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'R. x kordesii Wulff' rose References
Book  (2003)  Page(s) 196.  
Rosa 'Kordesii'
Book  (1997)  Page(s) 207.  Includes photo(s).
R. kordesii Kordes 1950. Description... This rose was never officially introduced by Herr Kordes but he used it extensively in the breeding of some very important hybrids. Offspring from this rose are particularly disease-resistant. Flowers double, pinkish-red, in small clusters...
Book  (1997)  Page(s) 34.  
The Kordes rose was also used in breeding Canadian Explorer roses at Agriculture Canada in Ottawa,
Book  (Jul 1993)  Page(s) 90.  
Kordes hybridized it with other garden roses to produce a race of hardy Climbers, most of which are repeat flowering...
Book  (Jun 1993)  Page(s) 60.  
The Kordesii roses, considered now to be a new species, originated from seeds discovered by Wilhelm Kordes on the supposedly sterile 'Max Graf', a Wichuraiana x Rugosa hybrid. From these, Kordes raised two seedlings of which one survived and grew to become the founding member.
Book  (1981)  Page(s) 97.  
In the development of Rosa kordesii, the following are salient facts:
1919 In the nursery of J.H. Bowditch of Connecticut, a chance seedling from R. rugosa x R. wichuraiana was found and introduced as 'Max Graf'. It displayed a vigorous trailing growth, very healthy foliage and great winter hardiness, and it soon gained considerable popularity in the United States for ground-cover purposes. The pinkish blooms were sterile for all practical purposes.
circa 1925 W. Kordes obtained a plant of 'Max Graf'; in spite of every effort they only managed to set seed on three occasions.
1940 Kordes obtained two seedlings from a 'Max Graf' self-cross; one of these was reminiscent of R. rugosa both in its foliage and in its upright growth habit; the other was more like R. wichuraiana with long trailing stems.
1942 The rugosa-type seedling and its progeny were destroyed by the winter frosts, but the other, although given no protection, came through unscathed and flowered in the following year with loose, double, red blooms, followed by bottle-shaped hips. More than 75% of the seeds germinated. This event, where an almost completely sterile hybrid produced highly fertile offspring, was explained in 1951 by H. D. Wulff after research into amphidiploids (= a doubling of each genome in the zygote).
1951 The seedling was named Rosa kordesii by H. D. Wulff and described by him in Der Züchter 21: pp. 123-132, in which it was shown conclusively that the new variety had indeed come from its authentic seed parents. Kordes immediately started to cross with this new rose, using it both as seed and pollen parent and raised thousands of seedlings from it. Among these was a group of recurrent plants of climbing habit and with exceptional resistance to winter frosts. The best were gradually put on the market....
Magazine  (Feb 1977)  Page(s) 1. trimester, p. 25-26.  
c'est de cette période de malheurs que date « Rosa Kordesii Wulf», issu du croisement d'un hybride pratiquement stérile : Rosa rugosa « Max Graf» avec « Rosa Wichuraïana ». On admet que Rosa rugosa « Max Graf » peut produire exceptionnellement une graine fertile sur quelques 1 000 fleurs, ce qui revient à dire que la trouver équivaut à chercher une aiguille dans une botte de foin. 
Magazine  (1977)  Page(s) Vol. 26, No. 3, pp. 703-708.  
Breeding for improvement of flowering attributes of winterhardy Rosa kordesii Wulff hybrids
Felicitas Svejda
G12 was obtained from open pollination of 'Max Graf' and a cytological examination by Dr D. R. Sampson, of this Station, found it to be tetraploid (2n = 4x = 28). G12 differs from R. kordesii in that it is very hardy at Ottawa where it shows little or no winterkill. It flowers non-recurrently and produces fewer flowers. It has single, pink flowers like 'Max Graf'. R. kordesii is regularly killed to the snow-line at Ottawa, it flowers recurrently and is more floriferous than G12. Unlike 'Max Graf, R. kordesii has double flowers.

The offspring from the cross of the recurrent R. kordesii with the non-recurrent seedling G12 segregated into non-recurrent and recurrent types in a ratio of 3:1 for a tetrasomic inheritance, assuming a duplex segregation and complete dominance.
Book  (1957)  Page(s) 24.  
Dr. H. D. Wulff, Kiel, treated the breeding result of this rose of Kordes, analysed it in detail and ascertained that the chromosome set doubled in a spontaneous mutation. Based on this research, this class of roses was introduced into the rose systematology under the name Rosa kordesii Wulff.
Magazine  (Jul 1953)  Page(s) 3. trimester, p. 75.  
Dans l'article « ROSA KORDESII » publié dans le dernier numéro, une erreur de traduction a donné : « les petits Etablissements Kordes ». Il faut lire : « les grands Etablissements Kordes ». Nous nous excusons auprès de M. KORDES, qui possède une des plus grandes cultures de roses en Allemagne.
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