From a single potato tuber to one tonne in a year? Yes, it can be done.

After I’d completed my PhD in October 1975, I stayed on in the UK for a couple of months to sort out ideas and initial drafts for several journal papers, before returning to Lima, Peru just before the end of December, where I was to begin a post-doctoral fellowship with the International Potato Center (CIP). I’d already been working with CIP since January 1973 but I was uncertain in January 1976 where I was going to be located, or what my responsibilities would be. I had spent the previous three years working in CIP’s germplasm program, collecting native varieties of potatoes throughout the Peruvian Andes, and studied the evolution and ethnobotany of cultivated potato species (which formed the basis of the thesis I submitted to the University of Birmingham).

Moving to Costa Rica
CIP Director General Richard Sawyer asked me to move to Costa Rica in Central America to establish a research program on adaptation of potatoes to warm, humid environments, and also to participate in and support other regional activities from CIP’s regional office in Toluca, Mexico. Following a reconnaissance and feasibility mission with CIP colleagues Drs Roger Rowe (head of breeding and genetics) and Ed French (head of plant pathology) to Costa Rica in early January, my wife Steph and I moved to Turrialba in April to be based at CATIE (Centro Agronómico Tropical de Investigación y Enseñanza).

Those first few months were a wake-up call. Not only did I have to establish my own program, hire support staff (Leda Avila as secretary, Jorge Aguilar as research assistant, and Moisés Pereira as technician), and develop the facilities I might need, I also had to navigate rather carefully through the ‘politics’ of a host institution that felt – certainly at that time and for several years subsequently – very insecure. With its limited budget, CATIE management saw my assignment in Turrialba merely as a ‘cheap pair of hands’ to contribute to its research program on inter-cropping systems. I had a hard time convincing CATIE colleagues that, in the first instance, my research should focus on testing and identifying germplasm that showed broad adaptation and could be included in the broader systems research. I also had those other commitments outside Costa Rica that had to be managed as well.

Well, the long and short of it, was that we encountered a serious problem with bacterial wilt, caused by Ralstonia solanacearum, and from then, the focus of my research turned from warm environment adaptation to resistance studies and agronomic management.

Potatoes in Costa Rica during the 1970s
Bacterial wilt was also a serious problem for farmers in certain areas of the lower elevation production zones in Costa Rica. Potatoes have never been a major crop in Costa Rica (rice and beans are much more important staples), but on the slopes of the Irazú volcano near Cartago to the east and northeast of San José (the capital of Costa Rica), potato production is the main economic activity. In the mid- to late-1970s there were only about 10,000 ha of potatoes grown, and about 95% of the production was centered on this Cartago region. Within the Ministry of Agriculture there were only a couple of staff dedicated to potatoes, one agronomist and one pathologist. The small size of the Costa Rican potato program (and others in Central America) was the justification for developing the Regional Cooperative Potato Program (PRECODEPA) in 1978.

Two varieties of Mexican origin, Atzimba and Rosita, made up almost 100% of the production. Atzimba had been developed originally for its resistance to late blight, caused by Phytophthora infestans.

A field of potatoes, var. Atzimba, above Cartago near San Juan de Chicua.

Potato fields of white-flowered var. Atzimba. Because of the steep slopes on the flanks of the Irazu volcano, farmers still use ox-drawn ploughs. These volcanic soils are very deep and fertile.

Mike Jackson using a motorized back-pack sprayer to fumigate potato seedlings in a virus resistance trial. Sprayers of this type produce a turbulent fine mist that effectively applies the pesticide. We were perhaps a little lax in terms of health and safety in the 70s!

In Costa Rica, however, it was extremely susceptible, because the climatic conditions permitted the cultivation of potatoes all year round somewhere in this rather restricted area on the flanks of the volcano. There was always fungal inoculum floating around, and farmers were often obliged to spray their crops at least once a week or more often. Believing that higher doses of fungicides would be more effective than the recommended dosage, the quantity of fungicide used was unacceptable. But it was difficult to persuade farmers to spray more effectively, to use machine powered back-pack sprayers rather than hand-pumped equipment that merely soaked the upper surfaces of the potato leaves. This is not very effective. The machine sprayers create a finer mist and also turbulence among the potato canopy and reach the undersides of the leaves where the fungus actually sporulates.

No healthy seed potatoes
As a vegetatively-propagated crop, potatoes are prone to the build up of several virus diseases that can, unless kept in check, result in a reduction of yield (or degeneration)  year on year. That’s why in many countries there are seed production systems to provide potato farmers with healthy planting stock each year. Three common viruses were prevalent in Costa Rica: potato virus X (PVX), potato virus Y (PVY), and potato leafroll virus (PLRV) – singly, or more commonly, in combination, and as such were a serious threat to the long-term viability of national potato production. More so, it has to be said, than other pests and diseases that affected the crop that could be controlled – if applied effectively and safely – by a range of chemical treatments.

