Well, that’s how The Sun newspaper reported our research, rather flippantly in a 55 word piece (Crunch time for boffins), back in December 1987.

And to emphasise the point, that story was printed alongside Page 3 model Suzanne, topless models being a daily feature of The Sun since 1970. But no longer.

Anyway, to cut a long story short, The Sun had come across an article that my colleague Dr Brian Ford-Lloyd (left) and I had written for a research bulletin at The University of Birmingham, where we both lectured in the School of Biological Sciences.

We had received a research grant from United Biscuits [1]—the makers of Walkers Crisps—to develop potatoes less susceptible to low temperature sweetening.

However, before I get into the details, let me explain how this grant came about.

In the mid-1980s, I was contacted by Dr John Vessey who was a research manager for United Biscuits in Lincolnshire. He and I had been colleagues at the International Potato Center (CIP) in Lima, Peru during 1973 and 1974. In fact, John and his wife Marian were our witnesses when Steph and I married in Lima.

John knew that I was making frequent visits CIP as I had a joint research project as well as supervising two Peruvian PhD students who were conducting their thesis research there.

Representing United Biscuits on the council of The Biscuit, Cake, Chocolate and Confectionery Alliance or BCCCA (dissolved in 2004) John proposed that I could (during one of my visits to Peru, and as a consultant to the BCCCA) scope the possibility of a cocoa conservation project similar to one that had been funded in Ecuador. A year later, John’s managing director at United Biscuits (whose name I forget), John, and Tony Lass, a cocoa agronomist from Cadbury’s, and I made a joint visit to Peru, and while traveling together we discussed a project to develop potatoes resistant to low temperature sweetening.

So, what is low temperature sweetening, and why is it important to the crisping industry? It’s a potato storage and processing issue.

After harvest, not all potatoes can be processed immediately into crisps (that’s potato chips in American parlance), and thousands of tonnes of tubers must be stored for quite long periods before processing. If the storage temperature is too high, then tubers will begin to sprout and quality lost. However, when potatoes are stored at low temperatures (typically below ~8–10°C), their starch starts breaking down into so-called reducing sugars (mainly glucose and fructose). That sugar build-up is what we call low-temperature sweetening. It matters because:

• Extra sugars make potatoes taste slightly sweet;
• When fried or baked at high heat, the sugars react with amino acids (the Maillard reaction), causing:
  • excessive browning or dark crisps/fries;
  • bitter flavours; and
  • higher acrylamide formation (a food safety concern).

And what the industry wants is a nice, pale yellow or light gold crisp. Anything darker leads to ‘black bits in crisp packets‘.

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Back in the 1980s, one of the main crisping potato varieties was cv. Record (now surpassed by a range of other varieties). Cv. Record was quite susceptible to low temperature sweetening. Would it be possible to develop a line (or lines) of cv. Record that were more resistant. And to achieve that aim without a costly and lengthy potato breeding project. That’s why we opted for a biotechnology approach, namely the generation of somaclonal variation.

Somaclonal variation is a type of genetic variation that appears in plants which are regenerated through plant tissue culture (in vitro culture), rather than grown from seeds.

It’s a two-step process (see Juned et al., 1991 below). Leaf disks must first be cultured on an appropriate nutrient medium to produce undifferentiated plant tissue, known as callus (left below). The second step, which usually involves transfer to another medium, is to induce the formation of shoots and roots (right below). The regenerated plantlets, known as somaclones, may not be exact copies of the original plant.

One of my former MSc genetic conservation students Susan Juned [2] joined the project as a Research Associate (and registering for a PhD). In the summer of 1990, one of my undergraduate tutees, Abigail Amey (née Gregory [3]) joined the project for two months as a research assistant.

Our research material was a small sack of potatoes of cv. Record, 170 tubers in total sent to us by John Vessey. From the outset we made decision that would have implications not only for this project per se, but more widely for seed potato production and in vitro conservation of plant genetic resources. It wasn’t rocket science. We just gave each tuber a unique number, R1 to R170, the aim being to follow subsequent generations of somaclones derived from each.

So, were we successful in producing cv. Record somaclones? The short answer is yes. And did we produce somaclones less susceptible to low temperature sweetening? Again the answer is a conditional yes. John Vessey gave us this feedback:

• The project was successful in that it produced cv. Record somaclones with lower reducing sugars in the tubers, but unsuccessful in that none entered commercial production . . . Shortly after the end of the project, Record was replaced by a superior variety, Saturna.
• The project very clearly showed the potential of somaclones but also emphasised that it needs to be combined with conventional breeding.
• Other important aspects were the demonstration that the commercial seed potato lines available were not genetically identical, as previously thought, and that regeneration of clones from single cells had to be as rapid as possible to avoid unwanted somaclonal variation.

