Chapter 6

Producing New Varieties

Elements Of Heredity And Plant-Breeding

New roses come into existence in two ways by a process known as mutation, or sporting, and from seed. The vast majority come in the latter way, and many hundreds of people are employed in widely scattered countries in an industry that has grown up around the raising of rose seedlings.

All plants are made up of thousands of cells. These cells differ from one another in size and shape, each having its own particular function. Many different types of cell are found in every part of each plant, whether it be the roots, branches, leaves, petals, sepals, stamens, stigma, seed-pod, or any other part. The different types of cell in the one part of the plant work in co-operation. Some form tissues that bring water and soil-derived food solution into the plant; some form tissues that impart rigidity; some work in the absorption of plant food from the air; some make up the colourful attractive flower; some make up the stamens, others the stigma, and so comprise the main reproductive organs of the plant.

Each cell contains a small body called a nucleus. Each nucleus contains minute rod-shaped bodies known as "chromosomes", so called because they stain readily with dyes for microscopic inspection. In reproduction, it is these chromosomes that transmit hereditary traits, or Mendelian factors. The alteration of any one chromosome will alter some characteristic of the plant, such as habit of growth, colour of flower, shape of petal, or number of petals. The number of chromosomes in the cells of different creatures varies. In any cell, of any type of rose, it is always some multiple of seven; it ranges from fourteen to forty-nine. Roses which have different numbers of chromosomes in their cells do not cross-fertilize readily. The great advances in rose-breeding have been due to unusual crossings between two types or species a crossing that may possibly never be repeated. The new hybrid has been used, in each instance, as a parent for many re-crossings. These hybrid roses and most other hybrid plants differ in one important respect from hybrid animals, such as the mule, the liger, the tigron and others, in that they retain fertility in at least some degree.

Each rose bloom, like most other flowers, is bisexual it is both male and female. The sex organs are in the flower and the calyx. The male organs are the stamens. They bear the anthers containing the pollen, which consists of the male cells for fertilization. The female organs are the pistils or styles. They are stalk-like, more or less tubular prolongations from the seeds within the calyx or seed-pod to the centre of the flower. They are usually coherent into one column, the stigma. The seeds in a calyx vary greatly in size, shape, colour, and number, from one to about thirty. Stamens surround the stigma in the centre of the bloom.

Neither pollen nor pistils are fertile until maturity. When a mature pollen cell reaches a mature receptive female cell (egg, ovary, or seed) their two nuclei fuse and the chromosomes from one cell add to those of the other, making a total that will persist in the body cells of the plant that will come from the seed now fertilized.

When a germ cell is formed the chromosomes of the body cells are halved in number. There is no division of individual chromosomes into halves. The chromosomes separate at random, and so each germ cell formed has a different assortment of chromosomes and hereditary factors with which to unite, in fertilization, with another germ cell. Of course the vast majority of germ cells are lost. Some encounter a germ cell with which they are incompatible, and no fertilization occurs. This accounts for many failures in rose-breeding.

Each chromosome carries a Mendelian factor, which is said to be either dominant or recessive. A dominant factor will assert itself more than a recessive factor in a new variety, and so a crossing seldom produces a rose with characteristics midway between those of its parents.

The raising of roses from species is relatively simple and uncomplicated. Self-pollinated seed from them produces seedlings true to type, for there is no complex ancestry. Crosses of these parents show definite characteristics of both parents. Mendel proved that the first generation of these crosses gives the dominant factor in prominence in three-quarters of the seedlings. When these are self-pollinated one-third of the progeny still shows both the dominant and recessive factors. The one-quarter of the original group of first-generation crosses that showed recessive factors, when now self-pollinated, all produce progeny of their same type.

