Anatomical study of the bud union in T-budded Rosa gallica ‘Duchesse d’Angoulême’ and ground cover rose ‘Vensar’ on selected rootstocks

Rootstocks used for garden roses in Europe typically originate from two species: the Eurasian Rosa canina and the Asian Rosa multiflora, while the budded cultivars can be taxonomically distant. Anomalies in union formation result in a low rate of bud survival on rootstock necks, and hence a low percentage of good quality shrubs in nursery production. The aim of this research was to observe the anatomical structure of the bud union. The Rosa canina ‘Inermis’, ‘Pfänders’, ‘Schmid’s Ideal’; R. laxa and R. multiflora were T-budded in the last week of July with the buds of two cultivars: C1 – Rosa gallica ‘Duchesse d’Angoulême’ and C2 – ground cover ‘Vensar’ MERCURY 2000. The scions C1 were prepared from i) generative shoots 14-18 days after petal shedding, and ii) non-flowering in current vegetative season. The scions of C2 were cut from blooming shoots with opened flowers. The budded rootstock necks were harvested for anatomical research after three months. Parenchyma and phloem cells were present at the place of component contact in both cultivars. In contrast to ‘Vensar’, distinctive anomalies in bud union were observed in ‘Duchesse d’Angoulême’, regardless of the rootstock used. The cross-sections often showed clusters of cells with an indistinct growth direction, layers of cork, necrosis, and voids in the region of component contact. The numerous necroses indicate anomalies in the union formation of the components. The greatest rate of succesfully grafted buds (90%) was observed for ‘Vensar’ on R. multiflora. The buds of this cultivar budded succesfully on R. laxa in 40% of cases, and in 70% on R. ‘Schmid’s Ideal’. Forty percent of ‘Duchesse d’Angoulême’ buds cut from generative shoots were succesful on R. laxa, ‘Pfänders’, and ‘Schmid’s Ideal’, while 55 and 50% of buds cut from vegetative shoots were succesful on ‘Schmid’s Ideal’ and ‘Pfänders’, respectively.