Chilly Treatment for Peruvian Lilies

Peter Thompson looks at the fascinating research into the germination of Alstroemerias which provides insight into several general principles.

Gardeners enjoy ploys and take pleasure in presenting them as garden lore to those innocent enough to be taken in. Garden lore has it that the germination of seeds which are naturally reluctant to produce seedlings is improved by soaking them in warm water for twenty four hours before sowing them. Occasionally this works - very often it is no more than an expedient suggestion trotted out in the guise of sage advice to avoid a confession of ignorance.

So it was with alstroemeria seeds. 'Yes, they're a bit tricky', you would be told, 'but soak them in warm water for twenty four hours before sowing them, and they'll germinate - but don't expect them all to come up at once - some will take months'. This fable, repeated in every book and seed catalogue, sufficed -until somebody who really needed to know tried it out, found that it was a waste of warm water and time, and set out to find someone who would provide the answer. The story of what followed is related here because it not only sheds light on how to germinate seeds of Peruvian lilies, but shows how the natural conditions in which plants live affect the ways they behave, and how similar responses can be shared with other species living in quite different parts of the world. It also provides an example of how the common interests of a number of different people can bring together the threads which together make up a tiny fraction of the fabric of gardening history.

The first act in the story opens during the summer of 1971-72 in Chile where Messrs. Watson, Cheese and Beckett were escaping the wintry weather of their native land by making collections of seeds and plants in a variety of places ranging from sea level to the high, dry Andean Alps. Amongst the many seeds they brought home were a number of species of alstroemeria; some from the frost-free, mist-shrouded coastal plain, which runs beside the Pacific Ocean north of Valparaiso, some from the hot dry sub-alpine hills and valleys inland around Santiago, and others from more southerly, cooler lowland plains amongst the forests of southern beech and pine. After their return to England a part of these collections with field notes describing the places where they had been found were sent to the Royal Botanic Gardens at Kew.

A few years later, by way of an entr'acte, the Parigo Horticultural Company became interested in breeding new varieties of alstroemeria. The well-known Ligtu Hybrids were already well established and had proved the commercial value of this plant as a cut-flower, capable of producing three crops in two years. Parigo were using the wider range of species now at their disposal to introduce richer colours and more exotic markings in a new strain which they had aptly christened Peacock Hybrids. But they had a problem; most of their seeds failed to germinate, and they found that many of the crosses they made were ineffective because only a very small proportion of the seeds produced gave rise to seedlings. They sought advice on their problem, and were told - you've guessed it - 'soak the seeds in water for twenty four hours'. They did so, and were unimpressed by the results.

Meanwhile at Kew, or to be more precise in the Physiology Section located at Wakehurst Place in Sussex, the scene was being set for act two. For some years experiments had been going on which looked at the conditions under which seeds germinated; a great variety of different kinds of plants had been examined - though as it happened species of alstroemeria had not played any major part in these investigations. The scientists at Wakehurst Place were particularly interested in the ways that seeds of plants which grow naturally in different parts of the world germinated in relation to climate and their local environment, and especially in the ways that closely related plants differed from or resembled one another in their responses. Then, one day, a letter arrived from Messrs. Parigo seeking advice on the best way to germinate seeds of different species of alstroemeria. The first part of the answer was simple enough - we didn't know; the second part was a suggestion that since they needed to know, and between us we could assemble suitable material for an investigation, which would also be of interest to us, we should try to find out.

Damien Keefe, a student at Bath University, was just about to arrive at Wakehurst Place to do a six-month stint as a sandwich student. Here was a man in search of a subject and alstroemerias became his lot. During the next few months, working under the supervision of Patricia Newman, he was able to unravel the mysteries of their germination so successfully that it became possible to describe precisely the conditions under which seeds of different species of alstroemeria germinated, so that virtually every seed capable of producing a seedling would do so. He was able to compare the germination behaviour of commercial strains of the Ligtu Hybrids and collections of nine different species, almost all of them obtained during Watson, Cheese and Beckett's expedition, for which there were field notes giving precise information on when and where they had been collected.

Parigo's request arrived when other experiments were being done on the germination responses of bluebells and the hoop petticoat daffodil amongst a number of monocotyledonous plants which produce showy flowers. These had one thing in common; they germinated most freely at comparatively low temperatures provided that for several weeks after being sown they had been kept very warm. There was no particular reason to think that alstroemerias would respond in a similar way, but this germination response was prominent in our thoughts at the time, and it seemed as good a place to make a start as any other.

Still comparatively unknown, though by no means an uncommon response, it is the exact opposite of the process which alpine gardeners know so well, and have used for many years, when they sow seeds in a cold frame in January to be frosted and thoroughly chilled; after which seedlings appear as temperatures rise during the spring.

