Professor Heslop Harrison began by stating that, almost certainly, the rose flora of our two counties was the richest in Britain and then showed a number of lantern slides in colour, depicting the whole of the Durham and Northumberland species. In doing so, he pointed out their distinguishing features and emphasized that for distributional and ecological reasons, as well as structural, Rosa dumetorum should be kept separate from R. canina, and R. dumalis (R. glauca) from R. caesia (R. coriifolia). It was stated, too, that the usual British ranges supplied for R. tomentosa and R. micrantha are quite incorrect, R. sherardi forms often being referred to R. tomentosa and R. Caesia forms to R. micrantha. As a matter of fact, both are very rare in Durham and there attain their northern limits.
Next, taking up the question of rose hybrids, he listed those found in the two counties, and insisted that, contrary to general opinions, many showed limited fertility, although he remarked that Durham R. villosa x spinosissima and R. dumalis x spinosissima were always sterile. Very much different were the cases of R. sherardi x spinosissima, R. rubiginosa x spinosissima, R. caesia x spinosissima, R. canina x sherardi and R. dumetorum x villosa. The first of these crosses he had reared up to the F4 generation, the second to the F3 lots and the third, fourth and fifth to the F2 lots. In each case, the F2 and succeeding lots, when the latter had been obtained, were much more fertile than the F1 generation. At this stage it was indicated that R. spinosissima was self-sterile.
Next, by the aid of lantern slides, he described the cytology of the roses, stressing the peculiarities of the Caninae and the Spinosissimae. From that he led up to experimental work with the hybrids between R. spinosissima on the one hand and R. sherardi, R. rubiginosa and R. caesia on the other. In all the hybrids reared F1 generations were obtained which manifested a certain degree of fertility, and the resulting F2 lots leant strongly toward the R. spinosissima parent when reared to maturity. In addition, many F2 plants remained herbaceous, and perished after a height of 2 cm. had been reached.
Professor Heslop Harrison emphasized that the F1 lots, whilst conforming, in a general sort of way, cytologically to the usual Caninae pattern, in their later meiotic stages on the female side showed important anomalies. As a result, amongst the seedlings, orthoploid plants were secured carrying chromosome complements of 14, 28, 35 and 42. Thus it was clear that a new polyploid series had been evolved by a distinctly novel mechanism. Further, amongst the seedlings there were encountered aneuploid plants with chromosome numbers 2n=24, 2n=32 and so on.
Apparently, in development a fairly heavy mortality rate takes place, leaving F2 plants, as far as present results indicate, possessing, like R. spinosissima, a balanced set of 28 chromosomes. These plants display a regular heterotype division like R. spinosissima and a normal homotype division, and are quite fertile. Further, this same fertility is manifested in the F3 and F4 generations. Incidentally, the lecturer pointed out that pinkness in all these crosses is dominant.
At this point the topic of the puzzling rose described by Smith as Rosa rubella was raised. This species (?) was erected in 1810 on the basis of Durham material, and its status has ever since been a problem to rhodologists. By comparisons made point by point with Smith's and other descriptions, and by a direct consideration of Winch's specimens, the speaker showed that in every respect R. rubella agreed with certain segregates in the F2 R. sherardi x spinosissima lots, as did his own R. rivalis described from Wheel Birks plants. He had, therefore, no hesitation in regarding R. rubella and R. rivalis as naturally occurring hybrids originating in a cross between R. sherardi and R. spinosissima. Obviously, since F2 plants so reared are fertile, the generation to which they belong remains undecided. Professor Heslop Harrison stated that in his opinion, based on certain experimental data, they actually belonged to the F2 lot.
The lecturer concluded by indicating a few of the investigations yet to be carried out on the wild roses of Durham and Northumberland.
The first point of interest is that a Caninae species pollinated by a regular polyploid can give rise, in the F2 and later generations, to new "species" with regularly pairing chromosomes rather than the special sort of chromosome arrangement found in the Caninae. Heslop Harrison identified Rosa rubella Smith as an F2 from a natural cross of R. sherardii pollinated by R. spinosissima.
Modern Roses 5 has R. rubella Smith as equivalent to R. x reversa Waldstein and Kitabel, identified as a hybrid of R. pendulina x spinosissima: "Fl. Red. Fr. ovate-oblong, scarlet, pendulous. Fol. dark green."
I don't know whether Waldstein and Kitabel bothered to make the indicated cross; so, for the moment, I'll have to accept the opinion of Heslop Harrison who did. Even so, the fact that they suspected R. pendulina of being involved tells us something about the appearance of R. x reversa.
Rosa sherardii, according to MR5, has ovoid or pear-shaped hips. Those of R. spinosissima are globular and black. The pendulous ovate-oblong fruit of the hybrid are different enough to suggest that R. pendulina was part of the ancestry, but these traits must be hidden within the chromosomes of R. sherardii.
