this accession.

4. This is a natural hybrid of S. acroscopicum and a domesticated potato that occurred before it was collected in 1955.

PI 230495 is Ochoa 2043.  The Ochoa 2043 isotype is consistent with the diploid features of this species.  That means that it must have become tetraploid at some point following the original collection, or perhaps the seeds collected from that original plant produced tetraploid progeny from a natural outcrossing.

5. This is hybrid of S. acroscopicum and a domesticated potato that occurred post-collection (i.e. contamination).

This now seems like the most likely explanation.  If contamination occurred in an early round of seed bulking, the self-compatible tetraploids could easily have become overrepresented in later bulkings.  Bryan (2006), mapped domesticated and wild species based on an AFLP marker set and placed this accession together with group Andigenum potatoes.  This conflicts with the RFLP map already mentioned from Miller (1999), that shows this accession grouping closely with the diploid S. acroscopicum accession PI 365314, far from the Andigenum clusters.  Raker (2002) also shows this accession grouping within the Andigenum group, although also closely with two S. candolleanum accessions.

Taken together, the two marker trees suggest to me that PI 230495 may be a hybrid between S. acroscopicum and an Andigenum type domesticated potato.  This is a true seed accession, so if it is a hybrid, and particularly one that has retained two independently segregating genomes, each seedling may have a different combination of parental genetics, with consequently different placement on these genetic trees.  The hybrid scenario makes a lot of sense to me, as it seems like a surprisingly large number of domesticated traits appeared in this single accession.

If it is a hybrid, it would most likely be an amphidiploid, of AAPP configuration, probably with disomic inheritance, since that is the standard case in potato allotetraploids.  The cytoplasmic inheritance would almost certainly have been from S. acroscopicum, since it is hard to imagine a scenario under which seeds would have been collected from a domesticated potato to include in this accession.  The hybrid would most likely be 4EBN, given that both parents are 2x(2EBN), although two other AAPP tetraploid species, S. agrimoniifolium and S. oxycarpum, are 2EBN.  That could be due to inheritance from an A genome ancestor with 1/2 EBN alleles, as appears to be the case with S. acaule, or it could be an indication that EBN allele dosage does not work as expected in allopolyploids.  It should be easy to sort this out with test crosses with diploid and tetraploid domesticated potatoes.

PI 365314

Good germination and moderately strong seedling growth.  Stems light to dark purple.  Flowers mostly dark blue, some light.  Collected in Arequipa, Peru, at the same site as PI 365315.  Hosaka (2012) found that this accession has W type cytoplasm.  It is pretty interesting that these two very similar accessions collected in the same area have different cytoplasm types.

PI 365315

Fair germination, although irregular, and slow seedling growth.  Stems light to dark purple.  Flowers light blue.  This appears to be the most phenotypically diverse of the three diploid accessions.  Collected in Arequipa, Peru, at the same site as PI 365315.  Hosaka (2012) found that this accession has M type cytoplasm.

PI 607891

Excellent germination and strong seedling growth.  All seedlings have dark purple stems.  Flowers dark blue.  Collected in Tacna, Peru, near to the collection site of PI 230495.  CIP public domain MTA.

Breeding

Crosses with S. tuberosum

Female Male Berry Set
Seed Set Germ Ploidy Source
S. tuberosum 4x S. acroscopicum 2x Low Low     Jackson (1999)
S. acroscopicum 2x S. tuberosum 4x None None     Jackson (1999)

Crosses with other species

Jackson (1999) found 0-12% 2n pollen for varieties of this species.

Female Male Berry Set
Seed Set Germ Ploidy Source
             

References

Solanum acroscopicum at Solanaceae Source

Solanum acroscopicum at GRIN Taxonomy

Solanum acroscopicum at CIP

Solanum acroscopicum at Plants of the World Online

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