This is diagrammatically represented in Mendel's Principles of Heredity by Bateson, to the third generation thus:

"D" represents the dominant factor and "r" the recessive factor. When two factors, dominant for the same characteristic, meet in a crossing the resulting progeny are pure for that characteristic but will vary greatly with the recessive factors present. The same applies to the meeting of factors recessive for the same characteristic. Recessive factors can be asserted in the course of further cross-fertilization. With each succeeding generation, whether from artificial or self-pollination, the proportions and relationships of the chromosomes in the progeny become infinitely more complex.

Modern cultivated roses are the result of many crossings and recrossings. Dominant and recessive factors have become highly complex. Often there are latent qualities suppressed through the presence of not only a dominant antagonistic factor but of a totally different factor. These unobtrusive factors often become apparent and important in later generations.

No two creatures are ever exactly alike. In creatures of the one variety and apparently alike the differences are so small as to be indiscernible, but they exist nevertheless. Their chromosomes are always in slightly different combination and there are always the latent powers of the recessive factors.

Sporting Or Mutation

Growth is the term used to signify division of existing cells to produce new cells of greater number. In this process the chromosomes separate and re-combine. Unless they do so exactly as before, some variation is produced and is called a "sport" or "mutant". The new cells with the new arrangement of chromosomes continue to multiply, producing growth. Thus a bush rose may sport and produce a climbing shoot, or any rose may sport and on its new branch produce blooms of a different colour. The great majority of such changes are so slight as to escape notice. Often an odd plant of some variety will be found growing much better than usual. The difference may be due to any one of many factors, but one of these possible factors is mutation. Advantage is frequently taken of this by nurserymen when propagating, so as to produce good vigorous plants for sale.

Climbing sports of bush roses are very common, and sports by way of colour variation are becoming frequent, possibly due to more intense inbreeding. Roses may sport in both ways. Good examples are:

RADIANCE GOLDEN DAWN OPHELIA

Just as a variety can sport, so can a sport revert to its original type. This is not at all uncommon in the case of some climbing sports, especially if pruned too hard. Some sports are much more "fixed".

No credit can be taken by man for the gaining of new varieties by sporting. A keen observer will select his buds for propagation from vigorous plants, and he will be quick to notice departures from usual colour of bloom or type of growth. Buds of these variations should be tried on understocks, and, if worth while, plants should be made available to rose-growers.

Much more credit is due to the man who raises roses from seed. There is no more intriguing form of gardening. It involves little expense and little effort, but needs patience and some imagination in the conception of a plan of action. There should always be a definite goal rather than haphazard working. A study of the genealogical tree of a variety will give some indication of its probable behaviour as a seed or pollen parent.

Some roses are almost sterile, but others appear very commonly in pedigrees; some for example, Soleil d'Or the first Pernetiana rose, are to be found in the pedigree of almost every modern rose. In addition, one variety may appear many times in the genealogical tree of any rose it may

 appear in each of several generations of either or both parents of the variety in question. In this regard, plants differ greatly from animals, for the lifetime of any one animal is limited to a relatively small number of years, whereas a variety of plant can be kept young, virile, and reproductive by continuing to produce new plants of it by vegetative means of reproduction  in the case of roses this would be by budding or by planting cuttings.

Crimson Glory was raised from seed gained by fertilizing a seedling of Catherine Kordes with pollen from W. E. Chaplin. Neither of these parents had very much perfume. Since then Crimson Glory has been very widely used in hybridization. It produces good pollen and sets seed freely. Crossed with Soeur The'rese, it produced Charlotte Armstrong (Plate 18), and with an unnamed seedling it gave Heart's Desire, while with Southport it has given Ena Harkness (Plate 34), Red Ensign, and William Harvey (Plate 40), and with Poinsettia it has given Fred W. Alesworth, Mardi Gras, Schlosser's Brilliant and Baden Baden.

