Floral bud damage compensation by branching and biomass allocation in genotypes of Brassica napus with different architecture and branching potential

Abstract

Plant branching is a key process in the yield elaboration of winter oilseed rape (WOSR). It is also involved in plant tolerance to flower damage because it allows the setting of new fertile inflorescences. Here we characterize the changes in the branching and distribution of the number of pods between primary and secondary inflorescences in response to floral bud clippings. Then we investigate the impacts of the modifications in branching on the biomass allocation and its consequence on the crop productivity (harvest index). These issues were addressed on plants with contrasted architecture and branching potential, using three genotypes (Exocet, Pollen, and Gamin) grown under two levels of nitrogen fertilization. Clipping treatments of increasing intensities were applied to either inflorescences or flower buds. We were able to show that restoration of the number of pods after clipping is the main lever for the compensation. Genotypes presented different behaviors in branching and biomass allocation as a function of clipping treatments. The number of fertile ramifications increased for the high intensities of clipping. In particular, the growth of secondary ramifications carried by branches developed before clipping has been observed. The proportions of yield and of number of pods carried by these secondary axes increased and became almost equivalent to the proportion carried by primary inflorescences. In terms of biomass allocation, variations have also been evidenced in the relationship between pod dry mass on a given axis and the number of pods set, while the shoot/root ratio was not modified. The harvest index presented different responses: it decreased after flower buds clipping, while it was maintained after the clipping of the whole inflorescences. The results are discussed relative to their implications regarding the identification of interesting traits to be target in breeding programs in order to improve WOSR tolerance.

Keywords: Brassica napus; allometry; architecture; biomass allocation; harvest index; plant resilience; plasticity; winter oilseed rape.

Figure 1

(A) Topology of the aerial parts of a WOSR plant. Left: topology before floral bud damage, right: after floral bud damage newly formed pods may be located on either existing inflorescences or on new inflorescences. New inflorescences may be carried by existing primary axes (1) or by new ones (2,3). (B) Diagram of the interaction between branching pattern and biomass allocation.

Figure 2

Classification trees based on tolerance indices of seed yield, number of pods and pod weight. (A) ClipFB, (B) ClipInflo.

Figure 3

Number of fertile primary (A) and secondary (B) axes per plant in ClipFB experiment for EHN, ELN, GHN, GLN, PHN and PLN. ^***0.05 / ^* 0.15 using Mann–Whitney tests. The meanings of the acronyms of the VN combinations are detailed in Table 1.

Figure 4

Number of fertile primary (A) and secondary (B) axes per plant in ClipInflo experiment for EHN, ELN, GHN and PHN. ^*** 0.05 / ^* 0.15 using Mann–Whitney tests. The meanings of the acronyms of the VN combinations are detailed in Table 1.

Figure 5

Pods distribution between different axes of the plant for ClipFB. Control (A), ClipFB4 (B), and ClipFB7 (C). Gray boxplots correspond to pods of primary inflorescences carried by existing primary axes. Green boxplots correspond to pods of secondary inflorescences carried by existing primary axes. Blue boxplots correspond to pods of primary inflorescences carried by new primary axes. Purple boxplots correspond to pods of secondary inflorescences carried by new primary axes. Results are expressed as a percentage of the total number of pods. The meanings of the acronyms of the VN combinations are detailed in Table 1.

Figure 6

Relationship between the number of pods and the total pod dry mass on the primary inflorescences for EHN, ELN, GHN, and PHN of ClipFB (A) and ClipInflo (B). Black, green and purple dots correspond to Control, ClipFB4 and ClipFB7 treatments, respectively. Black, red and blue dots correspond to Control, ClipI0 and ClipI4 treatments, respectively. The meanings of the acronyms of the VN combinations are detailed in Table 1. Linear mixed-models were used to assess the significance of the results.