Male-female interaction and temperature variation affect pollen performance in Citrus

Despite the extensive research work characterizing pollen performance in several plant species, less effort has been made to characterize it in some economically important species as Citrus, in which the failure of the sexual reproductive process, and subsequent parthenocarpic fruit development and seedlessness are prized characters. In this work we characterized pollen–pistil interaction in the three ancestral truetype Citrus species in order to determine the influence of the male and female genotypes, as well as of the temperature regime on pollen performance. Specifically, we characterized the effect of temperature on pollen grain germination in vitro, and on pollen tube growth in vivo in cut flowers and in planta under field temperature conditions. Results obtained showed that temperature variation has a strong effect on pollen germination, and on pollen tube kinetics and on their population size depending on the specific male–female combination. The optimum temperature for pollen germination in vitro was of 25 ◦C, while the most favorable temperature to accelerate in vivo pollen tube growth depended on the particular male–female interaction and ranged between 15 and 25 ◦C. Furthermore, temperature appears to have an effect on self-incompatibility reaction by affecting the place where pollen tubes are arrested. Overall, our results show that pollen performance is not only an inherent characteristic of the pollen genotype, but is largely dependent on the particular male–female combination and on genotype–temperature interactions.