Using architectural analysis to compare the shape of two hybrid tea rose genotypes

In the area of ornamental horticulture, it is necessary to compare individuals to assess the effect of an experimental treatment or to distinguish between two genotypes. This is especially true for the hybrid tea rose, a plant species widely used throughout the world as a garden rose and represented by a very large number of cultivars. Normally, this diversity is approached by a more or less subjective analysis of the shape, with terms such as upright or spreading, and compact vs. laxly branched. Even when evaluated by a panel of experts, this approach quickly reaches its limits when it is necessary to objectively quantify the differences observed. The architectural analysis proposed here allows us to satisfy this objective. Two rose genotypes were studied: Rosa hybrida ‘Radrazz’ Knock-Out® (KO) and ‘Meiratcan’, Lovely Meilland® (LM). These two genotypes share both architectural similarities and differences. As for the similarities: (i) the axes are of two highly differentiated types, long and short; (ii) the proportions of each type of axis vary from 100% of long axes for order 1, to 100% of short axes for the last branching order; and (iii) all of the flowering axes have a comparable profile, with the continuous development of their morphological components, from their base to their extremity. Despite these similarities, the two genotypes are very clearly differentiated. The number of orders and axes is greater for KO, whereas axis length and the number of metamers per axis are much greater for LM. The architectural analysis proposed here makes it possible to effectively quantify the major shape components of an ornamental plant like the rose. As a result, it provides a truly effective tool for objectively assessing plant shape.