|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. This is a high elevation species that typically ranges from about 9800 to 12800 feet.
The only accession of this species that I have grown differs from this description in having short stolons and broader leaflets. See below for speculation about these traits.
Vega (1995) found that this species is about as frost tolerant as domesticated potato.
|Condition||Type||Level of Resistance||Source|
|Colorado potato beetle||Invertebrate||Resistant||Kiru 2008|
|Early Blight||Fungus||Resistant||Prasad 1980|
|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|
The Mystery of PI 230495
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. 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. In addition, Dodds (1962) says that red pigments are unique to domesticated potatoes, but some of the flowers of this accession appear to be colored by red pigments. These traits caused me to suspect 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. Additionally, 3 and 4 are unlikely because this species and the domesticated potato have different genomes and presumably do not cross easily.
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). This at least is easy to test and I will count some plants of this species next year.
Number 2 seems the most likely and might be sufficient to explain the differences in traits versus what has been recorded for this species. Unfortunately, I didn’t realize that this was an unusual accession, so I haven’t grown a diploid to make comparisons. I plan to do that in 2019.
A diploid species with day neutral tuberization, short stolons, low glycoalkaloids, and good dormancy seems almost too good to be true, particularly since no one has remarked on these traits before. If they hold true in confirmed diploid accessions, this species could be quite promising for crossing with domesticated diploids, as it could introduce improved photoperiod and dormancy without the usual baggage of long stolons and high glycoalkaloids.
On the other hand, it is a member of clade 3 and therefore has the P genome, so will not cross easily with A genome domesticated varieties. 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.
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 not eaten a large amount.
I have found seeds of this species easy to germinate using the standard conditions for S. tuberosum.
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.
Crosses with S. tuberosum
|Female||Male||Berry Set||Seed Set||Germ||Ploidy||Source|
|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.
|Female||Male||Berry Set||Seed Set||Germ||Ploidy||Source|