Mixed results then, perhaps. But there was an unexpected outcome. The majority of somaclones were derived from just a few of the 170 tubers, each potentially (and quite unexpectedly) a different cv. Record clone. We suggested that the differential regeneration ability was due to genetic differences between tubers as it was found to be maintained in subsequent tuber generations. Furthermore, this would have major implications for seed potato production specifically and, more generally, for in vitro genetic conservation of vegetatively-propagated species.

We published this aspect of the project in Annals of Botany in 1991. Just click on the image below to read the full article.

We drew two important conclusions from this research project (apart from the success of generating clones with reduced low temperature sweetening).

First, it appears that the tubers of cv. Record were not genetically homogeneous.

Second, in terms of genetic conservation of crops that cannot be conserved long-term as seed but must be grown in field genebanks, grown continuously as tissue cultures, or cryopreserved at the temperature of liquid nitrogen, this statement is very important:

In vitro techniques are advantageous for many reasons, since field maintenance of germplasm has many risks attached to it. However, one of the criteria for efficient and acceptable in vitro storage of germplasm is the maintenance of the original genotype over a long period. The choice of material from which to establish an in vitro germplasm collection may therefore have long-term consequences since we may not be dealing with a random sample of plants within a genotype at the culture stage. What is actually conserved may be a genetically biased sample favouring an inherent ability to regenerate and multiply under in vitro conditions. 

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Low temperature sweetening is not the only darkening issue that occurs in potatoes. When potato tubers (as well as apples and other fruits) are bruised or cut, they will turn brown or darker if left exposed to air (see right). This is because of a process known as enzymic browning, a reaction of the enzyme polyphenol oxidase (PPO) with phenolic compounds in tubers. Melanins form, and tubers turn dark, or ‘blacken’. It’s a condition found in most potato varieties.

However, there is a species of wild potato, Solanum hjertingii Hawkes, found in northeast Mexico whose tubers do not darken when damaged or cut, or at the very least show minimum browning.

S. hjertingii is a tetraploid species, that’s to say it has 48 chromosomes. It was first described by Mason Professor of Botany at The University of Birmingham and potato taxonomist Professor Jack Hawkes in 1963, and named in honour of his Danish long-time collaborator and noted botanist, J Peter Hjerting. Jack and Peter collected together over many years in the southern USA, Mexico, Central America, Bolivia, and the southern cone countries of South America. An account and film of their 1958 expedition to the USA, Mexico, and Central America can be found here.

When I joined the Department of Plant Biology at The University of Birmingham in April 1981, Jack Hawkes had only 18 months to retirement and asked me to take on supervision of one of his PhD students, Lynne Woodwards.

Lynne successfully submitted her thesis in 1982, showing how S. hjertingii and some related species in the same taxonomic grouping, Series Longipedicellata Buk. from the southern USA to central Mexico did not darken, making comparisons among these species and cultivated potatoes (S. tuberosum). She also attempted crosses between S. hjertingii and cultivars but these were unsuccessful. However, crosses with some bridging species did produce hybrid progeny with little or no enzymic blackening. We published this paper in 1985.

After leaving CIP in the mid-1980s, one of my former colleagues, Dr Charles Brown, joined USDA-ARS, Vegetable and Forage Crops Research Unit, Prosser, Washington. In 2002 he published a paper on the transfer of the S. hjertingii trait into cultivated germplasm through bridging species [4].

Later in the 1980s, I had another PhD student, Ian Gubb, who I co-supervised with Professor Jim Callow (who had become Mason Professor of Botany after Jack Hawkes’ retirement) and Dr JC Hughes at the Institute of Food Research Institute in Norwich.

Having a strong biochemistry background, Ian quantified both enzyme and substrate levels in S. hjertingii and cultivars, demonstrating that the lack of enzymic browning in this wild species was a ‘true’ trait. This research was published in Annals of Applied Biology in 1989. Click on this image to read the full text. Ian completed his PhD in 1991.

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Both of these projects demonstrate the need for different approaches to tackle issues with crop productivity and value. Not only is there a need to identify and quantify the underlying causes of a problem, but also how to use genetic diversity to transfer a trait from one germplasm source to another. And if there is no apparent variation, how to generate it as we showed with the somaclones.

Having said that I suspect that in this genomic discovery and editing age, low temperature sweetening and enzymic browning will be overcome more efficiently than we contemplated almost 40 years ago.

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[1] Which became KP Agriculture.

[2] After leaving the project, Susan worked in the green energy industry and became involved in local and national politics for the Liberal Democrats. She now serves as the Leader of Stratford-upon-Avon District Council in  Warwickshire.

[3] Abigail graduated in July 1991 and moved to Durham University where she completed a PhD in plant biochemistry. In 2019, I invited her to participate in a project to publish online the films and narratives of potato collecting expeditions to the Americas made by Jack Hawkes. Abigail is a co-author of Plant Biology (2009) by Alison M Smith et al., and published by Garland Science.

[4] Culley, DE, BB Dean & CR Brown, 2002. Introgression of the low browning trait from the wild Mexican species Solanum hjertingii into cultivated potato (Solanum tuberosum L.). Euphytica 125:293–303.