Damien Keefe's first experiments produced encouraging results when seeds of several of the species and the Ligtu Hybrids, placed in high temperatures for the first four weeks, germinated well soon after being transferred to more chilly conditions. But this simple treatment, varied in its effectiveness from one species to another, and was never enough to persuade every viable seed to germinate. Something more was involved, and - searching for this something - he tried out a treatment which Patricia Newman was using to persuade seeds of St. Bernard's lily and asphodels to overcome their reluctance to produce seedlings. This involved excising a small amount of tissue lying immediately above the embryo, after making a small tear in the seed coat; a fiddly operation which alstroemerias make as simple as possible by marking the appropriate place to make the cut with a dark spot. First attempts were a disaster when the operation was done before sowing the seeds; every one of them rotted away within a few days during the initial phase at high temperatures. However, when delayed until this initial phase was completed and done immediately before the seeds were transferred to low temperatures, the removal of tissue close to the embryo was very successful, and resulted in the rapid germination of practically every viable seed in the samples being tested.

Perhaps one of the most interesting features to emerge from these results was the fact that all the species responded in a closely similar fashion: they shared almost identical responses to temperature; they depended on the same sequences of high and low temperatures; they reacted in very similar ways to small incisions made in their seed coats. The precise numbers that germinated varied considerably depending on the species and the previous history of the stock of seed, but in every one particular treatments consistently reduced or increased the proportions of seeds which produced seedlings.

As a finale, the recipe for ensuring that all viable seeds of these plants germinated was shown to run as follows:
• After sowing them, keep them for at least four weeks at high temperatures (25°C by day falling to 15°C at night);
• Then gouge out a small piece of tissue just above the embryo with the point of a knife, using the brown spot as a guide.
• Transfer the seeds to a temperature of 10°C or less.

Seedlings are produced most rapidly at about 10°C, but emerge remarkably quickly at temperatures which are much lower - even down to freezing point. A description can be found in The Garden (1979 Vol. 104) and a much more detailed account of the effects of temperature on the different species was published in Gartenbauwissenschaft (1979 Vol. 44) - a rather inaccessible source for those who garden in Britain. Unfortunately the paper which was published in the latter was not accepted for publication in the Journal of Horticultural Science, where it would be relatively easy to obtain, because the editor believed, misguidedly, that alstroemerias were insufficiently significant horticulturally to merit a mention in the journal!

But why, you may well ask should any plant produce seeds which are so contrary that they refuse to germinate when lying in warm soil, yet produce seedlings rapidly in cold - even at temperatures close to freezing point? Why, if seeds must germinate at low temperatures, should they also require

high ones first to which they appear at the time to be oblivious? Why, to complicate matters still further, should it actually be beneficial for the seed coat to suffer damage of a particular quite precise kind? Why, if all these requirements are part of some process of adapting to local conditions, should they be found throughout a group of species which grow under a variety of different conditions, experiencing different temperatures, and competing with different kinds of neighbouring plants? Why, to spread the net further, should these species from the feet of the Andes share similar germination responses with bluebells, almost confined to the British Isles, and with hoop petticoat daffodils from dry Iberian hillsides, to mention only two amongst a throng of unrelated plants?

Answers suggest themselves to some of these questions, but others pose riddles to which the solutions are still quite obscure. It can be plausibly argued in a general way, that this is a germination response which ensures that no seedlings are produced from seeds shed during mid-summer at a time, perhaps when drought is prevalent, but favours rapid germination as temperatures fall in the autumn: a strategy which is likely to be successful in areas with hot, dry summers and cool, but not too severe winters. It may be surmised that the response to high temperatures during the summer, which has no immediate effect but enables the seeds to germinate later, is more likely to lead to the germination of seeds which have been in contact with ' some water at that time than those which have remained consistently dry. If so it may help seeds to locate relatively well watered places within generally parched surroundings. The beneficial affects of damage to the seed coat could be a device to delay germination, even under ideal conditions, so that the seeds produced during a single season germinate over a spread of several years — providing a seed bank within the soil which retains a diverse gene pool even when unusually severe conditions kill a high proportion of the visible flowering plants.

Presumably the close tie-up between seeds germinating and particular conditions results from the processes of natural selection, by which plants and animals are believed to adapt to changing stresses in the world around them. Yet the species of alstroemeria looked at in these tests, and sharing notably similar responses are naturally distributed in places with rather different climates, and quite different floras. This suggests that the ancestral stock from which all these species derive possessed a germination strategy which has persisted with very little change as the different species evolved and became adapted to survive under different conditions. Germination is often spoken of as a rather plastic plant response, which is rather easily changed by circumstances. And indeed another, oft-repeated, morsel of garden lore has it that cultivated plants germinate in ways which are quite different to those of their wild ancestors because their germination responses have become adapted to the new needs and demands of crop plants. There is in fact very little evidence for this, and much more which suggests that, like the alstroemeria species, germination responses may not be easily changed, but may persist - even in the face of strong selective pressures - for long periods.

The gardener's lore, which proposed that soaking Peruvian lily seeds in warm water would make them germinate may have proved to be optimistically simple. The reality is more complicated, but much more interesting, and provides wider opportunities for gardeners who enjoy the exercise of imagination, and are not adverse to an occasional display of the skills of their craft. In this particular enterprise the botanists in the Jodrell Laboratory at Wakehurst Place learnt a fraction more about the ways that plants are adapted to their surroundings, and about the nature of such adaptations; Messrs. Parigo and countless other gardeners benefited from a precise recipe which enabled them to germinate alstroemeria seeds, not without difficulty - but at least with certainty. Mr. Keefe returned to Bath University having successfully and, we hope enjoyably, fulfilled the conditions of his sandwich course.