Success in budding of garden roses under cold climates – Effect of time and cultivar

Background and Objectives: Rose plant is known as a very important shrub in the ornamental horticulture sector. They are mostly propagated by asexual methods such as rooted cuttings, grafted rootstocks both on commercial and home gardening scales. While budding has long been selected as a reliable and preferred way of garden rose reproduction on selected rootstocks over the past centuries, still it faces many restrictions imposed mostly by the seasonal physiological stage of the plants. In this study, we try to determine the best time for budding garden roses under cold climatic conditions by comparing the results of three seasons and two methods of grafting.

Materials and methods: This study was carried out in the rose garden of the University of Tabriz during 2016-2017. Two cultivars of roses i.e., Rosa hybrida ‘Avalanche’ and R. hybrida ‘ Blue Moon’ were selected and budded onto Natal Briar rootstocks. Three times of grafting season i.e., September, March, and June were chosen to do budding by either T-budding or chip budding method. Scions were cut out and taken from three positions of mother stems: upper, middle, and bottom parts. The budding type in September and June was T-budding (shield budding) but chip budding was applied for the grafts done in March. Grafted plants were then investigated for their success in grafting and growth (%), number of days needed to bud burst, quality of flowering stem (fresh, dry weight of stem and flowers, length and diameter of stem and flower) and other related characteristics. The factorial experimental design was used to plan and analyze data of June grafts.

Results: June grafts indicated almost 100% success in budding and stem growth while those propagated in September and March. However, the time needed for bud break was the least for September and March compared to June grafts. The longest stems about 45 cm were produced in ‘Blue Moon’ budded in March, while cultivar ‘Avalanche’ generated flowers with the highest diameter (45 mm) on the shoots arising from June grafts. The percentage of flowering was obtained at 100% for the shoots originating from the upper layer of the mother stem in both cultivars, however, it decreased to about 66% for shoots grown from the lower layer in ‘Blue Moon’ cultivar. Time to flowering was the least for the ‘Avalanche’ shoots arising from the upper layer with about 33 days while it increased to about 45 days for shoots grown from the lower layer of ‘Blue Moon’ cultivar. In general, the overall quality of September grafts such as stem length, diameter, number of nodes, dry and fresh weight and SLA of flowering stems were better than the grafts done in March and September. Comparing the cultivars, it was revealed that ‘Blue Moon’ cultivar performed better than ‘Avalanche’ in terms of producing longer stems with lesser stem thorns, but ‘Avalanche’ produced the largest flowers

Conclusions: This experiment demonstrated that June time can be selected as the right season for budding garden roses in regions with similar cold winter months. Flowering stems grown in June showed lower quality when compared with the stems arising from the grafts of September or March. This could be probably induced because of the rapid release of buds from internal preventions as a consequence of spring strong growth stimulators accumulated within the buds. Comparing the time of budding shows that June budding can bring growers many benefits in terms of the fewer days needed to flower, and considering, on the other hand, the lowest risk of chilling damage on graft union as well as scion buds during the cold months of winter.