Selection of Hydrangea (<i>Hydrangea</i> spp.) Cultivars with High Potential for Unseasonable Flower Bud Production in Japan

Abstract

Hydrangea (Hydrangea spp.) flower buds usually differentiate from the end of summer through autumn, but some cultivars can also produce flower buds in spring. In the present study, we selected cultivars with high potential for such unseasonable flower bud production in Japan by evaluating the flower bud production on pinch-treatment-induced axillary shoots. We also examined the pinching time and the difference between the two shoot types: previously formed shoots that developed from buds formed in the previous autumn and basal shoots that formed in the current spring. We found that 'Christmas', 'Endless Summer', and 'Rosea' had the highest frequencies of unseasonable flower bud production on the axillary shoots of previously formed shoots (90.0%, 80.0%, and 90.0%, respectively) and basal shoots (90.0% for all three cultivars). When the buds were pinched in mid-April, the axillary shoots that formed on both shoot types flowered from early July to midAugust, which was approximately 1 month later than for seasonably produced flower buds in the same cultivars. In 2011, 98.0%, 90.5%, and 84.0% of the axillary shoots that developed on previously formed shoots flowered in 'Christmas', 'Endless Summer', and 'Rosea', respectively, while in 2012, 63.2%, 54.9%, and 75.3% flowered, respectively. Similar values were seen for the basal shoots, with the exception of 'Christmas' in 2011 and 'Endless Summer' in 2012, which both had lower flowering rates than previously formed shoots. In 'Rosea', flower bud differentiation started just after the pinch treatment, and the frequency of flower bud production decreased when the pinch treatment was conducted after late April. Thus, 'Christmas', 'Endless Summer', and 'Rosea' were considered to have high potential for unseasonable flowering following pinch treatment in early spring. However, unseasonable flower bud production may often be suppressed in pinched basal shoots.

Relation Between Floral Initiations on Apical Buds of Basal Shoots After the Autumn and Cultivar Differences in Unseasonal Flowering of Hydrangea

“…Unseasonal flowering can occur on both previously formed shoots and basal shoots. There are several reports of unseasonal flowering of hydrangea including our report (Adkins et al, 2002;Eid et al, 2016;Kitamura et al, 2018;Kudo et al, 2008;Nordli et al, 2011;Orozco-Obando et al, 2005). The above-mentioned reports focused on flower production from axillary buds developed by pinch treatment conducted in spring, terminal buds of cuttings, and a reduc-The Horticulture Journal 89 (4): 488-495.…”

“…'Endless Summer' and 'Rosea' were previously identified as cultivars with high potential for flower bud production on axillary buds developed by pinch treatment conducted after spring (Kitamura et al, 2018). Further, Adkins and Dirr (2003) studied flower production on terminal buds of cuttings of several hydrangea cultivars and identified 'Endless Summer' as a remontant cultivar.…”

“…In this study, 'Masja' and 'Rosea' were selected as representative cultivars with low and high potential for unseasonal flowering occurrence, respectively. Using these cultivars, floral initiations in axillary dormant buds that developed on the basal part of the plants were studied for floral initiation in November 2018 by dissecting them under a stereomicroscope, and the developmental stage of each apical meristem was determined according to Kosugi and Arai (1960) and Kitamura et al (2018) as follows. 0: vegetative; 1: initial primordium developed; 2: secondary inflorescence branched; 3: tertiary inflorescence branched; 4: quaternary inflorescence branched; 5: highly branched inflorescence.…”

State evaluation of some Hydrangea macrophylla (Thunb.) varieties after winter hardiness in the agrometeorological conditions of central Russia

“…(2006) получили межвидовые гибриды между H.scandens ssp. chinensis и H.macrophylla, которые цвели зимой и не впадали в состояние покоя [6,7]. Первая в истории ремонтантная крупнолистная гортензия, получившая признание и коммерческое продвижение, была получена известным растениеводом доктором Майклом Дирром на опытном участке оптового питомника в Миннесоте.…”