|Common Name(s)||Papa del zorro|
|Ploidy||Diploid (2x), tetraploid (4x)|
|Tuberization Photoperiod ||Day neutral|
|Cytoplasm Type||W, M (Hosaka 2009, as W, C)|
|Citation ||Ochoa: Agronomía (Lima) 18: 130. 1953.|
Solanum acroscopicum (acroscopicum refers to the tendency of the leaflets to point toward the terminal leaflet or apex) 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 smaller. 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.
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.
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 unspecific 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|
|Bacterial soft rot||Bacterium||Low resistance||Lojkowska 1989|
|Colorado potato beetle||Invertebrate||Resistant||Kiru 2008|
|Early Blight||Fungus||Resistant||Prasad 1980|
|Late Blight||Fungus||Somewhat Resistant||de Galarreta 1998|
|Late Blight||Fungus||Not Resistant||Tiwari 2015|
|Potato Leafroll Virus||Virus||Resistant||de Galarreta 1998|
|Potato Virus M||Virus||Not Resistant||de Galarreta 1998|
|Potato Virus S||Virus||Not Resistant||de Galarreta 1998|
|Potato Virus Y||Virus||Not Resistant||de Galarreta 1998|
|Potato Virus Y, C Strain||Virus||Resistant||Takacs 1999|
|Potato Virus Y, NTN Strain||Virus||Resistant||Takacs 2001|
|Root Knot Nematode||Invertebrate||Somewhat Resistant||Nirula 1967|
|Tobacco Mosaic Virus||Virus||Not Resistant||Horvath 1985|
|Wart||Fungus||Some with immunity||Nagaich 1980|
The first accession of this species that I grew, USDA PI 230495, turned out to have a lot of unexpected traits. It formed tubers under long day conditions, had very short stolons, and apparently very low glycoalkaloid content. Beyond that, although the morphology is 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. I can’t be totally certain, but these 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.
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. 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. I think the most likely explanation is that this is a tetraploid accession of S. acroscopicum, not a hybrid with another species, nor a misidentification. You can follow for the full analysis.
I initially suspected several possibilities:
|1. The chromosome count is incorrect.|
|2. This is a natural doubling of S. acroscopicum to tetraploidy.|
|3. This is a natural hybrid of S. acroscopicum and a domesticated potato that occurred before it was collected in 1955.|
|4. This is hybrid of S. acroscopicum and a domesticated potato that occurred post-collection (i.e. contamination).|
|5. This accession is misidentified and is not S. acroscopicum at all.|
We can probably rule out 3 and 5 as Miller (1999) found that this accession and a diploid accession of the same species grouped closely in an analysis of nuclear markers. Number 4 could still be true, assuming that the contamination occurred during seed bulking that has taken place since that study, but it seems suspicious that the plants are so uniform in having the ostensibly domesticated traits. It would be more likely to get a mix of contaminated and non-contaminated seed. I suppose it is still conceivable that this accession crossed with the domesticated potato more distantly and therefore groups with S. acroscopicum while retaining some domesticated traits. That is beyond my ability to test.
Number 1 does not seem sufficient to explain the differences in traits between this accession and the characteristics described for this species in Ochoa (2004), such as having having stolons up to 32 inches (80 cm). I have now done guard cell counts on both tetraploid and diploid accessions and found them to be consistent with the counts reported for domesticated potatoes, so this is more evidence that PI 230495 is, in fact, tetraploid.
Number 2 seems the most likely and might be sufficient to explain the differences in traits versus what has been recorded for this species. Another piece of evidence can be seen in pictures of the original collection of this accession. 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. It is easy to imagine that an unnoticed doubling could result in that plant becoming over-represented during seed increase, since the tetraploids are self compatible and produce many more and larger berries than the diploids.
Such domestication-friendly traits in a wild potato seems quite remarkable to me and probably valuable for breeding. S. acroscopicum is a member of clade 3 and therefore has the P genome, so might not cross easily with A genome domesticated varieties, but I will try that as soon as possible. Another way to look at the situation might be with S. acroscopicum as the foundation of a new domesticated line out of clade 3. It has many desirable traits and would allow breeding directly with the many P genome species that have valuable resistances that are difficult to pass into clade 4 domesticated potatoes. This is similar to the approach of breeding new varieties out of the 1EBN North American species, rather than crossing them into the domesticated potato.
The next steps to investigate will be chromosome doubling the diploid accessions and trying to make 4x x 2x crosses with this species. It will be interesting to see if short stolons and short day tuberization appear with any doubling or are unique to the tetraploid accession. If doubling produces these traits in the diploid accessions, that would be strong evidence that PI 230495 is also the result of doubling.
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 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.
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).
This species (or at least those accessions that I have grown) tuberizes 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.
Crosses with S. tuberosum
|S. tuberosum||S. acroscopicum||Low||Low||Jackson (1999)|
|S. acroscopicum||S. tuberosum||None||None||Jackson (1999)|
Crosses with other species
Jackson (1999) found 0-12% 2n pollen for varieties of this species.