Monday, May 21, 2007

Breeding new plants

Last week I discussed the way that many new cultivars originate from eagle-eyed gardeners and naturalists who notice variations in plant growth. This accounts for many new introductions, but among the more intensively selected garden plans a completely different way of raising new varieties is followed.
They are deliberately cross-pollinated to give raise to new forms.
The first humans probably undertook this process unwittingly as they slowly selected grains and vegetables for their improved traits – disease resistance, improved flavour, greater yield, and ease of cultivation.
Although the genetic basis of the improvements was not guessed at until one hundred years ago, gardeners soon realised that if two similar plants were grown alongside each other they would sometimes cross, and the resultant plants would sometimes (not always by any means!) be an improvement on both parents.
Today we know the general rules that apply in the process, having an understanding of the roles of dominant and recessive genes play in the recombination of DNA between the two parents. This has enabled professional plant breeders to be able to predict the results of their hybridisation with greater certainty.
Plant breeding has become a major industry in some parts of the world. We have all noticed the wide array of varieties of both flowers and vegetables on the seed market – these varieties are the results of years of work by breeders, mainly in the United States, Japan and Europe.
Think of the humble petunia. The varieties that were top of the pops twenty years ago – the Magic and Satin series – have long gone and have been replaced by a bewildering range of different types. These new varieties have improved resistance to mildew, they are more weather resistant and they flower sooner and longer. Bedding marigolds have undergone a similar transformation and modern Impatiens bear no resemblance to the taller-growing older types, and have a much wider colour range.
Similar changes have happened among vegetables, although not all gardeners will agree that the changes have been for the better. The introduction of F1 hybrids with their improved vigour and increased uniformity has suited commercial growers very well, but the increased price of seed and the uniformity of growing times have not always pleased home gardeners, who prefer to have a staggered harvest for their crop.
Sometimes gardeners think the old vegetable varieties tasted better too. I often hear how old tomato strains were much tastier that the varieties we purchase in the supermarket, but I am not convinced. I have grown a number of heritage forms over the years and I have never found one that tasted as nice as the modern F1 hybrids I grow. I accept that glasshouse varieties are bred to have thicker skins, and probably don’t have such a strong taste, but the modern varieties I grow outside have better and earlier crops, they are more disease resistant, and they taste better than the old ones I have tries.
The presence of professional breeders in the market makes it harder for the amateur to raise noteworthy varieties. I correspond with iris breeders in the Unites States, a few of whom make their living introducing new varieties. Professionals generally carry out rose breeding too – they raise literally thousands of seedlings to select each one they release onto the market. The amateur probably has to work among less popular varieties, or to try and beat the professionals by making the sorts of wild crosses they would not consider- maybe crossing a dwarf rose with a rampant climber, to see what would happen.
The process of cross-pollinating is the same for all plants. For the Pacific Coast irises I breed, I remove the male sexual organs form the flower I want to use as the father, having first determined that the pollen is shedding. I then remove the petals from the flower I have selected to be the mother, the pod parent. I use a paintbrush to apply the pollen onto the style arms that lead to the female sexual organs.
Rose breeders work in a similar manner. The stamen are removed from the male parent, and stored for a day or so to allow the pollen to ripen and drop. A female flower is prepared by the removal of all the petals and the stamen, and then the pollen from the male is brushed over the female parts.
This technique will work for most plants that have large flowers – camellias, rhododendrons, orchids, cacti even, all are bred in this manner, and I have crossed some of my garden pinks using this method. It might been be fun to cross some of those old heritage tomatoes with modern hybrids to see what happened.
I have been crossing my red Lapageria with a white flowered form, using an identical technique. It is too early to tell how well it is going to work but I do have some white flowers flushed with pink so I am hopeful that it will prove successful.
Sometimes, though, the plants perform better if the two varieties selected for crossing are simplyallowed to grow alongside each other. Dahlias, for example, are difficult o hand pollinate and are grown in this manner. I suspect that many new hebe and manuka varieties are also bred this way.
Be prepared for some disappointments if you are thinking of taking up plant breeding. Not all of your wonderful crosses will result in seeds – sometimes that plants are too distantly related, sometimes the weather is not right, and sometimes they are just stubborn - and then, once the seed is harvested, not all will germinate. As if that was not enough to deter you, the majority of your plants will show no improvement on their parents and will need to be discarded.
But, and it is a huge but, when you do find something new it is worth all the trouble. Proud parents have nothing on the breeder of a successful new dahlia, rose, orchid or Pacific Coast iris.

