Effect of Various Management Methods of Apical Flower Bud on Cut Flower Quality in Three Cultivars of Greenhouse Roses

In greenhouse roses, canopy management has been highly noted and emphasized during the past decades. It was recognized that improving canopy shape by implementing some techniques such as stem bending and flower bud removing can highly affect the marketable quality of cut roses. For most growers, the best method of flower bud treatment has not yet been described and determined physiologically. This experiment was designed to answer some questions related to this problem.
A plastic commercial cut rose greenhouse was selected to carry out the trial. Three greenhouse rose cultivars, namely Eros, Cherry Brandy and Dancing Queen, were selected as the first factor, and three methods of flower bud treatment along with bending types were chosen as the second factor. Cuttings were taken from mother plants and rooted under mist conditions. The first shoot emerging from the cutting was treated at pea bud stage by one of the following shoot bending at stem base with intact bud, immediate shoot bending at stem base after removing flower bud and shoot bending at stem base two weeks after flower bud removal. Some marketable stem properties including stem length, diameter and weight, and characteristics related to bud growth potential were measured, and then the data were subjected to statistical analysis.
Analysis of variance showed that cultivars differ in their marketable features. Cherry Brandy produced longer cut flowers with higher stem diameter compared to the two other cultivars. This cultivar was also good in stem weight trait; however its difference from Eros was not significant. Dancing Queen did not perform well in producing high quality stems on the whole. Regarding number of days until bud release and growth, Cherry Brandy’s buds spent fewest days until growing. In many studies, the effect of cultivar on rose shoot growth quality has been documented and explained. For instance, it was determined in Rosa hybrida ‘Fire and Ice’ that the rate of increase in stem length was about two times more than that in ‘Kardinal’ cultivar when both compared to control cultivar. These differences may have genetic and/or environmental origins. Methods of stem treatment significantly affected some shoot characteristics such as bud burst time, number and weight of growing shoots on bent stems and flower diameter, but no significant effect was observed on most important marketable traits. However, this factor interacted significantly with cultivar in some characteristics such as time of bud burst and the number of growing shoots on bent stems, showing that similar stem treatments can cause different results in different cultivars. Methods of stem treatment unexpectedly did not change the stem marketable qualities such as stem length and diameter, while it significantly altered time of bud burst, flower diameter and weight of shoot sprouts on bent stems. The most interesting result was that time of bud burst decreased from about 10 days in the immediate stem bending with intact bud to about 5 days in the treatment containing bending practice two weeks after the flower bud removal. This feature can be valuable, since it can decrease time of shoot growth and harvest time, thereby increasing stem production per time scale. The highest weight of shoot sprouts on bent stems obtained when bud removal performed at bending time, indicating that this phenomenon occurs as a consequence of apical dominance removal. Growers can adjust leaf area per plant by controlling the rate of bud growth with or without the number of bud sprouts on the bent stems through implementing different flower shoot management systems. It was reported in many studies that altering stem position, removing flower bud, defoliating and practicing similar activities can change hormone and carbohydrate balance inside the plant, which, in turn, may lead to new shape of plant canopy with different leaf areas and distribution patterns as a result of varying bud growth potential scattered in different positions within the canopy. On the other hand, interactive relations between sink and source organs can positively or negatively affect bud growth potential, which can be a powerful tool for growers to manipulate plant canopy development and cut flower quality.
In commercial rose greenhouses, growers are usually seeking methods which are simple and effective in practice. One of these important methods can be found in training and treating ways of growing stems. The findings of this study suggest that choosing a proper time for apical bud treatment and stem bending can highly influence some important qualitative traits in greenhouse roses. For instance, if the aim is to delay the crop harvest time, the practice of delayed apical bud removal treatment can be chosen as the best option to cause the delay. On the other hand, crop leaf area during the sunny summer days can be increased by adopting a proper treatment which leads to higher rate of bud burst on bent stems. During the winter days, however taking a practice with the potential of producing lower leaf area (by accurate timing and proper management of apical flower bud sink) can be a more useful way of efficient intercepting of incoming light. Taken together and assuming these kinds of manipulations as a tool, growers can make good decisions according to their existing greenhouse conditions, scheduled harvest time and many other influencing factors in order to obtain the highest possible number of cut flower stems.