Background Changes in the proportions of male and female flowers in monoecious plants in response to external environmental conditions are directly related to the reproductive fitness of plants. The monoecious cucumber plant was used in this study to assess the responses of sex differentiation and the breeding process to nutrient supply and the degree of artificial pollination using pollen solutions of different concentrations. Results We found that the nutrient supply significantly increased the number of female flowers after pollination, although the number of female flowers did not increase with the concentration of the pollination solution. The number of male flowers did not decrease even under the low nutrient concentration; consequently, the optimal benefits under different nutrient and pollen resources in the environment were maximized when the number of female flowers decreased due to low nutrient levels after pollination. Pollination treatment affected the fruit growth, seed set, and fruit yield. However, the number of fruit, fruit set percentage, and total seeds per plant did not increase with the pollination level, although the fruit weight and seed number in one fruit did increase. The trade-offs for cucumbers associated with flower differentiation with respect to nutrient supply and pollination may not be optimal for fruit growth or seed set. Conclusions It is concluded that the response of plant flowering to external factors is direct and instantaneous, and there may not be an overall and long-term resource allocation for fruit development and seed formation.

Background: Changes in the proportions of male and female flowers in monoecious plants in response to external environmental conditions are directly related to the reproductive fitness of plants. The monoecious cucumber plant was used in this study to assess the responses of sex differentiation and the breeding process to nutrient supply and the degree of artificial pollination using pollen solutions of different concentrations. Results: We found that the nutrient supply significantly increased the number of female flowers, although the number of female flowers did not increase with the strength of the pollination. The number of male flowers did not decrease even under the low nutrient concentration; consequently, the matching pattern of male and female flowers reflects the response of plants to nutrients and nutrient resources during flowering stage. Pollination treatment affected the fruit growth, seed set, and fruit yield. However, the number of fruit, fruit set percentage, and total seeds per plant did not increase with the pollination level, although individual fruit weight and seed number in one fruit did increase. Conclusions: It is concluded that the response of cucumber flowering to external factors is direct and instantaneous, and this matching pattern of male and female flowers may not be optimal for fruit development and seed formation. Keywords: Cucumber, Plant fitness, Sex differentiation, Monoecious, Pollen resource