Effects of Soil pH and Phosphorus onIn VitroPollen Competitive Ability and Sporophytic Traits in Clones ofViola tricolor

Abstract

Greenhouse‐grown clones of Viola tricolor were used to evaluate the importance of genetic effects on in vitro pollen tube growth rate in relation to the influence of two environmental soil factors—pH and phosphorus content. After 1 mo in different soil treatments, individual pollen tube growth rate was affected by a genotype by phosphorus interaction, while it was unaffected by either main effects. Though individuals differed in their response to phosphorus availability, the rank order of pollen donors remained consistent between treatments; i.e., the pollen donors with the highest pollen tube growth rate were the same in all soil conditions. Sporophytic traits were also affected by a genotype by phosphorus interaction. The response of pollen growth and sporophytic traits to soil phosphorus content were correlated within individuals in the high pH treatments. These results, in combination with a high value of clonal repeatability of pollen tube growth rate, indicate that pollen competitive ability has a genetic basis in this species. One prerequisite for this trait to have evolutionary effects on male fitness is thus fulfilled. Furthermore, if the response to phosphorus among pollen donors is more pronounced under natural conditions, variation in this environmental factor within populations has the potential to maintain some genetic variation in pollen tube growth rate even if this trait is constantly selected.