Monday, May 07, 2007

Smoking bushes

May has started out wonderfully. The succession of warm days and mild evenings has made this a delightful autumn. We have had no frosts to speak of in the Wairarapa valley, and the lack of wind has been a blessing for those of us who love autumn trees and shrubs. Most plants seem to have managed to hold onto their leaves longer than normal – some have not even coloured up yet.
There is, of course, a down side to this settled mild weather. It has meant that the lawns have kicked back into growth, and although they are scarcely at spring pace, they are still growing aplenty. Weeds are also whipping ahead. I turned over some soil about three weeks ago, planting autumn seedlings, and the bare dirt has been invaded. I needed to go over it again this weekend, weeding. The soil was nice and damp though, and the weeds all came out easily enough.
What with weeding and mowing, it was Sunday afternoon before I found any time to go and have a tour around the countryside, looking for autumn foliage. The Head Gardener is an unemployed bum now (for three days between jobs!) so she found the time to come with me and we made our way eastwards.
I was on the lookout for some colour on a group of smoke bushes that are among my favourite autumn shrubs. These particular plants are mature shrubs – perhaps as much as four metres high – and I have watched them since I was a child.
They are the American version of smoke bushes, Cotinus obovatus, so-called because the leaves are egg shaped. The European version, C. coggygria, probably better deserves the common name because this species has plumes of misty purplish flowers in early summer. These would be enough to earn the epithet of ‘smoke bush’, but they fade over the summer and become even smokier and more deserving of the name. They colour up in the autumn but the display is nowhere near as good as that of their American cousins.
C. obovatus is taller growing that its EU relative, and does not have the same amount of flowers, nor the same degree of smokiness. Maybe it is the politically correct smoke bush – the smokefree one. However, what is lacks in flower power it more than makes up for with foliage display. The leaves take on hues of orange, scarlet and purple as the winter approaches, giving a startling display.
The shrubs we looked at used to bring us a lot of trade, as each autumn we had people calling in at the nursery, asking what the shrubs were and where they could buy some. As we knew they would be in display each early May, we made sure we had plenty of stock.
Overseas it is possible to buy named clones of these beauties, with different coloured forms being favoured, but I do not think they have arrived in New Zealand yet.
There is a variety of the European form that is worth growing for a different foliage display, a deeply coloured form called ‘Royal Purple.’ This has deep wine purple coloured leaves with a shiny surface. It has gigantic flower heads of light mauve over summer, and then colours up almost as well as the American forms in autumn.
All the forms share a similar set of requirements. They like a sunny situation and prefer cool, free-draining soil. They do not like the soil to be over-rich, and they certainly do not need fertiliser applied. If grown in rich soil they grow rather coarsely and do not colour up so well. They do respond very well to trimming and shaping. The neater bushes will give better a better display of autumn foliage. They flourish in colder areas with dry summers.
After we had sated ourselves on the smoke bushes, we took off again, heading out into the country. We saw some wonderful poplars, and tasted some spicy wild apples growing on the side of a gravel road. We even saw a friend on a piebald horse accompanied by his young daughter on a rotund little pony, droving a ragged mob of sheep along the road near their farmlet. What we did not see was a great deal of autumn colour apart from an impressive avenue of scarlet oaks glistening in the late afternoon sun.
Early on Saturday morning I had taken my camera down to the municipal park to take some photographs of the autumn display. I headed straight to my favourite tree, a mature Ginkgo biloba. It was at its very best – covered with the bright gold leaves that this tree is so renowned for.
If you have room for one of these magnificent trees, at the risk of being sexist, make sure you find a male. They have better form and they do not have the messy fruits that the female trees bear at this time of the year.
The male trees like ‘Autumn Gold’, ‘Fairmount’, and ‘Saratoga’ all start out with relatively slender habits but become “rounded with maturity.” Sounds like every male I ever knew!
Many prize the female fruits for the plum-sized nut contained within the flesh, but, boy of boy, that flesh stinks! It has the most regnant dirty-socks smell, and it is very difficult to remove.
Just alongside the Ginkgo was an unidentified red-leaved Japanese maple, Acer palmatum. It is growing in a sheltered area away from the worst of the winds and like most of the red forms of this popular maple, it colours up spectacularly. When its leaves fall they mingle with the butter gold Ginkgo leaves the effect is worth an extra trip, so next weekend I’ll take the Head Gardener with me and we will go have a look.