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Solanum curtilobum

Common Name(s) Papa rucki
Aerial plant of the potato species Solanum curtilobum
Solanum curtilobum plant
Code cur
Synonyms  
Clade 4
Series Tuberosa
Ploidy Pentaploid (5x)
EBN 4
Tuberization Photoperiod Short day
Self-compatible Yes, but not stably
Genotype
AAAAA
Cytoplasm Type P
Citation
Juzepczuk & Bukasov: Trudy vsecouz. sezda genetike 3:609. 1929

Description

Solanum curtilobum distribution map Map note

S. curtilobum (curtilobum meaning “short nightshade,” which might refer to the leaves or the whole plant) is perhaps better included among the cultivated species than the wild, but as species that has two-fifths wild genetics, the dividing line isn’t entirely clear.  This species is treated more like a wild species in breeding programs.

This species is cultivated primarily in the highest elevations of the Andes, from northern Peru to southern Bolivia, where S. tuberosum ssp. andigenum will not survive due to frost.  None of the accounts of this species that I have found indicate that it has ever been found in Colombia, but the USDA lists three accessions from Colombia, which is a puzzle.  Plants grow about 12 to 16 inches tall, although some take a more wild-type rosette form.  Tubers most commonly have blue skin and white flesh.  They do not have the kind of diversity of form found in either parent species and are typically round to oval with shallow eyes.  Flowers usually blue.  S. curtilobum is high in glycoalkaloids and is only consumed after processing into chuno.

A chart showing the relationships between Andean domesticated potatoes
Relationships Between Andean Domesticated Potatoes

There are two proposed origins of S. curtilobum.  The first case is hybridization between tetraploid S. tuberosum ssp. andigenum and S. juzepczukii (Hawkes 1962), making its genetic composition 60% S. tuberosum ssp. andigenum and 40% S. acaule. The tuberosum parent is tetraploid and 4EBN, while S. juzepczukii is triploid and 2EBN.  To cross successfully, S. juzepczukii must have provided an unreduced (2n) gamete, giving the combination of a 2x tuberosum gamete and a 3x S. juzepczukii gamete for a 5x (pentaploid) progeny.   The second case is hybridization between triploid S. tuberosum ssp. andigenum and S. acaule (Gavrilenko 2013).  In that case, the triploid andigena would have acted as the female parent with a 2n ovule and S. acaule would have fertilized with normal haploid pollen.

Although it has an odd ploidy, S. curtilobum is self-compatible and is able to cross with other 4EBN species.  These crosses typically produce near-tetraploid aneuploids; that is, tetraploids with some extra chromosomes.  If these aneuploids are backcrossed to the tetraploid parent, they tend to lose the extra chromosomes.

S. curtilobum has not been synthesized by crossing the putative parent species.  This might be because it is hard to get the required 2n gamete from S. juzepczukii or it could be an indication that the hypothesized parents are not correct.

Resistances

Vega (1995) found that this species is a little more frost tolerant than domesticated potato.

Condition Type Level of Resistance Source
 Drought Abiotic  Somewhat resistant Machida-Hirano 2015 
 Frost Abiotic  Somewhat resistant Machida-Hirano 2015 
Late Blight Fungus Somewhat resistant Bachmann-Pfabe 2019
 Potato Virus X Virus  Somewhat resistant Machida-Hirano 2015 
 Root Knot Nematode Invertebrate  Somewhat resistant Machida-Hirano 2015 

Glykoalkaloid content

This species is generally used to make chuño or similarly processed potatoes, typically an indication of high glycoalkaloids.  Osman (1978) found TGA levels ranging from 3.8 to 29.0 mg / 100 g for this species, levels that are not particularly high.

Images

Mixed Solanum curtilobum potatoes
Tubers grown from true seed of S. curtilobum
Aerial plant of the potato species Solanum curtilobum
Solanum curtilobum plant
Aerial plant of the potato species Solanum curtilobum
Solanum curtilobum plant
Flower of the hybrid potato species Solanum curtilobum
Solanum curtilobum flower
       
       

Cultivation

This species is self compatible and will produce viable seed, but the seed does not produce true S. curtilobum.  Instead, first generation seeds usually produce aneuploids between tetraploid and pentaploid.  Subsquent self-pollinated generations converge toward tetraploidy.  True S. curtilobum can only be propagated clonally.

Breeding

I think it is kind of surprising that there hasn’t been more breeding done with S. curtilobum as a tetraploid.  After a few generations of selfing or crossing between varieties, they stabilize at the tetraploid level.  Pentaploid S. curtilobum has 3 copies of the andigenum genome and 2 copies of the acaule genome.  During the process of tetraploid stabilization, it will lose one copy of the andigenum genome, so the tetraploid is 50% andigenum and 50% acaule.  There ought to be plenty of interesting traits to explore in that mix.

S. curtilobum sets much less seed per berry than domesticated tetraploids and I would guess that this is because the uneven distribution of chromosomes doesn’t work out in a way that produces a viable seed much of the time.  Seed set improves with each generation of outcrossing in my experience.

Crosses with S. tuberosum

Female Male Berry Set
Seed Set Germ Ploidy Source
             

Crosses with other species

Female Male Berry Set
Seed Set Germ Ploidy Source
             

References

Solanum curtilobum at Solanaceae Source

Solanum curtilobum at GRIN Taxonomy

 

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