Effect of floral morphology on pollination in Brassica rapa L

Abstract

Flower structure, especially the anther–stigma separation (ASS), is well known to affect pollination efficiency, and thus to potentially increase or decrease seed production in crops. Therefore, investigating the relationship between flower characteristics and pollination ability is crucial to a full understanding of mechanisms to improve F1 seed production in Brassica rapa. We used image analysis to measure three flower characteristics: short stamen height (SSH); long stamen height (LSH); and pistil height (PH) in seven cultivars. We calculated the ratio of PH to LSH as an index of anther–stigma separation (ASS). We investigated the number of pollen grains (NPG) deposited on the stigma and the seed-set percentage (SSP) under open-pollination and self-pollination conditions (with and without insects, respectively). Nested ANOVA indicated significant differences between the seven cultivars in the floral characteristics except for PH. Moreover, much larger variation was observed in NPG and SSP than in floral characteristics. Although stepwise multiple regression analysis indicated that plants with relatively high PHs produced more seed under self-pollination, the number of seeds that resulted from self-pollination did not affect seed production because of incompatibility. Therefore, the effect of the spatial position of pistils on the F1 seed production was low. Possibly other factors such as the total pollen production and visiting times of pollinators were important factors in the low yields observed in some cultivars