When a variety is found with desirable qualities it should be used over and over again as a parent if it will set seed or produce good pollen. The one cross can be repeated each time, or it can be reversed, using each parent for its so far unused sex function, or a new parent rose can be brought into the crossing from time to time. Even if a thousand seedlings are raised and only one is good it must be regarded as an achievement. Hybrids crossed will give progeny varying enormously in characteristics, and those thousand seedlings, all of the one crossing, may include singles, doubles, whites, pinks, reds, yellows, weak growers, strong growers, and all the other possible variations. Mme A. Meilland (Plate 56) is now being used extensively as both a pollen parent and a seed-bearer. It is forming the basis of a new family of roses with its distinctive foliage and strong growth, and amongst its best known progeny we already have Alaska, Cannes Festival, Confidence (Plate 6), Grand'mere Jenny (Plate 37), Marcelle Gret, Minerve, Monte Carlo, Suzon Lotthe" (Plate 57), Symphonie, Tahiti, Royal Welcome, Maorilander, and others.

Some seed parents will be found to reproduce good qualities fairly frequently. Two or three good varieties should be chosen to provide pollen for fertilization of seed on these plants. Usually a definite line of crossing is adopted by each hybridist. With the increased complexity of ancestry of modern roses there has arisen a greater element of luck in the production of new roses. Mendel's law becomes more a consolation in explaining disappointments than a help in achieving success. Any crossing will never give two seedlings alike. Nature never repeats her creations.

Manual Fertilization And Chance Crossing

Chance fertilization has produced many good roses. The stamens are above the stigma and pollen can fall on to the female organ even before the bloom opens. Self-pollination may also be helped by wind or insects, or cross-pollination may result from insects carrying pollen from one variety to another. However, most of the best roses come from manual crosses.

The best time for artificial cross-pollination is early summer. In spring, roses are in their greatest and best flush of bloom, but atmospheric conditions are subject to variation sufficient to cause failure of the process of fertilization. In autumn, in addition to this same objection, there is often insufficient time for the seed to ripen. Rose flowers in early summer will be part of the second blooming. They will open more readily because of fewer petals than in spring or autumn, and so render fertilization easier.

Varieties must be chosen in accordance with the preconceived plan. All crosses may not be possible on the one day, for some of the blooms may not be in a fit condition. Roses open quickest just after sunrise.

A bloom of the variety chosen for pollen is selected when about half open. The stamens must not be showing. It can be cut, taken indoors, and kept in water until it opens, or it can be left on the plant. The former is probably the better, since no pollen is lost in wind or taken by bees. If the latter course is chosen the centre petals are removed by fingers or forceps, leaving only the outer two or three rows. The stamens are not touched. The bloom is then covered with butter-muslin eight or ten inches square. This is loosely tied round the flower-stem, and is to protect the pollen, as it ripens during the next hour or two, from pollution by insects with pollen from other roses. Mixing of pollens would destroy all certainty of origin of the male factor in fertilization.

A bloom of the variety chosen for seed-bearing is next selected. Like the pollen-parent bloom, it should be about half open. The stamens must not be showing, for then there would already have been a chance of self-fertilization. Here, too, the central petals are removed, exposing the immature stamens and stigma. With a narrow sharp knife or fine forceps the ring of stamens is carefully and completely removed. Injury to the stigma must be avoided. The bloom is covered with butter-muslin in just the same way as that of the pollen parent.

Different varieties require different times for the stigma to become receptive for application of pollen. In some, it matures within a few hours, while in others it needs a full day. When receptive, a stigma is sticky, a provision of Nature fox retention of any pollen applied by either accident or intent. Pollen ripens quickly. It becomes floury in appearance and adheres readily to the finger. It is rendered unfit for use if wet, or if dried from long exposure to a hot sun. Successful pollination after midday is rare.

Fertilization is most successful between sunrise and about 11 a.m., with no wind and the temperature above 70 degrees Fahrenheit. It can be done in either of two ways. The pollen-bearing bloom can be brought from indoors or be freshly cut from the plant, and the stamens are made to touch lightly the stigma of the prepared bloom. In the other method some pollen is taken from stamens on a fine camel-hair brush and transferred to the stigma. Fertilization does not actually occur until the pollen-grain meets the seed. This takes a few hours after pollination, and so the seed-bloom must be re-covered after pollination to prevent secondary pollination by insects. Such secondary pollination could possibly achieve fertilization before the planned work and so upset all plans. It is advisable to leave the cover in place for several days after pollination.

