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Studies of 30 years ago could change potato seed production systems

Group of native potatoes harvested by a family of farmers in Peru. Photo: A. Balaguer, International Potato Center.

Jorge Luis Alonso G., Lukas Bertschinger, Gregory A. Forbes and Paul C. Struik

The requirements of formal systems of potato seed production are impractical in the Andes and almost impossible to put in place due to the low incidence of virus permitted in the marketed seed and strict formal procedures. A recent study that analyzed the results of research done 30 years ago refutes the belief that all progeny tubers from plants grown from virus infected tubers will generally also become infected. This finding would affect the current formal systems as they all rely on that assumption. The present article describes the research done and suggests possible scenarios in which to apply the results.

Background

According to the Compendium of Potato Diseases, pathogens that attack the potato crop can be:

  • fungi
  • viruses and viroids
  • bacteria
  • phytoplasmas
  • oomycetes

Many of these pathogens spread through the plant and infect tubers. The percentage of infected tubers may accumulate across generations, resulting in seed lots with an increasing proportion of infected tubers, and in reduced vigor and productivity of the crop.

Researchers know this situation as seed degeneration.

A degenerated seed lot usually reduces the emergence, vigor, quality, and yield of a crop.

There are several ways to control seed-borne pathogens that contribute to degeneration.

One option is selecting seed for the subsequent season from the best performing plants in the field or the best-looking tubers from the harvest (positive selection).

Another option is obtaining seed from areas with low infection rates; such areas are known to produce a clean product.

In fact, the Andean farmers generate seed in the Highlands because they are aware of that such seed is more vigorous. Increased vigor can occur due to lower infection with pathogens.

Developed countries created formalized seed production systems, which remove pathogens from infected tissues in the first step of multiplication. In subsequent steps, those systems produce healthy seed tubers, certified to have produced under crop management regulations that prevent infection with pathogens. Only then the farmers receive the seed.

But the implementation of similar systems in developing countries has not yielded the expected results. Small-scale farmers continue to produce their seed or get it from other farmers. Most of the times this seed is of low sanitary quality because pathogens have accumulated in it from one cycle to another.

A farmer and his sister harvest potatoes on their family farm in Pampallacta, Peru. (Jim Richardson, National Geographic)

Yesterday’s results are today valid

There are interesting results from degeneration studies in the Andes published 30 years ago as part of a Ph.D. thesis.

Those studies were looking at the virus transfer from infected mother tubers to daughter tubers in contrasting growing environments,

But they never obtained broad recognition.

The publication of these results in scientific journals seemed difficult because the data did not correspond to the epidemiological theory accepted at the time.

Epidemiological theory and seed production specialists assumed that tubers coming from plants grown from infected seed tubers would also be infected. Usually, this kind of infection is called autoinfection.

The observations in traditional seed systems in Peru were the basis of the mentioned degeneration studies. The farmers there move potatoes to higher altitudes for some generations and later move them back to lower elevations, a practice that seems to increase the vigor of the crop.

For the degeneration studies cited above, researchers planted standardized potato plots at different altitudes above sea level. Then they examined the translocation of viruses from infected mother tubers to daughter tubers during two seasons.

For the experiments they used seed tubers infected with:

  • Potato virus X (PVX)
  • Potato virus (PVY), jointly infected with PVX
  • Andean potato mottling virus (APMoV)
  • Leaf Roll Virus (PLRV)

The percentage of infected daughter tubers was always found to be less than 100%, and sometimes as low as 30%.

With all the viruses that were studied, the proportion of infected daughter tubers decreased as the altitude increased.

A thorough review of research results has been made related with

  1. plant and virus genome expression under different conditions
  2. the interaction between virus, plant and environmental conditions, and
  3. the so-called RNA-silencing, a plant mechanism that limits the accumulation and spread of viruses after an infection i.e. a mechanism of plant defense against virus infection, virus counter-defense, and plant counter-counter-defense.

Results of these studies strengthen the rejection of the assumption of complete autoinfection and support the hypothesis that autoinfection depends on environmental conditions (particularly on temperature) and, consequently, may be much less than 100% under certain growing conditions. This could explain why traditional farmers in the Andes manage the seed as mentioned above.

The results of the study could also help develop more sustainable improved seed production systems which would be more in line with local reality.

What should be done next?

Only growth chamber experiments with contrasting temperatures and the most advanced research tools addressing host plant interaction at the molecular level can confirm the incomplete autoinfection.

The findings should be exploited for breeding potato varieties that exhibit less tuber infection with viruses, as a result of gene expression in function of specific growing conditions.

That information will be useful for designing seed production systems in developing countries, more sustainable and more adapted to local realities.

These results are of particular relevance given climate change.

Seed production and distribution systems and policies should be reviewed because of the facts mentioned above. This analysis will be essential for improving food security and providing farmers with more sustainable cropping practices.

For further information: See Incomplete Infection of Secondarily Infected Potato Plants — an Environment Dependent Underestimated Mechanism in Plant Virology (Frontier in Plant Science, 2017).

About Authors

Jorge Luis Alonso G. Redepapa content writer and White paper writer for the fresh and processed food industriesjorgealonso@redepapa.org

Lukas Bertschinger. Agroscope, Delegate for national and international research cooperation, Wädenswil, Switzerland — lukas.bertschinger@agroscope.admin.ch

Gregory A. Forbes. Senior Consultant, International Potato Center — gregaforbes@gmail.com

Paul C. Struik. Centre for Crop Systems Analysis, Plant Sciences, Wageningen University and Research, Wageningen, Netherlands — paul.struik@wur.nl

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