Identification of relevant morphological, topological and geometrical variables to characterize the architecture of rose bushes in relation to plant shape

Plant shape is a major component of the visual quality of ornamental plants. It is the result of their architectural construction. It can be analyzed by breaking down the plant into entities (axis, metamer) that can be characterized morphologically, topologically and geometrically. Eight bush rose cultivars were selected for their contrasting shapes (from upright to spreading) and their architecture was digitized at two scales, the plant and the axis, differentiating between short and long axes. Thirty-five variables were measured. Measurement acquisition is nevertheless tedious and time-consuming and not really compatible with an analysis involving a large number of individuals. To diminish these constraints, our approach aimed at reducing the number of variables measured, limiting ourselves to the ones most relevant for describing the architecture. A selection of variables was made using the following criteria: to represent the different categories of variables describing the plant architecture; to explain the variability observed; to present the weakest correlation between them. Seven variables were selected: at the plant scale, the number of determined axes, the number of long axes of order 3 and the branching order number; at the long axis scale, the number of metamers and the length of the axis; and at the short axis scale, the basal diameter of the axis and the branching angle of the cord in relation to the vertical axis. Four architectural profiles were differentiated based on these seven variables. Moreover, a high correlation was revealed between some of these architectural variables and a shape descriptor

Genotype × year interaction and broad-sense heritability of architectural characteristics in rose bush

The effect of genotype factors, year and their interaction was assessed on six architectural variables of eight cultivars of rose bush. Plants were grown in pots in a greenhouse in the spring of 2011 and 2012, two highly contrasted years in terms of the quantity of cumulative radiation, with a relative deviation (for 2012 compared to 2011) ranging from −24.6% (April) to +13.7% (March). Their architecture was digitized at two observation scales, the plant and the axis. Highly significant genotype (G) and year (Y) effects were revealed for all of the variables measured, as well as a G × Y interaction. Concerning the year effect, it was significantly higher in 2012 and for all of the variables measured. The G × Y interaction was due to (i) different genotype groupings according to year, (ii) difference response amplitudes between years according to genotype. Broad-sense heritability was calculated for each of these variables. It was moderate to high, ranging from 48% for the length of long axes to 98% for the number of metamers on long axes

3D phenotyping and QTL analysis of a complex character: rose bush architecture

Plant shape, and thereby plant architecture, is a major component of the visual quality of ornamental plants. We have been developing a new method for analyzing the entire plant architecture by 3D digitalization that allows an almost exhaustive description of rose bush architecture and generates a large number of variables, many of them inaccessible manually. We carried out a QTL analysis using this original phenotyping method. In order to evaluate a broader allelic variability as well as the effect of the genetic background on QTL detection, we used two connected, segregating, recurrent blooming populations. The number of QTLs per variable varied from three for the number of determined axes (NbDetA) to seven for the branching angle of order 2 long axes (AngLA2), the two populations taken together. Five new QTLs, located on the linkage groups (LGs) 2, 6, and 7, were detected for the branching angle of axes, and the QTL located on LG7 co-localized with RhBRC1, a branching repressor. Branching and stem elongation QTLs also co-located with RhBRC1, suggesting its pleiotropic nature. Year-specific QTLs were also revealed, that explained the genotype × year interactions observed for the number of order 3 short axes (NbSA3) and AngLA2 from a genetic point of view. We also evidenced an effect of the genetic background on QTL detection. This new knowledge should help to better reason the genetic improvement programs for rose bush architecture and, therefore, rose bush shape

Effect of high temperature on the production of 2n pollen grains in diploid roses and obtaining tetraploids via unilateral polyploidization

To integrate the gene pool of a wild species (primarily diploid) into a cultivated pool (primarily tetraploid), a crossing between a dihaploid cultivated rose and a hybrid of Rosa wichurana allowed to obtain interspecific diploid hybrids that produced 2n pollen grains. A return to a tetraploid level sought by breeders can then be considered using sexual polyploidization, obtained by crossing a tetraploid cultivated rose with these hybrids. Application of a high-temperature regime led to a small but significant increase in the percentage of 2n pollen grains in these hybrids of up to 4.6%. This result was obtained by applying high temperatures close to 32°C during the day to plants cultivated in a glasshouse during recurrent cycles of bloom. Crosses were made between an unreleased tetraploid hybrid tea rose, as a female, and the diploid hybrid that produces the most 2n pollen grains. Tetraploid (42.1%) and triploid (57.9%) offspring were obtained. The use of these 2n pollen grains of the first division restitution type should facilitate the introgression of complex traits of interest

A new approach to predict the visual appearance of rose bush from image analysis of 3D videos

International audienceSensory methods applied to ornamental plants enable studying more objectively plant visual qualitykey drivers of consumer preferences. However, management upkeep of a trained panel for sensory profile is time-consuming, not flexible and represents non-negligible costs. The present paper achieves the proof of the concept about using morphometrical descriptors upkeep of a trained panel for sensory profile is time-consuming, not flexible and represents non-negligible costs. The present paper achieves the proof of the concept about using morphometrical descriptors integrating 2D image features from rotating virtual rose bush videos to predict their visual appearance according to different sensory attributes. Using real plants cultivated under a shading gradient and imaged in rotation during three development stages, acceptable prediction error of the sensory attributes ranging from 6.2 to 19.8% (normalized RMSEP) were obtained with simple ordinary least squares OLS) regression models and linearization. The most accurate model obtained was for the flower quantity perception.Finally, a secondary analysis highlighted in most of the studied traits a significant influence of defoliation, stressing herefore the impact of the leaves on plant architecture, and thus on the visual appearance

Ornamental plants architectural characteristics in relation to visual sensory attributes: a new approach on the rose bush for objective evaluation of the visual quality

International audienceWithin ornamental horticulture context, visual quality of plants is a critical criterion for consumers looking for immediate decorative effect products. Studying links between architecture and its phenotypic plasticity in response to growing conditions and the resulting plant visual appearance represents an interesting lever to propose a new approach for managing product quality from specialized crops. Objectives of the present study were to determine whether architectural components may be identified across different growing conditions (1) to study the architectural development of a shrub over time; and (2) to predict sensory attributes data characterizing multiple visual traits of the plants. The approach addressed in this study stands on the sensory profile method using a recurrent blooming modern rose bush (Rosa hybrida ‘Radrazz’) presented in rotation using video stimuli. Plants were cultivated under a shading gradient in three distinct environments (natural conditions, under 55 and 75% shading net). Architecture and video of the plants were recorded during three stages, from 5 to 15 months after plant multiplication. Except for visual traits at the scale of the organs, panel performance was highly satisfying for most of the sensory attributes listed. Strong correlations (Spearman’s coefficient ranging from 0.72 to 0.98) were found between them and architectural variables extracted from phytomer to plant scale data. Acceptable to very satisfying models were obtained (Q2 ranged from 0.49 to 0.95, normalized RMSEP <17.3%) with simple ordinary least squares regression and variable transformation to encompass non-linear relationships. The proposed approach presents therefore a powerful way to gain a better insight into the architecture of shrub plants together with their visual appearance to target processes of interest in order to optimize growing conditions or select the most fitting genotypes across breeding programs, with respect to contrasted consumer preferences