The stem of each seed-pod should be labelled with a tag of some material that will retain legible markings for at least several months. Thin zinc labels are excellent. The writing should be in pencil; wetting will always make them easier to read. Each label should give the names of both parents, and indicate which gave the pollen and which the seed.

When fertilization has occurred the seed-pod will begin to increase in size within a few weeks. When it has failed the hip will slowly shrivel, die and fall. Pods take from four to eight months to ripen, by which time most of them are at least partly red or yellow. It is best to leave them ungathered from the plants until their stems commence to shrivel. This is all irrespective of whether the pollination has been done by Nature or by hand.

"After-ripening"

In the past, hybridists at this stage opened the hips  with a sharp knife, removed the seeds, which varied in colour from cream to brown, and then planted them. Only about five per cent of the seeds germinated. More recently, seeds have been submitted to a process of "after-ripening" before sowing. This consists of keeping ripe rose-seed at a temperature of about 41 degrees Fahrenheit in moist conditions for a time. Neither 32 nor 50 degrees Fahrenheit will after-ripen seed although fluctuations between those temperatures are effective, especially if the average is about 41 degrees Fahrenheit. This is what commonly happens in Nature, in cool climates. The seed can be kept in moist sand, but ripens much faster in granulated peat. Late July is the best time for after-ripening and seed-sowing.

The seeds are removed from the hip as usual and are dropped into a cup of water. Those that sink are usually fertile; those that float are usually infertile.

Granulated peat is superior to sand for after-ripening, because it gives an easy and regular supply of moisture and air. It is naturally highly acid. It can he neutralized with lime  or leached with water until nearly neutral. Unneutralized peat often injures rose rootlets if they become too long before being transplanted to soil. It is unfortunate that some seeds germinate as well as after-ripen at 41 degrees Fahrenheit. By using this method it is said to be possible to get nearly one hundred per cent germination of seed when good female parents are used. Such results were formerly quite impossible, but it means too much trouble and expense for most amateurs. It well repays the hybridist who is doing a large amount of work.

We can crudely, but fairly closely, imitate the after-ripening procedure in our gardens by removing the hips  and burying them in the beds or in boxes of light  soil. They must be kept wet and buried until the outer case of the hip commences rotting. The seeds are then removed from the pods. This will give a much higher percentage of germination than the five per cent obtained by the old method. Cool garden positions will be best for the seeds.

From this stage all seeds are treated in the same manner, irrespective of which of the three methods has been employed. If the old method is followed the seeds will be hard. The floating test could be used to decrease the percentage of failures to germinate. Tips of small roots will often be visible on after-ripened seed.

It is discouraging when seeds, which are apparently viable, fail to germinate, or die soon after shooting. A large percentage will grow if well selected, even crudely after-ripened, and given good conditions with sufficient time.

Seeds And Seed Beds

The soil in which rose seeds are to be sown should be sterilized in some way. This is mainly to kill fungi, which cause damping-off of young seedlings, but weed seeds can be killed too. In any case, a light sandy loam should be used. Fungi can be destroyed by mixing three tablespoonsful of formaldehyde in each bushel of soil and storing it in a container for a few days. Baking the soil in pans over a fire will kill both fungi and weed seeds. It will also reduce organic matter but this is unimportant at this stage of rose culture. The seed contains enough food to nourish the plant for some weeks, by which time it would be safe to commence manuring. Organic matter not only feeds plants but harbours fungi. After sterilization the soil should be frequently stirred and aired for two or three days, especially if formaldehyde has been used.

