Abstract
In Brassica crops there are various inter- and intra-specific diversity of pollination requirement to set seeds, ancl the insect pollination enhances seed set percentage not only in monogenomic Brassica species, B. campestris and B.oleracea (FREE 1970), but also in digenomic Brassica species, B.napus and B. juncea (OLSSON 1960, OHSAWA and NAMAI 1987). However, there is no cletailed information on pollen flow correlated with behavior of insect pollinators within a Brassica crop population. Accordingly, we studied the pollen fiow associated with visiting behavior of insect pollinators and estimated the promising planting pattern f'or hybrid seed production in Brassica napus using cytoplasmic male sterility (cms). In the Ist experiment, the correlation between pollination behavior of insect pollinators and cross-pollination efficiency was clarified. Twenty plants of cms B. napus cv. Isuzu-natane as seed parent were grown in isolation cage (L 3.4 m xW 1.4 m XH 1.6 m) without insects. The pollen parents, B.napus cv. Bronowski and cv. Waseaburana were grown in pots and carried together into the cage at the onset of the experiment. Artificially reared Shimahanaabu (Eristalis cerealis) was used as insect pollinators and released one by one into the cage. The visiting behavior of the insects were observed continuously and the visiting time lengths of each Shimahanaabu were recorded from 9:OO to 11:30 a.m. for 6 days during the period from May 5 to May 10. Each Shimahanaabu was compelled to visit the pollen parent first before visiting the seed parent. The flowers visited by Shimahanaabu were sampled immediately after Shimahanaabu left, and pollen grains deposited on each stigma were counted.
