PARENT SESSION
Poster Session 24: Agro-Ecology
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

An applied ecological study on the F₁ seed production of brassicaceous vegetables.
Flowering synchronization and pollinator visitation; which is more influenced factor on inter-line crossing?

Ishizuka, Daigo¹, Horisaki, Atsushi², Niikura, Satoshi², Konuma, Akihiro^*,3, ¹ Graduate School of Science and Technology, Niigata, Niigata, Japan² Tohoku Seed Co., Utsunomiya, Tochigi, Japan³ Plant Ecology Group, Tsukuba, Ibaraki, Japan

ABSTRACT- F₁ hybrid seed is a main supply source of seed for vegetable production presently. Many seed of commercial vegetables are produced by crossing of two inbred lines as parents, which express heterosis, utilizing insect pollinators in field. It is often observed that the inter-line crossing rate of those seed fluctuates over years. The lower inter-line crossing rate cause economic loss both seed provider and vegetable producer. Ecological studies of wild plants reported that production of outcrossed seed is influenced by several factors, for example, flowering-synchronization with mating partners, density of flowering individuals or behavior of pollinators. Outcrossing rates in wild plant differ over populations or fluctuate over reproductive events even in plant species with selfing nature. It appears that fluctuation of inter-line crossing rate in F₁ hybrid seed production is caused by the same factors of fluctuating outcrossing rate in wild plant. The matter in F₁ seed production is equivalent to a major subject in plant ecology. Therefore, ecological study utilizing F₁ seed production system will be beneficial for both plant ecology and agriculture. In this paper, we present our current study regarding the relative importance of flowering synchronization and pollinator visitation on outcrossing, which utilized artificial population employing two inbred lines of Brassica rapa that are adopted as parents in the F₁ hybrid seed production. The number and species of flower visitors were recorded in each line. The blooming flowers in selected branches of nine individuals of each line were also recorded daily. Based on the record, we calculated level of flowering synchronization between the lines and mean frequency of pollinator visitation. After maturation, all seed pods developed from observed flowers were collected and determined whether inter-line crossed or not. We analyzed the influence of flowering synchronization and pollinator visitation on inter-line crossing with other factors that were mean temperature of blooming time, position of flower in branch and line. Nominal logistic regression analysis showed that higher level of flowering synchronization increased inter-line crossing, but pollination frequency was not effective.

Key words: F₁ hybrid seed production, flowering synchronization, frequency of pollinator visitation, self-incompatibility