American Rose Annual 73: 120-126 (1988)
A THORNLESS FORM OF FORTUNIANA
Dr. Robert E. Basye

In general, both banksiae and laevigata are quite reluctant to cross with other species. But they cross very easily with each other. Through the years I have grown several hundred seedlings of R. banksiae x R. laevigata, always using a single, thornless banksiae. All bore a close resemblance to Fortuniana except that the flowers were single. The double flowers of Fortuniana may have come from a banksian parent which was double. All the seedlings were thorny, as might be expected. Rarely would a cross bear a hip or two, but even the few F2 seedlings had thorns.

Then in 1969 I obtained a seedling (69-348) of R. banksiae x R. laevigata which was not so stingy in producing hips. But the seeds rarely sprouted, the reason being, as I soon learned, that most of them contained no embryo. Nevertheless, in 1984. two F2 seedlings were produced, one of which had a few thorns and the other of which was completely thornless, with perfectly smooth midribs of the leaves. The latter rose bears the number 85-04 and is the subject of this article. I shall call it simply 'Thornless Fortuniana.'

I thought surely 'Thornless Fortuniana would prove to be a diploid, with 14 chromosomes, as is 69-348 and Fortuniana. I was quite surprised when the somatic count showed that it was a triploid, with 21 chromosomes! One explanation might be that it arose as an outcross, 69-348 x (some tetraploid). This is highly unlikely for three reasons. First, 69-348, like its parents, blooms very early and is through blooming before most roses begin. Second, 69-348, like its parents, is reluctant to accept foreign pollen. And third, the influence of an outside pollen parent should be readily apparent, even to an amateur. On the contrary, 'Thornless Fortuniana' appears to be an exact replica of Fortuniana except 1) the thorns are missing, 2) the flowers are single, in contrast to the double flowers of Fortuniana, 3) the leaves are slightly darker green and glossier, and 4) the chromosome count is 21 instead of 14.

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