A Probabilistic Model of Flower Fertility and Factors Influencing Seed Production in Winter Oilseed rape (Brassica napus L.)

The number of pods per plant and the number of seeds per pod are the most variable yield components in winter oilseed rape (WOSR). The production of a seed is the combination of several physiological processes, namely formation of ovules and pollen grains, fertilization of the ovules and development of young embryos, any problem in these processes may result in seed abortion or pod abortion. Both the number of ovules per pod and the potential for the ovule to develop into a mature seed may depend on pod position in the plant architecture and time of appearance. Furthermore, the expansion (basipetal) of ramifications is in inverse order of the initiation (acropetal) in WOSR. The complex developmental pattern of WOSR makes it difficult to analyze. In this thesis, we first investigated the variability of the following yield components (a) ovules/pod, (b) seeds/pod, and (c) pods/axis in relation to two explanatory variables. These two variables include (1) flower and inflorescence position and (2) time of pod appearance, linked to the effect of assimilate availability. Based on these experiments, we developed a probabilistic model to simulate the number of ovules per ovary and seeds per pod according to the biological phenomena of flower fertility. The model can deduce the distribution of the number of pollen grains per stigma and distinguish the factors that influence the yield. Meanwhile, we compared our model to another model of flower fertility in kiwifruit developed by Lescourret et al., and improved the computation for the distribution of pollen grain number in our model.. In the last, we tested our model on the other species including cacao tree and soybean. The main contents are as follows: 1 The number and position of flowers and pods were recorded for the main stem (R0) and inflorescences R1, R4, R7, R9 and R11. The variety was Mendel. The results indicated that for the main stem, the number of ovules per pod decreased for a few ranks and then tended to increase and again to decrease at the end. On the ramifications R1 and R4, the number of ovules increased at first then remained constant with the pod rank, but it remained constant along the inflorescence on the other ramifications. However, the mean number of ovules per pod increased with ramifications from top to bottom. The number of seeds per pod did not vary with the pod rank at the basal positions and decreased afterwards along the inflorescence, but it did not differ between inflorescences. The number of ovules and seeds per pod did not vary with the time of pod appearance for the pods. However, the number of ovules and seeds per pod can be impacted by the time of pod appearance on the plant scale. 2 To analyze the effect of available assimilates on the yield components, different trophic states were created by clipping the main stem, ramifications or basal flowers. The results indicated that clipping the main stem or ramifications increased the number of ovules per pod, seeds per pod and pods per axis. However, clipping te l-0 06 12 71 6, v er si on 1 30 J ul 2 01 1