The recent report that Rosa fedtschenkoana played a part in the development of the Damasks gave short shrift to the possibility that Rosa alba might have been involved. Certainly the Albas have glaucous leaves and canes, and the hips are somewhat oblong — though not so long and spindle shaped as some of the Damasks.
Rosa dumalis, allied to R. canina, has bluish green glaucous leaflets. It is native to west Asia, and a likely candidate for parent of R. alba. R. fedtschenkoana of Turkestan may be to R. dumalis what R. rubella Smith is to R. sherardii — a fertile tetraploid derivative of a natural hybrid.
In which case, whatever genes are alleged to have entered the Damasks from R. fedtschenkoana could as easily have entered from R. alba, which the authors of the recent report did not examine. And apparently they were not aware that R. moschata sometimes has glaucous leaves — like the autumnal variety Graham Thomas rescued and reintroduced.
The suggestion that R. moschata was the seed parent of the Damasks does have some merit. Mattiolus, a 16th century Italian, mentioned a rose that was called Damaschine and Moschette. This was apparently our Rosa moschata. Other varieties picked up the names, presumably because they were seedlings from the original Damask/Musk rose. Dodoens (16th century Dutch), however, wrote that Rosa damascena of the Italians was called Rosa Alba in England. Even back then the connection between Albas and Damasks was assumed.
Another interesting datum in Hesslop Harrison's report is that many of the F2 plants from R. sherardii x spinosissima died when they reached a height of 2 cm. Michurin had a similar problem when he crossed Kazanlik x Persian Yellow. Fortunately he had some Dog rose seedlings of suitable size that he was growing to propagate some other roses. He grafted the surviving seedlings before they died, and was thus able to bring them to maturity.
If anyone wants to repeat Hesslop Harrison's experiment with Sherardi x Spinosissima, it would be a good idea to have some seedling Dog roses ready to serve as rootstocks for the seedlings. It would be very interesting to learn what those lost plants might have turned out to be — particularly the diploids.
Another oddity of the Caninae clan is (or was) 'Placidie', a sport of 'Cuisse de Nymphe'. Though the parent has strong prickles, the sport was nearly thornless. It had dark green leaves, very unusual for an Alba, and brilliant pink flowers. It seems that 'Cuisse de Nymphe' may be a hybrid Alba (Alba itself being a presumed hybrid), and that 'Placidie' originated by a loss of some chromosomes.
Reports on the sterility of hybrids of Caninae species with those with regularly pairing chromosomes has been overstated. The obvious meiotic problems of the F1 hybrids gets sorted out in the F2 and later generations. And with seedling Dog roses available for rootstocks, yet other variations might be preserved.
Tackholm first suggested that the Caninae species originated as hybrids of high polyploids with diploid species — to explain the polyploid ova (3x, 4x, 5x) and monoploid (1x) pollen. Subsequent research indicates that this is an unlikely possibility. Hybrids usually break down the special chromosomal arrangement of the Caninae species, rather than build it up. The alternative is that some high polyploid began losing chromosomes — to what advantage? — and continued until there were only 7 pairs, the rest remaining unpaired.
Research in wheat and wheat hybrids has revealed the existence of "genes" which influence crossover frequency: some increasing, some decreasing. The Caninae species presumably carry a preponderance of the crossover inhibiting genes, which prevent the unpaired chromosomes from forming crossovers (required for pairing). When such a species is pollinated by another species with regularly pairing chromosomes, crossover inhibition is relaxed, and formerly unpaired chromosomes can form crossovers and become paired. The Caninae system breaks down, in many cases. Unless a pollen grain happens to carry an excess of crossover inhibiting genes.
Or, if a species with regularly pairing chromosomes is pollinated by a Caninae species, the hybrids could have reduced pairing — which would be a good thing in a triploid, possibly making it a bit more fertile. Sterility in triploids is often the result of excess "pairing", which allows the formation of trivalents (groups of 3 chromosomes). When this occurs it is very difficult for meiosis to sort out a balanced set of 7, 14 or 21 chromosomes. Pollen or ova with 10 or 11 chromosomes are unlikely to be viable.
And if this triploid is backcrossed (as pollen parent) to the Caninae species, some of the pollen would carry an excess of crossover inhibiting genes. Voila! An Alba-like variety could result having the habit and chromosome arrangement of a Caninae, but with some qualities derived from the other species.
Of course, the most striking fact about Heslop Harrison's experiment is that the breakdown product of Sherardi x Spinosissima resembled R. pendulina enough to suggest to Waldstein and Kitabel that this species was involved in the cross. This supports Hurst's opinion that polyploid species are built up from the chromosomes of diploid species. In which case it is not so surprising that different crosses might produce similar results.