Wednesday, August 26, 2009

Finding A Good Quality Of Roses

By Marshall Clewis

Where can we find new rose genes for increasing the hardiness of everblooming hybrid tea varieties? Although the hybrid teas (not to mention the floribundas and grandifloras) already contain the "blood" of at least four species, rose breeders seem to agree

Hybridizers look with envy on the hardiness and disease resistance of various species but hesitate to bring in the genes of these by intercrossing, fearing too much domination from these genes and a complete loss of the hybrid tea, Actually, a large number of species clamor for attention as potential parents for "the roses of the future."

The difficulty with many is they are diploids, whereas the hybrid teas in general are tetraploids. That is, the number of chromosomes in many of the hardy species is 14 (twice the number in the pollen cells or egg cells) since a pollen and an egg cell unite at fertilization to produce the zygote, or new plant, whereas in hybrid teas the chromosome count is 28, or four times the haploid number 7, hence the "tetra" part of the name tetraploid.

lt is possible to cross diploids and tetraploids to produce fertile offspring. The first generation will be triploids with 21 chromosomes and their reproductive cells of chromosome numbers, between 7 and 14 are not usually fertile unless they are exactly 7s or l4s; this does occur occasionally. There is often enough fertile pollen from a triploid plant to enable the breeder to raise descendants. In fact, this is exactly how the hybrid teas originated, by crossing of teas from Asia having the diploid chromosome number with gallicas and other tetraploid species of Europe.

The first hybrids were undoubtedly triploids, but their pollen placed on flowers of tetraploids produced enough tetraploid plants to originate the new race of hybrid teas. These hyrbids exhibit exemplary resistance against pests so there was no need of spraying them with ortho rose pride. However, when Rom foeridri, in the form of Persian Yellow, was brought into the "gene pool" of hybrid teas, no such difficulty was experienced and no use of ortho rose pride, for R. foerida was already a tetraploid. When polyanthas, which are diploids, were crossed with hybrid teas to produce floribundas, the original difficulties of crossing parents of differing chromosome number were repeated.

A good many rose breeders have obtained new varieties by dusting pollen of R. spinosissima altaica (the Altai rose) on pistils of hybrid teas. In the diploid group, use could be made of R. rugosa, R. blanda and R. nizida. To use R. mgosa, not for the raising of new hybrid rugosas, but for a small infusion of hardier genes without too much change in the character of the hybrid teas, one should take a triploid rugosa variety, such as the Arnold rose and attempt to cross it back on hybrid teas. To use R. blanda or R. nizida, one might have to first produce the triploid hybrid by his own breeding. The chances are it would be well worth using in rose breeding projects, both those intended to develop hybrid teas or shrub roses.

About the Author:

No comments: