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Meyers, S.L.

“Why are there red potatoes in my field?”

Last week’s harvest saw reports of “red potatoes” appearing in sweetpotato fields.  There was speculation that the light-orange-skinned ‘Beauregard’ had altered its genetic make-up to the point that it had changed its skin color at multiple locations within the same field.  While genetic mutations do occur in sweetpotato, there is a far more likely explanation.  As a colleague of mine says, “The simplest answer is usually the right answer.”

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‘LA 07-146′ (second row from bottom) in a field of ‘Beauregard’.

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‘LA 07-146′ (top) and ‘Beauregard’ (bottom) sweetpotato storage roots.

What are these red potatoes?

‘LA 07-146’ is a relatively new sweetpotato variety from the LSU sweetpotato breeding program.  It has red to slightly purple skin, deep orange flesh, and a sugar content similar to ‘Evangeline’ sweetpotato.  The variety consistently yields 15-20% more than ‘Beauregard’.  While growers in Louisiana can grow ‘LA 07-146’ for the fresh market, its production outside Louisiana is restricted and requires a license from ConAgra Foods.  Despite its propensity to outyield current varieties, ‘LA 07-146’ has been grown by only a limited number of sweetpotato growers in Mississippi- and mostly on a trial basis.

 

How do varieties get mixed?

It is not uncommon to comingle sweetpotato varieties in the production setting.  However, most incidences of comingling are subtle as the vast majority of fresh-market sweetpotato varieties have similar leaf shapes and color and have storage roots with orange skin and flesh.  The comingling of varieties typically occurs when sweetpotato “seed” of one variety are accidentally bedded with another variety.  This can happen when the seeding buggy is not thoroughly emptied between varieties.  It can also occur when seed are saved from fields with multiple varieties planted near one another.  For example, if ‘Beauregard’ and ‘LA 07-146’ were grown next to one another in production fields, vines from ‘LA 07-146′ plants could grow into rows planted with ‘Beauregard’.  If the vines touch the soil, they can form storage roots that would likely reach canner size by harvest.  When the field is harvested, the ‘LA 07-146′ canners would be saved in a bin of ‘Beauregard’ for seed the next spring.  Often, the comingled seed will produce slips that are indistinguishable from one another and will be planted together in the production field the following season.

For growers who use the same field for sweetpotato production in consecutive years, it is possible that sweetpotato storage roots left in the production field can overwinter if winter conditions are mild.  These roots can then emerge the following spring and produce vines and storage roots.

 

Mutations do occur in sweetpotato.

Sweetpotatoes frequently mutate in the production environment.  The most obvious mutations occur as changes in foliage color (see below), or storage root flesh or skin color.  While mutations are common, the likelihood of several plants in the same field mutating the exact same way is implausible.

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Leaf variegation is one common type of mutation.

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Conclusion: In this case, the red potatoes appeared in the same row and in consecutive hills.  There was no mutation event or overwintered plants from the previous year.  It would appear that a few ‘LA 07-146’ slips were accidentally planted in a field of ‘Beauregard’ sweetpotato.  Despite even the best growers’ efforts to isolate varieties, mixing of varieties does occur.

 

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