The Breeding System of Pontederia cordata L.

Abstract

The results of an artificial pollination program demonstrate the presence of an incompatibility system in Pontederia cordata L. (Pontederiaceae), which is a tristylous member of the Monocotyledoneae. Self-incompatibility is apparently strongest in the short-styled form, slightly weaker in the long-styled form, and much weaker in the mid-styled form. Corresponding differences in the strength of incompatibility were also noted in "illegitimate" cross pollinations among the 3 floral forms. Fruit production following interiorm pollinations between anthers and stigmas at an equivalent level (i.e., legitimate pollinations) was markedly higher than from illegitimate ones, although not as high as expected. Observations on inflorescences collected in the field indicate that fruit production under natural conditions exceeds that of artificially, legitimately pollinated plants in the greenhouse. In most field populations examined all 3 floral forms were present, although in many instances the forms were unequally re-represented. Possible explanations are offered to account for this inequality. The reproductive floral morphology of other taxa of Pontederiaceae is reviewed and the conflicting repports for several species pointed out. The breeding system of Pontederia cordata is compared with that of the related Eichhornia crassipes, although data for the latter species are incomplete.