Costa Rica did not have a seed production program in the 1970s (and I haven’t been able to determine whether the foundations we at CIP laid in terms of seed production were maintained) even though many farmers did try to source their seed tubers from farms located at the highest elevations. Many farmers kept  the smallest tubers from a commercial production or ware crop as ‘seed potatoes’ with the inevitable degeneration this practice brought with it. The main problem was that seed stocks were not being constantly being replenished with healthy tubers in a foundation seed initiative. The challenge was therefore to develop a seed production program that could effectively supply the seed potato needs of the country – several thousand tonnes annually.

Although healthy, virus-free stocks of Atzimba and Rosita were readily available, as well as bacterial wilt resistant varieties like MS-35-22 from tissue cultures initially but most often as a small number of virus-free tubers, how was it going to be possible to quickly multiply these seed stocks to a quantity that would begin to have some impact on potato yields in the short term?

Jim Bryan showing Jorge Aguilar, on the right, and a techician from the Costa Rican national potato program how to make single node cuttings.

The challenge
In 1979, CIP seed production specialist Jim Bryan joined me in Costa Rica on a one-year sabbatical to focus on the seed production needs of the Central American region. And together – with colleagues from the Ministerio de Agricultura y Ganadería – we developed a rapid multiplication program, not only to provide the foundation seed for Costa Rica, but also to put into practice many of the ideas that Jim had been developing at CIP headquarters in Peru, but which had not been tested in an actual production context. And at the same time we set ourselves a challenge: to produce one tonne of potatoes from a single tuber in a year (since the growing conditions in Costa Rica permitted more or less all-year-round production).

We converted our screen-houses in Turrialba full-time to this rapid multiplication project. We were sent a small quantity of basic seed tubers that had passed through tissue culture in Lima to eradicate viruses, or received actual tissue culture stocks that we grew on in a makeshift chamber at the plant pathology laboratory in the University of Costa Rica in San José, managed by my good friends and colleagues Drs Luis Carlos González Umaña (a bacteriologist with whom I collaborated over several years on bacterial wilt research) and virologist Rodrigo Gámez Lobo (who became the first director of the biodiversity institute, INBio).

But how to rapidly multiply limited seed stocks? Obviously we had to maintain the health of this basic seed, so only grew the tubers in pots inside the screen-house, in a ‘compost’ of sugarcane bagasse mixed with coarse river sand for better drainage. Having first sterilized this mixture, it was an excellent medium for growing potatoes in pots.

Once we had these plants established we could then start to take a whole range of cuttings: stem cuttings, single node cuttings (usually from young seedlings), sprout cuttings, and leaf-bud cuttings. Rooted cuttings could be grown on in the screen-house to produce more ‘mother plants’ or transplanted directly to the field. The same with single node cuttings and sprout cuttings. Leaf bud cuttings were made from senescing stems (or potato vines) and the axillary buds swelled to form a small tuber.

Each cutting was derived from an axillary bud, and these were stimulated to grow once the apical meristem had been removed from each stem. Cuttings were ‘planted’ in coarse river sand, kept constantly watered, and after a couple of weeks or thereabouts, most had produced healthy roots. Sometimes we used a rooting hormone, but mostly this was not necessary.

Stem cuttings

Single node cuttings

Sprout cuttings

Leaf bud cuttings

Going to the field

With the mixture of rooted cuttings planted directly in the field, plus the numerous tubers from cuttings in the screen-house, it was possible to produce hundreds of ‘daughter’ plants from each ‘mother’ plant that we grew only in the screen-house. And taken over a year, we did show that it was possible to produce one tonne of potatoes from a single tuber. Establishing a basic seed program based on the rapid multiplication of important varieties ensured that there was a constant replenishment of healthy seed available to farmers.

Spreading the word
Through PRECODEPA, we held several training courses in Turrialba on rapid multiplication techniques, and also produced a small brochure (in English and Spanish).

Rapid Multiplication Techniques for Potatoes_Page_01

Click on this image to open the brochure as a PDF file.

Storing seed tubers
Once we had harvested tubers from the screen-house – and for our other research projects – we had to have somewhere to store our seed stocks. At that time, my two colleagues from CIP headquarters in Lima, Dr Bob Booth and Mr Roy Shaw, had designed and promoted in many parts of the world low coast diffused light storage units. And based on their design, we built a prototype for warm humid conditions in Turrialba. It consisted of a double skin of corrugated fiberglass sheets, a wide overlapping roof to provide shade in the strong tropical sun, and an air conditioner to keep the temperature around 20C or so.

We placed bags of sand inside the store and kept them constantly wet, and therefore increased the humidity inside. We also monitored both the temperature and relative humidity as can be seen in one of the photos in the gallery below. Under these diffused light conditions, potato sprouts grow slowly and sturdy. certainly for our needs it was a viable and efficient option for potato storage.

Did we succeed?
I have no idea to what extent the seed production program prospered. One of the issues was commitment from the Ministry itself, but also the continuity of personnel in the potato program.

I left Costa Rica in November 1980 and returned to Lima, expecting to move to another CIP regional office early in 1981. The regional office in Los Baños, Philippines was mooted as a likely venue. As it turned out I resigned from CIP in March 1981 and joined the School of Biological Sciences – Department of Plant Biology at the University of Birmingham. Ten years later I did end up in Los Baños when I joined IRRI. But that’s another story.