Left: PATRICK ANDERSON (H.T.). Dark pink. Below. DIAMOND JUBILEE (H.T.). Chrome yellow. Plate 16 NEW YORKER. Plate 17

All of this may seem laborious, but only a small amount of soil is needed, and it will save many failures. The importance of killing weed seeds becomes obvious when one realizes how quickly they germinate and how slowly some rose seeds germinate. As tiny two-leafed plants there is often not enough difference between weeds and roses for the amateur, or even the experienced man, to distinguish with certainty. If weeds are allowed to grow to a size at which they can be identified by the novice, they have developed big root systems as well, and their removal will cause much soil disturbance with probable damage to young roses.

Sowing rose seeds in open ground precludes the sterilization of the soil to a sufficient depth. Planting in pots or trays is much better in every way, except that more frequent watering is needed. The young plants are delicate and must never be allowed to become dry.

Small seeds should be planted about one-quarter of an inch deep. Larger seeds may be covered by about half an inch. The soil should be at least four inches deep in the pots or trays, and firmly pressed. Crocks should be used to ensure good drainage. The sowings are made in such a way as to be easily marked one cross to each pot or to each row in a tray. The seeds are placed at least one inch apart, and the soil is well saturated with water after planting, but thereafter is kept just moist.

Uniform moisture and cool soil are ideal for germination. Light is unnecessary in the early stages. Some varieties always germinate slowly, others are moving in as short a time as ten days, especially some after-ripened seeds. The trays should always be kept at least two years. A few seeds take as long as five years to germinate.

The Care Of Seedlings

The tiny plants are very easily killed by sudden temperature variations, damping-off, or mildew, to which they are nearly all susceptible at this age, even though they are highly disease-resistant in a few weeks. Excessive watering helps to spread mildew and a fungus that rots the young stems. Weekly spraying with Alboleum or a wettable sulphur preparation will save many young plants.

The first two leaves are not serrated. In a week or two the third leaf appears and is a typical rose leaf in miniature. When the plant has four or five leaves it should be moved to open ground and planted a foot from its neighbour, with fifteen to eighteen inches between rows. The namings of the crosses must not be lost or confused in the moving. Seedlings that germinate early will be moved in winter at about the usual planting time. Their removal will leave bigger spaces between seedlings that germinate later. These latter will not then be crowded. They can be planted out in suitable weather at a later date.

The earliest of the seedlings will bloom in November, and lateral shoots, and even thin base shoots, will soon appear. Blooming continues all through the summer and autumn. Any seedlings with promising blooms should be budded on to stocks in February or March. It is seldom possible to get good budding-wood from them earlier. These budded plants can be placed in the rose beds in July for further observation over the next few years. They will give much better growth and blooms than the original seedlings on their own roots.

Many seedlings do not give good flowers until their second or third year. Admittedly the vast majority are never of any consequence, but hasty discarding is inadvisable.

By the time the last budding of new seedlings is done, the new season's hips will be ripening, and the new season's sowing preparations can be commenced. Raising roses from seed needs patience, enthusiasm, and good fortune, but there is always the spur to keep on striving, even if one does no more than plant, in a simple way, each year only a few self-pollinated seeds. Many quite good roses will be raised. Some years there will be none worth while, some years several of interest, and some years, possibly, a rose of real distinction to be hailed by all rose-lovers the world over. Each great rose comes from just one seed. Who knows which seeds will produce the roses of tomorrow better roses than we have today?

One American hybridist raises fifty thousand rose seedlings each year. He has produced several All-America Rose Selection winners, and when he gains this award his firm buds a quarter of a million plants of that variety for sale in its first year. It is quite a gamble, for, though the stakes are high, the standard of roses is improving rapidly and the competition is very keen. He discards many thousands of seedlings that would have been regarded as superb creations only a very few years ago.

The All-America Rose Selection scoring system gives fifty-five per cent of the points to qualities of the plant and only forty-five per cent of the flower. Consequently, some of the varieties that score well are not quite show flowers, but all of them give pleasing blooms on husky plants good roses for garden and home uses. Several Floribunda roses have won this coveted award. They give people, in and around their homes, plants, flowers, and colour effects that were not possible with older roses.

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